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Genetic and physiological studies on potassium and nitrogen uptake and utilization in wheat Woodend, John J. 1986

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GENETIC AND PHYSIOLOGICAL STUDIES ON POTASSIUM AND NITROGEN UPTAKE AND UTILIZATION IN WHEAT by John J . WOODEND B. S c , U n i v e r s i t y of Zimbabwe, 1974 M.Sc, U n i v e r s i t y of Saskatchewan, 1980 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES Department of Botany We accept t h i s t h e s i s as conforming to the req u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA September 1986 9.John J . Woodend, 1986 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6(3/81) i i ABSTRACT Experiments were undertaken to examine the extent of v a r i a t i o n f o r potassium and nitrogen uptake and u t i l i z a t i o n i n wheat and a l s o to address some issues of relevance to the improvement of these t r a i t s . These issues included the i n h e r i t a n c e of these t r a i t s and the d i f f i c u l t i e s that could a r i s e due t o (1) the methodology that i s used to measure ion f l u x e s and u t i l i z a t i o n , (2) ontogenetic v a r i a t i o n i n the expression of these t r a i t s , and (3) the growth stage at which n u t r i e n t u t i l i z a t i o n i s evaluated. To compare v a r i e t i e s developed during d i f f e r e n t periods i n the h i s t o r y of wheat breeding, the v a r i e t i e s were assigned to f i v e groups on the ba s i s of height and o r i g i n . N u t r i e n t f l u x e s were measured e i t h e r as average net f l u x e s or short-term net f l u x e s . N u t r i e n t u t i l i z a t i o n was expressed as shoot f r e s h weight per p l a n t , e f f i c i e n c y r a t i o or u t i l i z a t i o n e f f i c i e n c y . S u b s t a n t i a l v a r i a t i o n was observed f o r a l l t r a i t s except potassium and ni t r o g e n e f f i c i e n c y r a t i o s . Although short-term net potassium f l u x e s were n e g a t i v e l y c o r r e l a t e d with root potassium c o n c e n t r a t i o n , some of the d i f f e r e n c e s i n f l u x were not a s s o c i a t e d with d i f f e r e n c e s i n root potassium c o n c e n t r a t i o n . These d i f f e r e n c e s must t h e r e f o r e be h e r i t a b l e . Due to the complexity of the r e g u l a t i o n of n i t r a t e uptake, genotypic d i f f e r e n c e s i n short-term net n i t r a t e f l u x were not examined i n r e l a t i o n to root n i t r a t e c o n c e n t r a t i o n . Therefore, some of the v a r i a t i o n i n n i t r a t e f l u x c ould be due to d i f f e r e n c e s i n root i i i n i t r a t e c o n c e n t r a t i o n or some other f a c t o r ( s ) which regulates n i t r a t e uptake. S i g n i f i c a n t d i f f e r e n c e s between groups were a l s o observed. The t a l l v a r i e t i e s had the highest potassium and n i t r a t e f l u x e s but were not s i g n i f i c a n t l y d i f f e r e n t from the t r i p l e dwarfs. The double dwarfs were the poorest performers f o r both n u t r i e n t uptake and u t i l i z a t i o n . In gener a l , the t a l l t r a d i t i o n a l v a r i e t i e s were more vigorous and hence showed the highest shoot weight per plan t and u t i l i z a t i o n e f f i c i e n c i e s . These f i n d i n g s are examined i n r e l a t i o n to the contention that p l a n t breeding under high f e r t i l i t y c o n d i t i o n s may have r e s u l t e d i n a d e c l i n e i n the a b i l i t y of p l a n t s to acquire and u t i l i z e mineral n u t r i e n t s . The i n h e r i t a n c e of short-term net potassium f l u x , shoot weight per p l a n t , potassium e f f i c i e n c y r a t i o and potassium u t i l i z a t i o n e f f i c i e n c y was studi e d i n four crosses. Complex modes of i n h e r i t a n c e were observed f o r a l l the t r a i t s . For one of the crosses s i g n i f i c a n t r e c i p r o c a l e f f e c t s were observed f o r shoot weight per p l a n t , e f f i c i e n c y r a t i o and u t i l i z a t i o n e f f i c i e n c y . Narrow sense h e r i t a b i l i t i e s f o r the two t r a i t s most l i k e l y to be s e l e c t e d f o r , namely short-term net potassium f l u x and shoot weight per p l a n t , i n d i c a t e d that s e l e c t i o n f o r these t r a i t s should be c a r r i e d out amongst f a m i l i e s rather than amongst s i n g l e p l a n t s . D i a l l e l a n a l y s i s f o r n i t r a t e uptake and u t i l i z a t i o n i n d i c a t e d that both a d d i t i v e and dominance gene e f f e c t s are important i n the determination of these t r a i t s . The e f f e c t of developmental changes i n potassium uptake and i v u t i l i z a t i o n on v a r i e t a l comparisons and genetic s t u d i e s was i n v e s t i g a t e d by comparing the performance of s i x v a r i e t i e s at d i f f e r e n t stages of growth over a five-week p e r i o d . The rankings of the v a r i e t i e s f o r short-term net potassium f l u x and shoot weight per plan t were found to be f a i r l y c o n s i s t e n t . C o r r e l a t i o n s between average net f l u x e s f o r d i f f e r e n t time periods as w e l l between short-term and average net f l u x e s were poor. These f i n d i n g s i n d i c a t e that s e l e c t i o n f o r d i f f e r e n c e s i n uptake should be based on f l u x e s obtained from s o l u t i o n s i d e n t i c a l i n concentration to the growth s o l u t i o n rather than on p e r t u r b a t i o n f l u x e s obtained by d e p l e t i o n of a s o l u t i o n much more concentrated than the growth s o l u t i o n . A l l measures of potassium u t i l i z a t i o n based on ve g e t a t i v e growth were poorly c o r r e l a t e d with performance at the adul t stage. S i g n i f i c a n t negative rank c o r r e l a t i o n s between shoot f r e s h weight per plan t and g r a i n weight per plant were obtained most l i k e l y due to d i f f e r e n c e s i n harvest index. This f i n d i n g c a s t s some doubt on the usefulness of veg e t a t i v e measures of n u t r i e n t u t i l i z a t i o n as i n d i c a t o r s of nu t r i e n t - u s e e f f i c i e n c y f o r a crop i n which the economic product c o n s i s t s of g r a i n . V TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES v i i i LIST OF FIGURES x i v LIST OF APPENDICES xv ACKNOWLEDGEMENTS xv i I . INTRODUCTION. 1 I I . VARIATION FOR POTASSIUM AND NITROGEN UPTAKE AND UTILIZATION 5 1. L i t e r a t u r e review 5 1.1. Plant mineral n u t r i t i o n 5 1.1.1. N u t r i e n t uptake 5 1.1.2. N u t r i e n t u t i l i z a t i o n 10 1.1.3. Genetic v a r i a b i l i t y i n mineral n u t r i t i o n 17 1.2. Wheat c u l t i v a t i o n : some h i s t o r i c a l , agronomic and p h y s i o l o g i c a l aspects 19 2. M a t e r i a l s and Methods 23 2.1. Wheat l i n e s 23 2.2. Pl a n t c u l t u r e 23 2.3. N u t r i e n t uptake and u t i l i z a t i o n determination 28 2.4. I n f l u x k i n e t i c s 30 3. Res u l t s and Dis c u s s i o n 32 I I I . GENETIC BASIS OF DIFFERENCES IN POTASSIUM AND NITROGEN UPTAKE AND UTILIZATION 61 1. L i t e r a t u r e review 61 1.1. N u t r i e n t uptake 61 1.2. N u t r i e n t u t i l i z a t i o n 62 2. M a t e r i a l s and Methods 65 v i 2.1. Generation mean and variance a n a l y s i s 65 2.2. D i a l l e l a n a l y s i s 69 3. R e s u l t s and D i s c u s s i o n 71 3.1. Short-term net potassium f l u x 78 3.2. Shoot weight per plan t 78 3.3. Potassium e f f i c i e n c y r a t i o 83 3.4. Potassium u t i l i z a t i o n e f f i c i e n c y 85 3.5. D i a l l e l a n a l y s i s 89 IV. COMPLICATING FACTORS IN THE GENETIC ANALYSIS OF AND SELECTION FOR ATTRIBUTES GOVERNING EFFICIENT MINERAL NUTRITION 95 1. L i t e r a t u r e review 95 1.1. Seed s i z e and mineral element s u b s t i t u t i o n 96 1.2. C o r r e l a t i o n between s e l e c t e d t r a i t s and performance 97 1.3. Ontogenetic changes i n n u t r i e n t uptake and u t i l i z a t i o n 1 00 2. M a t e r i a l s and Methods 104 2.1. Ontogenetic changes i n potassium uptake and u t i l i z a t i o n 105 2.2. C o r r e l a t i o n between potassium u t i l i z a t i o n at the v e g e t a t i v e stage and i n g r a i n production 106 3. R e s u l t s and D i s c u s s i o n 109 3.1. Ontogenetic v a r i a t i o n i n potassium uptake and u t i l i z a t i o n 109 3.2. C o r r e l a t i o n between measures of potassium u t i l i z a t i o n at the vegeta t i v e and adult stages, and genotype x environment i n t e r a c t i o n 127 V. GENERAL DISCUSSION 139 VI. CONCLUSIONS 150 GLOSSARY 1 52 v i i LITERATURE CI TED 153 Appendices 1 66 v i i i LIST OF TABLES 1. Composition of n u t r i e n t s o l u t i o n s used i n potassium and potassium plus n i t r a t e - l i m i t e d experiments 27 2. V a r i e t a l grouping on the basi s of height and o r i g i n 35 3. Short-term and average net potassium f l u x e s , root potassium concentrations (±SE) and root f r e s h weights of the 24 v a r i e t i e s when grown under po t a s s i u m - l i m i t e d c o n d i t i o n s 36 4. Short-term net potassium and n i t r a t e f l u x e s and root weights of the 24 v a r i e t i e s when grown under potassium and n i t r a t e - l i m i t e d c o n d i t i o n s 37 5. Analyses of variance f o r short-term net potassium and n i t r a t e f l u x e s (STNKF and STNNF r e s p e c t i v e l y ) and root weight per pla n t (RWt/pl) i n the potassium and potassium plus n i t r a t e - l i m i t e d experiments 38 6. Comparison of group means for short-term net potassium and n i t r a t e f l u x e s , average potassium f l u x and root f r e s h weight per pla n t 38 7. C o r r e l a t i o n c o e f f i c i e n t s between various f l u x e s and between f l u x e s and root weights f o r the 24 v a r i e t i e s when grown under potassium and potassium plus n i t r a t e - l i m i t e d c o n d i t i o n s 39 8. K i n e t i c parameters (+SE) and root potassium concentrations of eigh t v a r i e t i e s when grown under pot a s s i u m - l i m i t e d c o n d i t i o n s 47 9. N i t r a t e uptake k i n e t i c parameters (±SE) of eight v a r i e t i e s when grown under potassium plus n i t r a t e - l i m i t e d c o n d i t i o n s 48 10. Shoot f r e s h weights per p l a n t , potassium e f f i c i e n c y r a t i o s (KER) and potassium u t i l i z a t i o n e f f i c i e n c i e s (KUE) of the 24 v a r i e t i e s when grown under potassium-l i m i t e d c o n d i t i o n s 51 11. Shoot f r e s h weight per p l a n t , potassium and nitrogen e f f i c i e n c y r a t i o s (KER and NER r e s p e c t i v e l y ) , and potassium and nit r o g e n u t i l i z a t i o n e f f i c i e n c i e s (KUE and NUE r e s p e c t i v e l y ) of the 24 v a r i e t i e s when grown under potassium plus n i t r a t e - l i m i t e d c o n d i t i o n s 52 i x 12. Analyses of variance f o r shoot weight per pla n t (SWt.), potassium and nitrogen e f f i c i e n c y r a t i o (KER and NER r e s p e c t i v e l y ) and potassium and nitrogen u t i l i z a t i o n e f f i c i e n c y (KUE and NUE r e s p e c t i v e l y ) i n the potassium and potassium plus n i t r a t e - l i m i t e d experiments 53 13. Comparison of group means f o r shoot weight per pla n t (SWt.), potassium and nitrogen e f f i c i e n c y r a t i o s (KER and NER r e s p e c t i v e l y ) and potassium and nitrogen u t i l i z a t i o n e f f i c i e n c i e s (KUE and NUE r e s p e c t i v e l y ) i n the potassium plus n i t r a t e - l i m i t e d experiment 54 14. Generation means (upper f i g u r e s ) , number of p l a n t s per generation (parentheses) and variances (lower f i g u r e s ) fo r short-term net potassium uptake i n the four crosses...73 15. Generation means (upper f i g u r e s ) , number of p l a n t s per generation (parentheses) and variances (lower f i g u r e s ) fo r shoot weight per plant i n the four crosses ....74 16. Generation means (upper f i g u r e s ) , number of p l a n t s per generation (parentheses) and variances (lower f i g u r e s ) fo r potassium e f f i c i e n c y r a t i o i n the four crosses 75 17. Generation means (upper f i g u r e s ) , number of p l a n t s per generation (parentheses) and variances (lower f i g u r e s ) fo r potassium u t i l i z a t i o n e f f i c i e n c y i n the four crosses ~ 76 1 8 . Analyses of variance for e f f i c i e n c y r a t i o i n the crosses NP 52 x Jupateco 73 and NP 52 x Tesia 79 77 19. Analyses of variance for potassium e f f i c i e n c y r a t i o i n the crosses NP 52 x N a i n a r i 60 and N a i n a r i 60 x Yecora 70 77 20. Comparison of r e c i p r o c a l progenies for short-term net potassium f l u x (STNKF), shoot weight per p l a n t , potassium e f f i c i e n c y r a t i o (KER) and potassium u t i l i z a t i o n e f f i c i e n c y (KUE) i n the four crosses 79 21. Estimates of the mean (m), pooled a d d i t i v e [a] and dominance [d] gene e f f e c t s f o r short-term net potassium uptake i n the four crosses 79 22. P e r f e c t f i t estimates of the mean (m), pooled a d d i t i v e [ a ] , dominance [d] and d i g e n i c e p i s t a t i c components (aa = a d d i t i v e x a d d i t i v e , ad = a d d i t i v e x dominance and dd = dominance x dominance) of means for short-term net potassium uptake i n the four crosses 80 X 23. Estimates of the F2 , genotypic (Var G), a d d i t i v e (Var A) and dominance (Var D) variances and h e r i t a b i l i t i e s (H = broad sense, h 2= narrow sense) for short-term net potassium uptake i n the four crosses 80 24. Estimates of the mean (m), pooled a d d i t i v e [d] and dominance [d] gene e f f e c t s f or shoot f r e s h weight per plant i n the four crosses 82 25. Estimates of the F , genotypic (Var G), a d d i t i v e (Var A) and dominance (Var 2 D) variances and h e r i t a b i l i t i e s (H = broad sense, h = narrow sense) for shoot weight per p l a n t i n the four crosses 82 26. Estimates of the mean (m), pooled a d d i t i v e [a] and dominance [d] gene e f f e c t s f o r potassium e f f i c i e n c y r a t i o i n the four crosses 84 27. P e r f e c t f i t estimates of the mean (m), pooled a d d i t i v e [ a ] , dominance [d] and dige n i c e p i s t a t i c components (aa = a d d i t i v e x a d d i t i v e , ad = a d d i t i v e x dominance, dd = dominance x dominance) of generation means f o r potassium e f f i c i e n c y r a t i o i n the four crosses 84 28. Estimates of F , genotypic (Var G), a d d i t i v e (Var A) and dominance f/Var D) variances and h e r i t a b i l i t i e s (H = broad sense, h = narrow sense) for potassium e f f i c i e n c y r a t i o i n the four crosses 86 29. Estimates of mean (m), pooled a d d i t i v e [a] and dominance [d] gene e f f e c t s f o r potassium u t i l i z a t i o n e f f i c i e n c y i n the four crosses 86 30. P e r f e c t f i t estimates of the mean (m), pooled a d d i t i v e [ a ] , dominance [d] and dige n i c e p i s t a t i c components (aa = a d d i t i v e x a d d i t i v e , ad = a d d i t i v e x dominance, and dd = dominance x dominance) of means for shoot weight per plant and potassium u t i l i z a t i o n e f f i c i e n c y i n the cross NP 52 x N a i n a r i 60 87 31. Estimates of F,, genotypic (Var G), a d d i t i v e (Var A) and dominance (Var D) variances and h e r i t a b i l i t i e s (H = broad sense, h = narrow sense) for potassium u t i l i z a t i o n e f f i c i e n c y i n the four crosses 88 32. Mean short-term net potassium f l u x e s of p a r e n t a l l i n e s and Fj ' s i n the 7 x 7 h a l f d i a l l e l 90 33. Mean short-term net n i t r a t e f l u x e s of the p a r e n t a l l i n e s and F x ' s i n the 7 x 7 h a l f d i a l l e l , 90 34. Mean shoot f r e s h weights per pla n t of the p a r e n t a l l i n e s and F, 's i n the 7 x 7 h a l f d i a l l e l 91 x i 35. Mean potassium e f f i c i e n c y r a t i o s of the p a r e n t a l l i n e s and F i ' s i n the 7 x 7 h a l f d i a l l e l 91 36. Mean potassium u t i l i z a t i o n e f f i c i e n c i e s of the p a r e n t a l l i n e s and F i ' s i n the 7 x 7 h a l f d i a l l e l 92 37. Mean nitr o g e n e f f i c i e n c y r a t i o s of the p a r e n t a l l i n e s and F ^ s i n the 7 x 7 h a l f d i a l l e l 92 38. Mean nitrogen u t i l i z a t i o n e f f i c i e n c i e s of the p a r e n t a l l i n e s and F j / s i n the 7 x 7 h a l f d i a l l e l 93 39. Analyses of variance for short-term net potassium and n i t r a t e f l u x e s (STNKF and STNNF r e s p e c t i v e l y ) , shoot f r e s h weight per p l a n t , potassium and n itrogen e f f i c i e n c y r a t i o s (KER and NER r e s p e c t i v e l y ) and potassium and nitrogen u t i l i z a t i o n e f f i c i e n c i e s (KUE and NUE r e s p e c t i v e l y ) i n the 7 x 7 h a l f d i a l l e l 94 40. Analyses of variance for general and s p e c i f i c combining a b i l i t y (GCA and SCA r e s p e c t i v e l y ) for short-term net n i t r a t e f l u x (STNNF), shoot f r e s h weight per p l a n t , potassium and n itrogen e f f i c i e n c y r a t i o s (KER and NER r e s p e c t i v e l y ) and n itrogen u t i l i z a t i o n e f f i c i e n c y (NUE) i n the 7 x 7 h a l f d i a l l e l 94 41. Short-term net potassium f l u x e s (umol/g/h) and root potassium concentrations (umol/g) of the s i x v a r i e t i e s as determined at weekly i n t e r v a l s . Fluxes are given on top l i n e and root potassium concentrations on bottom l i n e 114 42. C o r r e l a t i o n c o e f f i c i e n t s between various short-term net potassium f l u x e s . Product-moment c o r r e l a t i o n c o e f f i c i e n t s are shown above the diagonal and Spearman's rank c o r r e l a t i o n c o e f f i c i e n t s are shown below the diagonal 115 43. Average net potassium f l u x e s of the 6 v a r i e t i e s over one-week periods 116 44. C o r r e l a t i o n c o e f f i c i e n t s between various potassium f l u x e s for the v a r i e t i e s which were included i n the k i n e t i c and ontogenetic e f f e c t s t u d i e s . Product-moment c o r r e l a t i o n c o e f f i c i e n t s are given above the diagonal and Spearman's rank c o r r e l a t i o n c o e f f i c i e n t s are given below the diagonal 117 45. C o r r e l a t i o n s between short-term and average net f l u x e s i n the experiment designed to examine the e f f e c t of ontogenetic changes in potassium uptake and u t i l i z a t i o n on genotypic comparisons 118 x i i 46. Shoot (top l i n e ) and root (bottom l i n e ) r e l a t i v e growth r a t e s of the 6 v a r i e t i e s over a five-week p e r i o d 1 1 2 47. Potassium e f f i c i e n c y r a t i o s (g/mmol) and u t i l i z a t i o n e f f i c i e n c i e s (g2/mmol) of the 6 v a r i e t i e s over a five-week p e r i o d . Potassium e f f i c i e n c y r a t i o s are shown on the top l i n e and potassium u t i l i z a t i o n e f f i c i e n c i e s are shown on the bottom l i n e 124 48. C o r r e l a t i o n s between potassium e f f i c i e n c y r a t i o s obtained at d i f f e r e n t growth stages of s i x v a r i e t i e s . Product-moment c o r r e l a t i o n c o e f f i c i e n t s are given above the diagonal and Spearman's rank c o r r e l a t i o n c o e f f i c i e n t s are given below the diagonal 125 49. C o r r e l a t i o n s between potassium u t i l i z a t i o n e f f i c i e n c i e s obtained at d i f f e r e n t growth stages of the s i x v a r i e t i e s . Product-moment c o r r e l a t i o n c o e f f i c i e n t s are given above the diagonal and Spearman's rank c o r r e l a t i o n c o e f f i c i e n t s are given below the d i a g o n a l . . . . 126 50. Shoot and root f r e s h weights of the 16 v a r i e t i e s when grown under p o t a s s i u m - l i m i t i n g c o n d i t i o n s i n the growth room and under n a t u r a l c o n d i t i o n s 129 51. Shoot and root potassium concentrations of the 16 v a r i e t i e s when grown i n the growth room and under n a t u r a l c o n d i t i o n s 130 52. Potassium e f f i c i e n c y r a t i o s (KER) and u t i l i z a t i o n e f f i c i e n c i e s (KUE) of the 16 v a r i e t i e s when grown under p o t a s s i u m - l i m i t i n g c o n d i t i o n s i n the growth room and under n a t u r a l c o n d i t i o n s 131 53. Analyses of v a r i a n c e , i n c l u d i n g expectations of mean squares, f o r root and shoot f r e s h weight per plant of the 16 v a r i e t i e s when grown i n the growth room and under n a t u r a l c o n d i t i o n s 132 54. Analyses of v a r i a n c e , i n c l u d i n g expectations of mean squares, f o r potassium e f f i c i e n c y r a t i o (KER) and u t i l i z a t i o n e f f i c i e n c y (KUE) of the 16 v a r i e t i e s when grown i n the growth room and under n a t u r a l c o n d i t i o n s 132 55. C o r r e l a t i o n c o e f f i c i e n t s between root weights, shoot weights, potassium e f f i c i e n c y r a t i o s (KER) and u t i l i z a t i o n e f f i c i e n c i e s (KUE) of the 16 v a r i e t i e s when grown i n the growth room and under n a t u r a l c o n d i t i o n s 133 x i i i 56. Genotypic and phenotypic v a r i a n c e s , and broad sense h e r i t a b i l i t i e s for root and shoot weight per p l a n t , potassium e f f i c i e n c y r a t i o and u t i l i z a t i o n e f f i c i e n c y (KER and KUE r e s p e c t i v e l y ) 133 57. Number of t i l l e r s per p l a n t , straw and g r a i n weight per p l a n t , t o t a l dry weight per p l a n t , harvest index (HI) and potassium u t i l i z a t i o n i n g r a i n production of the 12 v a r i e t i e s grown under n a t u r a l c o n d i t i o n s 136 58. C o r r e l a t i o n c o e f f i c i e n t s between measures of potassium u t i l i z a t i o n based on ve g e t a t i v e growth (under two c o n d i t i o n s ) and g r a i n production 137 x i v LIST OF FIGURES 1. Potassium i n f l u x isotherms f o r the v a r i e t i e s NP 52 (1 , A ) , C 306 (2,B ), Jupateco 73 ( 3 , 0 ) and Moti (4, • ) .. .43 2. Potassium i n f l u x isotherms f o r the v a r i e t i e s Pb 8A (1 , • ) , Lerma Rojo 64 (2, A ) , Arjun ( 3 , 0 ) and Tesia 79 (4, • ) 44 3. N i t r a t e i n f l u x isotherms for the v a r i e t i e s Jupateco 73 (1 , • ) , Moti ( 2 , 0 ) , Tesia 79 (3,t>) and Arjun (4, A ) 45 4. N i t r a t e i n f l u x isotherms for the v a r i e t i e s Sonora 64 ( 1 , 0 ) , NP 52 (2, • ) , C 306 ( 3 , A ) and Pb 8A (4, © ) 46 5. Shoot ( s o l i d symbols) and root (open symbols) f r e s h weights of the v a r i e t i e s NP 52 ( A ) , C 306 (•) and Pb 8A ( • ) 120 6. Shoot ( s o l i d symbols) and root (open symbols) f r e s h weights of the v a r i e t i e s Sonora 64 ( • ) , Tesia 7 9 ( A ) and Moti ( • ) 121 I X V LIST OF APPENDICES 1 . Pedigrees and height c a t e g o r i e s of v a r i e t i e s 166 2. Woolf-Augustinsson-Hofstee p l o t s for potassium i n f l u x k i n e t i c s i n the v a r i e t i e s NP 52 ( • ) , C 306 ( • ) , Moti ( A ) and Jupateco 73 ( © ) ,168 3. Woolf-Augustinsson-Hofstee p l o t s for potassium i n f l u x k i n e t i c s i n the v a r i e t i e s Pb 8A ( • ) , Lerma Rojo 64 ( A ), Ar jun ( © ) and Te s i a 79 ( • ) 169 4. Woolf-Augustinsson-Hofstee p l o t s for n i t r a t e i n f l u x k i n e t i c s i n the v a r i e t i e s NP 52 ( • ) , C 306 ( A ) , Sonora 64 ( • ) and Pb 8A ( • ) 170 5. Woolf-Augustinsson-Hofstee p l o t s f o r n i t r a t e i n f l u x k i n e t i c s i n the v a r i e t i e s Jupateco 73 ( • ), Arjun ( A ) , Moti (•) and Yecora 70 ( A ) 171 x v i ACKNOWLEDGEMENTS I wish to express my deepest a p p r e c i a t i o n to Drs. A.D.M. Glass and CO. Person under whose guidance t h i s study was undertaken, f o r t h e i r h e l p f u l advice, patience and f i n a n c i a l a s s i s t a n c e . I am a l s o g r a t e f u l to the members of my Advisory Commitee, Drs. A.J.F. G r i f f i t h s , C. Wehrhahn and F.B. H o l l f o r t h e i r advice and c o n s t r u c t i v e c r i t i c i s m . Sincere a p p r e c i a t i o n i s extended to Dr. M.Y. S i d d i q i f or h i s a s s i s t a n c e and constant encouragement. I am a l s o g r a t e f u l to Kojwang Ochieng, Fred Ming, L o r i S l a t e r , Adela Mukuka and Helen Glavina f o r t h e i r kindness and encouragement. Aknowledgement i s made to the U n i v e r s i t y of B r i t i s h Columbia f o r f i n a n c i a l a s s i s t a n c e i n the form of a Graduate F e l l o w s h i p . 1 I . INTRODUCTION Plant breeding has made a major c o n t r i b u t i o n to the improvement of crop p r o d u c t i v i t y and q u a l i t y over the l a s t century. However, the approach of t h i s d i s c i p l i n e has l a r g e l y been e m p i r i c a l rather than a n a l y t i c a l . Hence the s e l e c t i o n of s u p e r i o r genotypes has been based l a r g e l y on the s u b j e c t i v e judgement of the breeder, a s s i s t e d where p r a c t i c a b l e , by o b j e c t i v e measures of plant performance. O c c a s i o n a l l y , as i n the production of h y b r i d s , p r e d i c t i v e formulae have a l s o been used. Although these s t r a t e g i e s have proved h i g h l y s u c c e s s f u l , the need fo r b e t t e r e x p l o i t a t i o n of genetic resources and a more sound approach to plant breeding has l e d to i n c r e a s i n g i n t e r e s t i n a more a n a l y t i c a l and broad based approach; one that i n c l u d e s and makes use of f i n d i n g s i n other d i s c i p l i n e s of p l a n t research. Such an approach would inc l u d e s e l e c t i o n f o r p h y s i o l o g i c a l t r a i t s that are l i k e l y to improve p r o d u c t i v i t y or enhance t o l e r a n c e / r e s i s t a n c e to various s t r e s s e s . One of the areas now r e c e i v i n g i n c r e a s i n g a t t e n t i o n i s n u t r i e n t - u s e e f f i c i e n c y which, i f improved, could r e s u l t i n the development of productive genotypes b e t t e r s u i t e d to n u t r i t i o n a l l y marginal environments or b e t t e r able to make use of high f e r t i l i z e r a p p l i c a t i o n s . Despite longstanding awareness of i n t r a s p e c i f i c v a r i a t i o n f o r t r a i t s governing n u t r i e n t - u s e e f f i c i e n c y only f a i r l y r e c e n t l y has there been a c o n s c i e n t i o u s e f f o r t to include s e l e c t i o n f o r these t r a i t s i n p l a n t breeding programmes. This 2 endeavour i s now e s p e c i a l l y important due to the p r e s s i n g need to increase food production by expanding crop production i n t o marginal areas rather than r e l y i n g on improved p r o d u c t i v i t y alone. In a d d i t i o n , concern over the negative e c o l o g i c a l impact of heavy f e r t i l i z e r a p p l i c a t i o n and i n c r e a s i n g f e r t i l i z e r costs have given f u r t h e r impetus to the need for n u t r i e n t - e f f i c i e n t genotypes. As f o r other d e s i r a b l e t r a i t s , the improvement of a t t r i b u t e s governing mineral n u t r i t i o n r e q u i r e s adequate genetic v a r i a t i o n , an understanding of t h e i r i n h e r i t a n c e , and the a v a i l a b i l i t y of r e l i a b l e and convenient s e l e c t i o n techniques. However, a number of problems impinge upon these basic requirements. These problems a r i s e due to the f o l l o w i n g : (1) methodological d i f f i c u l t i e s i n the proper q u a n t i f i c a t i o n of some of the t r a i t s , (2) ontogenetic v a r i a t i o n i n t h e i r expression, (3) t h e i r marked p l a s t i c i t y and s e n s i t i v i t y to environmental e f f e c t s and, (4) i n the case of n u t r i e n t uptake, complications a s s o c i a t e d with i t s r e g u l a t i o n by the i n t e r n a l n u t r i e n t s t a t u s of the r o o t s . Because these d i f f i c u l t i e s can have profound i m p l i c a t i o n s f o r the genetic improvement of n u t r i e n t uptake and u t i l i z a t i o n i t i s imperative that they be given due c o n s i d e r a t i o n . Therefore, i n t h i s study, i n a d d i t i o n to examining the v a r i a t i o n f o r , and i n h e r i t a n c e of, potassium and n i t r o g e n uptake and u t i l i z a t i o n , s t u d i e s on the e f f e c t of some of these problems on v a r i e t a l comparisons, genetic s t u d i e s and s e l e c t i o n e f f i c i e n c y were a l s o undertaken. Wheat was s e l e c t e d f o r t h i s study p r i m a r i l y because the 3 physiology of mineral n u t r i t i o n among the d i v e r s e types that have been developed over the l a s t century has not been adequately examined. The worldwide importance of t h i s crop i n a d d i t i o n to i t s w e l l documented h i s t o r y of c u l t i v a t i o n and improvement a l s o made i t an i d e a l candidate f o r t h i s study. As such, marked changes i n breeding o b j e c t i v e s and agronomic p r a c t i c e s are c l e a r l y evident over the l a s t century. For example, i n c o u n t r i e s such as India and Mexico the t a l l t r a d i t i o n a l v a r i e t i e s which were s e l e c t e d and grown under c o n d i t i o n s of low to moderate f e r t i l i t y have now been replaced by dwarf types renowned fo r t h e i r outstanding y i e l d performance under high f e r t i l i t y c o n d i t i o n s . Although these c o n t r a s t i n g types have been examined for d i f f e r e n c e s i n a number of morphological and p h y s i o l o g i c a l t r a i t s , t h e i r physiology with respect to mineral n u t r i t i o n has received very l i t t l e a t t e n t i o n . The s p e c i f i c o b j e c t i v e s of the study were as f o l l o w s : 1 . To examine a diverse c o l l e c t i o n of wheat genotypes, s e l e c t e d so as to be r e p r e s e n t a t i v e of the types that have been developed over the l a s t eighty years, f o r d i f f e r e n c e s i n potassium and nitrogen uptake and u t i l i z a t i o n . 2 . To determine the i n h e r i t a n c e of potassium and nitrogen uptake and u t i l i z a t i o n as w e l l as the extent of genotype x environment i n t e r a c t i o n with respect to potassium u t i l i z a t i o n . 3. To examine the ontogenetic changes i n potassium uptake and u t i l i z a t i o n i n s e l e c t e d genotypes and to thereby determine the i m p l i c a t i o n s of these changes upon genotypic comparisons, genetic s t u d i e s and s e l e c t i o n e f f i c i e n c y . 4 4 . To determine the r e l a t i o n s h i p between measures of potassium u t i l i z a t i o n based on vegetative growth and g r a i n production with a view to assessing the r e l i a b i l i t y of using measures based on ve g e t a t i v e growth as i n d i c a t o r s of e f f i c i e n c y i n g r a i n production. 5 I I . VARIATION FOR POTASSIUM AND NITROGEN UPTAKE AND UTILIZATION 1. L i t e r a t u r e review 1.1. Plant mineral n u t r i t i o n The processes involved i n p l a n t mineral n u t r i t i o n are both numerous and complex and many remain poorly understood. For s i m p l i c i t y these processes may be viewed as the a c q u i s i t i o n of n u t r i e n t s from the s o i l s o l u t i o n , t h e i r t r a n s p o r t to a c t i v e s i t e s w i t h i n the p l a n t , and f i n a l l y t h e i r u t i l i z a t i o n i n v a r i o u s biochemical and b i o p h y s i c a l processes which c o n t r i b u t e t o growth. Various aspects of p l a n t mineral n u t r i t i o n have been discussed i n numerous p u b l i c a t i o n s (47, 48, 70, 88, 89, 114). Only those issues of relevance to t h i s study w i l l be reviewed. 1.1.1.; N u t r i e n t uptake N u t r i e n t uptake can be measured as e i t h e r i n f l u x or net f l u x depending on the o b j e c t i v e s of the experiment. U n i d i r e c t i o n a l f l u x e s are u s u a l l y measured by means of s u i t a b l e r a d i o i s o t o p e s w i t h care being taken to remove any free space r a d i o l a b e l by d e s o r p t i o n . The measured net uptake of an inorganic ion i s composed of the balance between i n f l u x and e f f l u x and i s u s u a l l y determined by monitoring the d e p l e t i o n of the e x t e r n a l s o l u t i o n over a f a i r l y short p e r i o d . Because the uptake s o l u t i o n i s u s u a l l y more concentrated than the s o l u t i o n i n which the p l a n t s were p r e v i o u s l y grown, t h i s approach y i e l d s what may be termed a " p e r t u r b a t i o n f l u x " . Although t h i s approach can be c r i t i c i z e d f o r a number of reasons, i t i s 6 nonetheless widely used and convenient. For both i n f l u x and net f l u x , the values obtained are dependent upon the n u t r i e n t c o n c e n t r a t i o n provided during growth as w e l l as the c o n c e n t r a t i o n of the uptake s o l u t i o n . The r e l a t i o n s h i p between the i n t e r n a l n u t r i e n t s t a t u s of the roots and the r a t e of n u t r i e n t uptake has been, and s t i l l i s , the subject of numerous st u d i e s designed to examine the i n t r i g u i n g and d i f f i c u l t q uestion of the r e g u l a t i o n of n u t r i e n t uptake. Opinions d i f f e r as to which root c h a r a c t e r i s t i c to use as the b a s i s f o r expressing r a t e of n u t r i e n t uptake. Among those used are root f r e s h weight, dry weight, length, surface area, volume and p r o t e i n content. The use of most, i f not a l l of these c h a r a c t e r i s t i c s i s open to some c r i t i c i s m . For example, root weight may not adequately r e f l e c t the extent of the a b s o r p t i v e surface and, as a r e s u l t , comparisons based on rate of n u t r i e n t uptake per u n i t root weight can be misleading (82). When root length i s used i t i s e s s e n t i a l that s i m i l a r root segments be used since i t has been shown that ion uptake v a r i e s along the length of the root (34, 120, 121). Kolosov (82) made a more d e t a i l e d study of d i f f e r e n t i a l n u t r i e n t uptake along the root a x i s and devised a method f o r d i f f e r e n t i a t i n g between regions of a c t i v e and passive ion uptake. This approach undoubtedly provides a b e t t e r p i c t u r e of n u t r i e n t uptake but i t i s f a r too complicated and time- consuming f o r the r o u t i n e comparison of various genotypes. C l e a r l y , there are a number of c o m p l i c a t i o n s l i k e l y to be encountered when attempting to make r e l i a b l e comparisons between genotypes. Recently i t has been 7 shown that d i f f e r e n c e s i n morphological development over a short time p e r i o d can have a profound e f f e c t on genotypic comparisons (108). Although i t i s commonly assumed that surface area i s the most important determinant of uptake, t h i s has been shown not to be so i n w e l l - s t i r r e d s o l u t i o n s . By comparing the c o n t r i b u t i o n s of d i f f e r e n t p a r t s of the root system to t o t a l surface area, volume and l e n g t h with t h e i r c o n t r i b u t i o n to t o t a l potassium uptake, R u s s e l l and Clarkson (120) showed that uptake i s more c l o s e l y r e l a t e d to volume than to surface area or l e n g t h . Even when surface area i s used, Kolosov (82) maintains that the c a l c u l a t i o n s are l i k e l y to be erroneous since the root i s not a c y l i n d e r . Because i t has been shown that root weight and volume are c l o s e l y c o r r e l a t e d (120), root weight can thus be used as a sound b a s i s on which to express n u t r i e n t uptake r a t e s . Although i t i s u s e f u l to base v a r i e t a l or i n t e r s p e c i f i c comparisons on uptake r a t e s determined at a s i n g l e c o n c e n t r a t i o n , i t i s considered more meaningful to employ k i n e t i c parameters (49). These parameters provide a more comprehensive assessment of the p r o p e r t i e s of the t r a n s p o r t systems under study f o r a p a r t i c u l a r growth stage and set of c o n d i t i o n s . The k i n e t i c approach was developed by Epstein and Hagen (48) and has since been employed i n numerous s t u d i e s . Their s t u d i e s were i n i t i a l l y concerned with the i n f l u x of potassium i n t o the e x c i s e d roots of l o w - s a l t (grown i n calcium sulphate only) b a r l e y p l a n t s . They observed that potassium i n f l u x 8 e x h i b i t e d a hyp e r b o l i c s a t u r a t i o n response to i n c r e a s i n g e x t e r n a l concentration and, furthermore, that the response was phasic. At higher concentrations (l-50mM) a more complex response was observed. To c h a r a c t e r i z e t h i s e s s e n t i a l l y b i p h a s i c response the terms Mechanism I and Mechanism I I were introduced; the former being o p e r a t i v e over the low conce n t r a t i o n range up to about 1mM and the l a t t e r being operative over the range 1-50mM. This b i p h a s i c response has since been observed f o r many other n u t r i e n t s (3, 47). By l i k e n i n g t h i s response to that of enzyme-catalyzed r e a c t i o n s which can be described by the well-known M i c h a e l i s -Menten equation (123), Epstein and Hagen (48) proposed a c a r r i e r - k i n e t i c model f o r ion uptake. According to t h i s model the k i n e t i c parameters V m a x (maximum uptake v e l o c i t y ) and K m ( e x t e r n a l c o n c e n t r a t i o n at which h a l f the maximum i n f l u x i s att a i n e d ) can be c a l c u l a t e d and employed to make be t t e r comparisons between genotypes. In enzyme s t u d i e s v m a x i s dependent upon the q u a n t i t y of enzyme i n c l u d i n g i t s p u r i t y (123). The parameter K m i s much more complex and, u n l i k e V M A X i s independent of the substrate and enzyme co n c e n t r a t i o n s . More s p e c i f i c a l l y , K m i s the r a t i o of three r a t e constants which can only be determined with great d i f f i c u l t y . Therefore, i t s s i g n i f i c a n c e cannot be measured with c e r t a i n t y (38) and i t i s thus best regarded as an apparent K m or loose d i s s o c i a t i o n constant. This parameter serves various purposes i n enzyme s t u d i e s i n a d d i t i o n to p r o v i d i n g a measure of the a f f i n i t y of the enzyme for i t s substrate (123). As such, a 9 high K m i n d i c a t e s that there i s a low a f f i n i t y between enzyme and substrate because i t means that a higher substrate c o n c e n t r a t i o n i s required to saturate the enzyme. In an analogous manner, the K has been used to c h a r a c t e r i z e the m a f f i n i t y of the root t r a n s p o r t system f o r the n u t r i e n t of i n t e r e s t . The tedium involved i n the measurement of these parameters has l e d to the development of l e s s demanding techniques which req u i r e fewer o b s e r v a t i o n a l u n i t s . Claassen and Barber (31) developed a d e p l e t i o n technique which enables an a d d i t i o n a l parameter C . ( e x t e r n a l c o n c e n t r a t i o n at which net n u t r i e n t min uptake ceases) to be obtained. Barber (13) and N i e l s e n (106) have suggested that t h i s parameter be used as an a d d i t i o n a l measure of e f f i c i e n c y i n n u t r i e n t a c q u i s i t i o n . However, d e s p i t e reports of considerable v a r i a t i o n f o r t h i s parameter (13, 106), i t has not proved to be popular i n k i n e t i c s t u d i e s . The use of the c a r r i e r - k i n e t i c approach i s not without i t s drawbacks and c r i t i c i s m s . C r i t i c i s m has been d i r e c t e d not so much at i t s use, but rather at the i n t e r p r e t a t i o n of the r e s u l t s of i n f l u x isotherm a n a l y s i s . Clarkson (33), Clarkson and Hanson (34), Cram (38) and Wyn Jones (143) have addressed t h i s issue i n great d e t a i l . Perhaps the most cautionary note issued i s that because the s a t u r a t i o n k i n e t i c s observed can be explained by both a c t i v e and passive processes, a r o u t i n e k i n e t i c a n a l y s i s cannot y i e l d any meaningful information on the mechanism of ion uptake. As regards the parameters themselves, the major c r i t i c i s m i s that they are presented as though they are 10 constants (33, 34). Because i t has been demonstrated that they are a f f e c t e d by pl a n t v i g o u r , growth "demand", age, and i n t e r n a l n u t r i e n t s t a t u s of the roots (33, 34, 38, 45, 70, 88) they Should be used with due c a u t i o n . Cram (38) maintains that i n f l u x isotherms can only be used to d i f f e r e n t i a t e between k i n e t i c a l l y d i s t i g u i s h a b l e a l t e r n a t i v e s and that the parameters obtained from a f i t t e d r ectangular hyperbola cannot a p r i o r i be taken to c h a r a c t e r i z e the t r a n s p o r t system. Hence an apparent K cannot n e c e s s a r i l y be considered as a measure of the a f f i n i t y of a c a r r i e r f o r the transported substance. There i s c l e a r l y c o n s i d e r a b l e disagreement on the appropriate use of these parameters. In general, the area of i n f l u x k i n e t i c s remains a h i g h l y contentious one. Although most measures of n u t r i e n t uptake are based on short time p e r i o d s , average values over an extended p e r i o d can a l s o be obtained. W i l l i a m s (142) developed a procedure f o r c a l c u l a t i n g the average rate of absorption per u n i t root weight using an approach analogous to that used i n the determination of r e l a t i v e growth r a t e . This approach enables n u t r i e n t uptake ra t e s during growth to be c a l c u l a t e d and then r e l a t e d t o root and shoot growth over a s p e c i f i c time i n t e r v a l . 1.1.2. N u t r i e n t u t i l i z a t i o n The e f f i c i e n c y of n u t r i e n t u t i l i z a t i o n has been defined i n s e v e r a l ways thus making i t imperative that any reference to 11 n u t r i e n t use e f f i c i e n c y be c l a r i f i e d . Indices used include q u a l i t a t i v e measures such as the expression of d e f i c i e n c y symptoms and various measures based on ve g e t a t i v e growth or g r a i n production. Clark (32) defined an e f f i c i e n t p l a n t as "one that grows b e t t e r , produces more dry matter and develops fewer d e f i c i e n c y symptoms than another when grown at low n u t r i e n t l e v e l s " . Other researchers have opted f o r more s p e c i f i c d e f i n i t i o n s which are e i t h e r p h y s i o l o g i c a l , agronomic or e c o l o g i c a l . Even these d e f i n i t i o n s range from broad o p e r a t i o n a l ones (57, 58, 73, 95, 96, 101, 102) to more d e t a i l e d and complex d e f i n i t i o n s (26, 35, 41, 63, 64, 66, 81, 125, 133). In e c o l o g i c a l s t u d i e s n u t r i e n t c y c l i n g i s u s u a l l y included to give a broader d e f i n i t i o n of nu t r i e n t - u s e e f f i c i e n c y (133). The expression of d e f i c i e n c y symptoms has been used as an i n d i c a t o r of tolerance to l i m i t i n g n u t r i e n t c o n d i t i o n s i n many stu d i e s (15, 22, 56, 112, 113). However, because the appearance and s e v e r i t y of d e f i c i e n c y symptoms can vary c o n s i d e r a b l y i n response to changing environmental c o n d i t i o n s , t h i s index i s sometimes considered to be u n r e l i a b l e . Gabelman and G e r l o f f (64) reported that i n a l f a l f a the use of d e f i c i e n c y symptoms as an i n d i c a t o r f o r e f f i c i e n c y can be misleading since i t i s the f a s t e r growing genotypes that e x h i b i t these symptoms e a r l i e r than the slow growing genotypes. S t i l l , c r i t i c i s m of t h i s index on the b a s i s of i t s l a b i l i t y i s perhaps u n f a i r since i t has been demonstrated that other i n d i c e s can vary c o n s i d e r a b l y i n response to changing environmental c o n d i t i o n s (10, 35, 68). 12 In terms of a c t u a l economic y i e l d produced, nutrient-use e f f i e n c y has been defined as the amount of harvestable product produced per u n i t of n u t r i e n t a p p l i e d to or taken up by the p l a n t . The former measure does not d i f f e r e n t i a t e between a c q u i s i t i o n and u t i l i z a t i o n whereas the l a t t e r i s a measure of what Coltman et a l . (35) r e f e r to as " i n t e r n a l u t i l i z a t i o n " . Measures based on the amount of n u t r i e n t a p p l i e d are more convenient for agronomic s t u d i e s whereas those based on the amount of n u t r i e n t taken up are more appropriate f o r p h y s i o l o g i c a l s t u d i e s . Gabelman and G e r l o f f (63, 64) e s t a b l i s h e d the e s s e n t i a l c r i t e r i o n f o r c l a s s i f y i n g genotypes as i n e f f i c i e n t or e f f i c i e n c t w ith respect to dry matter production. Their approach e n t a i l s growing the p l a n t s at both l i m i t i n g and adequate n u t r i e n t l e v e l s and then comparing dry matter production at the two l e v e l s . A c c o r d i n g l y , a genotype can only be considered to be i n e f f i c i e n t i f i t y i e l d s poorly at the low n u t r i e n t l e v e l but j u s t as w e l l as an e f f i c i e n t one at the high n u t r i e n t l e v e l . This prevents p h y s i o l o g i c a l l y impaired genotypes from being c l a s s i f i e d as i n e f f i c i e n t f o r reasons other than t h e i r i n a b i l i t y to make e f f e c t i v e use of n u t r i e n t s at l i m i t i n g l e v e l s . Although i t i s very u s e f u l for the examination of v a r i e t a l d i f f e r e n c e s , t h i s approach i s very demanding p a r t i c u l a r l y i f n u t r i e n t l e v e l s are to be maintained throughout the growth pe r i o d . A l s o , i t does not e a s i l y lend i t s e l f to genetic s t u d i e s . I t should be pointed out that i n most s t u d i e s the n u t r i e n t of i n t e r e s t has been a p p l i e d i n a s i n g l e dose at the beginning of the experiment and 13 that the p l a n t s have been grown separately to prevent any competition e f f e c t s . S a t i s f a c t o r y measures of n u t r i e n t - u s e e f f i c i e n c y are then obtained i f i t can be demonstrated that a l l the a p p l i e d n u t r i e n t has been.taken up by the plant (63, 64). However, i n some st u d i e s i t has been shown that at the time considered most appropriate f o r h a r v e s t i n g , not a l l the n u t r i e n t has been taken up by a l l genotypes (68). In t h i s instance d i f f e r e n c e s i n n u t r i e n t - u s e e f f i c i e n c y must then be a t t r i b u t e d to both d i f f e r e n t i a l uptake and i n t e r n a l u t i l i z a t i o n . A s i m i l a r approach based on r e l a t i v e y i e l d has been adopted i n f i e l d s t u d i e s (58, 73, 101, 102). To do so, p a i r e d p l o t s , one of which receives no f e r t i l i z e r while the other i s adequately f e r t i l i z e d are set up i n an appropriate design. An index of r e l a t i v e y i e l d i s then obtained as the r a t i o of y i e l d without f e r t i l i z e r to that with f e r t i l i z e r . When used i n conjunction with the a c t u a l y i e l d data, t h i s approach provides a sound b a s i s f o r s e l e c t i o n . Of course s e l e c t i o n f o r adaptation to low n u t r i e n t c o n d i t i o n s can simply be undertaken by growing the genotypes i n one environment. To enable more convenient e v a l u a t i o n of n u t r i e n t - u s e e f f i c i e n c y and the study of i t s i n h e r i t a n c e , the concept of e f f i c i e n c y r a t i o was developed (63, 64, 66). This r a t i o , sometimes known as the u t i l i z a t i o n quotient represents the amount of biomass produced per u n i t of n u t r i e n t present, i . e . i t i s the r e c i p r o c a l of c o n c e n t r a t i o n . I t can be based on t o t a l biomass produced (roots plus shoots) or only on the amount of above-ground biomass produced. Normally i t s c a l c u l a t i o n does 14 not take n u t r i e n t d i s t r i b u t i o n i n t o account but assumes instead that the n u t r i e n t i s uniformly d i s t r i b u t e d throughout the p l a n t ; an assumption which has been shown to be i n c o r r e c t (92). Hence i t i s conceivable that although a genotype may have a low average n u t r i e n t c o n c e n t r a t i o n , i t s n u t r i e n t c o n c e n t r a t i o n at a c t i v e l y growing s i t e s may be s i m i l a r to that of a v a r i e t y w i t h a higher average n u t r i e n t c o n c n t r a t i o n . C a l c u l a t i o n s based on o v e r a l l content are even more suspect due to the uneven d i s t r i b u t i o n of the n u t r i e n t between roots and shoots. A l s o , the d i f f e r e n t r o l e s that the n u t r i e n t plays i n the shoots and roots r e q u i r e s more c a r e f u l c o n s i d e r a t i o n before an o v e r a l l average value can be used f o r the c a l c u l a t i o n of n u t r i e n t - u s e e f f i c i e n c y . Clarkson (34) maintains that the use of average values has probably obscured some very i n t e r e s t i n g f i n d i n g s i n p l a n t mineral n u t r i t i o n . Although w e l l taken, t h i s c r i t i c i s m represents a major challenge to p l a n t p h y s i o l o g i s t s since i t r e q u i r e s that the n u t r i e n t l e v e l s i n the p l a n t be very c a r e f u l l y monitored. For the researcher who i s i n t e r e s t e d i n improving n u t r i e n t - u s e e f f i c i e n c y i t i s questionable whether such d e t a i l e d and tedious s t u d i e s would r e a l l y be worth the e x t r a e f f o r t r e q u i r e d . Despite i t s s i m p l i c i t y and widespread use, the e f f i c i e n c y r a t i o has a number of shortcomings some of which have already been a l l u d e d t o . Chapin I I I (28) maintains that because i t can be a f f e c t e d by s e v e r a l f a c t o r s which have q u i t e d i f f e r e n t p o t e n t i a l s to c o n t r i b u t e to p r o d u c t i v i t y , a d i f f e r e n t index might be p r e f e r r e d . Such f a c t o r s would include luxury 15 consumption, la r g e vacuolar storage reserves, the development of f i b r o u s and c u t i c u l a r t i s s u e , and the accumulation of sugars and storage carbohydrates. He suggests that the index be based on a c t u a l p h y s i o l o g i c a l processes such as r e s p i r a t i o n , photosynthesis or net a s s i m i l a t i o n r a t e i n s t e a d . Although these are v a l i d c r i t i c i s m s which undoubtedly re q u i r e more c a r e f u l c o n s i d e r a t i o n i n studi e s undertaken to e s t a b l i s h the underlying p h y s i o l o g i c a l b a s i s of d i f f e r e n c e s i n nu t r i e n t - u s e e f f i c i e n c y , i t i s h i g h l y u n l i k e l y that they can be taken i n t o c o n s i d e r a t i o n during the r o u t i n e screening and breeding for improved n u t r i e n t -use e f f i c i e n c y . In an a g r i c u l t u r a l context the e f f i c i e n c y r a t i o i s undoubtedly inadequate as a measure of nu t r i e n t - u s e e f f i c i e n c y . Studies i n d i c a t e that those genotypes with the highest e f f i c i e n c y r a t i o are not n e c e s s a r i l y the highest y i e l d e r s (64, 66, 85, 92, 94). A l s o , t h i s index does not i n d i c a t e how nu t r i e n t - u s e e f f i c i e n c y might best be improved. Spedding (129) and Spedding et a l . (130) c o r r e c t l y point out that i t should be r e a d i l y apparent from an index how the e f f i c i e n c y of the process or system can be improved. S i d d i q i and Glass (125) provided a c r i t i c a l a n a l y s i s of the e f f i c i e n c y r a t i o and concluded that n u t r i e n t concentration rather than n u t r i e n t content should be considered i n the d e r i v a t i o n of a more appropriate index. As such, they proposed the adoption of an index termed " e f f i c i e n c y of u t i l i z a t i o n " which i s the amount of biomass produced per u n i t of t i s s u e n u t r i e n t c o n c e n t r a t i o n . This i s c l e a r l y a better index because 16 i t takes the a c t u a l amount of biomass produced i n t o c o n s i d e r a t i o n . In a s i m p l i f i e d form i t i s the product of the e f f i c i e n c y r a t i o and the amount of biomass produced per p l a n t . For comparative purposes they suggested that a " u t i l i z a t i o n index" ( r a t i o of e f f i c i e n c i e s of u t i l i z a t i o n ) be used i n a manner analogous to that used f o r the comparison of water-use e f f i c i e n c y . This index i s thus a r a t i o of the biomass r a t i o to the t i s s u e c o n c e n t r a t i o n r a t i o (125) and i t shows how, i f one i s to adopt a f a i r l y s i m p l i s t i c approach, n u t r i e n t - u s e e f f i c i e n c y can be improved. Unfortunately i t i s not c l e a r i f such an endeavour would be as s t r a i g h t f o r w a r d as the index i n d i c a t e s . A l s o , the use of the u t i l i z a t i o n index does pose a s t a t i s t i c a l problem when comparing a la r g e number of v a r i e t i e s . Because i t cannot be subjected to r o u t i n e s t a t i s t i c a l a n a l y s i s , e v a l u a t i o n s must t h e r e f o r e be l a r g e l y s u b j e c t i v e . This issue i s of c r u c i a l importance i n p h y s i o l o g i c a l s t u d i e s where i t has been shown that e r r o r v a r i a t i o n i s considerable (55, 68, 91, 126, 127). Nutrient-use e f f i c i e n c y has a l s o been c a l c u l a t e d i n a manner analogous to that used f o r the c a l c u l a t i o n of average net f l u x . Keay et a l . (81) termed t h i s measure " s p e c i f i c u t i l i z a t i o n r a t e " . E s s e n t i a l l y i t i s the average rate of dry matter production per u n i t n u t r i e n t taken up per u n i t time. However, because the causal connection between n u t r i e n t uptake and biomass production i s not e x c l u s i v e , the use of t h i s approach has been discouraged (76, 98). There i s some debate over the c o n d i t i o n s under which n u t r i e n t - u s e e f f i c i e n c y should be determined. Barber (11) and 17 F i s c h e r (57, 58) maintain that e v a l u a t i o n s should be done under high f e r t i l i t y c o n d i t i o n s such that the y i e l d s obtained can be considered to be economical. Their arguement i s e s s e n t i a l l y an economic one and not one that i s based on b i o l o g i c a l e f f i c i e n c y . C l e a r l y , i f the o b j e c t i v e i s to produce genotypes which are more productive under low f e r t i l i t y c o n d i t i o n s , v a r i e t a l comparisons should be made under these c o n d i t i o n s . Blum (17), on the other hand, has proposed that s e l e c t i o n be done under high f e r t i l i t y c o n d i t i o n s but that the s e l e c t i o n c r i t e r i a i nclude those a t t r i b u t e s that are l i k e l y to improve performance under low f e r t i l i t y c o n d i t i o n s . This approach i s u n l i k e l y to be s u c c e s s f u l since these a t t r i b u t e s are only l i k e l y to be manifest under the appropriate c o n d i t i o n s . 1.1.3. Genetic v a r i a b i l i t y i n mineral n u t r i t i o n Many s t u d i e s have been undertaken to examine the extent of genetic v a r i a t i o n i n mineral n u t r i t i o n . Aspects examined incl u d e d i f f e r e n t i a l growth and y i e l d response to varying n u t r i e n t l e v e l s , " n u t r i e n t uptake i n c l u d i n g i t s r e g u l a t i o n and k i n e t i c s , t r a n s l o c a t i o n , accumulation, s u s c e p t i b i l i t y to low and t o x i c n u t r i e n t l e v e l s , and e f f i c i e n c y of u t i l i z a t i o n . The extent of t h i s v a r i a t i o n has been documented i n s e v e r a l p u b l i c a t i o n s (20, 23, 25, 29, 32, 35, 47, 49, 50, 66, 69, 75, 85, 94, 100, 111, 134, 136). The considerable v a r i a t i o n observed augurs w e l l f o r the development of n u t r i e n t - e f f i c i e n t 18 c u l t i v a r s provided that t h i s v a r i a b i l i t y can be adequately e x p l o i t e d i n p l a n t breeding programmes. Such genotypes would be expected to perform w e l l under c o n d i t i o n s of n u t r i e n t l i m i t a t i o n or make b e t t e r use of heavy a p p l i c a t i o n s of f e r t i l i z e r . Although the v a r i a b i l i t y observed i n a number of these t r a i t s i s l a r g e l y g e n e t i c , d i f f e r e n c e s i n ion uptake should be examined more c a r e f u l l y due t o the complexity of t h i s t r a i t . Some d i f f i c u l t i e s i n the i n t e r p r e t a t i o n of genotypic d i f f e r e n c e s may a r i s e due to the methodology used to measure n u t r i e n t uptake, i t s v a r i a t i o n with p l a n t age, and a l s o because i t i s governed by the i n t e r n a l n u t r i e n t s t a t u s of the r o o t s . F i t t e r and Hay (60) thus argue that ion uptake i s not g e n e t i c a l l y f i x e d and that some of the d i f f e r e n c e s observed may be p a r t l y a r t e f a c t u a l due to the use of s t a r v a t i o n media p r i o r to making the f l u x determinations. Studies on potassium uptake i n barley have c l e a r l y shown that i n f l u x i s extremely s e n s i t i v e to the i n t e r n a l root potassium co n c e n t r a t i o n (70). For n i t r a t e uptake the s i t u a t i o n i s more complex with the p o s s i b i l i t y that i n f l u x may be subject to feedback c o n t r o l by organic pools as w e l l (34, 37, 39). The k i n e t i c parameter K m has aso been shown to be a f f e c t e d by i n t e r n a l root n u t r i e n t s t a t u s although i n a l e s s p r e d i c t a b l e manner than V (33, 45, 70, 88). This i s unquestionably an e x c i t i n g area of research f o r p l a n t p h y s i o l o g i s t s and i t has generated a considerable amount of controversy. For the p l a n t g e n e t i c i s t , however, these complications can lead to great d i f f i c u l t y i n the e l u c i d a t i o n of the genetic b a s i s of observed 19 d i f f e r e n c e s i n n u t r i e n t uptake r a t e . At issue i s the extent to which observed d i f f e r e n c e s are due to d i f f e r e n c e s i n i n t e r n a l n u t r i e n t s t a t u s of the roots or a c t u a l genetic d i f f e r e n c e s i n uptake c a p a c i t y . The proper r e s o l u t i o n of t h i s question r e q u i r e s that root n u t r i e n t concentrations be a l s o considered when making comparisons f o r uptake r a t e s . Although some researchers have taken cognisance of t h i s issue when r e p o r t i n g t h e i r r e s u l t s (69, 71, 91, 126, 127), others have tended to overlook t h i s very important c o n s i d e r a t i o n . However, f o r other n u t r i e n t s such as n i t r a t e f o r which the feedback c o n t r o l s are more complex, i t i s questionable whether simultaneous c o n s i d e r a t i o n of the i n t e r n a l root n u t r i e n t s t a t u s i s r e a l l y meaningful f o r the proper i n t e r p r e t a t i o n of genotypic d i f f e r e n c e s i n uptake. 1.2. Wheat c u l t i v a t i o n : some h i s t o r i c a l , agronomic and p h y s i o l o g i c a l aspects. Because the m a t e r i a l used i n t h i s study i s re p r e s e n t a t i v e of wheat v a r i e t i e s developed over a considerable p e r i o d of time during which breeding o b j e c t i v e s and agronomic p r a c t i c e s have changed c o n s i d e r a b l y , a b r i e f d i s c u s s i o n of these changes i s incl u d e d . U n t i l the mid-1960's most wheat-producing areas, p a r t i c u l a r l y those i n developing c o u n t r i e s , were planted to landraces and improved t a l l t r a d i t i o n a l v a r i e t i e s . In general 20 these v a r i e t i e s were s e l e c t e d and grown under c o n d i t i o n s of low to moderate f e r t i l i t y , t h e i r main v i r t u e being s u r v i v a l under humid t r o p i c a l c o n d i t i o n s rather than y i e l d p o t e n t i a l (84). The mid-1960's represented a watershed i n wheat production i n many of these areas since i t marked the beginning of what i s p o p u l a r l y known as the "Green Re v o l u t i o n " . The s o - c a l l e d Green Revolution o r i g i n a t e d i n Mexico where, s t a r t i n g i n 1943, a cooperative a g r i c u l t u r a l research programme was undertaken by the R o c k e f e l l e r Foundation and the Mexican government. Because s o i l f e r t i l i t y s t u d i e s i n d i c a t e d that n i t r o g e n d e f i c i e n c y was u b i q u i t o u s , major emphasis was placed on the improvement of s o i l f e r t i l i t y and the development of v a r i e t i e s b e t t e r able to perform under high f e r t i l i t y c o n d i t i o n s . The s h u t t l e breeding s t r a t e g y adopted not only halved the time required to produce a v a r i e t y but a l s o l e d to the development of widely adapted p h o t o p e r i o d - i n s e n s i t i v e s t r a i n s which could be grown i n other p a r t s of the world (18,. 19). Although the programme i n i t i a l l y met w i t h some success, i t soon became apparent that lodging was severely l i m i t i n g f u r t h e r y i e l d increases (18). S u i t a b l e dwarfing genes were th e r e f o r e sought and f i n a l l y obtained from the Japanese v a r i e t y Norin 10'. Their use r e s u l t e d i n the development of a number of semidwarf v a r i e t i e s b e t t e r able to perform under high f e r t i l i t y c o n d i t i o n s . In response to the need for much shorter v a r i e t i e s responsive to even higher n i t r o g e n l e v e l s , double dwarfs were subsequently developed. The spectacular y i e l d increases 21 a s s o c i a t e d with the widespread c u l t i v a t i o n of these v a r i e t i e s under optimal c o n d i t i o n s became known as the Green Revolution. This remarkable improvement i n g r a i n p r o d u c t i v i t y was not unprecedented. The Japanese had e a r l i e r achieved equally s p e c t a c u l a r r e s u l t s by adopting a s i m i l a r approach (6). More r e c e n t l y t r i p l e dwarfs have been produced presumably for c u l t i v a t i o n under even higher f e r t i l i t y c o n d i t i o n s . As of 1975 these v a r i e t i e s were not widely grown due to f e r t i l i z e r shortages as w e l l as the lack of adequate disease r e s i s t a n c e (115). A number of agronomic s t u d i e s have been undertaken to compare the t a l l t r a d i t i o n a l types with the v a r i o u s dwarf v a r i e t i e s . Of p a r t i c u l a r i n t e r e s t has been t h e i r response to n i t r o g e n a p p l i c a t i o n . A l l r e p o r t s show that under high f e r t i l i t y c o n d i t i o n s the dwarf types are f a r s u p e r i o r to the t a l l types (18, 19, 53, 59, 65, 77, 84). S i m i l a r f i n d i n g s have been reported i n s t u d i e s on r i c e (54). In terms of nitrogen u t i l i z a t i o n as measured by the increase i n g r a i n production per u n i t increase i n a p p l i e d n i t r o g e n , the dwarf types are, as expected, superior to the t a l l types. In surveys done i n I n d i a , average g r a i n - n i t r o g e n conversion r a t i o s of 17-20 kg/kg N and 8-12 kg/kg N were reported f o r the dwarf and t a l l types r e s p e c t i v e l y (5, 6). S i m i l a r s t u d i e s have not been reported for potassium and phosphate. Other comparative s t u d i e s have examined a t t r i b u t e s such as growth and development, dry matter production and p a r t i t i o n i n g , t i l l e r i n g , s p i k e l e t f e r t i l i t y , r o o t i n g , and n i t r o g e n metabolism 22 (2, 3, 7, 41, 43, 53). The most s i g n i f i c a n t f i n d i n g i s that although these v a r i e t i e s produce s i m i l a r amounts of above-ground biomass, there are marked d i f f e r e n c e s i n t h e i r harvest i n d i c e s (84). Kulshrestha and J a i n (84) reported values of 16-30% and 35-46% fo r the t a l l and dwarf types r e s p e c t i v e l y . The dwarf types a l s o e x h i b i t e d greater t i l l e r i n g and s p i k e l e t f e r t i l i t y . Only a few p h y s i o l o g i c a l s t u d i e s have been reported. A b r o l e t . a l . (2) examined i n v i t r o n i t r a t e reductase a c t i v i t y (NRA) i n ten c o n t r a s t i n g genotypes at f i v e n itrogen l e v e l s and reported s i g n i f i c a n t d i f f e r e n c e s i n enhancement of NRA. However they observed no a s s o c i a t i o n between NRA enhancement and height phenotype. Kulshrestha and Tsunoda (83) examined e i g h t v a r i e t i e s and found that the dwarfs had higher photosynthetic and r e s p i r a t o r y rates per u n i t l e a f area than the t a l l types. S i g n i f i c a n t d i f f e r e n c e s between the v a r i o u s dwarf types were a l s o evident. I t i s s u r p r i s i n g that the n u t r i e n t a c q u i s i t i o n and' u t i l i z a t i o n p r o p e r t i e s of these v a r i e t i e s have not been examined i n great d e t a i l . Such s t u d i e s would not only enable t h e i r physiology w i t h respect to mineral n u t r i t i o n to be b e t t e r understood, but they could a l s o p o s s i b l y e x p l a i n t h e i r d i f f e r i n g response to f e r t i l i z e r a p p l i c a t i o n . In a d d i t i o n , such f i n d i n g s could prove informative f o r the genetic improvement of n u t r i e n t -use e f f i c i e n c y . 23 2 . M a t e r i a l s and Methods 2 . 1 . Wheat l i n e s L i m i t e d seed q u a n t i t i e s of a div e r s e c o l l e c t i o n of wheat v a r i e t i e s were obtained from the I n t e r n a t i o n a l Maize and Wheat Improvement Centre (CIMMYT) i n Mexico and the A g r i c u l t u r a l Research I n s t i t u t e i n New D e l h i , I n d i a . The v a r i e t i e s were grown i n a nursery to increase seed q u a n t i t i e s and a l s o to check t h e i r u n i f o r m i t y . Twenty four of these v a r i e t i e s were s e l e c t e d f o r t h i s study. The names, o r i g i n , height phenotypes and pedigrees of the s e l e c t e d v a r i e t i e s are given i n Appendix 1 . The l i n e s were s e l e c t e d so as to be r e p r e s e n t a t i v e of d i f f e r e n t periods i n the h i s t o r y of wheat breeding; periods c h a r a c t e r i z e d by d i f f e r e n t o b j e c t i v e s , p a r t i c u l a r l y with respect to response to i n c r e a s i n g s o i l f e r t i l i t y . As such they included t a l l t r a d i t i o n a l types s e l e c t e d and grown under c o n d i t i o n s of low to moderate f e r t i l i t y i n In d i a and Mexico, as w e l l as va r i o u s dwarf types bred for improved performance under high f e r t i l i t y c o n d i t i o n s . The dwarf types comprised semidwarfs, double dwarfs and t r i p l e dwarfs. 2 . 2 . P l a n t c u l t u r e I n i t i a l l y the twenty four v a r i e t i e s were examined f o r d i f f e r e n c e s i n potassium and nitrogen uptake and u t i l i z a t i o n . Two experimental approaches were adopted; potassium-limited and both potassium and n i t r a t e - l i m i t e d . The former was used to 24 examine only potassium uptake and u t i l i z a t i o n whereas the l a t t e r was used to study the uptake and u t i l i z a t i o n of both elements c o n c u r r e n t l y . The reasons f o r i n c l u d i n g both elements at l i m i t i n g l e v e l s i n the second type of experiment were as f o l l o w s . F i r s t to examine n u t r i e n t uptake and u t i l i z a t i o n under c o n d i t i o n s of dual n u t r i e n t l i m i t a t i o n . Second to enable a more expansive genetic a n a l y s i s of uptake and u t i l i z a t i o n t o be undertaken bearing i n mind that space l i m i t a t i o n precluded the use of l a r g e , and hence more r e l i a b l e sample s i z e s f o r the generation mean and variance a n a l y s i s . The experiments were conducted i n a growth room maintained on 25/l8±2°C day/night temperature regime and 16h photoperiod. L i g h t i n g was provided by ' V i t a - l i t e ' f l u o r e s c e n t tubes t o give a -2 -1 photosynthetIC f l u x d e n s i t y of 200 ±10 uE m s . R e l a t i v e humidity was not monitored. Because the l i g h t i n t e n s i t y over the experimental area was not h i g h l y v a r i a b l e , a l l the experiments were l a i d out i n a completely randomised design. A l l the experiments were done i n 721 c a p a c i t y blackened p l e x i g l a s s tanks designed to hold 96 p l e x i g l a s s d i s c s which supported the p l a n t s . Only 48 of these l o c a t i o n s were used i n most s t u d i e s so as to reduce a e r i a l competition and root entanglement. Each tank a l s o had a mixing compartment f o r the placement of a c i r c u l a t i o n pump (Model IC-2, Brinkman Instruments) and a i r s t o n e f o r a e r a t i o n of the n u t r i e n t s o l u t i o n . The s o l u t i o n s were continuously mixed v i a a system of p e r f o r a t e d PVC tubes. N u t r i e n t l e v e l s were replenished by pumping i n the appropriate s o l u t i o n s i n t o the mixing compartment of each tank 25 using v a r i a b l e speed p e r i s t a l t i c pumps ( F l u i d Metering, I n c . ) . The q u a n t i t y of s o l u t i o n i n each tank was maintained by a l l o w i n g any excess s o l u t i o n to d r a i n o f f . Seeds were s u r f a c e - s t e r i l i z e d i n 1% sodium h y p o c h l o r i t e , thoroughly r i n s e d and germinated overnight on moist f i l t e r paper i n s t e r i l e p e t r i p l a t e s . Uncontaminated seeds showing good germination were then placed on the gauze of c o l l a r e d p l e x i g l a s s d i s c s (5-6 seeds per d i s c ) p a r t i a l l y embedded i n t r a y s of moist s t e r i l e sand. The seeds were then covered with moist s t e r i l e sand and the t r a y s sealed i n black polyethylene bags. Two days l a t e r the bags were removed and the t r a y s were then placed i n an i l l u m i n a t e d area. A f t e r two more days the d i s c s were gen t l y removed from the t r a y s , washed free of sand i n running water and then placed i n the tanks. A f t e r 3-4 days the p l a n t s were thinned so that each d i s c held three even s i z e d s e e d l i n g s . A maintained potassium co n c e n t r a t i o n of lOpM was adopted as the s t r e s s l e v e l on the b a s i s of the f i n d i n g s of S i d d i q i and Glass (126, 127). P r e l i m i n a r y observations i n d i c a t e d that p l a n t s grown at t h i s c o n c e n t r a t i o n developed i n c i p i e n t potassium d e f i c i e n c y symptoms by two weeks. For the experiments r e q u i r i n g the i m p o s i t i o n of n i t r o g e n s t r e s s , a n i t r a t e concentration of 30uM was used. This c o n c e n t r a t i o n was based on the r e s u l t s of p r e l i m i n a r y s t u d i e s i n which p l a n t performance at various n i t r a t e l e v e l s was v i s u a l l y assessed. Due to the h i g h l y d e t r i m e n t a l e f f e c t of nitrogen s t r e s s , symptoms of i n c i p i e n t d e f i c i e n c y were not used as a c r i t e r i o n f o r determining the appropriate s t r e s s c o n c e n t r a t i o n . 26 The compositions of the n u t r i e n t s o l u t i o n s used are given i n Table 1. Both are m o d i f i c a t i o n s of the s o l u t i o n used by Johnson et a l . (80). The s o l u t i o n used i n the potassium-l i m i t e d experiments was prepared such that when d i l u t e d 100 times i t provided a potassium concentration of 1OuM and the other n u t r i e n t s , except calcium, at 1/I00th the standard c o n c e n t r a t i o n . For the potassium plus n i t r a t e - l i m i t e d experiments ammonium phosphate was replaced with potassium phosphate thus a l l o w i n g f o r the nitrogen l e v e l to be maintained by p r o v i d i n g n i t r a t e s e p a r a t e l y as calcium n i t r a t e . When d i l u t e d 100 times t h i s s o l u t i o n a l s o provided potassium at a co n c e n t r a t i o n of 10pM. However, the i n i t i a l c o ncentrations of some of the other n u t r i e n t s were not i d e n t i c a l to those i n the po t a s s i u m - l i m i t e d experiments. For t h i s and other reasons, any d i f f e r e n c e s i n pla n t performance between the two types of experiments cannot be a t t r i b u t e d to any one s p e c i f i c f a c t o r . To maintain the d e s i r e d n u t r i e n t l e v e l s , potassium and n i t r a t e c o n centrations were monitored d a i l y and the pumping rat e s adjusted i f necessary. Potassium was measured by flame photometry (Instrumentation Laboratory 443) and n i t r a t e by the U.V. ab s o r p t i o n method of Cawse (27). During the course of the experiments the potassium and n i t r a t e concentrations v a r i e d from 7-12yM and 22-38uM r e s p e c t i v e l y . N u t r i e n t uptake and u t i l i z a t i o n were determined a f t e r three weeks of growth. A growth pe r i o d of three weeks was se l e c t e d p r i m a r i l y to f a c i l i t a t e the experiments, p a r t i c u l a r l y the genetic s t u d i e s i n which observations had to be made on 27 Table 1. Composition of n u t r i e n t stock s o l u t i o n s used i n potassium and potassium plus n i t r a t e - l i m i t e d experiments. K + - l i m i t e d K ++ NOf - l i m i t e d * Compound Concentration (ml/1) (ml/1) Ca(N0 3) 2 .4H20 1M 6.5 KN0 3 1M 1 .0 NH 4H 2P0 4 1M 2.0 MgS0 4 1M 1.0 1 .0 KH2PO A 200mM 5.0 CaSO 4 1 OmM -< 250 KC1 50mM H 3 B O 3 25mM MnSO4.H20 2.0 mM ZnS0 4.7H 20 2. OmM >- 1.0 1 .0 CuS0 4.5H 20 0. 5mM H 2Mo0 4 0. 5mM FeNa-EDTA 4 OmM 1.0 1 .0 * N i t r a t e provided separately as C a ( N 0 3 ) 2 to give approximately 30uM n i t r a t e throughout the growth p e r i o d . 28 s u f f i c i e n t l y l a r g e i n d i v i d u a l p l a n t s . 2.3. N u t r i e n t uptake and u t i l i z a t i o n determination Net n u t r i e n t f l u x e s were determined by d e p l e t i o n of a 200uM potassium n i t r a t e plus 0.5mM calcium sulphate s o l u t i o n at a o temperature of 21 C. A l l f l u x determinations were done s t a r t i n g f i v e hours a f t e r the beginning of the l i g h t c y c l e to reduce the e f f e c t s of d i u r n a l v a r i a t i o n i n n u t r i e n t uptake. The p l a n t s were i n i t i a l l y placed i n a l a r g e volume of aerated uptake s o l u t i o n f o r 10 minutes to allo w f o r e q u i l i b r a t i o n of the root f r e e space. They were then g e n t l y placed i n 190ml of aerated uptake s o l u t i o n h eld i n PVC v e s s e l s . Depletion was measured by drawing 1ml samples a f t e r 30 and 60 minutes and determining t h e i r potassium and n i t r a t e concentrations as described p r e v i o u s l y . Roots were then e x c i s e d , spun i n a basket c e n t r i f u g e f o r 20 seconds to remove surface water and weighed. Three estimates of net f l u x could t h e r e f o r e be obtained f o r the time periods 0-30, 0-60 and 30-60 minutes. In the po t a s s i u m - l i m i t e d s t u d i e s the roots and shoots were ashed s e p a r a t e l y at 450 C f o r 24h and 48h r e s p e c t i v e l y and the ash suspended i n 20ml of d i s t i l l e d water f o r potassium determination. Root potassium concentrations were determined p r i m a r i l y f o r the purpose of examining and i n t e r p r e t i n g v a r i e t a l d i f f e r e n c e s i n potassium uptake p r i o r to undertaking the genetic s t u d i e s . However, i n the potassium plus n i t r a t e - l i m i t e d experiments root n u t r i e n t concentrations were not determined. 29 Instead, the shoots were d r i e d at 80° C f o r 48h, weighed and f i n e l y ground i n a mortar and p e s t l e . Part of t h i s sample was used f o r t o t a l n itrogen determination by CHN a n a l y s i s (Elemental Analyzer, Model 1106, C a r l o Erba Instumentazione) and the r e s t was ashed and then analyzed f o r potassium. N u t r i e n t u t i l i z a t i o n was expressed as shoot weight, e f f i c i e n c y r a t i o and u t i l i z a t i o n e f f i c i e n c y . Fresh weights were used i n the p o t a s s i u m - l i m i t e d experiments whereas dry weights were used i n the potassium plus n i t r a t e - l i m i t e d s t u d i e s . To obtain estimates of potassium uptake during growth average net f l u x e s on an hourly b a s i s over a 16-day p e r i o d (5-21 days a f t e r germination) were c a l c u l t e d . To do so, average root and shoot weights and t h e i r potassium contents were obtained and average f l u x e s then c a l c u l a t e d according to the method of Wi l l i a m s (142) as shown below. l o g R_ - l o g R. c_ - C. Average f l u x = —^—= £_L • _ f L where R j and R 2 are the root weights, and and C 2 are the t o t a l p l a n t potassium contents at times tj and t 2 r e s p e c t i v e l y . The values f o r time t j were obtained before t r a n s f e r r i n g the p l a n t s t o the hydroponic tanks. Because a l l c a l c u l a t i o n s were based on average values f o r each h a r v e s t , s t a t i s t i c a l a n a l y s i s of t h i s data was not undertaken. 30 2.4. I n f l u x k i n e t i c s Nine v a r i e t i e s were s e l e c t e d f o r a more d e t a i l e d study of t h e i r potassium and n i t r a t e uptake p r o p e r t i e s i n the range of Mechanism I . For each study, only eight of these v a r i e t i e s were used. The requirements of these s t u d i e s precluded the examination of a l a r g e r number of v a r i e t i e s . The p l a n t s were grown as p r e v i o u s l y described under e i t h e r potassium or potassium and n i t r a t e - l i m i t e d c o n d i t i o n s . Due to the requirement for a larg e number of o b s e r v a t i o n a l u n i t s a l l 96 l o c a t i o n s i n a tank were used. Twelve d i s c s , each holding three p l a n t s were assigned to each v a r i e t y . This allowed for three f l u x determinations to be made at the two lowermost e x t e r n a l c o n c e n t r a t i o n s and two r e p l i c a t e s to be used f o r the three higher c o n c e n t r a t i o n s . Potassium i n f l u x measurements at e x t e r n a l concentrations of 10, 25, 50, 100, and 200uM potassium n i t r a t e p l u s 0.5mM calcium 86 sulphate were determined using Rb as a t r a c e r . D i f f i c u l t i e s encountered when attempting t o measure f l u x e s at low 86 concentrations by the d e p l e t i o n technique n e c e s s i t a t e d that Rb be used. I n i t i a l l y the p l a n t s were placed i n a larg e volume of aerated but u n l a b e l l e d s o l u t i o n i d e n t i c a l i n composition to the uptake s o l u t i o n to allow f o r e q u i l i b r a t i o n of the root f r e e space. Thereafter they were placed i n 190ml of aerated and l a b e l l e d s o l u t i o n of known s p e c i f i c a c t i v i t y . A f t e r 10 minutes the p l a n t s were removed from the v e s s e l s and the free space r a d i o l a b e l removed by desorption i n i c e - c o l d u n l a b e l l e d uptake 31 s o l u t i o n f o r 10 minutes. To reduce the quenching e f f e c t of a l a r g e root mass, only a sample of the roots was ashed, suspended i n 10ml of d i s t i l l e d water and then counted (Searle Isocap/300 S c i n t i l l a t i o n Counting System, Searle A n a l y t i c , I n c . ) . I n f l u x values were then computed and root potassium concentrations determined as w e l l . For n i t r a t e , i n f l u x e s at e x t e r n a l c o ncentrations of 30, 70, 100, 200 and 300uM potassium n i t r a t e plus 0.5mM calcium sulphate were obtained by d e p l e t i o n . Samples (1ml) from the uptake s o l u t i o n were drawn a f t e r 15 and 30 minutes. I n f l u x isotherms based on the Michaelis-Menten formalism were f i t t e d to the data and the k i n e t i c parameters V and K c max m obtained by l i n e a r i z a t i o n of the Michaelis-Menten equation using the Wolf- Augustinsson-Hofstee p l o t (123). P l o t s f o r potassium and n i t r a t e i n f l u x are shown i n Appendices 2, 3, 4 and 5. 32 3. R e s u l t s and Dis c u s s i o n The extent of v a r i a t i o n f o r potassium and ni t r o g e n uptake and u t i l i z a t i o n was i n i t i a l l y examined across a l l the v a r i e t i e s . T h e r e a f t e r , so as to enable the comparison of v a r i e t i e s developed during d i f f e r e n t periods i n the h i s t o r y of wheat breeding the v a r i e t i e s were assigned to f i v e height c a t e g o r i e s as shown i n Table 2. I t should be pointed out that these are simply height phenotypes and that they do not n e c e s s a r i l y r e f l e c t genetic c h a r a c t e r i z a t i o n (65). A l s o , some of the des i g n a t i o n s are not i n agreement with those reported elsewhere (77). S t i l l , t h i s system of c l a s s i f i c a t i o n served as a convenient means of a s s i g n i n g the v a r i e t i e s to d i f f e r e n t periods i n the h i s t o r y of wheat breeding; periods c h a r a c t e r i z e d by d i f f e r e n t o b j e c t i v e s p a r t i c u l a r l y w i t h respect to response to i n c r e a s i n g s o i l f e r t i l i t y . The d e p l e t i o n technique used to measure both potassium and n i t r a t e f l u x e s y i e l d e d three values f o r short-term net f l u x f o r the time periods 0-30, 0-60 and 30-60 minutes. This was done to ensure that a r e l i a b l e measure of f l u x would be obtained. In general uptake r a t e s f o r the 0-60 and 30-60 minute periods were s i m i l a r t o , or lower than, those f o r the 0-30 minute p e r i o d . The reported values are g e n e r a l l y those f o r the 0-30 minute p e r i o d . Only i n those instances i n which there was an obvious e r r o r due, for example, to uptake v e s s e l contamination were d i f f e r e n t time periods used. S i g n i f i c a n t d i f f e r e n c e s i n short-term net potassium and 33 n i t r a t e uptake were observed i n both the potassium and potassium plus n i t r a t e - l i m i t e d experiments (Tables 3, 4 and 5). D i f f e r e n c e s were as great as t h r e e f o l d f o r short-term f l u x e s and twofold f o r average net potassium f l u x . The extent of v a r i a t i o n p a r a l l e l s that observed i n other s t u d i e s (69, 126, 127). S i g n i f i c a n t d i f f e r e n c e s i n both potassium and n i t r a t e uptake were a l s o observed between groups (Tables 5 and 6). The t a l l Indian v a r i e t i e s e x h i b i t e d the highest f l u x e s but they were not s i g n i f i c a n t l y d i f f e r e n t from the t r i p l e dwarfs except f o r potassium uptake under c o n d i t i o n s of potasssium and n i t r a t e l i m i t a t i o n (Table 6). The t a l l Mexican types were s i m i l a r to the t a l l Indian types and not s i g n i f i c a n t l y d i f f e r e n t from the semidwarfs f o r potassium uptake. However, they e x h i b i t e d s i g n i f i c a n t l y higher n i t r a t e f l u x e s than the semidwarfs. The double dwarfs showed the lowest uptake rates although they were not s i g n i f i c a n t l y d i f f e r e n t from the semidwarfs and t r i p l e dwarfs, s i g n i f i c a n t l y surpassing the l a t t e r only f o r potassium uptake under p o t a s s i u m - l i m i t i n g c o n d i t i o n s . For average net potassium uptake which, for reasons already given, was not subjected to ro u t i n e s t a t i s t i c a l a n a l y s i s , the t a l l v a r i e t i e s showed the highest values although they were not much greater than the value for the semidwarfs (Table 6). The double dwarfs again showed the lowest f l u x e s which were only s l i g h t l y lower than the value f o r the t r i p l e dwarfs. V a r i a t i o n i n average net potassium f l u x was co n s i d e r a b l y lower than that f o r short-term f l u x . A l s o , average net potassium f l u x e s were poorly c o r r e l a t e d with short-term f l u x e s 34 (Table 7). Comparison of the two f l u x e s shows that for most of the v a r i e t i e s average net f l u x e s were considerably lower than short-term f l u x e s (Table 3). This i s to be expected since average f l u x e s are acclimated f l u x e s from a s o l u t i o n of low potassium concentration whereas short-term f l u x e s were determined by d e p l e t i o n of a s o l u t i o n of much higher c o n c e n t r a t i o n . Pettersson and Jensen (111) a l s o reported very l i t t l e v a r i a t i o n for average potassium f l u x but considerable v a r i a t i o n f o r potassium i n f l u x i n barley s e e d l i n g s grown for seven days under high potassium c o n d i t i o n s . They the r e f o r e argued that p o t e n t i a l i n f l u x rates are e x p l o i t e d to only a l i m i t e d extent to meet the n u t r i e n t demand of the p l a n t . I t i s d i f f i c u l t to f o l l o w t h e i r arguement because they compared the i n f l u x values of p l a n t s grown under low potassium c o n d i t i o n s with average f l u x e s obtained under high potassium c o n d i t i o n s . I f , on the other hand, one compares t h e i r data f o r the i n f l u x e s of p l a n t s grown under high potassium c o n d i t i o n s with that for average net f l u x e s , they are found to be e s s e n t i a l l y s i m i l a r . These f i n d i n g s do nonetheless r a i s e the issue of the r e l a t i o n s h i p between f l u x e s during growth i n low n u t r i e n t s o l u t i o n s and those obtained by perturbing the system, i . e . t r a n s f e r r i n g the p l a n t s to a high n u t r i e n t s o l u t i o n so as to obtain an e a s i l y measureable f l u x value. Of t h i s more w i l l be s a i d l a t e r when p e r t u r b a t i o n and average net f l u x e s w i l l be compared at various stages of growth. Due to the w e l l known negative feedback e f f e c t of root potassium concentration on i n f l u x (70), potassium f l u x e s were 35 Table 2. V a r i e t a l grouping on the b a s i s of height and o r i g i n Group Height (cm)* V a r i e t i e s T a l l , Indian >91 T a l l , Mexican >91 Semidwarfs 76-90 Double dwarfs 61-75 T r i p l e dwarfs <60 NP 52, NP 718, Pusa 4, Pb 8A, Pb 9D, C 306, K-13 N a i n a r i 60, Chapingo 53, Yaqui50, Yaqui 54 Penjamo 62, P i t i c 62, Sonora 64, Lerma Rojo 64, Kalyansona, S i e t e Cerros, Pavon 76, Jupateco 73 Yecora 70, Tesia 79, Arjun M o t i , UP 301 * As measured i n seed increase nursery i n Vancouver. 36 Table 3. Short-term and average net potassium f l u x e s , root potassium concentrations (±SE) and root f r e s h weights of the 24 v a r i e t i e s when grown under p o t a s s i u m - l i m i t e d c o n d i t i o n s . Net K flux(umol/g/h) R 0 0 t [K +] Root weight V a r i e t y Short-term Average (umol/g) (g/plant) NP 52 7 .3 1.9 38 7±1 .36 0 .73 NP 718 5 .2 1 .8 44 ,0±2 .31 0 .61 Pusa 4 4 8 1 .5 38 2±1 .48 1 .04 Pb 8A 4 .4 1.6 43 7±0 .87 1 .00 Pb 9D 4 .4 1.5 35 0±2 .37 1 .16 C 306 4 .8 1.5 41 ,7±2 .70 1 .09 K-1 3 4 .8 1 .5 39 ,1±2 .00 1 .10 N a i n a r i 60 4 7 1.9 45 2±1 .28 0 .85 Chapingo 53 3 .6 1 .6 44 . 1 ±1 .15 1 .32 Yaqui 50 3 .6 1 .8 53 4±2 .14 0 .70 Yagui 54 5 .3 1 .6 43 .4±1 .15 1 .19 Penjamo 62 2 .4 1.9 53 .7±2 .49 0 .91 P i t i c 62 5 .8 1 .5 33 2±4 .47 1 .07 Sonora 64 5 2 1 .4 40 1 ±2 .36 0 .77 Lerma Rojo 64 2 6 1.4 44 ,9±1 .75 1 .15 Kalyansona 4 .2 1 .3 47 ,5±1 .84 0 .80 S i t e Cerros 3 .0 1 .7 46 ,4±0 .95 0 .78 Pavon 76 3 .9 1 .4 44 ,3±5 .90 0 .96 Jupateco 73 3 6 1 .4 48 9±2 .21 0 .78 Yecora 70 3 0 1 .3 40 5±0 .97 0 .75 Tesia 79 2 7 1 .4 45 6±1 .52 0 .62 Ar jun 3 . 1 1 .3 45 6±1 .88 0 .78 Moti 5 .2 1.7 47 2±3 .18 0 .72 UP 301 4 6 1.0 40. 4±1 .87 0 .90 LSD (0.05) 1.2 0.18 37 Table 4. Short-term net potassium and n i t r a t e f l u x e s and root weights of the 24 v a r i e t i e s when grown under potassium and n i t r a t e - l i m i t e d c o n d i t i o n s . V a r i e t y Net K + f l u x (umol/g/h) Net n i t r a t e f l u x (umol/g/h) Root weight (g/plant) NP 52 6.3 5.7 1 .02 NP 718 5.3 7.5 0.78 Pusa 4 4.5 6.7 1 .28 Pb 8A 3.2 4.2 0.86 Pb 9D 2.8 3.6 1 .37 C 306 2.8 5.4 1.19 K-13 4.0 6.6 1 .50 N a i n a r i 60 5.6 2.7 1 .05 Chapingo 53 2.3 4.0 1 .54 Yaqui 50 2.5 7.5 1.10 Yaqui 54 : 5.5 6.5 1 .22 Penjamo 62 1 .8 2.8 1 .30 P i t i c 62 4.9 5.7 1.14 Sonora 64 4.2 8.4 0.76 Lerma Rojo 64 1 .5 2.2 1 .32 Kalyansona 3.4 4.2 0.95 S i e t e Cerros 3.0 3.5 1 .04 Pavon 76 3.2 4.5 1.15 Jupateco 73 3.3 3.4 1.16 Yecora 70 3.7 5.2 0.93 Tesia 79 3.2 4.1 0.86 Arjun 2.3 3.1 0.99 Moti 3.4 6.5 1.01 UP 301 2.8 3.0 0.71 LSD (0.05) 1 .0 1 . 1 0.21 38 Table 5. Analyses of variance f o r short-term net potassium and n i t r a t e f l u x e s (STNKF and STNNF r e s p e c t i v e l y ) and root weight per plant (RWt/pl) i n the potassium and potassium plus n i t r a t e -l i m i t e d experiments. Mean squares K + - l i m i t e d expt. K ++ N03~ - l i m i t e d expt. Source DF STNKF Rwt/pl STNKF STNNF RWt/pl Groups 4 9.29* 0.15* 4.13* 6.39* 0.21* V a r i e t i e s 19 2.95* 0.11* 4.87* 9.80* 0.14* w i t h i n groups E r r o r 48 0.546 0.012 0.352 0.438 0.017 * S i g n i f i c a n t at the 5% l e v e l Table 6. Comparison of group means f o r short-term net potassium and n i t r a t e f l u x e s , average potassium f l u x and root f r e s h weight per p l a n t . Net f l u x e s (umol/g/h) Group NKF (1) NKF (2) ANKF STNNF Root Wt.1 Root Wt. TI 5.1 a 4.1 a 1.7 5.7 a 0.96 ab 1.14 a TM 4.3 ab 4.0 ab 1.7 5.2 a 1 .02 a 1 .23 a SD 3.8 be 3.2 be 1 .6 4.3 b 0.90 ab 1.10 a DD 2.9 c 3.1 c 1 .3 4.2 b 0.72 b 0.93 b TD 4.9 ab 3.1 c 1.4 4.8 ab 0.81 b 0.86 b NKF (1): Short-term K f l u x i n po t a s s i u m - l i m i t e d experiment NKF (2): Short-term K + f l u x i n K + plus N03°-limited experiment ANKF: Average net potassium f l u x l:Root weights i n potas s i u m - l i m i t e d experiment. 2 :Root weights i n potassium plus n i t r a t e - l i m i t e d experiment TI: T a l l I ndian; TM: T a l l Mexican; SD: semidwarfs; DD: Double dwarfs; TD: t r i p l e dwarfs. 39 Table 7. C o r r e l a t i o n c o e f f i c i e n t s between various f l u x e s and between f l u x e s and root weights f o r the 24 v a r i e t i e s when grown under potassium and potassium plus n i t r a t e - l i m i t e d c o n d i t i o n s . Character p a i r s r Spearman's r STNKF(1):STNKF(2) 0.79* 0.75* STNKF(1):ANKF 0.25 0.27 STNKF(1):Root [ K + ] -0.57* STNKF(1) :Root weightO) 0.04 STNKF(2):Root we i ght (2) -0.23 STNKF(2):STNNF(2) 0.49 0.53 STNNF:Root weight -0.14 (1) : P o tassium-limited experiment (2) : Potassium plus n i t r a t e - l i m i t e d experiment STNKF: Short-term net potassium f l u x STNNF: Short-term net n i t r a t e f l u x ANKF: Average net potassium f l u x 40 examined i n r e l a t i o n to root potassium concentration i n order to e s t a b l i s h i f the observed d i f f e r e n c e s i n f l u x were a c t u a l l y genetic or simply due to d i f f e r e n c e s i n root potassium c o n c e n t r a t i o n , and to s e l e c t the appropriate l i n e s for the i n h e r i t a n c e s t u d i e s . A l l root potassium concentrations were c o r r e c t e d f o r the potassium taken up during the uptake experiments before examining the c o r r e l a t i o n between short-term potassium f l u x and root potassium c o n c e n t r a t i o n . A s i g n i f i c a n t negative c o r r e l a t i o n was observed (Table 7) thus i n d i c a t i n g that some of the d i f f e r e n c e s i n f l u x may be due to d i f f e r e n c e s i n root potassium c o n c e n t r a t i o n . However, t h i s i s c l e a r l y not so where higher uptake rates are a s s o c i a t e d with higher root potassium conce n t r a t i o n or where l a r g e d i f f e r e n c e s i n f l u x are as s o c i a t e d - wi t h small d i f f e r e n c e s i n root potassium c o n c e n t r a t i o n . These d i f f e r e n c e s i n f l u x must the r e f o r e be h e r i t a b l e and could r e s i d e i n the uptake mechanism per se and/or i n the extent of the absorptive s u r f a c e . Because f l u x e s were expressed on a root weight b a s i s , i t i s not p o s s i b l e to d i s t i n g u i s h between these two a l t e r n a t i v e s . S i m i l a r l y , Glass and P e r l e y (69) and S i d d i q i and Glass (126, 127) concluded that some of the v a r i a t i o n i n potassium i n f l u x observed i n a number of barley v a r i e t i e s i s l i k e l y to be h e r i t a b l e because f l u x e s were not r e l a t e d to root potassium c o n c e n t r a t i o n . With regard to n i t r a t e f l u x e s , root n i t r a t e concentrations were not taken i n t o c o n s i d e r a t i o n when comparing f l u x e s . I f e l t that due to the complexity of the r e g u l a t i o n of n i t r a t e i n f l u x (37, 39), simultaneous c o n s i d e r a t i o n of only root n i t r a t e 41 c o n c e n t r a t i o n would not s u f f i c e t o d i f f e r e n t i a t e between p h y s i o l o g i c a l and genetic d i f f e r e n c e s . Therefore, some of the d i f f e r e n c e s i n n i t r a t e f l u x may be due to d i f f e r e n c e s i n root n i t r a t e concentration or some other f a c t o r which governs n i t r a t e uptake. However, i t i s u n l i k e l y that the magnitude of some of the d i f f e r e n c e s i n n i t r a t e f l u x can be explained by d i f f e r e n c e s i n root n i t r a t e c o n c e n t r a t i o n . S t i l l , the d i f f e r e n c e s of smaller magnitude should be viewed with c a u t i o n . C o r r e l a t i o n s between various f l u x e s and between f l u x e s and root weights were a l s o examined. Potassium f l u x e s i n the two types of experiments were w e l l c o r r e l a t e d (Table 7). A s i g n i f i c a n t c o r r e l a t i o n between potassium and n i t r a t e f l u x e s i n the potassium plus n i t r a t e - l i m i t e d experiments was a l s o observed. A l l the c o r r e l a t i o n s between short-term f l u x e s and root weights were not s i g n i f i c a n t (Table 7 ) . In c o n t r a s t , Lindgren (91) observed a s i g n i f i c a n t negative c o r r e l a t i o n between root weight and phosphate uptake i n beans. He considered t h i s c o r r e l a t i o n to be of great s i g n i f i c a n c e to the proper s e l e c t i o n of genotypes for the i n h e r i t a n c e studies since only those l i n e s with s i m i l a r root weights but d i f f e r e n t f l u x e s were included i n the genetic study. This was not considered to be an issue i n t h i s study. While there i s some relevance to the study of the c o r r e l a t i o n between f l u x e s and root weights, i t should be borne i n mind that shoot growth a l s o has an e f f e c t on n u t r i e n t uptake (104, 141). Hence some attempt should be made to include t h i s f a c t o r i n any such s t u d i e s . However, the d i f f i c u l t y of doing so 42 must a l s o be acknowledged. Potassium and n i t r a t e i n f l u x k i n e t i c s i n the Mechanism I range were a l s o examined i n eight v a r i e t i e s r e p r e s e n t a t i v e of the v a r i e t a l types under study with the exception of the t a l l Mexican types. I n f l u x isotherms were found to be i n agreement wit h the Michaelis-Menten formalism (Figures 1,2, 3 and 4). L i n e a r i z a t i o n of t h i s data by the Woolf-Augustinsson-Hofstee p l o t (123) as shown i n Appendices 2, 3, 4 and 5 y i e l d e d the k i n e t i c parameters V and K . Up to twofold d i f f e r e n c e s i n max m V were observed f o r both n u t r i e n t s (Tables 8 and 9). max D i f f e r e n c e s i n K were as great as t h r e e f o l d . Due to the small m sample s i z e the v a r i e t i e s were not grouped f o r comparative purposes. However, some comparisons could s t i l l be made. For potassium i n f l u x the lowest a f f i n i t e s were recorded f o r the three t a l l v a r i e t i e s whereas the double dwarf Te s i a 79 e x h i b i t e d the highest a f f i n i t y (Table 8 ) . In general the dwarfs had higher a f f i n i t i e s than the t a l l types. For n i t r a t e uptake no trend i n a f f i n i t y was observed. However, the t r i p l e dwarf Moti d i d e x h i b i t a much lower a f f i n i t y than a l l the other v a r i e t i e s (Table 9). A f f i n i t i e s f o r the t a l l types, semidwarfs and double dwarfs were comparable. As for uptake, the k i n e t i c parameter K m should a l s o be examined i n r e l a t i o n to root potassium c o n c e n t r a t i o n . Studies have shown that a decrease i n root potassium concentration r e s u l t s i n a d e c l i n e i n K m (45). Therefore, one would expect that v a r i e t i e s with a high potassium c o n c e n t r a t i o n might be c h a r a c t e r i z e d by a low a f f i n i t y . This was indeed found to be so for the t r i p l e dwarf Moti which had 44 8r POTASSIUM CONCENTRATION CmM) Figure 2. Potassium i n f l u x isotherms f o r the v a r i e t i e s Pb 8A (1 , L J ) , Lerma Rojo 64 ( 2 , A ) , Arjun (3,©) and Tesia 79 (4,#) 45 - 8 r NITRATE CONCENTRATION ( mM ) Figure 3. N i t r a t e i n f l u x isotherms f o r the v a r i e t i e s Jupateco 73 (1, • ), Moti (2, O ), Tesia 79 (3, •) and Arjun ( 4 , A ) . 46 NITRATE CONCENTRATION CmM) Figure 4. N i t r a t e i n f l u x isotherms f o r the v a r i e t i e s Sonora 64 NP 52 ( 2 r E ) ) , C 306 ( 3 , A ) and Pb 8A (4,©). Table 8. K i n e t i c parameters ( ± SE) and root potassium concentrations of eig h t v a r i e t i e s grown under potassium-limited c o n d i t i o n s . Root [K+] V m a x Apparent K V a r i e t y (umol/g) (umol/g/h) (mM) NP 52 31 . 4±0 .59 1 1 . 7±0. 98 0. 0270±0. 0051 C 306 28. 4±0 .76 8. 0±0. 66 0. 0244±0. 0048 Pb 8A 30. 9±0 .81 7. 9±0. 39 0. 0184±0. 0025 Lerma Rojo 64 35. 8±0 .15 5. 9±0. 22 0. 0132±0. 0015 Jupateco 73 46. 9±1 .79 6. 0±0. 32 0. 0108±0. 0021 Tesia 79 39. 6±1 .14 4. 9±0. 21 0. 0079+0. 0014 Ar jun 35. 8±0 .59 5. 8±0. 44 0. 0119±0. 0031 Moti 53. 5±1 .40 7. 7±0. 50 0. 0116±0. 0026 48 Table 9. N i t r a t e uptake k i n e t i c parameters ( ± SE) of eight v a r i e t i e s when grown under potassium plus n i t r a t e - l i m i t e d c o n d i t i o n s . V a r i e t y Vmax (umol/g/h) Apparent K (mM) m NP 52 C 306 Pb 8A Sonora 64 Jupateco 73 Arjun Tesia 79 Moti 7.8±0.86 6.0±0.48 6.4±0.64 10.910.88 7.2*0.29 4.910.59 6.410.95 7.9±1.08 0.046910.0142 0.034310.0089 0.054910.0138 0.052110.0109 0.034810.0044 0.033710.0231 0.0684+0.0231 0.119510.0293 49 the highest root potassium concentration (Table 8 ) . However, considerable d i f f e r e n c e s i n K m were observed for the other v a r i e t i e s which had s i m i l a r root potassium co n c e n t r a t i o n s . These d i f f e r e n c e s are thus l i k e l y to r e s i d e i n a c t u a l genetic d i f f e r e n c e s i n the transport systems of these v a r i e t i e s . I t i s c l e a r that n u t r i e n t uptake presents a formidable task for the g e n e t i c i s t i n t e r e s t e d i n e l u c i d a t i n g i t s genetic b a s i s . D i f f i c u l t i e s a r i s e due to problems with proper q u a n t i f i c a t i o n (average versus p e r t u r b a t i o n f l u x e s ) , c o r r e l a t i o n with root weight (91) and r e g u l a t i o n by root n u t r i e n t c o n c e n t r a t i o n . C l e a r l y these are issues that the g e n e t i c i s t and plant breeder should bear i n mind and, i f p o s s i b l e , take i n t o c o n s i d e r a t i o n i n h i s or her s t u d i e s . However, i t i s not c l e a r how some of these d i f f i c u l t i e s can be d e a l t with without making genetic s t u d i e s too tedious and perhaps even i n t r a c t a b l e . To date these problems have been circumvented by r e s t r i c t i n g the genetic s t u d i e s t o only those l i n e s i n which these issues are not a problem. Hence l i n e s have been s e l e c t e d such that they a l l have s i m i l a r root weights (91) or root n u t r i e n t c o n c e n t r a t i o n s . I t i s unfortunate that t h i s r e s u l t s i n the e l i m i n a t i o n of rather i n t e r e s t i n g m a t e r i a l from such s t u d i e s . Due to the problem with v a r i a b l e root potassium concentration and i t s e f f e c t on potassium uptake, a method of a d j u s t i n g f l u x e s f o r d i f f e r e n c e s i n root potassium concentration was considered f o r the genetic s t u d i e s . This would have required that both f l u x and root potassium conce n t r a t i o n measurements be made on i n d i v i d u a l p l a n t s . A l s o , because the r e l a t i o n s h i p between root potassium 50 c o n c e n t r a t i o n and f l u x i s genotype-specific (126), i t would not have been p o s s i b l e to adopt a standard adjustment. Therefore, c l o s e r examination of these d i f f i c u l t i e s precluded such an approach. A l s o , one must question the v a l i d i t y of such an a n a l y s i s and i t s relevance to the improvement of n u t r i e n t uptake. I maintain that while c o n s i d e r a t i o n of a l l the c o m p l e x i t i e s of n u t r i e n t uptake and i t s r e g u l a t i o n i s indeed i n t r i g u i n g and important, these issues cannot r e a d i l y be taken i n t o c o n s i d e r a t i o n i n genetic s t u d i e s . Therefore i t i s imperative that p l a n t p h y s i o l o g i s t s be cautious i n t h e i r recommendations to p l a n t breeders and that breeders c a r e f u l l y examine the r e s u l t s obtained i n i n h e r i t a n c e s t u d i e s of these t r a i t s . Three i n d i c e s , namely shoot weight, e f f i c i e n c y r a t i o and u t i l i z a t i o n e f f i c i e n c y were used to evaluate n u t r i e n t - u s e e f f i c i e n c y . The r e s u l t s obtained i n the p o t a s s i u m - l i m i t e d and potassium plus n i t r a t e - l i m i t e d experiments are given i n Tables 10 and 11 r e s p e c t i v e l y . S i g n i f i c a n t d i f f e r e n c e s between v a r i e t i e s and groups were observed for a l l measures of e f f i c i e n c y (Tables 12 and 13). V a r i a t i o n f o r shoot weight was intermediate between that for e f f i c i e n c y r a t i o and u t i l i z a t i o n e f f i c i e n c y and, u n l i k e i n other s t u d i e s (35, 66, 94) v a r i a t i o n for e f f i c i e n c y r a t i o was n e g l i g i b l e . I t may be that d i f f e r e n c e s i n methodology are r e s p o n s i b l e f o r t h i s d i f f e r e n c e . In other s t u d i e s the l i m i t i n g n u t r i e n t has been a p p l i e d i n a s i n g l e dose at the beginning of the experiment whereas i n these s t u d i e s the n u t r i e n t was continuously provided at a l i m i t i n g l e v e l . Table 10. Shoot f r e s h weights per p l a n t , potassium e f f i c i e n c y r a t i o s (KER) and potassium u t i l i z a t i o n e f f i c i e n c i e s (KUE) of the 24 v a r i e t i e s when grown under pota s s i u m - l i m i t e d c o n d i t i o n s . V a r i e t i e s Sht. weight (g/plant) KER (g/mmol) KUE (g2/mmol) NP 52 1 .78 9.5 16.9 NP 718 1 .35 8.6 11.8 Pusa 4 1 .74 8.7 15.1 Pb 8A 1 .71 8.6 14.6 Pb 9D 1 .79 9.2 16.5 C 306 1 .90 9.2 17.3 K-1 3 1 .56 8.2 12.4 N a i n a r i 60 1 .67 7.7 12.9 Chapingo 53 1 .64 7.1 11.7 Yaqui 50 1 .22 7.2 8.8 Yaqui 54 1 .73 8.0 13.8 Penjamo 62 1 .36 6.6 9.1 P i t i c 62 1 .70 9.7 16.4 Sonora 64 1 .30 7.8 10.1 Lerma Rojo 64 1 .51 8.5 12.9 Kalyansona 1 .20 8.0 9.7 S i e t e Cerros 1 .23 7.8 9.6 Pavon 76 1 .45 9.1 13.3 Jupateco 73 1.15 7.8 9.8 Yecora 70 1.11 8.3 9.2 Tesia 79 1 .05 7.2 7.6 Arjun 1 .07 8.0 8.6 Moti 1 .43 9.3 13.3 UP 301 1 .09 8.5 9.2 LSD (0.05) 0.22 0.8 2.5 52 Table 11. Shoot f r e s h weight per p l a n t , potassium and nitrogen e f f i c i e n c y r a t i o s (KER and NER r e s p e c t i v e l y ) , and potassium and n i t r o g e n u t i l i z a t i o n e f f i c i e n c i e s (KUE and NUE r e s p e c t i v e l y ) of the 24 v a r i e t i e s when grown under potassium plus n i t r a t e -l i m i t e d c o n d i t i o n s . Sht. weight KER KUE NER NUE V a r i e t i e s (g/plant) (g/g) (g2/g) (g/g) (g2/g) NP 52 1 .50 15.0 2.5 28.2 4.7 NP 718 1 .27 15.3 2.0 26. 1 3.4 Pusa 4 1 .60 15.7 2.5 24.0 3.8 Pb 8A 1 .40 17.2 2.6 25.7 3.9 Pb 9D 1 .53 17.3 2.8 26.7 4.3 C 306 1 .83 14.8 2.6 24.2 4.3 K-13 1 .47 16.6 2.7 24.9 4. 1 N a i n a r i 60 1 .57 18.9 2.4 23.9 3.9 Chapingo 53 1 .60 16.0 2.9 23.9 4.4 Yaqui 50 1 .33 16.5 2.5 23.0 3.5 Yaqui 54 1 .40 17.6 2.9 23.9 4.0 Penjamo 62 1 .33 16.5 2.5 23.2 3.5 P i t i c 62 1 .53 15.4 2.5 24.8 4.1 Sonora 64 1 .07 16.6 2.0 22.4 2.8 Lerma Rojo 64 1 .37 15.9 2.3 25.7 3.8 Kalyansona 1.13 16.0 2.0 24.5 3.1 S i e t e Cerros 1.13 15.5 1.9 24.2 3.0 Pavon 76 1 .40 16.7 2.5 25. 1 3.7 Jupateco 73 1 .20 17.0 2.3 23.6 3.1 Yecora 70 1 .27 15.7 2.1 21.6 2.9 Tesia 79 1.10 16.3 2.0 22.4 2.7 Ar jun 1.10 16.9 1.9 23.9 2.7 Moti 1 .40 14.3 2.1 23.6 3.4 UP 301 0.87 16.0 1.5 22. 1 2.1 LSD (0.05) 0.24 1.0 0.4 1.3 0.6 53 Tale 12. Analyses of variance f o r shoot weight per plant (SWt.), potassium and nitrogen e f f i c i e n c y r a t i o (KER and NER r e s p e c t i v e l y ) and potassium and nitrogen u t i l i z a t i o n e f f i c i e n c y (KUE and NUE r e s p e c t i v e l y ) i n the potassium and potassium plus n i t r a t e - l i m i t e d experiments. Mean squares K + - l i m i t e d expt. K + p l u s NO^-limited expt. Source DF SWt. KER KUE SWt. KER KUE NER NUE Groups 4 0.74* 4.57* 78.08* 0.39* 1.61* 1.34* 21.20* 4.44* V a r i e t i e s 19 0.11* 1.41* 16.12* 0.09* 2.32* 0.19* 4.18* 0.62 i n groups Residual 48 0.02 0.26 2.38 0.02 0.35 0.05 0.64 0.15 * S i g n i f i c a n t l y d i f f e r e n t at the 5% l e v e l . 54 Table 13. Comparison of group means f o r shoot weight per pla n t (SWt.), potassium and nitrogen e f f i c i e n c y r a t i o s (KER and NER r e s p e c t i v e l y ) , potassium and n i t r o g e n u t i l i z a t i o n e f f i c i e n c i e s (KUE and NUE r e s p e c t i v e l y ) i n the potassium and potassium plus n i t r a t e - l i m i t e d experiments. K + - l i m i t e d expt. K+ plus N0~ - l i m i t e d expt. SWt. KER KUE SWt. KER KUE NER NUE Group (g) (g/g) (g 2/g) (g) (g/g) ( g V g ) (g/g) (g 2/g) TI 1.68a 8.8a TM 1.57a 7.5c SD 1.36b 8.2b DD 1.08c 7.8bc TD 1.26bc 8.9a 1 5 . 0a 1 .51a 16. 0a 1 1 .8b 1 .48a 16. 2a 1 1 .3b 1 .27b 16. 2a 8 . 5c 1 . 14b 16. 3a 1 1 .3b 1 . 13b 15. 2b 2.5a 25.7a 4.1a 2.7a 23.7bc 4.0a 2.3b 24.2b 3.4b 2.0bc 22.6c 2.8c 1.8c 22.8c 2.7c Values w i t h i n the same column followed by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t at the 5% l e v e l according to Scheffe 's t e s t . TI: T a l l Indian v a r i e t i e s TM: T a l l Mexican v a r i e t i e s SD: Semidwarfs DD: Double dwarfs TD: T r i p l e dwarfs 55 In both experiments the t a l l vigorous v a r i e t i e s had s i g n i f i c a n t l y higher shoot weights than a l l the dwarf types (Tables 10 and 11). The dwarf types had s i m i l a r shoot weights under potassium plus n i t r a t e - l i m i t i n g c o n d i t i o n s whereas under p o t a s s i u m - l i m i t i n g c o n d i t i o n s the double dwarfs had s i g n i f i c a n t l y lower shoot weights than the s i n g l e dwarfs but not the t r i p l e dwarfs. D i f f e r e n c e s i n both potassium and nit r o g e n e f f i c i e n c y r a t i o s although rather small were nonetheless s i g n i f i c a n t (Tables 10, 11 and 12). For potassium e f f i c i e n c y r a t i o d i f f e r e n c e s between groups were more evident under potassium-l i m i t i n g c o n d i t i o n s than under c o n d i t i o n s of dual n u t r i e n t l i m i t a t i o n (Table 13). Under potassium plus n i t r a t e - l i m i t i n g c o n d i t i o n s only the t r i p l e dwarfs d i f f e r e d s i g n i f i c a n t l y from the other v a r i e t a l types. Under potassium- l i m i t i n g c o n d i t i o n s the t r i p l e dwarfs e x h i b i t e d the highest e f f i c i e n c y r a t i o but they were not s i g n i f i c a n t l y d i f f e r e n t from the t a l l Indian types. The t a l l Mexican types showed the lowest e f f i c i e n c y r a t i o which was only s l i g h t l y exceeded by that of the double dwarfs. The semidwarfs were intermediate between the t a l l Mexican and Indian types and not s i g n i f i c a n t l y d i f f e r e n t from the double dwarfs. For nit r o g e n e f f i c i e n c y r a t i o the t a l l Indian v a r i e t i e s e x h i b i t e d the highest value and were s i g n i f i c a n t l y d i f f e r e n t from a l l the other types. S i m i l a r values were observed f o r the t a l l Mexican types, double dwarfs and t r i p l e dwarfs. The semidwarfs had the second highest nitrogen e f f i c i e n c y r a t i o but were not s i g n i f i c a n t l y d i f f e r e n t 56 from the semidwarfs. For both potassium and nitrogen u t i l i z a t i o n e f f i c i e n c y the t a l l Indian v a r i e t i e s showed the highest values although for the l a t t e r they were s i m i l a r to the t a l l Mexican types (Table 13). The t a l l Mexican types, semidwarfs and t r i p l e dwarfs had s i m i l a r potassium u t i l i z a t i o n e f f i c i e n c i e s under p o t a s s i u m - l i m i t i n g c o n d i t i o n s whereas under potassium plus n i t r a t e - l i m i t i n g c o n d i t i o n s these types were s i g n i f i c a n t l y d i f f e r e n t . The double dwarfs e x h i b i t e d the lowest u t i l i z a t i o n e f f i c i e n c y under p o t a s s i u m - l i m i t i n g c o n d i t i o n s but under potassium plus n i t r a t e -l i m i t i n g c o n d i t i o n s they were not s i g n i f i c a n t l y d i f f e r e n t from the other dwarf types. For nitrogen u t i l i z a t i o n e f f i c i e n c y the semidwarfs showed a s i g n i f i c a n t l y higher value than the other dwarfs. C l e a r l y , there i s considerable v a r i a b i l i t y f o r potassium and n i t r o g e n uptake and u t i l i z a t i o n i n the wheat v a r i e t i e s examined. With regard to potassium and n i t r a t e uptake some of t h i s v a r i a b i l i t y i s undoubtedly h e r i t a b l e although a s i z e a b l e p r o p o r t i o n of i t i s probably a s s o c i a t e d with d i f f e r e n c e s i n root n u t r i e n t c o n c e n t r a t i o n . There i s the r e f o r e some scope for the improvement of these t r a i t s i f i t i s considered worthwhile and i f r e l i a b l e and convenient s e l e c t i o n techniques can be developed. This issue w i l l be discussed i n more d e t a i l l a t e r . The r e s u l t s of t h i s study are a l s o i n t e r e s t i n g i n that they provide an opportunity to examine the changes that have occurred over a time p e r i o d i n which n u t r i e n t s e l e c t i o n regimes and o b j e c t i v e s have changed c o n s i d e r a b l y . As such, the t a l l 57 t r a d i t i o n a l types were s e l e c t e d and grown under c o n d i t i o n s of low to moderate s o i l f e r t i l i t y (115) whereas the dwarf types were s e l e c t e d under c o n d i t i o n s of i n c r e a s i n g f e r t i l i t y , p a r t i c u l a r l y so for nitrogen l e v e l . These r e s u l t s can therefore be viewed i n r e l a t i o n t o the contention that s e l e c t i o n under high f e r t i l i t y c o n d i t i o n s may have masked or i n a d v e r t a n t l y l e d to the diminution of t r a i t s governing e f f i c i e n t mineral n u t r i t i o n (25, 34, 73). Rao and Rains (114) proposed that the low a f f i n i t y f o r n i t r a t e observed i n b a r l e y r e l a t i v e to that i n maize and ryegrass might be due to i n t e n s i v e breeding f o r high nitrogen response and thus poor a c q u i s i t i o n e f f i c i e n c y . Unfortunately they d i d not examine these species under the same c o n d i t i o n s but p r e f e r r e d i n s t e a d to compare t h e i r f i n d i n g s on a few barley v a r i e t i e s with the r e s u l t s obtained for the other species i n q u i t e d i f f e r e n t experiments. One must therefore s e r i o u s l y question the v a l i d i t y of t h e i r c o n c l u s i o n . A l s o , i t appears u n l i k e l y that s e l e c t i o n for superior h y b r i d performance in maize has taken place under c o n d i t i o n s which are markedly d i f f e r e n t from those which have p r e v a i l e d i n barley breeding. In an extended study Cacco et a l . (25) examined sulphate and n i t r a t e uptake i n 13 maize hybrids developed over a 45-year per i o d during which s e l e c t i o n regimes apparently changed co n s i d e r a b l y . They observed that the r e c e n t l y developed hybrids bred f o r improved performance under high f e r t i l i t y c o n d i t i o n s a l s o e x h i b i t e d higher n i t r a t e and sulphate i n f l u x e s per u n i t root p r o t e i n i n studies using excised r o o t s . In view of these f i n d i n g s they speculated that the high f e r t i l i z e r requirement of 58 modern hybrids might be due to a decrease i n a f f i n i t y or inadequate s o i l b u f f e r i n g . Therefore, i t seems that because they observed the highest i n f l u x e s i n the s e e d l i n g s of modern h y b r i d s , they expected these types to be more e f f i c i e n t i n n u t r i e n t a c q u i s i t i o n under f i e l d c o n d i t i o n s and hence to have a lower f e r t i l i z e r requirement. This kind of reasoning seems rather s i m p l i s t i c . There i s c l e a r l y considerable danger in t r y i n g to e x t r a p o l a t e from s e e d l i n g s t u d i e s under c o n t r o l l e d c o n d i t i o n s t o performance under f i e l d c o n d i t i o n s . As a r e s u l t , such comparisons should be made wit h the utmost care. I t may be that i n t h e i r s t u d i e s d i f f e r e n c e s i n growth could a l s o have had a n o t i c e a b l e e f f e c t on t h e i r f i n d i n g s . That i s , because the modern hybrids are l i k e l y f a s t e r growing and e a r l i e r maturing than the o l d h y b r i d s , t h e i r higher i n f l u x e s may have been a f u n c t i o n of t h e i r growth r a t e s rather than being due to d i f f e r e n c e s i n uptake c a p a c i t y alone. In view of the dramatic changes i n f e r t i l i z e r a p p l i c a t i o n that have been a s s o c i a t e d with the development of the v a r i e t i e s examined i n t h i s study, i t i s tempting to r e l a t e the r e s u l t s obtained to the l i k e l y e f f e c t of s e l e c t i o n under d i f f e r e n t n u t r i e n t regimes. Any attempt to do so should keep i n mind the genetic d i v e r s i t y of the m a t e r i a l , the major s e l e c t i o n pressure a p p l i e d , i . e . s e l e c t i o n f o r improved y i e l d under high nitrogen c o n d i t i o n s , the number of genotypes studied and the nature of the i n v e s t i g a t i o n s undertaken. For example, some of the morphological types were poorly represented i n t h i s study. Also of importance i s the r e l a t i o n s h i p between average and 59 p e r t u r b a t i o n f l u x e s which was found to be poor (Table 7) and the f a c t that a l l measures of u t i l i z a t i o n were based on vegetative growth. Although there appeared to be a trend f o r some of the t r a i t s , t h i s was not c o n s i s t e n t f o r a l l t r a i t s . For both potassium and n i t r a t e uptake there appeared to be a decreasing trend but the r e c e n t l y developed t r i p l e dwarfs proved to be an exception, e x h i b i t i n g f l u x e s s i m i l a r to those of the t a l l types (Table 6). The only t r i p l e dwarf included i n the k i n e t i c s t u d i e s d i d however show the lowest a f f i n i t y for n i t r a t e (Table 9). For potassium uptake the dwarf types c l e a r l y showed higher a f f i n i t i e s than the t a l l types (Table 8). No trends were apparent f o r e i t h e r potassium or nitrogen e f f i c i e n c y r a t i o (Table 13). However, the t a l l vigorous v a r i e t i e s g e n e r a l l y proved s u p e r i o r to the dwarf types when u t i l i z a t i o n was expressed as shoot weight or u t i l i z a t i o n e f f i c i e n c y . Therefore, the r e s u l t s obtained i n t h i s study do not f u l l y support the contention that s e l e c t i o n under high f e r t i l i t y c o n d i t i o n s n e c e s s a r i l y leads to the diminution or submergence of t r a i t s governing e f f i c i e n t mineral n u t r i t i o n . I f t h i s were t r u e , one would expect a decreasing trend to be observed with the t a l l types e x h i b i t i n g the highest values f o r n u t r i e n t uptake and u t i l z a t i o n . However, i t should a l s o be kept i n mind that the t r a n s i t i o n from one morphological type to another d i d not c o i n c i d e e x a c t l y with changes i n f e r t i l i z e r p r a c t i c e . A l s o , a number of l i n e s s e l e c t e d under c o n d i t i o n s of lower f e r t i l i t y were subsequently used i n the breeding of m a t e r i a l b e t t e r s u i t e d 60 to higher f e r t i l i t y c o n d i t i o n s . I t might be argued the r e f o r e that t h i s m a t e r i a l does not r e a l l y provide a good opportunity to examine t h i s hypothesis. A b e t t e r approach would require that a population e x h i b i t i n g considerable v a r i a b i l i t y f o r the t r a i t s of i n t e r e s t be subjected to s e l e c t i o n ( f o r agronomic t r a i t s ) under d i f f e r e n t n u t r i e n t c o n d i t i o n s f o r a considerable p e r i o d of time. Thereafter the s e l e c t e d l i n e s would be evaluated f o r the expression of t r a i t s considered important i n nut r i e n t - u s e e f f i c i e n c y and these f i n d i n g s then r e l a t e d to the n u t r i e n t regimes that p r e v a i l e d during the s e l e c t i o n process. Short of t h i s , one must r e l y on the kind of experiments undertaken i n t h i s study while keeping i n mind t h e i r shortcomings. I t i s u n l i k e l y that s e l e c t i o n under high n u t r i e n t c o n d i t i o n s w i l l n e c e s s a r i l y lead to a diminution of t r a i t s governing e f f i c i e n t mineral n u t r i t i o n p a r t i c u l a r l y i f the s e l e c t i o n c r i t e r i a are d i s t a n t l y r e l a t e d to nutrient-use e f f i c i e n c y . There i s c l e a r l y no causal r e l a t i o n s h i p between s e l e c t i o n f o r improved performance under high f e r t i l i t y c o n d i t i o n s and the expression of t r a i t s governing e f f i c i e n t n u t r i e n t - u s e e f f i c i e n c y . Rather, as pointed out by Clarkson ( 3 4 ) , s e l e c t i o n under high f e r t i l i t y c o n d i t i o n s would l i k e l y mask d i f f e r e n c e s i n nutrient-use e f f i c i e n c y and thus lead to the inadvertant r e t e n t i o n of v a r i e t i e s which might be considered undesirable under low f e r t i l i t y c o n d i t i o n s . These v a r i e t i e s could be c h a r a c t e r i z e d by poor n u t r i e n t a c q u i s i t i o n and u t i l i z a t i o n e f f i c i e n c y under f i e l d c o n d i t i o n s . Whether these a t t r i b u t e s can be adequately demonstrated i n seedling s t u d i e s under c o n t r o l l e d c o n d i t i o n s i s a moot p o i n t . 61 I I I . GENETIC BASIS OF DIFFERENCES IN POTASSIUM AND NITROGEN UPTAKE AND UTILIZATION 1. L i t e r a t u r e review The number of d e f i n i t i v e genetic s t u d i e s on a t t r i b u t e s governing mineral n u t r i t i o n lags f a r behind the number of re p o r t s on the extent of genetic v a r i a t i o n f o r these t r a i t s . In p a r t i c u l a r , only a few s t u d i e s have been reported on the g e n e t i c s of n u t r i e n t uptake. This p a u c i t y of information i s probably due to the d i f f i c u l t i e s a l l u d e d to e a r l i e r as w e l l as a general lack of i n t e r e s t i n t h i s area. For animal systems, however, a c o n s i d e r a b l e amount of work has been done i n attempts to b e t t e r understand the genetic b a s i s of ion t r a n s p o r t (122, 128). 1.1. N u t r i e n t uptake H e t e r o s i s f o r ion uptake has been reported i n a number of s t u d i e s (23, 96, 103). However such f i n d i n g s do not provide f o r a good understanding of the genetic b a s i s of ion uptake because the h e t e r o t i c response can be explained by a number of genetic models. Lindgren (91) conducted a d e t a i l e d study on phosphate uptake i n beans using a s p e c i f i c number, region and length of 62 excised r o o t s . He reported l a r g e environmental variances and an absence of maternal e f f e c t s . Some crosses showed dominance for low phosphate uptake whereas others showed dominance f o r high uptake r a t e . Broad-sense h e r i t a b i l i t i e s ranged from 37.4-43.3%. Narrow-sense h e r i t a b i l i t i e s ranged from 37.0-43.3%. Motto et a l . (103) used a f i v e - p a r e n t complete d i a l l e l to examine combining a b i l i t y f o r V and K for sulphate uptake i n 3 max m maize. They reported s i g n i f i c a n t general and s p e c i f i c combining a b i l i t i e s f o r both parameters thus demonstrating that both a d d i t i v e and dominance gene e f f e c t s are important i n the determination of these t r a i t s . In a d d i t i o n , they detected s i g n i f i c a n t r e c i p r o c a l e f f e c t s f o r both parameters. 1.2. N u t r i e n t u t i l i z a t i o n The i n h e r i t a n c e of n u t r i e n t u t i l i z a t i o n has been examined using i n d i c e s such as the expression of d e f i c i e n c y symptoms, plant weight and the e f f i c i e n c y r a t i o . Reported modes of i n h e r i t a n c e range from simple monogenic c o n t r o l to more complex q u a n t i t a t i v e models. Weiss (139) reported i r o n d e f i c i e n c y c h l o r o s i s i n soybeans to be i n h e r i t e d i n a monogenic r e c e s s i v e * manner. S i m i l a r f i n d i n g s have been reported f o r i r o n d e f i c i e n c y c h l o r o s i s i n tomatoes (138), boron d e f i c i e n c y c h l o r o s i s i n c e l e r y (113) and tomatoes (137), magnesium d e f i c i e n c y c h l o r o s i s i n c e l e r y (112) and c h l o r i d e - i n d u c e d c h l o r o s i s i n soybeans (1). In view of the known complexity of mineral uptake and 63 u t i l i z a t i o n , Weiss (139) expressed some s u r p r i s e at f i n d i n g that i r o n d e f i c i e n c y c h l o r o s i s was simply i n h e r i t e d . Perhaps h i s system of c l a s s i f y i n g h i s p l a n t s as e i t h e r normal or c h l o r o t i c , d e s p i t e the presence of p l a n t s e x h i b i t i n g v a r i o u s degrees of c h l o r o s i s , l e d to t h i s simple model. Recent f i n d i n g s i n d i c a t e that t h i s simple model i s no longer tenable (R. L. Chaney, personal communication). Harvey (75) used pla n t dry weight as h i s measure of e f f i c i e n c y and reported that both tomato and corn hybrids were intermediate to t h e i r parents with respect to both potassium and n i t r a t e u t i l i z a t i o n . He concluded that t h i s intermediacy was due to e i t h e r p a r t i a l dominance or a mode of i n h e r i t a n c e i n which dominance i s d i v i d e d between f a c t o r s f o r e f f i c i e n c y and i n e f f i c i e n c y . Because s e v e r a l d i f f e r e n t s t r a i n s were in v o l v e d i n hybrids which showed intermediate response, he p r e f e r r e d the l a t t e r model. In more recent genetic terminology, t h i s intermediate response could b e t t e r be a t t r i b u t e d to a d d i t i v e gene a c t i o n . P l a n t dry weight has a l s o been used i n other s t u d i e s with q u i t e d i f f e r e n t r e s u l t s . Shea et a l . (124) reported that s u s c e p t i b i l i t y to potassium d e f i c i e n c y i n beans was simply i n h e r i t e d with i n e f f i c i e n c y being completely dominant. O ' S u l l i v a n et a l . (107) observed s i g n i f i c a n t dominance and a d d i t i v e x a d d i t i v e e f f e c t s i n a study on nitrogen u t i l i z a t i o n i n tomatoes and, l i k e Shea et al_. (124), found no r e c i p r o c a l d i f f e r e n c e s . In an extensive study on potassium u t i l i z a t i o n i n tomatoes, Makmur (94) reported predominantly a d d i t i v e gene 64 e f f e c t s although dominance and e p i s t a t i c e f f e c t s were s i g n i f i c a n t i n some cross e s . Narrow sense h e r i t a b i l i t i e s exceeded 60% and maternal e f f e c t s were absent. Fawole et a l . (55) i n a study on phosphate u t i l i z a t i o n i n beans reported s i g n i f i c a n t a d d i t i v e , dominance and e p i s t a t i c e f f e c t s although only a d d i t i v e and dominance x dominance e f f e c t s c o n t r i b u t e d s i g n i f i c a n t l y i n i n e f f i c i e n t x i n e f f i c i e n t c r o s s e s . Broad sense h e r i t a b i l i t y estimates exceeded 70% whereas narrow sense h e r i t a b i l i t y estimates ranged from 54-113%. Genetic s t u d i e s based on the e f f i c i e n c y r a t i o have been reported by Baker (10), Giordano et a l . (68) and Whiteaker et a l . (140). Baker (10) examined the potassium e f f i c i e n c y r a t i o i n beets and reported complete and p a r t i a l dominance for e f f i c i e n c y . However, some of h i s data, p a r t i c u l a r l y the backcross data, d i d not support h i s c o n c l u s i o n s . Giordano et a l . (68) used both pl a n t weight and the e f f i c i e n c y r a t i o i n t h e i r study on calcium u t i l i z a t i o n i n ' tomatoes. They found that the i n h e r i t a n c e of e f f i c i e n c y based on the calcium e f f i c i e n c y r a t i o was r e l a t i v e l y simple i n that a l l crosses could be adequately described by a 3-parameter model i n v o l v i n g only a d d i t i v e and dominance e f f e c t s . For pla n t weight a 3-parameter model s u f f i c e d f o r only a few of the cross e s . In most of the crosses e p i s t a t i c e f f e c t s had to be included i n the model f o r a b e t t e r f i t to the data. Maternal e f f e c t s were not detected f o r e i t h e r measure of e f f i c i e n c y . Whiteaker et aJL. (140) observed a v a r i e t y of segregation patterns c o n s i s t e n t with dominant and a d d i t i v e gene a c t i o n i n 65 t h e i r study on phosphate u t i l i z a t i o n i n beans. In a d d i t i o n , they reported marked t r a n s g r e s s i v e segregation such that p l a n t s exceeding t h e i r parents by 50% were observed i n the F 2 generation. U n l i k e most s t u d i e s i n which n u t r i e n t u t i l i z a t i o n i s assessed under n u t r i e n t - l i m i t i n g c o n d i t i o n s , Rice (117) conducted h i s st u d i e s on phosphorus u t i l i z a t i o n i n beans at a very high n u t r i e n t l e v e l . He observed s i g n i f i c a n t v a r i a t i o n f o r u t i l i z a t i o n as measured by dry weight even a f t e r c o r r e c t i n g f o r d i f f e r e n c e s i n seed weight. In h i s genetic s t u d i e s i n which two e f f i c i e n t l i n e s were used, he reported p a r t i a l dominance and q u a n t i t a t i v e i n h e r i t a n c e i n crosses i n v o l v i n g one parent, and h e t e r o s i s and dominance i n crosses i n v o l v i n g the other parent. 2. M a t e r i a l s and Methods Two approaches were adopted i n the genetic s t u d i e s : generation mean and variance a n a l y s i s and d i a l l e l a n a l y s i s . The former method was used to examine the i n h e r i t a n c e of potassium uptake and u t i l i z a t i o n . D i a l l e l a n a l y s i s was used to study the i n h e r i t a n c e of both potassium and nitrogen uptake and u t i l i z a t i o n . 2.1. Generation mean and variance a n a l y s i s Based on the r e s u l t s obtained i n the i n i t i a l experiments 66 designed to compare various v a r i e t i e s , f i v e l i n e s were s e l e c t e d f o r the genetic s t u d i e s . When s e l e c t i n g these l i n e s due c o n s i d e r a t i o n was given to the w e l l known negative feedback e f f e c t of i n t e r n a l potassium conce n t r a t i o n on i n f l u x . Hence although some l i n e s e x h i b i t e d marked d i f f e r e n c e s i n potassium uptake, they were not included i f they a l s o showed s i z e a b l e d i f f e r e n c e s i n root potassium c o n c e n t r a t i o n . This was done to ensure that the observed d i f f e r e n c e s i n uptake were due to a c t u a l genetic d i f f e r e n c e s rather than d i f f e r e n c e s i n root potassium c o n c e n t r a t i o n . For each of the four crosses the p a r e n t a l , F± , F 2 and backcross generations were examined under the same c o n d i t i o n s . Due to unforeseen circumstances a l l the generations were not produced under i d e n t i c a l environmental c o n d i t i o n s as o r i g i n a l l y intended. Space l i m i t a t i o n s and the need to grow a l l the generations under the same n u t r i e n t c o n d i t i o n s r e q u i r e d that a l l the generations be grown i n the same tank. As a r e s u l t only 96 pl a n t s could be examined i n each c r o s s . The p l a n t s were grown under p o t a s s i u m - l i m i t i n g c o n d i t i o n s and short-term net potassium uptake and u t i l i z a t i o n determined a f t e r three weeks. Due to the smaller root mass of i n d i v i d u a l p l a n t s the p e r i o d of d e p l e t i o n was extended such that 1ml samples were drawn a f t e r 1h and 3h. Generation mean and variance a n a l y s i s was done according to the methods of Bulmer (21), Mather and J i n k s (97), Matzinger (99), and Rowe and Alexander (119). A f t e r c a l c u l a t i n g generation means and variances the procedure adopted was as 67 f o l l o w s . 1. R e c i p r o c a l F± s were tes t e d f o r d i f f e r e n c e s using a t - t e s t . ' I f not s i g n i f i c a n t l y d i f f e r e n t , the F 1 ' s were pooled and means and variances r e c a l c u l a t e d . I f s i g n i f i c a n t l y d i f f e r e n t , separate analyses were done for each Fj . 2. For those t r a i t s i n which generation means appeared to be s i m i l a r , as was the case f o r e f f i c i e n c y r a t i o , an o v e r a l l a n a l y s i s of variance of generation means was done before proceeding with the genetic a n a l y s i s . 3. For each t r a i t a 3-parameter model based on the mean (m), pooled a d d i t i v e [a] and dominance [d] gene e f f e c t s was then f i t t e d by the weighted l e a s t squares technique of Mather and J i n k s (97). These parameters and t h e i r standard e r r o r s were estimated using the computational procedure of Rowe and Alexander (119). Adequacy of the 3-parameter model was then t e s t e d using a j o i n t s c a l i n g t e s t (97) and the s t a t i s t i c a l s i g n i f i c a n c e of the pooled gene e f f e c t s t e s t e d i f the model proved adequate. 4 . When the 3-parameter model proved inadequate a 6-parameter model i n c l u d i n g d i g e n i c e p i s t a t i c e f f e c t s was f i t t e d according to the method of Mather and J i n k s (97). The p e r f e c t f i t estimates of these parameters are given below where [aa] i s the a d d i t i v e x a d d i t i v e , , [ad] the a d d i t i v e x dominance, and [dd] the dominance x dominance gene e f f e c t s and P , , B^, B 2, Fj and F 2 are the means of the var i o u s generations. 68 m = 1/2P J + 1/2P2 + 4F 2 - 2 ^ - 2B < 2 [a] = ^/2Pl - \ / 2 P ± [d] = 6B 1 + 6B 2 - 8F 2 - F x - 3/2P r -3/2P 2 [aa] = 2Bj + 2B 2 - 4F"2 [ad] = 2Bj " P t - 2B2, + P 2 [dd] = P1 + P 2 + 2F 1 + 4F 2 - 4^ - 4B 2 The standard e r r o r s of these estimates were then computed and used to t e s t the s t a t i s t i c a l s i g n i f i c a n c e of the gene e f f e c t s . No attempts were made to f i t other models when some of the e p i s t a t i c e f f e c t s proved not s i g n i f i c a n t . P r i o r to f i t t i n g the 6-parameter model an attempt was made to transform the data f o r a b e t t e r f i t to a simple additive-dominance model. Only a l o g a r i t h m i c t ransformation was attempted. This transformation proved u n s u i t a b l e i n a l l cases. Hence a l l the analyses were based on the a c t u a l data obtained. 5. Broad sense h e r i t a b i l i t i e s (H) were obtained a f t e r c a l c u l a t i n g the environmental (Var E) and genotypic (Var G) variances from the p a r e n t a l (Var Pl and Var P 2 ) , F j ( V a r F j ) , and F 2 ( V a r F 2) v a r i a n c e s as shown below. Var E = (Var Pl + Var P 2 + Var F^/3 Var G = Var F 2 - Var E H = Var G/Var F 2 6. The a d d i t i v e (Var A) and dominance (Var D) variances were c a l c u l a t e d from the phenotypic v a r i a n c e s of the v a r i o u s generations as shown below. Var A - 4Var F 2 - 2Var Bl - 2VarB 2 Var D = 4Var Bj + 4Var B, - 4Var F £ - Var Pl - Var P 2 - 2Var Fj 69 The standard e r r o r s of these variances were estimated according to the method of Bulmer (21) whereby the standard e r r o r of a mean square M based on f degrees of freedom i s given byJ2M / f . 7. Narrow sense h e r i t a b i l i t i e s were then c a l c u l a t e d as 2.2. D i a l l e l a n a l y s i s The d i a l l e l c r o s s i n g scheme was set up as a 7 x 7 h a l f d i a l l e l w ith no r e c i p r o c a l s . Only s e l f s and F j ' s were included. The p l a n t s were grown under potassium plus n i t r a t e - l i m i t e d c o n d i t i o n s i n two tanks each of which comprised a block i n a randomized complete block design with two r e p l i c a t i o n s . Each o b s e r v a t i o n a l u n i t c o n s i s t e d of three p l a n t s . A f t e r three weeks short-term net potassium and n i t r a t e f l u x e s were determined by d e p l e t i o n . Shoot f r e s h and dry weights were obtained and potassium and nitrogen u t i l i z a t i o n i n d i c e s determined as p r e v i o u s l y described. I n i t i a l l y an o v e r a l l a n a l y s i s was done fo r each t r a i t to determine i f there were s i g n i f i c a n t d i f f e r e n c e s between the e n t r i e s i n the d i a l l e l . Thereafter analyses f o r general and s p e c i f i c combining a b i l i t i e s were done according to the method of G r i f f i n g (74) as f o l l o w s : hVar A/Var F 2. 70 Source DF SS MS General combining a b i l i t y p - 1 SSgca MSgca S p e c i f i c combining a b i l i t y p(p - 3)/2 SSsca MSsca E r r o r SSe Me' where, 1 V 2 4 2 SSgca = Z^Xf. X.. r ( p - 2)'- L rp(p - 2) 2 r r ( p - 2) " r ( p - 1)(p - 2) Vx.. SSsca = — -2 - • Z)x.2. + X?. Me' = Me/r In the above equations, Sx.. = t o t a l of a l l F 1 ' s f o r each v a r i e t y X.. = t o t a l of a l l F j ' s i n the d i a l l e l x..= t o t a l f o r each F, Me = e r r o r mean square obtained i n the i n i t i a l a n a l y s i s for d i f f e r e n c e s between F j ' s r = number of r e p l i c a t i o n s p = number of p a r e n t a l l i n e s 71 3. R e s u l t s and Dis c u s s i o n The generation means and variances of the v a r i o u s t r a i t s examined are shown i n Tables 14, 15, 16 and 17. D i f f e r e n c e s between generation means f o r short-term net potassium f l u x (Table 14), shoot weight per pla n t (Table 15) and potassium u t i l i z a t i o n e f f i c i e n c y (Table 17) seemed large enough not to warrant any s t a t i s t i c a l t e s t s before doing the genetic a n a l y s i s . However, because d i f f e r e n c e s i n potassium e f f i c i e n c y r a t i o seemed rather small (Table 16), s t a t i s t i c a l a n a l y s i s was f i r s t done to determine i f the generation means were d i f f e r e n t . In a l l the crosses s i g n i f i c a n t d i f f e r e n c e s between generation means were observed (Tables 18 and 19). Therefore, the genetic b a s i s of d i f f e r e n c e s i n the expression of t h i s t r a i t was a l s o examined. Before d i s c u s s i n g the f i n d i n g s of these s t u d i e s , some b r i e f comments of c l a r i f i c a t i o n are necessary. F i r s t i t should be pointed out that the sign of the a d d i t i v e component [a] i s dependent upon p a r e n t a l d e s i g n a t i o n . I f the p a r e n t a l l i n e showing higher expression of the t r a i t i s designated P x, then t h i s component w i l l always be p o s i t i v e . I f the p a r e n t a l l i n e w ith lower expression of the t r a i t i s designated P±, then the value f o r [a] w i l l be negative. Second, by d e f i n i t i o n any dominance d e v i a t i o n d may be p o s i t i v e or negative. Due to the c a n c e l l a t i o n of p o s i t i v e and negative e f f e c t s [d] may ther e f o r e be small or even zero even when i n d i v i d u a l gene e f f e c t s show pronounced dominance (97). This c l e a r l y demonstrates one of the 72 d i f f i c u l t i e s f a c i n g the q u a n t i t a t i v e g e n e t i c i s t and one of the problems a s s o c i a t e d with t r y i n g to i n t e r p r e t gene e f f e c t s . T h i r d , i t i s important to note that the method used to c a l c u l a t e the a d d i t i v e and dominance variances as o u t l i n e d i n the M a t e r i a l s and Methods s e c t i o n does not give the values of these variances as a p r o p o r t i o n of the F^ genetic v a r i a n c e . Consequently the c a l c u l a t e d a d d i t i v e and dominance variances may, on occasion, be found to exceed the F^ genetic v a r i a n c e . Bulmer's (21) method f o r c a l c u l a t i n g these variances was adopted so as to enable t h e i r standard e r r o r s to be determined as w e l l . Both Bulmer (21) and G i l b e r t (67) maintain that the p r e c i s i o n of the variance estimates should be determined so as to evaluate t h e i r usefulness i n f u r t h e r c a l c u l a t i o n s . To obtain the estimates as a p r o p o r t i o n of the F 2 genetic v a r i a n c e , the a d d i t i v e variance would have to be m u l t i p l i e d by 1/2 and the dominance variance by 1/4. Before attempting to f i t any models to the data, d i f f e r e n c e s between r e c i p r o c a l F ^ s i n the crosses NP 52 x Jupateco 73, NP 52 x N a i n a r i 60 and N a i n a r i 60 x Yecora 70 were examined. No r e c i p r o c a l d i f f e r e n c e s f o r short-term net potassium f l u x were observed i n a l l crosses (Table 20). For shoot weight per p l a n t , potassium e f f i c i e n c y r a t i o and potassium u t i l i z a t i o n e f f i c i e n c y only the cross NP 52 x N a i n a r i 60 showed s i g n i f i c a n t r e c i p r o c a l d i f f e r e n c e s (Table 20). Therefore, f o r t h i s cross two separate, analyses were done each using a d i f f e r e n t F . For the other crosses the F,'s were pooled. 73 Table 14. Generation means (upper f i g u r e s ) , number of p l a n t s per generation (parentheses) and variances (lower f i g u r e s ) f o r sh o r t - term net potassium uptake i n the four c r o s s e s . Short-term net potassium uptake (umol/g/h) Generation Cross 1 Cross 2 Cross 3 Cross 4 F i RF B„ 7. 49 (8) 7. 11 (8) 6. 61 (8) 4 .41 (8) 0. 557 0. 467 0. 316 0 .258 5. 79 (8) 6. 67 (10) 4. 95 (13) 2 .82 (13) 1 . 561 0. 551 0. 823 1 .159 5. 52 (6) 6. 06 (8) 5. 25 (8) 2 .08 (8) 0. 454 0. 106 0. 186 0 .354 5. 18 (10) 6. 02 (6) — — 2 .35 (6) 0. 193 0. 190 — — 0 .167 5. 63 (43) 5. 65 (38) 5. 62 (48) 2 .45 (40) 1 . 124 0. 731 0. 866 0 .641 3. 93 (13) 5. 91 (8) 4. 07 (11) 2 .08 (12) 0. 339 0. 477 0. 558 0 .718 2. 95 (8) 4. 81 (8) 3. 60 (8) 1 .68 (8) 0. 1 26 0. 190 0. 454 0 .254 Cross 1: NP 52 x Jupateco 73 Cross 2: NP 52 x N a i n a r i 60 Cross 3: NP 52 x Tesia 79 Cross 4: N a i n a r i 60 x Yecora 70 RF : R e c i p r o c a l F. 74 Table 15. Generation means (upper f i g u r e s ) , number of p l a n t s per generation (parentheses) and variances (lower f i g u r e s ) f o r shoot f r e s h weight per plant i n the four c r o s s e s . Shoot f r e s h weight/plant (g) Generation Cross 1 Cross 2 Cross 3 Cross 4 B 1 F l RF 1 B, 1 .53 (8) 1 .48 (8) 1 .53 (8) 1 .65 (8) 0 .017 0 .013 0 .034 0 .014 1 .47 (8) 1 .76 (10) 1 .44 (13) 1 .50 (13) 0 .037 0 .053 0 .057 0 .091 1 .47 (6) 1 .56 (8) 1 .33 (8) 1 .54 (8) 0 .023 0 .040 0 .021 0 .029 1 .42 (10) 2 . 1 4 (6) - 1 .51 (6) 0 .030 0 .064 — 0 .018 1 .42 (43) 1 .86 (38) 1 .35 (48) 1 .35 (40) 0 .057 0 .111 0 .069 0 .094 1 .42 (13) 1 .96 (16) 1 .34 (11) 1 .29 (12) 0 .086 0 .067 0 .099 0 .051 1 . 1 1 (8) 1 .75 (8) 1 .06 (8) 1 . 12 (8) 0 .007 0 .054 0 .009 0 .014 Cross 1: NP 52 x Jupateco 73 Cross 2: NP 52 x N a i n a r i 60 Cross 3: NP 52 x Tesia 79 Cross 4: N a i n a r i 60 x Yecora 70 RF : R e c i p r o c a l F 75 Table 16. Generation means (upper f i g u r e s ) , number of p l a n t s per generation (parentheses) and variances (lower f i g u r e s ) for potassium e f f i c i e n c y r a t i o i n the four c r o s s e s . Potassium e f f i c i e n c y r a t i o (g/mmol) Generation Cross 1 Cross 2 Cross 3 Cross 4 P, 7.41 (8) 7.13 0.098 0.048 B, 6.94 (8) 7.65 0.051 0.256 P, 6.73 (6) 7.40 0.131 0.086 RF 6.89 (10) 8.13 i 0.028 0.071 F 6.97 (43) 7.36 1 0.166 0.232 B 6.85 (8) 7.56 1 0.146 0.167 P 6.88 (8) 7.25 2 0.062 0.066 (8) 7. 41 (8) 7. 01 (8) 0. 178 0. 090 (10) 7. 07 (13) 7. 54 (13) 0. 1 14 0. 467 (8) 7. 25 (8) 7. 19 (8) 0. 1 1 1 0. 224 (6) — — • 7. 57 (6) — — 0. 171 (38) 7. 53 (48) 7. 80 (40) 0. 236 0. 434 (16) 7. 01 (11) 7. 43 (12) 0. 125 0. 139 (8) 7. 20 (8) 7. 58 (8) 0. 049 0. 148 Cross 1: NP 52 x Jupateco 73 Cross 2: NP 52 x N a i n a r i 60 Cross 3: NP 52 x Tesia 79 Cross 4: N a i n a r i 60 x Yecora 70 RF : R e c i p r o c a l F. 76 Table 17. Generation means (upper f i g u r e s ) , number of p l a n t s per generation (parentheses) and variances (lower f i g u r e s ) f o r potassium u t i l i z a t i o n e f f i c i e n c y i n the four crosses. Potassium u t i l i z a t i o n e f f i c i e n c y (g /mmol) Generation Cross 1 Cross 2 Cross 3 Cross 4 F l RF. B. 11.5 (8) 1 .031 10.18 (8) 2.219 10.13 (6) 0.199 9.66 (10) 1 .727 9.88 (43) 2.847 9.68 (13) 2.929 7.60 (8) 0.334 10.56 (8) 0.406 13.52 (10) 6.571 11.61 (8) 2.767 17.40 (6) 5.817 12.17 (38) 4.591 14.87 (16) 5.581 12.66 (8) 3.243 11 .34 (8) 1 .951 10.25 (13) 3. 139 9.73 (8) 1 .082 10.31 (48) 4.224 9.34 (11) 3.389 7.61 (8) 0.324 11.63 (8) 1 .291 11.18 (13) 4.290 10.99 (8) 0.850 11.40 (6) 0.956 10.46 (40) 4.502 9.68 (12) 3.534 8.45 (8) 0.583 Cross 1: NP 52 x Jupateco 73 Cross 2: NP 52 x N a i n a r i 60 Cross 3: NP 52 x Tesia 79 Cross 4: N a i n a r i 60 x Yecora 70 RF: R e c i p r o c a l F 77 Table 18. Analyses of variance f o r e f f i c i e n c y r a t i o i n the crosses NP 52 x Jupateco 73 and NP 52 x Tesia 79. NP 52 x Jupateco NP 52 x Tesia 79 Source DF Mean square Mean square Generations Re s i d u a l 5 0.424* 90 0.124 0.910* 0.153 * S i g n i f i c a n t at the 5% l e v e l Table 19. A n a l y s i s of variance f o r potassium e f f i c i e n c y r a t i o i n the crosses NP 52 x N a i n a r i 60 and N a i n a r i 60 x Yecora 70. NP 52 x N a i n a r i 60 N a i n a r i 60 x Yecora 70 Source DF Mean square DF Mean square Generations 6 0.805* 6 0.993* Resi d u a l 87 0.055 88 0.318 * S i g n i f i c a n t at the 5% l e v e l 78 3.1. Short-term net potassium f l u x For short-term net potassium f l u x three of the four crosses showed a poor f i t to an additive-dominance model and f o r the cross N a i n a r i 60 x Yecora 70 which was adequately described by t h i s model, both the a d d i t i v e and dominance e f f e c t s were s i g n i f i c a n t (Table 21). Upon f i t t i n g a 6-parameter model to the three c r o s s e s , a l l gene e f f e c t s except the a d d i t i v e x dominance e f f e c t s proved to be s i g n i f i c a n t (Table 22). The signs of the dominance e f f e c t s were c o n s i s t e n t w i t h the mean values shown i n Table 14. For the crosses NP 52 x Jupateco 73 and NP 52 x Tesia 79 i n which negative dominance e f f e c t s were obtained (Table 22), low uptake r a t e s seemed dominant to high uptake r a t e s . In the c r o s s NP 52 x N a i n a r i 60 which showed a p o s i t i v e dominance e f f e c t (Table 22), high uptake r a t e seemed dominant (Table 14). Both a d d i t i v e and dominance variances had l a r g e standard e r r o r s (Table 23) thus r a i s i n g some doubt as to t h e i r usefulness. S t i l l , narrow sense h e r i t a b i l i t i e s were c a l c u l a t e d and found to be rather low. Broad sense h e r i t a b i l i t i e s were about 60% (Table 23) and were co n s i d e r a b l y higher than those reported by Lindgren (91) i n h i s study on phosphate uptake i n beans. Narrow sense h e r i t a b i l i t i e s ranged from 31 to 59% (Table 23). Because a negative estimate of a d d i t i v e variance was obtained i n the cross N a i n a r i 60 x Yecora 70, an estimate of narrow sense h e r i t a b i l i t y c o u ld not be obtained f o r t h i s c r o s s . 3.2. Shoot weight per p l a n t For shoot weight per plant a l l the crosses except NP 52 x 79 Table 20. Comparison of r e c i p r o c a l F progenies f o r short-term net potassium f l u x (STNKF), shoot weight per p l a n t , potassium e f f i c i e n c y r a t i o (KER) and potassium u t i l i z a t i o n e f f i c i e n c y (KUE) i n three c r o s s e s . t values Cross STNKF SWt./plant KER KUE NP 52 x Jupateco 73 1.22 0.64 1.20 0.84 NP 52 x N a i n a r i 60 0.23 2.64* 4.82* 5.33* N a i n a r i 60 x Yecora 70 0.97 0.32 1.56 0.81 * S i g n i f i c a n t l y d i f f e r e n t at 5% l e v e l Table 21. Estimates of mean (m), pooled a d d i t i v e [a] and dominance [d] gene e f f e c t s f o r short-term net potassium uptake i n the four c r o s s e s . Cross m [a ] [d] 7C?3> NP 52 x Jupateco 73 5. 238 2. 319 0.204 8.38* NP 52 x N a i n a r i 60 5. 918 1 . 033 0.1 26 13.56* NP 52 x Tesia 79 5. 126 1 . 420 0. 130 28.12* N a i n a r i 60 x Yecora 70 2. 986 1 . 306* -0.868* 3.55 * S i g n i f i c a n t at the 5% l e v e l 80 Table 22. P e r f e c t f i t estimates of the mean (m), pooled a d d i t i v e [ a ] , dominance [d] and d i g e n i c e p i s t a t i c components (aa = a d d i t i v e x a d d i t i v e , ad = a d d i t i v e x dominance and dd = dominance x dominance) of means f o r short-term net potassium f l u x i n the four crosses. Cross Component NP52 x Jupateco 73 NP52 x N a i n a r i 60 NP52 x Tesia 79 m 8.30 3.40 9.55 [a] 2.27* 1.15* 1.51* [d] -7.87* 6.36* -11.41* [aa] -3.08* 2.56* -4.44* [ad] -0.82 -0.78 -1 .25 [dd] 5.06* -3.72* 7.11* * S i g n i f i c a n t at the 5% l e v e l Table 23. Estimates of the F 2 , genotypic (Var G), a d d i t i v e (Var A) and dominance (Var D) variances and h e r i t a b i l i t i e s (H = broad sense, h 2 = narrow sense) f o r short-term net potassium uptake i n the four c r o s s e s . Cross Var Var G Var A±SE Var D±SE H h2 NP52 x Jupateco 73 1.124 0.651 0.70+1.95 0.30±3.58 58 31 NP52 x N a i n a r i 60 0.731 0.469 0.87±0.92 0.04+1.45 64 59 NP52 x Tesia 79 0.866 0.547 0.70+1.10 0.20+1.85 63 40 Nain. 60 x Yecora 70 0.641 0.379 -1.19±1.27 4.00±2.34 59 — N a i n a r i 60 abbreviated as Nain. 60 81 Jupateco 73 showed a good f i t to a simple additive-dominance model (Table 24). A d d i t i v e e f f e c t s were s i g n i f i c a n t i n a l l the crosses and only the cross NP 52 x N a i n a r i showed a s i g n i f i c a n t dominance e f f e c t . Due to the s i g n i f i c a n t r e c i p r o c a l F j d i f f e r e n c e s i n the cross NP 52 x N a i n a r i 60, two separate analyses were done f o r t h i s c r o s s . The two F j ' s of t h i s cross behaved g u i t e d i f f e r e n t l y depending on which l i n e was used as the female parent (Table 15). When the t a l l Indian v a r i e t y NP 52 was used as the female parent the F 1 was intermediate between the two parents. When the t a l l Mexican v a r i e t y N a i n a r i 60 was used as the female parent a marked h e t e r o t i c e f f e c t was observed such that the Fj^ g r e a t l y exceeded both parents. This r e c i p r o c a l e f f e c t probably r e s u l t e d p a r t l y due to d i f f e r e n c e s i n seed s i z e (51 mg/ seed f o r N a i n a r i 60 and 28 mg/seed f o r NP 52). Variance estimates again proved to have lar g e standard e r r o r s and f o r two of the crosses estimates of a d d i t i v e variance were negative (Table 25). Broad sense h e r i t a b i l i t i e s ranged from 60-82% (Table 25). Narrow sense h e r i t a b i l i t i e s were very high f o r the cross NP 52 x N a i n a r i 60 and rather low f o r the cross N a i n a r i 60 x Yecora 70. The high values observed i n the cross NP 52 x Na i n a r i 60 are suspect since they g r e a t l y exceeded the estimates for broad sense h e r i t a b i l i t y (Table 25). In other s t u d i e s the i n h e r i t a n c e of e f f i c i e n c y based on shoot weight has been found to be v a r i a b l e . Shea et a l . (124) reported i n e f f i c i e n c y f o r potassium use i n beans to be completely dominant. More complex modes of i n h e r i t a n c e were reported by Fawole et a l . (55), Giordano et aJL. (68), Makmur 82 Table 24. Estimates of the mean (m), pooled a d d i t i v e [a] and dominance [d] gene e f f e c t s f o r shoot f r e s h weight per p l a n t i n the four c r o s s e s . Cross m [a] [d] X<3) NP52 x Jupateco 73 1 .327 0.205* 0.138 3.57 NP52 x N a i n a r i 60 1 .71 1 -0.198 0.069 24.20* NP52 x N a i n a r i 60(a) 1 .618 -0.144* 0.499* 0.45 NP52 x Tesia 79 1 .304 0.233* 0.056 2.42 Na i n a r i 60 x Yecora 70 1 .367 0.262* 0.119 4.05 * S i g n i f i c a n t at the 5% l e v e l (a) A n a l y s i s based on r e c i p r o c a l F Table 25. Estimates of F , genotypic (Var G), a d d i t i v e (Var A) and dominance (Var D) variances and h e r i t a b i l i t i e s (H=broad sense, h 2=narrow sense) f o r shoot f r e s h weight per p l a n t i n the four c r o s s e s . Cross Var F 2 Var G Var A±SE Var D±SE H h 2 NP52 x Jupateco 73 0.057 0.040 -0. 02±0. 10 0.20±0. 17 70 — NP52 x N a i n a r i 60 0.111 0.075 0. 21±0. 13 -0.03±0. 18 68 95 NP52 x N a i n a r i 60* 0.111 0.066 0. 2 1 ±0. 13 -0.04±0.19 60 95 NP52 x T e s i a 79 0.069 0.048 -0. 04±0. 12 0.06± 0.21 69 — Nain.60 x T e s i a 79 0.094 0.077 0. 09±0. 12 0.03±0.19 82 49 * A n a l y s i s based on r e c i p r o c a l F j Na i n a r i 60 abbreviated as Nain. 60 83 (94) and O' S u l l i v a n et a l . (107). In c o n t r a s t to previous r e p o r t s on the gen e t i c s of n u t r i e n t - use e f f i c i e n c y , r e c i p r o c a l e f f e c t s were observed i n one of the crosses. I t i s s u r p r i s i n g that s i m i l a r f i n d i n g s have not been reported i n beans where one might expect to observe a marked r e c i p r o c a l e f f e c t due to d i f f e r e n c e s i n seed s i z e . 3.3. Potassium e f f i c i e n c y r a t i o There was i n i t i a l l y some concern i n the i n v e s t i g a t i o n s on potassium e f f i c i e n c y r a t i o because the d i f f e r e n c e s between generation means seemed too small to warrant genetic a n a l y s i s (Table 16). However, these d i f f e r e n c e s were found to be s t a t i s t i c a l l y s i g n i f i c a n t . Due to the s i g n i f i c a n t d i f f e r e n c e between r e c i p r o c a l F ^ s i n the cross NP 52 x N a i n a r i 60, two separate analyses were done for t h i s c r o s s . Of the f i v e crosses two gave a good f i t to a simple a d d i t i v e - dominance model although f o r one of them (NP 52 x N a i n a r i 60) n e i t h e r of these e f f e c t s was s i g n i f i c a n t (Table 26). For the other cross (NP 52 x Jupateco 73) only the a d d i t i v e e f f e c t was s i g n i f i c a n t . S u r p r i s i n g l y when a 6-parameter model was f i t t e d to two of the crosses (NP 52 x N a i n a r i 60 and N a i n a r i 60 x Yecora 70) none of the e p i s t a t i c e f f e c t s proved s i g n i f i c a n t (Table 27). This most l i k e l y occurred due to the lar g e standard e r r o r s a s s o c i a t e d w i t h these e f f e c t s . For the cross NP 52 x Tesia 79 s i g n i f i c a n t dominance, a d d i t i v e x a d d i t i v e and dominance x dominance e f f e c t s were detected (Table 27). Broad sense h e r i t a b i l i t i e s ranged from 52-73% (Table 28). Narrow 84 Table 26. Estimates of mean (m), pooled a d d i t i v e [a] and dominance [d] gene e f f e c t s f o r potassium e f f i c i e n c y r a t i o i n the four c r o s s e s . Cross m [a] [d] 3?3) NP 52 x Jupateco 73 7. 101 0.211* -0.299 3.22 NP 52 x N a i n a r i 60 7. 232 -0.070 0.292 7.73 NP 52 x N a i n a r i 60(a) 7. 139 -0.042 0.826 9.67* NP 52 x Tesia 79 7. 296 0.080 -0.031 24.60* N a i n a r i 60 x Yecora 70 7. 369 -0.239 0. 176 17.54* * S i g n i f i c a n t at the 5% l e v e l (a) A n a l y s i s based on r e c i p r o c a l Table 27. P e r f e c t f i t estimates of the mean (m), pooled a d d i t i v e [ a ] , dominance [d] and di g e n i c e p i s t a t i c components (aa = a d d i t i v e x a d d i t i v e , ad = a d d i t i v e x dominance, dd = dominance x dominance) of generation means for potassium e f f i c i e n c y r a t i o i n three c r o s s e s . Component Cross NP52 x Nain. 60 NP52 x Tesia 79 Nain. 60 x Yecora 70 m 6.21 9.27 8.56 [a] -0.06 0.11 -0.29* [d] 2.68* -4.93* -1 .82 [aa] 0.98 -1.96* -1 .26 [ad] 0.30 -0.09 0.79 [dd] -0.76 2.91* 0.61 * S i g n i f i c a n t at the 5% l e v e l 85 sense h e r i t a b i l i t i e s were h i g h l y v a r i a b l e , ranging from 18% i n the c r o s s NP 52 x N a i n a r i 60 to 99% i n the cross NP 52 x Tesia 79 (Table 28). The very high values observed i n the crosses NP 52 x Jupateco 73 and NP 52 x Tesia 79 must be considered suspect since they exceeded the estimates of broad sense h e r i t a b i l i t y . 3.4. Potassium u t i l i z a t i o n e f f i c i e n c y For potassium u t i l i z a t i o n e f f i c i e n c y a l l the crosses except NP 52 x N a i n a r i 60 gave a good f i t to an additive-dominance model (Table 29). In a l l three crosses which gave a good f i t to t h i s model a d d i t i v e e f f e c t s were s i g n i f i c a n t but f o r the cross N a i n a r i 60 x Yecora 70, dominance e f f e c t s were a l s o s i g n i f i c a n t (Table 29). When a 6-parameter model was f i t t e d to the data f o r the cross NP 52 x N a i n a r i 60 no gene e f f e c t s proved to be s i g n i f i c a n t (Table 30) most l i k e l y due to the l a r g e standard e r r o r s of the e f f e c t s . As f o r the other t r a i t s , variance estimates were a s s o c i a t e d with l a r g e standard e r r o r s (Table 31). Broad sense h e r i t a b i l i t i e s ranged from 31- 80% and narrow sense h e r i t a b i l i t i e s were rather low, ranging from 19-46%. Because the estimate of a d d i t i v e variance f o r the cross NP 52 x N a i n a r i 60 was negative, an estimate of narrow sense h e r i t a b i l i t y could not be obtained for t h i s c r o s s . Of p a r t i c u l a r concern i n these s t u d i e s were the l a r g e standard e r r o r s a s s o c i a t e d with the variance estimates (Tables 23, 25, 28 and 31). Because variance estimates are u s u a l l y a s s o c i a t e d w i t h l a r g e standard e r r o r s , G i l b e r t (67) has r a i s e d some doubts regarding the usefulness of variance a n a l y s i s i n the 86 Table 28. Estimates of F , genotypic (Var G), a d d i t i v e (Var A) and dominance (Var D) variances and h e r i t a b i l i t i e s (H = broad sense, h 2 = narrow sense) f o r potassium e f f i c i e n c y r a t i o i n the four c r o s s e s . Cross Var ? 2 Var G Var A±SE Var D±SE H h 2 NP52 x Jupateco 73 0. 166 0. 091 0. 27±0. 19 - o . 18±0. 31 55 81 NP52 x Nain. 60 0. 232 0. 165 0. 08 ±0. 35 0. 50±0. 57 71 18 NP52 x Nain. 60* 0. 232 0. 170 0. 08±0. 35 0. 52±0. 57 73 18 NP52 x Tesia 79 0. 236 0. 123 0. 46±0. 24 -0. 44±0. 37 52 99 Nain . 60 x Yecora 70 0. 434 0. 330 0. 52±0. 56 0. 07±0. 90 65 60 * A n a l y s i s based on r e c i p r o c a l F, Table 29. Estimates of mean (m), pooled a d d i t i v e [a] and dominance [d] gene e f f e c t s f or potassium u t i l i z a t i o n e f f i c i e n c y i n the four c r o s s e s . Cross m [a] [d] "— 27 X < 3 ) NP 52 x Jupateco 73 9. 56 1.869* 0.405 4.85 NP 52 x N a i n a r i 60 12. 15 -1.518 0.221 21.62* NP 52 x N a i n a r i 60(a) 1 1 . 53 -1 .038 3.183 15.68* NP 52 x Tesia 79 9. 56 1 .866* 0.506 5.55 N a i n a r i 60 x Yecora 70 9. 99 1 .567 1.119* 0.25 * S i g n i f i c a n t at the 5% l e v e l (a) A n a l y s i s based on r e c i p r o c a l F x 87 Table 30. P e r f e c t f i t estimates of the mean (m), pooled a d d i t i v e [ a ] , dominance and di g e n i c e p i s t a t i c components (aa = a d d i t i v e x a d d i t i v e , ad = a d d i t i v e x dominance, and dd = dominance x dominance) of means f o r shoot weight per pl a n t and potassium u t i l i z a t i o n e f f i c i e n c y i n the cross NP 52 x N a i n a r i 60. Potassium u t i l i z a t i o n e f f i c i e n c y Component Shoot weight Cross 1 Cross 2 m 1.615 3.510 14.310 [a] -0.135* -1 .050 -1.050 [d] 1 .035 26.540 -0.850 [aa] 0.000 8.10 -2.700 [ad] -0.130 -0.600 -0.600 [dd] -1.090* -18.440 3.940 * S i g n i f i c a n t at the 5% l e v e l Cross 2 a n a l y s i s i s based on r e c i p r o c a l F, 88 Table 31. Estimates of F 2, genotypic (Var G), a d d i t i v e (Var A) and dominance (Var D) variances and h e r i t a b i l i t i e s (H = broad sense, h 2= narrow sense) f o r potassium u t i l i z a t i o n e f f i c i e n c y i n the four crosses. Cross Var F 2 Var G Var A±SE Var D±SE H h 2 NP 52 x Jupateco 73 2 .85 2. 01 1 . 10±4. 12 5 .83±7.23 71 NP 52 x N a i n a r i 60 4 .59 2. 45 -5. 94±8. 56 21 .70±15.67 53 NP 52 x N a i n a r i 60* 4 .69 1 . 44 -5. 94±8. 56 17 .62116.14 31 NP 52 x Tesia 79 4 .22 3. 1 1 3. 84±5. 28 4 .74±8.77 74 Nain. 60 x Yecora 70 4 .50 3. 59 2. 36±6. 16 9 .62+10.15 80 * A n a l y s i s based on r e c i p r o c a l F 89 study of q u a n t i t a t i v e t r a i t s . Sprague (131) maintains that i f variance a n a l y s i s i s to prove u s e f u l , then i t i s e s s e n t i a l that the populations be adequately sampled. Unfortunately space l i m i t a t i o n s and the requirements of the experiments made i t d i f f i c u l t to grow l a r g e populations i n t h i s study. 3.5. D i a l l e l a n a l y s i s The mean values of the various t r a i t s f o r the p a r e n t a l l i n e s and F ^ s i n the 7 x 7 h a l f d i a l l e l are shown i n Tables 32, 33, 34, 35, 36, 37 and 38. P r i o r to undertaking the analyses f o r general and s p e c i f i c combining a b i l i t i e s , analyses were done to determine i f the F j ' s were s i g n i f i c a n t l y d i f f e r e n t . Because the F 's were found not to be s i g n i f i c a n t l y d i f f e r e n t f o r s h o r t -term net potassium f l u x and potassium u t i l i z a t i o n e f f i c i e n c y (Table 39), a n a l y s i s f o r general and s p e c i f i c combining a b i l i t y was not done f o r these two t r a i t s . For a l l the other t r a i t s both general and s p e c i f i c combining a b i l i t y e f f e c t s proved to be s i g n i f i c a n t (Table 40). Because the inbred l i n e s used i n t h i s study were not assumed to be a random set of l i n e s from a h y p o t h e t i c a l p o p u l a t i o n , the d i a l l e l a n a l y s i s was not expanded to include estimates of a d d i t i v e and dominance variances. Therefore, the only conclusion that can be reached from t h i s study i s that both a d d i t i v e and dominance gene e f f e c t s are important i n the determination of these t r a i t s . 90 Table 32. Mean short-term net potassium f l u x e s of p a r e n t a l l i n e s and F,'s i n the 7 x 7 h a l f d i a l l e l . 1 2 3 4 5 6 7 1. N a i n a r i 60 6.4 5.3 6.3 5.7 5.6 5.6 7.1 2. NP 52 6.0 4.9 4.8 5.4 5.6 5.4 3. Chapingo 53 5.1 4.2 4.7 4.3 4.8 4. Jupateco 73 4.1 5.9 4.6 4.0 5. Yecora 70 2.5 5.4 4.5 6. Tesia 79 3.5 4.4 7. Pusa 4 4.4 Table 33. Mean short-term net n i t r a t e f l u x e s of the pa r e n t a l l i n e s and F.'s i n the 7 x 7 h a l f d i a l l e l . 1 2 3 4 5 6 7 1. N a i n a r i 60 6.7 7.3 6.7 7.0 5.8 7.5 5.6 2. NP 52 5.4 5.9 6.7 4.5 5.4 6.1 3. Chapingo 53 6.5 5.2 5.7 5.1 5.6 4. Jupateco 73 5.6 7.6 6.7 5.2 5. Yecora 70 3.2 5.4 5.7 6. Tesia 79 4.7 5.1 7. Pusa 4 5.2 Table 34. Mean shoot f r e s h weights per p l a n t of the pa r e n t a l l i n e s and F^'s i n the 7 x 7 h a l f d i a l l e l . 1 2 3 4 5 6 7 1. N a i n a r i 60 1.41 1 .00 1 .32 1.20 1.07 1 .34 1 .45 2. NP 52 1 .38 1 .10 1.30 1.13 0.83 1 .34 3. Chapingo 53 1 .14 1.24 1.63 1 .50 1 .40 4. Jupateco 73 0.94 1.37 1 .33 1 .27 5. Yecora 70 1.05 0.97 1 .35 6. Tesia 79 0.90 1 .18 7. Pusa 4 1 .50 Table 35. Mean potassium e f f i c i e n c y r a t i o s of pa r e n t a l l i n e s and F 's i n the 7 x 7 h a l f d i a l l e l . 1 2 3 4 5 6 7 1. N a i n a r i 60 23.8 23. 5 23 .2 22.4 22.2 23.2 24.4 2. NP 52 24. 0 21 .9 22.4 22.4 22.3 23.7 3. Chapingo 53 22 .0 22.0 20.9 20.5 22.7 4. Jupateco 73 22.9 21 .8 23.2 24.3 5. Yecora 70 23.9 23.2 22.3 6. Tesia 79 22.8 24.2 7. Pusa 4 25.1 92 Table 36. Potassium u t i l i z a t i o n e f f i c i e n c i e s of the p a r e n t a l l i n e s and F^'s i n the 7 x 7 h a l f d i a l l e l . 1 2 3 4 5 6 7 1. N a i n a r i 60 3.4 2.8 4.1 2.9 2.8 3.5 4.2 2. NP 52 3.5 3.1 3.2 2.5 2.1 3.1 3. Chapingo 53 2.9 3.3 3.6 2.7 3.6 4. Jupateco 73 3.0 3.3 3.8 3.9 5. Yecora 70 3.1 2.1 2.9 6. Tesi a 79 2.7 3.3 7. Pusa 4 4.8 Table 37. Mean ni t r o g e n e f f i c i e n c y r a t i o s of the p a r e n t a l l i n e s and F.'s i n the 7 x 7 h a l f d i a l l e l . 1 2 3 4 5 6 7 1. N a i n a r i 60 27.2 27.0 27.4 26.2 24.7 25.8 25.8 2. NP 52 27.4 26.4 26.9 24.0 24.5 26.7 3. Chapingo 53 26.2 26.3 24.0 24.7 26.4 4. Jupateco 73 25.5 23.6 26.2 25.3 5. Yecora 70 23. 1 23.7 24.1 6. T e s i a 79 24.4 25.7 7. Pusa 4 25.6 93 Table 38. Mean nitrogen u t i l i z a t i o n e f f i c i e n c i e s of the p a r e n t a l l i n e s and F / s i n the 7 x 7 h a l f d i a l l e l . 1 2 3 4 5 6 7 1. N a i n a r i 60 3.9 3.2 4.5 3.3 3.1 3.9 3.9 2. NP 52 4.0 3.8 3.8 2.7 2.3 3.7 3. Chapingo 53 3.5 4.0 4.1 3.9 4.1 4. Jupateco 73 3.3 3.6 4.3 4.1 5. Yecora 70 3.0 2.1 3.1 6. Tesia 79 2.8 3.5 7. Pusa 4 4.8 94 Table 39. Analyses of variance f o r short-term potassium and n i t r a t e f l u x e s (STNKF and STNNF r e s p e c t i v e l y ) , shoot f r e s h weight per p l a n t , potassium and nitrogen e f f i c i e n c y r a t i o s (KER and NER r e s p e c t i v e l y ) , and potassium and nit r o g e n u t i l i z a t i o n e f f i c i e n c i e s (KUE and NUE r e s p e c t i v e l y ) i n the 7 x 7 h a l f d i a l l e l . Mean squares Source DF STNKF STNNF SWt/pl KER KUE NER NUE F j ' s 20 1.170 1.510* 0.071* 2.142* 0.609 2.791* 0.78* Blocks 1 0.002 2.477* 0.287* 1.449 0.187 0.006 0.86 Residual 20 0.688 0.554 0.029 0.760 0.301 0.314 0.34 * S i g n i f i c a n t at the 5% l e v e l Table 40. Analyses of variance f o r general and s p e c i f i c combining a b i l i t y (GCA and SCA r e s p e c t i v e l y ) f o r short-term net n i t r a t e f l u x (STNNF), shoot f r e s h weight per p l a n t , potassium and n i t r o g e n e f f i c i e n c y r a t i o s (KER and NER r e s p e c t i v e l y ) and nitrogen u t i l i z a t i o n e f f i c i e n c y i n the 7 x 7 h a l f d i a l l e l . Mean squares Source DF STNNF SWt/pl KER NER NUE GCA 6 6.696* 0.095* 4.939* 7.445* 1.712* SCA 14 1.200* 0.061* 0.944* 0.796* 0.403* Error 20 0.277 0.015 0.380 0.157 0.170 * S i g n i f i c a n t at the 5% l e v e l 95 1V. COMPLICATING FACTORS IN THE GENETIC ANALYSIS OF AND SELECTION FOR ATTRIBUTES GOVERNING EFFICIENT MINERAL NUTRITION 1. L i t e r a t u r e review Genetic s t u d i e s of a t t r i b u t e s governing e f f i c i e n t mineral n u t r i t i o n are subject to a number of d i f f i c u l t i e s as are studies of other p h y s i o l o g i c a l t r a i t s as w e l l as some morphological t r a i t s (62). Clarkson (33, 34), Cram (38, 40), Evans (51, 52), Mahon (93) and Pan et a l . (108) have discussed some of these d i f f i c u l t i e s . They include the f o l l o w i n g : (1) a lack of convincing demonstration of the relevance of such t r a i t s f or the genetic improvement of plant performance, (2) the p l a s t i c i t y and v a r i a b i l i t y of expression of p h y s i o l o g i c a l t r a i t s during the p l a n t ' s l i f e , (3) the intimacy of a s s o c i a t i o n between these t r a i t s and other growth and p h y s i o l o g i c a l processes and, i n the case of n u t r i e n t uptake, r e g u l a t i o n by the i n t e r n a l root n u t r i e n t c o n c e n t r a t i o n , (4) mineral element s u b s t i t u t i o n and seed s i z e e f f e c t s which can complicate the e v a l u a t i o n of nu t r i e n t - u s e e f f i c i e n c y , and (5) the degree of c o r r e l a t i o n between the t r a i t s which are s e l e c t e d for and the a c t u a l performance of the s e l e c t e d genotypes under f i e l d c o n d i t i o n s . Some of these issues can have profound i m p l i c a t i o n s for the i n t e r p r e t a t i o n of genotypic v a r i a t i o n , the genetic a n a l y s i s of any d i f f e r e n c e s and the e f f e c t i v e n e s s of s e l e c t i o n . Hence they re q u i r e c a r e f u l c o n s i d e r a t i o n i n any studies on nutrient-use e f f i c i e n c y and i t s improvement. 96 1.1. Seed s i z e and mineral element s u b s t i t u t i o n D i f f e r e n c e s i n seed s i z e and source have long been known to a f f e c t emergence, s e e d l i n g vigour and shoot development (86). These f a c t o r s , i n c l u d i n g d i f f e r e n c e s i n seed n u t r i e n t content, have a l s o been shown to a f f e c t the e s t i m a t i o n of n u t r i e n t - u s e e f f i c i e n c y (63, 64, 66). However, the e f f e c t of seed s i z e has been found to be i n c o n s i s t e n t . Rice (117) reported that although d i f f e r e n c e s i n seed weight were s i g n i f i c a n t under greenhouse c o n d i t i o n s , the e f f e c t was not c o n s i s t e n t i n s t u d i e s conducted i n a b i o t r o n . Because of the importance of these e f f e c t s to the proper estimation of n u t r i e n t - u s e e f f i c i e n c y , researchers have attempted to c o r r e c t f o r these d i f f e r e n c e s when making v a r i e t a l comparisons. Techniques for c o r r e c t i o n have included removal of p a r t s of the seeds, p a r t i c u l a r l y the cotyledons, and the a d d i t i o n of v a r i a b l e amounts of the l i m i t i n g n u t r i e n t to the c u l t u r e medium (63, 64, 66, 124). These measures have proved s u c c e s s f u l i n d i f f e r e n t i a t i n g between maternal and genetic e f f e c t s . However, t h e i r use i s l i m i t e d to the screening of various genotypes since they cannot be used i n genetic s t u d i e s i n which a large number of i n d i v i d u a l p l a n t s have to be examined. Mi n e r a l element s u b s t i t u t i o n has been reported i n number of s t u d i e s (64, 66, 94). Of p a r t i c u l a r i n t e r e s t i s the s u b s t i t u t i o n of sodium fo r potassium. Both of these ions are capable of performing an osmoregulatory r o l e . This e f f e c t has obvious i m p l i c a t i o n s for the e v a l u a t i o n of n u t r i e n t - u s e 97 e f f i c i e n c y , p a r t i c u l a r l y i f there i s d i f f e r e n t i a l uptake of the s u b s t i t u t i n g ion and i f i t i s not considered i n the e v a l u a t i o n of n u t r i e n t - u s e e f f i c i e n c y . This e f f e c t can pose serious d i f f i c u l t y f o r genetic s t u d i e s on n u t r i e n t - u s e e f f i c i e n c y since i t i s not c l e a r how i t can be taken i n t o c o n s i d e r a t i o n i n such s t u d i e s . 1.2. C o r r e l a t i o n between s e l e c t e d t r a i t s and performance An a d d i t i o n a l requirement for the s u c c e s s f u l use of p h y s i o l o g i c a l t r a i t s as s e l e c t i o n c r i t e r i a i n a plant breeding programme i s that there be a good c o r r e l a t i o n between the t r a i t of i n t e r e s t and p l a n t performance. Plant performance would include y i e l d or t o l e r a n c e / r e s i s t a n c e to some s t r e s s . While the a s s o c i a t i o n between some p h y s i o l o g i c a l t r a i t s and p l a n t performance i s obvious, i n most instances t h i s i s not so. This s i t u a t i o n a r i s e s p r i m a r i l y due to the complexity of plant physiology, growth and p r o d u c t i v i t y . Mahon (93), i n p a r t i c u l a r , has addressed the complexity of the a s s o c i a t i o n between p h y s i o l o g i c a l t r a i t s and performance. In h i s a n a l y s i s he emphasises the h i e r a r c h i c a l nature of p h y s i o l o g i c a l processes and t h e i r tendency to be a f f e c t e d by a number of f a c t o r s . Both these phenomena complicate attempts to f i n d a simple r e l a t i o n s h i p between p h y s i o l o g i c a l t r a i t s and p l a n t performance. I t should be pointed out that there are a l s o methodological problems which must be confronted i n such s t u d i e s . As Mahon 98 (93) p o i n t s out, i t i s not s u f f i c i e n t t o simply examine the c o r r e l a t i o n between the expression of a s p e c i f i c t r a i t and plant performance i n a number of genotypes. C l e a r l y , i n such stud i e s other f a c t o r s may a f f e c t the a s s o c i a t i o n between the t r a i t of i n t e r e s t and plant performance. I d e a l l y the s t u d i e s should be done using near-isogenic l i n e s which show v a r i a b l e expression of the t r a i t of i n t e r e s t ; a c o n d i t i o n which i s undoubtedly very d i f f i c u l t t o achieve f o r p h y s i o l o g i c a l t r a i t s . Therefore, these s t u d i e s must of n e c e s s i t y be based on examination of the c o r r e l a t i o n between performance and expression of the t r a i t i n a number of genotypes. With regard to mineral n u t r i t i o n i t i s held that the i d e a l genotype should have a high V m a x , low and Cmin , a l a r g e root system and high e f f i c i e n c y r a t i o (13, 16, 24, 30, 33, 41, 66, 111). I t i s u s e f u l , t h e r e f o r e , to examine the c o r r e l a t i o n between some of these t r a i t s and p l a n t performance under n u t r i e n t - l i m i t i n g c o n d i t i o n s . Baker et a l . (9) conducted f i e l d , greenhouse and l a b o r a t o r y experiments to examine the r e l a t i o n s h i p between phosphate accumulation i n the ear leaves of s i x corn hybrids under f i e l d c o n d i t i o n s and various root c h a r a c t e r i s t i c s and phosphate uptake as measured under c o n t r o l l e d c o n d i t i o n s . They found that the d i f f e r e n c e s i n phosphate accumulation could not be e x p l a i n e d by d i f f e r e n c e s i n the phoshate absorption p r o p e r t i e s of the r o o t s . In a study designed to examine the r e l a t i o n s h i p between sulphate uptake and p r o d u c t i v i t y Cacco et a l . (24) examined 99 sulphate i n f l u x and gr a i n y i e l d i n 12 inbreds and 10 hy b r i d s . They observed that i n general inbreds were c h a r a c t e r i z e d by low K ' s and V 's whereas the hybrids had high K 's and V", 's. A m max 3 m max good c o r r e l a t i o n between the s i z e of the sulphate pool (amount of sulphate taken up during the du r a t i o n of the uptake period) and p r o d u c t i v i t y was obtained. In a f u r t h e r study (25) they found a good c o r r e l a t i o n between y i e l d and both n i t r a t e and sulphate uptake (as determined on 9-day-old seedlings grown under high n u t r i e n t c o n d i t i o n s ) i n corn hybrids developed over a pe r i o d of 45 years. Landi et al^. (87) a l s o observed a good c o r r e l a t i o n between potassium and sulphate uptake and g r a i n y i e l d i n a study i n v o l v i n g s i x corn h y b r i d s . Unfortunately a l l these studies have been done under high n u t r i e n t c o n d i t i o n s . A l s o , uptake r a t e s have been determined for only very short time periods and at a very e a r l y stage of growth. For these reasons, the f i n d i n g s i n these s t u d i e s should be i n t e r p r e t e d with a great deal of c a u t i o n . Glass and Pe r l e y (69) examined the c o r r e l a t i o n between potassium uptake and growth i n 10 ba r l e y v a r i e t i e s grown under c o n d i t i o n s of potassium s t r e s s . They found that although there was no c o r r e l a t i o n between i n f l u x and growth f o r a l l 10 v a r i e t i e s , when some of the v a r i e t i e s were excluded, a s i g n i f i c a n t c o r r e l a t i o n was obtained between f r e s h weight a f t e r two weeks and both V and K . Therefore, they concluded that max m the k i n e t i c parameters can be used as p r e d i c t o r s of performance under c o n d i t i o n s of potassium s t r e s s . No s t u d i e s on the c o r r e l a t i o n between e f f i c i e n c y of 100 n u t r i e n t u t i l i z a t i o n at the vegetative stage and i n the production of grain have been reported. However, the data from s t u d i e s on n u t r i e n t u t i l i z a t i o n at the vegetative stage can be used to examine the c o r r e l a t i o n between the e f f i c i e n c y r a t i o and dry or f r e s h matter production. The r e s u l t s i n d i c a t e that those genotypes with the highest e f f i c i e n c y r a t i o are not n e c e s s a r i l y the highest y i e l d e r s (64, 66, 92, 127). Perhaps i t would be more adviseable to examine the r e l a t i o n s h i p between the " s p e c i f i c u t i l z a t i o n r a t e " and dry or f r e s h matter production rather than that between the e f f i c i e n c y r a t i o and p r o d u c t i v i t y because the e f f i c i e n c y r a t i o does not s t r i c t l y represent the amount of dry or f r e s h matter produced per u n i t n u t r i e n t taken up. 1.3. Ontogenetic changes i n n u t r i e n t uptake and u t i l i z a t i o n The ontogenetic changes i n the expression of some p h y s i o l o g i c a l t r a i t s , sometimes perhaps erroneously r e f e r r e d to as "ontogenetic d r i f t " , are of i n t e r e s t to the pla n t p h y s i o l o g i s t i n that they pose a number of i n t e r e s t i n g questions regarding the r e l a t i o n s h i p between t r a i t expression and a l l the other changes o c u r r i n g i n the growing p l a n t . For the plant g e n e t i c i s t or breeder they are more l i k e l y to be problematic but nonetheless very thought- provoking. Due to the bearing of these changes on genotypic comparisons, the separation of genetic from epi g e n e t i c e f f e c t s and hence s e l e c t i o n e f f i c i e n c y , 101 the g e n e t i c i s t studying these t r a i t s needs t o be b e t t e r acquainted w i t h these i s s u e s . This aspect of genetic s t u d i e s on p h y s i o l o g i c a l t r a i t s seems to have been s o r e l y neglected. However, i n recent s t u d i e s on s a l i n i t y t o l e r a n c e (132) there appears to be a greater a p p r e c i a t i o n of both the genetic and epigen e t i c aspects of p h y s i o l o g i c a l t r a i t e xpression. Ontogenetic changes i n n u t r i e n t uptake have been w e l l documented and examined i n r e l a t i o n to growth, changes i n the r a t i o of root weight or surface area to shoot or t o t a l p l a n t weight, r e g u l a t i o n by root n u t r i e n t c o n c e n t r a t i o n and ageing. This i s an extremely complex t o p i c due to the number of i n t e r a c t i n g f a c t o r s which a f f e c t n u t r i e n t uptake during p l a n t growth. In g e n e r a l , when p l a n t s are grown under c o n d i t i o n s of n u t r i e n t s t r e s s , uptake rate per u n i t root weight or surface area has been found to increase over the f i r s t few weeks of growth and then d e c l i n e f a i r l y r a p i d l y p r i o r to t o t a l c e s s a t i o n ' at maturity (78, 104). When uptake i s expressed on a per pla n t b a s i s the p e r i o d of greatest uptake occurs much l a t e r on and c o i n c i d e s with the p e r i o d of greatest growth (110). Two aspects of plant growth, namely growth r a t e and the r a t i o of root to shoot growth are relevant to these changes. Hence i n i t i a l l y when r e l a t i v e growth rate i s u s u a l l y h i g h e s t , a small root system has to meet the requirements of the r a p i d l y growing p l a n t . A f t e r approximately two weeks lower uptake r a t e s per u n i t root weight or surface area are able to meet the p l a n t ' s requirements due to the lar g e increase i n the r a t i o of root to 102 shoot growth. When ion uptake i s examined i n r e l a t i o n to the changes i n the c o n c e n t r a t i o n of the ion i n the r o o t s , i n t e r p r e t a t i o n of these changes i s complicated by the occurrence of other developmental changes. These include root ageing and i t s e f f e c t on membrane p r o p e r t i e s and hence the extent of passive and a c t i v e i n f l u x . Changes i n the growth rate of shoots and roots a l s o important. Jensen (78) conducted both short and long-term stud i e s on potassium uptake i n a s i n g l e wheat v a r i e t y and concluded that r e g u l a t i o n by root potassium conce n t r a t i o n alone cannot account f o r the changes i n f l u x . He argued that the changes i n f l u x observed over the f i r s t few weeks of growth are due to a reduction i n the number and/or d e c l i n e i n a c t i v i t y of ion c a r r i e r s . He a t t r i b u t e d the d e c l i n e i n i n f l u x over the 20-60 day p e r i o d a f t e r germination to an increase i n the proportion of m e t a b o l i c a l l y i n a c t i v e and c o l l a p s e d roots and the subsequent s l i g h t increase i n i n f l u x to an increase i n passive uptake. In a study on potassium i n f l u x i n barley v a r i e t i e s grown under c o n d i t i o n s of potassium l i m i t a t i o n , S i d d i q i and Glass (126) observed a t h r e e f o l d increase i n root potassium co n c e n t r a t i o n from day 8 to day 13 a f t e r germination and a concomitant decrease i n V and an increase i n K . However the max m degree of response was not the same f o r a l l v a r i e t i e s . These r e s u l t s thus i n d i c a t e that over short time p e r i o d s , p a r t i c u l a r l y during the e a r l y stages of growth, r e g u l a t i o n by root potassium co n c e n t r a t i o n can be an important determinant of developmental 103 changes i n i n f l u x . The e f f e c t of ontogenetic v a r i a t i o n i n uptake on genotypic comparisons and the g e n e t i c - p h y s i o l o g i c a l i n t e r p r e t a t i o n of such d i f f e r e n c e s has not been adequately examined. However, a few st u d i e s are a v a i l a b l e f o r the examination of t h i s q u e s t i o n . From the s t u d i e s of S i d d i q i and Glass (126) i n which the k i n e t i c parameters for potassium uptake were examined i n four barley v a r i e t i e s at days 8 and 13 a f t e r germination, i t i s evident that there was a change i n the ranking of the v a r i e t i e s with respect to both V m a x and . Jensen (79) conducted a study i n which two bar l e y v a r i e t i e s p r e v i o u s l y grown under high potassium c o n d i t i o n s were subsequently subjected to d i f f e r e n t potassium regimes p r i o r to i n f l u x determination. He found that i f the p l a n t s were continuously grown under high potassium c o n d i t i o n s , the d i f f e r e n c e s i n i n f l u x were n e g l i g i b l e . However, a f t e r t r a n s f e r to a potassium-free medium i n f l u x values increased d r a m a t i c a l l y and d i f f e r e n c e s between the v a r i e t i e s became more apparent the longer the p l a n t s were kept under these c o n d i t i o n s . Although the i n f l u x rankings of the v a r i e t i e s d i d not change a p p r e c i a b l y , the extent of the d i f f e r e n c e i n i n f l u x d i d change over time. These r e s u l t s are i n agreement with those obtained i n other s t u d i e s i n which i t has been found that v a r i e t a l d i f f e r e n c e s i n i n f l u x tend to more apparent under c o n d i t i o n s of n u t r i e n t l i m i t a t i o n (45, 48, 91, 126). A l s o , these f i n d i n g s perhaps provide some support f o r F i t t e r and Hay's (60) contention that the d i f f e r e n c e s i n i n f l u x may be l a r g e l y a r t e f a c t u a l due to the p r o v i s i o n of s t a r v a t i o n media p r i o r to 104 the determination of i n f l u x . Few s t u d i e s have examined ontogenetic changes i n n u t r i e n t -use e f f i c i e n c y at the vegetative stage. In view of the f i n d i n g s on potassium n u t r i t i o n i n barley (125, 126, 127) i t seems that developmental changes i n u t i l i z a t i o n as measured by the e f f i c i e n c y r a t i o are u n l i k e l y to have a major e f f e c t on genotypic comparisons. On the other hand, because u t i l i z a t i o n e f f i c i e n c y i s p r i m a r i l y dependent upon shoot weight, marked changes i n t h i s index are to be expected during growth. E x a c t l y how these changes are l i k e l y to a f f e c t genotypic comparisons for n u t r i e n t - u s e e f f i c i e n c y i s not too c l e a r . I f the v a r i e t i e s being compared e x h i b i t marked d i f f e r e n c e s i n growth p a t t e r n , as might be expected f o r v a r i e t i e s which d i f f e r c o n s i d e r a b l y i n maturity, these d i f f e r e n c e s could have a s i g n i f i c a n t bearing on comparative s t u d i e s based on u t i l i z a t i o n e f f i c i e n c y . 2. M a t e r i a l s and methods Two types of experiments were done to i n v e s t i g a t e some of the problems l i k e l y to be encountered i n genetic s t u d i e s on, and s e l e c t i o n f o r , potassium uptake and u t i l i z a t i o n . In one study the ontogenetic changes i n potassium uptake and u t i l i z a t i o n were examined i n a number of v a r i e t i e s over a f i v e week p e r i o d . In the second s e r i e s of experiments the c o r r e l a t i o n between p h y s i o l o g i c a l t r a i t s determined at the v e g e t a t i v e stage and performance at the adult stage, i . e . i n g r a i n production, was 105 examined. The l a t t e r s t u d i e s were a l s o designed to examine the extent of genotype x environment i n t e r a c t i o n with respect to potassium u t i l i z a t i o n . 2.1. Ontogenetic v a r i a t i o n i n potassium uptake and u t i l i z a t i o n This experiment was designed to examine the ontogenetic changes i n potassium uptake and u t i l i z a t i o n i n s i x c o n t r a s t i n g v a r i e t i e s over a f i v e week p e r i o d . These changes were r e l a t e d to the changes i n root potassium c o n c e n t r a t i o n , shoot and root growth r a t e s , and p a r t i t i o n i n g of growth between roots and shoots. Of primary i n t e r e s t i n these s t u d i e s was the bearing of these changes on genotypic comparisons f o r these t r a i t s , i n v e s t i g a t i o n s of t h e i r i n h e r i t a n c e and s e l e c t i o n f o r t h e i r improvement. Six v a r i e t i e s were grown i n a s i n g l e tank under potassium-l i m i t e d c o n d i t i o n s as p r e v i o u s l y described. The v a r i e t i e s were s e l e c t e d so as to be r e p r e s e n t a t i v e of the c o n t r a s t i n g types under study. At weekly i n t e r v a l s s t a r t i n g one week a f t e r germination net potassium f l u x e s , root potassium concentrations, e f f i c i e n c y r a t i o s and u t i l i z a t i o n e f f i c i e n c i e s were determined as p r e v i o u s l y o u t l i n e d . For each time p e r i o d three r e p l i c a t e s each c o n s i s t i n g of three p l a n t s were used. Uptake volumes of 190ml were chosen f o r the f i r s t three weeks. Thereafter, volumes of 750ml were employed to accomodate the l a r g e r root mass. Root and shoot r e l a t i v e growth r a t e s were computed as 106 o u t l i n e d by Hunt (76). Average net f l u x e s f o r one-week periods were c a l c u l a t e d according to the method Wi l l i a m s (142). 2.2. C o r r e l a t i o n between potassium u t i l i z a t i o n at the v e g e t a t i v e stage and i n g r a i n production These experiments were designed to (1) compare a number of v a r i e t i e s f o r d i f f e r e n c e s i n potassium u t i l i z a t i o n at the adult stage, i . e . i n g r a i n production, (2) examine the r e l a t i o n s h i p between e f f i c i e n c y of potassium u t i l i z a t i o n at the vegetative and a d u l t p l a n t stages, and (3) determine the extent of genotype x environment i n t e r a c t i o n with respect to potassium u t i l i z a t i o n . Because the v a r i e t i e s could not be grown to maturity i n the growth room, the adult plant experiment had to be done under n a t u r a l c o n d i t i o n s . Furthermore, the i n a b i l i t y to locate a s u i t a b l e ( p o t a s s i u m - l i m i t i n g ) f i e l d s i t e d i c t a t e d that the p l a n t s be grown h y d r o p o n i c a l l y under p o t a s s i u m - l i m i t i n g c o n d i t i o n s . To v a l i d a t e the comparison between measures of potassium u t i l i z a t i o n at the v e g e t a t i v e and a d u l t p l a n t stages, e v a l u a t i o n of u t i l i z a t i o n at the vegetative stage a l s o had to be done under n a t u r a l c o n d i t i o n s . Because the same v a r i e t i e s were grown i n both the growth room and under n a t u r a l c o n d i t i o n s for the e s t i m a t i o n of potassium u t i l i z a t i o n at the v e g e t a t i v e stage, t h i s study a l s o enabled the extent of genotype x environment i n t e r a c t i o n with respect to potassium u t i l i z a t i o n to be examined. 107 For the v e g e t a t i v e stage experiment 16 v a r i e t i e s were grown i n a s i n g l e tank i n a completely randomised design w i t h three r e p l i c a t i o n s . The experiment was c a r r i e d out i n May when c o n d i t i o n s tended to be overcast and r a i n y . A f t e r three weeks the p l a n t s were harvested and potassium e f f i c i e n c y r a t i o s and u t i l i z a t i o n e f f i c i e n c i e s determined. For the ad u l t p l a n t experiment 12 v a r i e t i e s were grown to maturity ( s t a r t i n g i n May) i n a completely randomised design w i t h three r e p l i c a t i o n s . To reduce competition, the number of p l a n t s per d i s c was reduced to two. The s i z e of the experiment required that two tanks be used with each one h o l d i n g s i x v a r i e t i e s . As expected,, these experiments proved extremely d i f f i c u l t to c a r r y out. During the l a t e r stages of growth l a r g e q u a n t i t i e s (6-121) of d i s t i l l e d water had to be added d a i l y to each tank to compensate f o r t r a n s p i r a t i o n a l l o s s e s . As a r e s u l t i t proved extremely d i f f i c u l t to maintain the d e s i r e d l e v e l of potassium. In general the l e v e l tended to be lower than 10UM. At maturity the extent of t i l l e r i n g was recorded and the p l a n t s harvested. The v e g e t a t i v e p a r t s and g r a i n were separated, d r i e d at 80°C for 48h and weighed. The straw was then ground i n a Wiley m i l l and samples of both the g r a i n and straw ashed f o r potassium a n a l y s i s . E f f i c i e n c y of potassium u t i l i z a t i o n i n g r a i n production was then computed as the amount of g r a i n produced per u n i t of potassium taken up i n both the straw and g r a i n . The r e l a t i o n s h i p between potassium u t i l i z a t i o n at the v e g e t a t i v e and g r a i n production stages was then examined by c o r r e l a t i n g the r e s u l t s obtained at the v e g e t a t i v e stage i n both the growth room 108 and under n a t u r a l c o n d i t i o n s with those obtained at the adult p l a n t stage under n a t u r a l c o n d i t i o n s . Genotype x environment i n t e r a c t i o n with respect to potassium u t i l i z a t i o n was examined by means of a combined a n a l y s i s of variance f o r the 16 v a r i e t i e s grown i n the growth room and under n a t u r a l c o n d i t i o n s . A l l three measures of u t i l i z a t i o n were examined. The analyses were undertaken using a completely random model (36, 46) as shown below where g, e, and r r e f e r to the number of genotypes, environments and r e p l i c a t i o n s used. Source DF MS Expectations of mean squares Genotypes 9-1 MSX z z a. cr + r CTge + recTc^-Environments e-1 MS2 c r + rCTjge + r g o ^ G x E (g-D ( e - l ) MS3 2. 3 cr + rCTcje Residual MS4 o-2 Broad sense h e r i t a b i l i t i e s on a l i n e mean b a s i s were obtained f i r s t computing the genotypic variance as MS 1 - MS^/re and the phenotypic variance as e r g + crge/e + 0 ~ / r e . The estimate of h e r i t a b i l i t y was then obtained by d i v i d i n g the genotypic variance by the phenotypic v a r i a n c e . To obtai n a b e t t e r e v a l u a t i o n of the genotype x environment i n t e r a c t i o n , rank c o r r e l a t i o n s for a l l the t r a i t s over the two environments were a l s o computed. 109 3. R e s u l t s and D i s c u s s i o n Three issues of importance for the genetic improvement of mineral n u t r i t i o n were examined. They included (1) ontogenetic v a r i a t i o n f o r potassium uptake and u t i l i z a t i o n and i t s e f f e c t on genotypic comparisons and genetic s t u d i e s , (2) the extent of genotype x environment i n t e r a c t i o n with respect to potassium u t i l i z a t i o n , and (3) the r e l a t i o n s h i p between measures of potassium u t i l i z a t i o n obtained at the v e g e t a t i v e and adult p l a n t stages. Although the e f f e c t of d i f f e r e n c e s i n seed s i z e was not i n v e s t i g a t e d s y s t e m a t i c a l l y , the r e s u l t s of some of the genetic s t u d i e s i n d i c a t e that t h i s might be an important c o n s i d e r a t i o n i n the e s t i m a t i o n of u t i l i z a t i o n e f f i c i e n c y . 3.1. Ontogenetic v a r i a t i o n i n potassium uptake and u t i l i z a t i o n The e f f e c t of ontogenetic v a r i a t i o n i s important for two reasons. F i r s t i t can have a major bearing on the e f f e c t i v e n e s s of s e l e c t i o n i f the ranking of v a r i e t i e s changes considerably during growth. This might require that a standard time a f t e r germination be s e l e c t e d f o r making comparisons between v a r i e t i e s . Presumably t h i s time p e r i o d would be decided upon a f t e r c a r e f u l l y examining the r e l a t i o n s h i p between measures of n u t r i e n t uptake and u s e - e f f i c i e n c y at the v e g e t a t i v e stage and performance at the a d u l t stage. Second, because ontogenetic 110 v a r i a t i o n imparts both a genetic and epi g e n e t i c component to v a r i a t i o n f o r n u t r i e n t uptake and u t i l i z a t i o n , i t i s of importance to the proper genetic a n a l y s i s of these t r a i t s and hence t h e i r improvement. Whether the two e f f e c t s can a c t u a l l y be separated s a t i s f a c t o r i l y i s not c l e a r . Even i f t h i s can be achieved by combining data on uptake rates and u t i l i z a t i o n with that f o r root potassium concentrations and growth, i t i s questionable i f these f i n d i n g s could be of p r a c t i c a l value to the genetic improvement of these t r a i t s . Despite these r e s e r v a t i o n s , i t i s s t i l l imperative that t h i s issue be addressed. F a i l u r e to do so could r e s u l t i n erroneous co n c l u s i o n s regarding genetic d i f f e r e n c e s between v a r i e t i e s . A l s o , without some a p p r e c i a t i o n of the causes and consequences of the changes that occur during growth s e l e c t i o n p r a c t i c e s adopted could prove f r u i t l e s s . Such would be the case i f s e l e c t i o n i s not c a r r i e d out at an appropriate stage or i f i s based on epi g e n e t i c rather than genetic d i f f e r e n c e s between v a r i e t i e s . To i n v e s t i g a t e the e f f e c t of ontogenetic v a r i a t i o n on t r a i t e xpression and v a r i e t a l d i f f e r e n c e s , observations were made on s i x v a r i e t i e s over a p e r i o d of f i v e weeks. Of p a r t i c u l a r i n t e r e s t i n t h i s study was the c o r r e l a t i o n between observations made at d i f f e r e n t times and the consistency of v a r i e t a l ranking fo r potassium uptake and u t i l i z a t i o n . The l a t t e r would undoubtedly be the most important c o n s i d e r a t i o n f o r s e l e c t i o n purposes. Due to space l i m i t a t i o n s , only s i x v a r i e t i e s were included I l l i n t h i s study. However, they were s e l e c t e d so as to include the va r i o u s types under study. As such they included t a l l t r a d i t i o n a l types and va r i o u s dwarf v a r i e t i e s . The t a l l types were g e n e r a l l y l a t e - maturing, achieving mid-flowering stage 3-4 weeks a f t e r the dwarf types. I t i s important when e v a l u a t i n g the f i n d i n g s of t h i s study to keep i n mind the small sample s i z e used. C o r r e l a t i o n c o e f f i c i e n t s should therefore be i n t e r p r e t e d with due care. The highest short-term f l u x e s were observed at one week, i . e . two days a f t e r t r a n s f e r r i n g the p l a n t s to the tanks, with the exception of the v a r i e t y Moti whose f l u x at 4 weeks was s i m i l a r to that at one week (Table 41). A f t e r one week the f l u x e s of some of the v a r i e t i e s tended to s t a b i l i z e whereas those of others showed some e r r a t i c v a r i a t i o n . S i g n i f i c a n t d i f f e r e n c e s between v a r i e t i e s were observed at a l l stages and the t a l l Indian v a r i e t y c o n s i s t a n t l y had the highest f l u x e s (Table 41). S i g n i f i c a n t c o r r e l a t i o n s were obtained between short-term net potassium f l u x e s measured at 1 and 2 weeks, 2 and 3 weeks, 1 and 3 weeks, 2 and 5 weeks, 3 and 5 weeks, and 4 and 5 weeks (Table 42). A l l rank c o r r e l a t i o n c o e f f i c i e n t s were not s i g n i f i c a n t probably due to the small sample s i z e used. Fluxes obtained at 4 weeks d i d not c o r r e l a t e with those determined e a r l i e r on. This lack of c o r r e l a t i o n was probably mainly due to the anomolous behaviour of the v a r i e t y M o t i . Ontogenetic changes i n average net potassium f l u x were not c o n s i s t e n t although f o r most of the v a r i e t i e s f l u x e s i n i t i a l l y increased and then decreased (Table 43). For the v a r i e t y C 306, 112 f l u x e s showed an i n i t i a l d e c l i n e but increased s l i g h t l y over the 4-5 week pe r i o d . In general average net potassium f l u x e s for the d i f f e r e n t time periods were poorly c o r r e l a t e d as were the v a r i e t a l rankings (Table 44). A number of negative c o r r e l a t i o n s were obtained although only the c o r r e l a t i o n between the 1-2 and 3-4 week periods was s i g n i f i c a n t . The average net potassium f l u x e s were a l s o compared with i n f l u x e s from a s o l u t i o n of 1OpM K+ (86R d) as determined i n the k i n e t i c s t u d i e s . Only the 1-2 week and 2-3 week average f l u x e s were found to be s i g n i f i c a n t l y c o r r e l a t e d with i n f l u x (Table 44). Of more relevance i n these s t u d i e s were the c o r r e l a t i o n s between short-term net f l u x e s and average net f l u x e s during growth. Because v a r i e t a l comparisons would most probably be based on short-term f l u x e s which tend to be e a s i e r to measure, i t i s very important that these f l u x e s be compared with the a c t u a l f l u x e s during growth. Should these c o r r e l a t i o n s be found to be poor, i t would r a i s e some doubt as to the usefulness of short-term p e r t u r b a t i o n f l u x e s as measures of uptake e f f i c i e n c y . Only the c o r r e l a t i o n s between short-term f l u x e s and the average net f l u x e s f o r the one week periods immediately preceding and f o l l o w i n g the time of short-term f l u x determination were examined. Short-term f l u x e s at one and two weeks proved to be s i g n i f i c a n t l y c o r r e l a t e d with average f l u x e s over the 1-2 week p e r i o d (Table 45). However, short-term f l u x e s at 2 weeks were not s i g n i f i c a n t l y c o r r e l a t e d w i t h average f l u x e s over the 2-3 week p e r i o d . Average net f l u x e s over the 3-4 week pe r i o d were n e g a t i v e l y c o r r e l a t e d with short-term f l u x e s at 3 113 and 4 weeks. A l l other c o r r e l a t i o n s were p o s i t i v e but not s i g n i f i c a n t (Table 45). These s t u d i e s thus i n d i c a t e that s e l e c t i o n on the b a s i s of average net f l u x e s , aside from being d i f f i c u l t due to the requirement f o r plan t d e s t r u c t i o n , i s confronted with the a d d i t i o n a l problem of poor c o r r e l a t i o n between measures made at d i f f e r e n t times. This poor c o r r e l a t i o n may be due to d i f f e r e n c e s i n growth and the p a r t i t i o n i n g of growth between shoots and roots i n l a t e and e a r l y maturing types. As regards short-term f l u x e s , i t seems that they do not s a t i s f a c t o r i l y represent f l u x e s during growth although they do give f a i r l y c o n s i s t e n t v a r i e t a l ranking over time. Again i t should be emphasized that the sample s i z e used i n t h i s study cannot r e a l l y be considered adequate f o r any d e f i n i t i v e conclusions to be drawn. However, i t can s t i l l be s a i d that the use of short-term p e r t u r b a t i o n f l u x e s as s e l e c t i o n c r i t e r i a should be undertaken with extreme c a u t i o n . Cram (40) has a l s o cautioned against the use of t h i s approach. The ontogenetic changes i n f l u x e s and the v a r i a t i o n i n v a r i e t a l ranking were examined i n r e l a t i o n to changes i n root potassium c o n c e n t r a t i o n and growth. For four of the v a r i e t i e s (NP 52, Pb 8A, C 306 and Tesia 79) root potassium concentration increased to a maximum at three weeks and then d e c l i n e d (Table 41). For Sonora 64 and Moti root potassium concentration increased and then remained f a i r l y constant. The decrease i n root potassium c o n c e n t r a t i o n observed i n the t a l l v a r i e t i e s NP 52, Pb 8A and C 306 probably r e s u l t e d from changes i n growth. 114 Table 41. Short-term net potassium f l u x e s (umol/g/h) and root potassium concentrations (umol/g) of the s i x v a r i e t i e s as determined at weekly i n t e r v a l s . Fluxes are given on top l i n e and root potassium concentrations on bottom l i n e . Time V a r i e t y 1 Week 2 Weeks 3 Weeks 4 Weeks 5 Weeks NP 52 Pb 8A C 306 Sonora 64 Tesia 79 Moti 10.7a 31 .0 8.7b 32.5 7.2c 25.0 6.5d 29.5 6.4d 34.3 6.2d 31 .2 6.4a 32.1 3.4c 37.1 5.6b 35.9 3.2c 33.6 1 .9d 43.7 3.1c 40.0 5.8a 39.9 4.1b 43.5 4.0b 38.7 3.2c 44.9 2.5d 52.8 3.2c 56.3 5. 6a 25.2 4.2bc 34.2 4.9b 28.9 3 ,8c 39.1 3.7c 40.6 6. 3a 49.4 5.1a 22.8 4.0b 26.1 5.2a 24.3 3.1c 47.7 2.9c 36.4 4.6ab 51 .1 Means w i t h i n the same column followed by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t at the 5% l e v e l according to Duncan's m u l t i p l e range t e s t . 115 Table 42. C o r r e l a t i o n c o e f f i c i e n t s between various short-term net potassium f l u x e s . Product-moment c o r r e l a t i o n c o e f f i c i e n t s are given a b o v e t h e diagonal and Spearman's rank c o r r e l a t i o n c o e f f i c i e n t s are given below the di a g o n a l . £fK(D 0 K ( 2 ) 0 K ( 3 ) 0 K ( 4 ) 0 K ( 5 ) 0 K ( 1 ) 0.72* 0.93* 0.23 0.50 0 K ( 2 ) 0.89 0.89* 0.47 0.84* 0 K ( 3 ) 0.90 0.93 0.43 0.72* 0 K ( 4 ) 0.09 0.43 0.50 0.78* 0 K ( 5 ) 0.43 0.77 0.67 0.77 * S i g n i f i c a n t at the 5% l e v e l 0 K ( 1 ) : Short-term net potassium f l u x at 1 week 0 K ( 2 ) : Short-term net potassium f l u x at 2 weeks 0 K ( 3 ) : Short-term net potassium f l u x at 3 weeks 0 K ( 4 ) : Short-term net potassium f l u x at 4 weeks 0 K ( 5 ) : Short-term net potassium f l u x at 5 weeks 116 Table 43. Average net potassium f l u x e s of the 6 v a r i e t i e s over one-week pe r i o d s . Average net potassium f l u x (umol/g/h) V a r i e t y 1-2 weeks 2-3 weeks 3-4 weeks 4-5 weeks NP 52 0.97 1.16 0.51 0.61 C 306 0.91 0.79 0.47 0.56 Pb 8A 0 . 8 1 0.99 0.59 0.48 Sonora 64 0.68 0.77 0.79 0.69 Tesia 79 0.81 1.05 0.68 0.20 Moti 0.74 1.11 0.67 0.61 117 Table 44. C o r r e l a t i o n c o e f f i c i e n t s between various potassium f l u x e s f o r the v a r i e t i e s which were included i n the k i n e t i c and ontogenetic e f f e c t s t u d i e s . Product-moment c o r r e l a t i o n c o e f f i c i e n t s are given above the diagonal and Spearman's rank c o r r e l a t i o n c o e f f i c i e n t s are given below the diagonal. £fK( 1 ) jefK(2) 0K(3) J0K(4) J0K(5) J0K( 1 ) 0.31 -0.89* -0.03 0.93* J0K(2) 0.36 -0.20 -0.41 0.93* #K(3) -0.80 -0.16 -0.06 0.35 0K(4) 0.33 -0.26 0.26 0.09 J0K(5) 0.47 0.08 -0.70 0.20 * S i g n i f i c a n t at the 5% l e v e l 0K(1): Average net potassium f l u x over 1-2 weeks 0K(2): Average net potassium f l u x over 2-3 weeks j0K(3): Average net potassium f l u x over 3-4 weeks j0K(4): Average net potassium f l u x over 4-5 weeks J0K(5): Potassium i n f l u x at an e x t e r n a l c o n c e n t r a t i o n of 10UM 118 Table 45. C o r r e l a t i o n s between short-term and average net f l u x e s i n the experiment designed to examine the e f f e c t of ontogenetic changes i n potassium uptake and u t i l i z a t i o n on genotypic comparisons. Characters r Spearman's r STNKF(1) :ANKF(1~2) 0.74* 0.70 STNKF(2) :ANKF(1-2) 0.79* 0.70 STNKF(2) :ANKF(2-3) 0.18 0.09 STNKF(3) :ANKF(2-3) 0.30 0.27 STNKF(3) :ANKF(3-4) -0.69 -0.70 STNKF(4) :ANKF(3-4) -0.40 -0.54 STNKF(4) :ANKF(4-5) 0.46 0.41 STNKF(5) :ANKF(4-5) 0.46 0.24 * S i g n i f i c a n t at the 5% l e v e l STNKF: Short-term net potassium f l u x ANKF: Average net potassium f l u x Numbers i n parentheses r e f e r to the times when short-term net potassium f l u x e s were determined and the time periods over which average net potassium f l u x e s were measured. 119 As i s evident from Figures 5 and 6, these v a r i e t i e s , u n l i k e the dwarf types, e x h i b i t e d a marked increase i n growth over the 3-5 week p e r i o d . This increase i n growth most l i k e l y had a d i l u t i o n e f f e c t thus r e s u l t i n g i n the lower root potassium concentrations a f t e r three weeks. The reasons f o r the decrease i n the v a r i e t y T e s i a 79 are not c l e a r . Perhaps, because t h i s was the e a r l i e s t v a r i e t y , the decrease might be p a r t l y due to l o s s of potassium from the r o o t s . I t has been reported that as p l a n t s mature there i s a considerable l o s s of potassium (14). More importantly, f o r any one v a r i e t y the changes i n short-term net potassium f l u x d i d not p a r a l l e l the changes i n root potassium c o n c e n t r a t i o n . Therefore, the changes i n f l u x cannot be a t t r i b u t e d to r e g u l a t i o n by root potassium c o n c e n t r a t i o n . The lack of c o r r e l a t i o n between average net potassium f l u x e s obtained over d i f f e r e n t time i n t e r v a l s (Table 42) was probably p a r t l y due to d i f f e r e n c e s i n growth. For the dwarf v a r i e t i e s r e l a t i v e growth rates d e c l i n e d considerably over the 3-5 week p e r i o d whereas those f o r the t a l l types, except Pb 8A, a c t u a l l y increased (Table 46). Therefore, i t seems that there are d i f f e r e n c e s i n growth p a t t e r n between the t a l l and dwarf types. The t a l l late-maturing types i n i t i a l l y grew at rates comparable to the dwarf types but, because of t h e i r l a t e m a t u r i t y , showed considerably higher growth r a t e s l a t e r on when the early-maturing types were slowing down i n growth. I t should be pointed out that i t i s not simply a question of growth r a t e s that i s relevant to the changes i n net f l u x e s . Changes i n the r a t i o of root surface area or weight to shoot 120 Figure 5. Shoot ( s o l i d symbols) and root (open symbols) f r e s h weights of the v a r i e t i e s NP 52 (A), C 306 (•) and Pb 8A (•). 121 4r TIME ( WEEKS) Figure 6. Shoot ( s o l i d symbols) and root (open symbols) f r e s h weights of the v a r i e t i e s Sonora 64 (•), Te s i a 79 (A) and Moti (•). 122 Table 46. Shoot (top l i n e ) and root (bottom l i n e ) r e l a t i v e growth r a t e s of the 6 v a r i e t i e s over a five-week p e r i o d . R e l a t i v e growth rates (g/g/day) V a r i e t y 1-2 weeks 2-3 weeks 3-4 weeks 4-5 weeks NP 52 0. 186 0. 159 0. 107 0. 128 0. 137 0.099 0.141 0. 133 C 306 0. 180 0. 141 0. 108 0. 1 26 0. 143 0. 105 0. 103 0.121 Pb 8A 0.065 0. 168 0.121 0.095 0.099 0. 124 0. 140 0.093 Sonora 64 0. 1 57 0. 126 0. 109 0.084 0.091 0.075 0.061 0.091 Tesia 79 0. 153 0.151 0.113 0.024 0.099 0. 128 0. 1 03 0.009 Moti 0.131 0. 1 45 0.085 0.059 0.070 0.087 0.078 0.037 123 weight would a l s o be important i n accounting f o r changes i n net f l u x . Because these s t u d i e s were not undertaken to examine these issues i n great d e t a i l , the changes observed and the poor c o r r e l a t i o n s obtained w i l l not be discussed i n d e t a i l nor w i l l f u r t h e r attempts be made to account f o r the observations made. S u f f i c e i t to say that d i f f e r e n c e s i n maturity are undoubtedly important i n e v a l u a t i n g n u t r i e n t uptake. These d i f f e r e n c e s would be expected to be confounded with a c t u a l genetic d i f f e r e n c e s i n uptake c a p a c i t y thus making e f f e c t i v e s e l e c t i o n for n u t r i e n t uptake e f f i c i e n c y d i f f i c u l t . Potassium e f f i c i e n c y r a t i o s showed a marked decrease a f t e r one week and then remained f a i r l y constant (Table 47). This i s to be expected since the shoots would i n i t i a l l y have a low potassium c o n c e n t r a t i o n and hence a very high e f f i c i e n c y r a t i o . I t i s d o u b t f u l that the developmental changes i n e f f i c i e n c y r a t i o are p h y s i o l o g i c a l l y meaningful since t h i s would i n d i c a t e that the p l a n t s are much more e f f i c i e n t at u t i l i z i n g potassium i n the very e a r l y stages of growth. I t i s not c l e a r why t h i s should be so. Again, t h i s i l l u s t r a t e s the inadequacy of the e f f i c i e n c y r a t i o as a measure of n u t r i e n t - u s e e f f i c i e n c y . For a l l the v a r i e t i e s potassium u t i l i z a t i o n e f f i c i e n c i e s remained f a i r l y constant over the f i r s t few weeks and then increased d r a m a t i c a l l y mainly as a r e s u l t of i n c r e a s i n g shoot weight (Table 47). C o r r e l a t i o n s between potassium use e f f i c i e n c y based on shoot weight were not c a l c u l a t e d . Instead, the consistency of performance of the d i f f e r e n t v a r i e t i e s as i l l u s t r a t e d i n Figures 124 Table 47. Potassium e f f i c i e n c y r a t i o s (g/mmol) and u t i l i z a t i o n e f f i c i e n c i e s ( g 2 /mmol) of the 6 v a r i e t i e s over a five-week p e r i o d . Potassium e f f i c i e n c y r a t i o s are shown on the top l i n e and potassium u t i l i z a t i o n e f f i c i e n c i e s on the bottom l i n e . Time a f t e r germination V a r i e t y 1 week 2 week 3 weeks 4 weeks 5 weeks NP 52 25.3 7.8 7.0 8.5 8.7 3.1 3.4 9.4 23.9 64. 1 Pb 8A 28.3 8.4 7.8 9.1 10.0 4.8 5.1 12.8 31.1 83.7 C 306 30.5 8.5 8.2 9.4 9. 1 4.5 3.5 10.9 29.4 55.5 Sonora 64 23.2 7.7 6.8 6.8 7.2 3.1 3.0 6.5 13.6 26.2 Tesia 79 18.1 7.7 6.5 6.8 6.5 2.4 2.9 7.1 16.6 18.6 Moti 25.7 8.2 7.0 7.1 6.8 3.0 2.5 5.8 10.8 15.6 LSD(1) 4.8 0.5 0.4 0.5 1 .7 LSD(2) 1 .5 0.5 2.2 5.8 37.2 LSD(1): LSD(0.05) for potassium e f f i c i e n c y r a t i o LSD(2): LSD(0.05) f o r potassium u t i l i z a t i o n e f f i c i e n c y 125 Table 48. C o r r e l a t i o n s between potassium e f f i c i e n c y r a t i o s obtained at d i f f e r e n t growth stages of s i x v a r i e t i e s . Product-moment c o r r e l a t i o n c o e f f i c i e n t s are given above the diagonal and Spearman's rank c o r r e l a t i o n c o e f f i c i e n t s are given below the d i a g o n a l . KER(1) KER(2) KER(3) KER(4) KER(5) KER( 1 ) 0.86* 0.92* 0.83* 0.78* KER(2) 0.99* 0 . 9 1 * 0.74* 0.64 KER(3) 0.99* 0.97 0.90* 0.82* KER(4) 0.81 0.83 0.89 0.94* KER(5) 0.77 0.73 0.84 0.73 * S i g n i f i c a n t at the 5% l e v e l KER(1): Potassium e f f i c i e n c y r a t i o at 1 week KER(2): Potassium e f f i c i e n c y r a t i o at 2 weeks KER(3): Potassium e f f i c i e n c y r a t i o at 3 weeks KER(4): Potassium e f f i c i e n c y r a t i o at 4 weeks KER(5): Potassium e f f i c i e n c y r a t i o at 5 weeks 126 Table 49. C o r r e l a t i o n s between potassium u t i l i z a t i o n e f f i c i e n c i e s obtained at d i f f e r e n t growth stages of s i x v a r i e t i e s . Product- moment c o r r e l a t i o n c o e f f i c i e n t s are shown above the diagonal and Spearman's rank c o r r e l a t i o n c o e f f i c i e n t s are shown below the di a g o n a l . KUE(1) KUE(2) KUE(3) KUE(4) KUE(5) KUE ( 1 ) 0.81* 0.87* 0.83* 0.79* KUE(2) 0.93 0.92* 0.84* 0.90* KUE(3) 0.79 0.94 0.98* 0.95* KUE(4) 0.79 0.94 1 .00* 0.92* KUE(5) 0.84 0.94 0.89 0.89 * S i g n i f i c a n t at the 5% l e v e l KUE(1): Potassium u t i l i z a t i o n e f f i c i e n c y at 1 week KUE(2): Potassium u t i l i z a t i o n e f f i c i e n c y at 2 weeks KUE(3): Potassium u t i l i z a t i o n e f f i c i e n c y at 3 weeks KUE(4): Potassium u t i l i z a t i o n e f f i c i e n c y at 4 weeks KUE(5): Potassium u t i l i z a t i o n e f f i c i e n c y at 5 weeks 127 5 and 6 was examined. These f i n d i n g s show that there were some changes i n ranking at 4 and 5 weeks for the v a r i e t i e s C 306 and Pb 8A (Figure 5), and Sonora 64 and Tesia 79 (Figure 6). For potassium e f f i c i e n c y r a t i o and u t i l i z a t i o n e f f i c i e n c y c o r r e l a t i o n c o e f f i c i e n t s were computed. A l l the c o r r e l a t i o n s for potassium u t i l i z a t i o n e f f i c i e n c y were p o s i t i v e and s i g n i f i c a n t (Table 49). For potassium e f f i c i e n c y r a t i o only the c o r r e l a t i o n between measures at 2 and 5 weeks f a i l e d to achieve s i g n i f i c a n c e (Table 48). The good c o r r e l a t i o n s between observations made at d i f f e r e n t times i n d i c a t e that s e l e c t i o n f o r these t r a i t s should be c o n s i s t e n t . 3.2. C o r r e l a t i o n between measures of potassium u t i l i z a t i o n at the v e g e t a t i v e and adult stages, and genotype x environment i n t e r a c t i o n To examine the extent of genotype x environment i n t e r a c t i o n with respect to potassium u t i l i z a t i o n the performance of 16 v a r i e t i e s was evaluated under two c o n t r a s t i n g c o n d i t i o n s . Root growth was a l s o examined i n t h i s study. U n l i k e the p l a n t s grown i n the growth room, those grown under n a t u r a l c o n d i t i o n s d i d not e x h i b i t any i n c i p i e n t potassium d e f i c i e n c y symptoms despite t h e i r lower potassium concentrations (Table 51). They were l a r g e r than those grown i n the growth room and, i n p a r t i c u l a r , had considerably greater root weights (Table 50). In keeping with t h e i r lower potassium c o n c e n t r a t i o n s , they had considerably higher potassium 128 e f f i c i e n c y r a t i o s (Table 52). D i f f e r e n c e s i n potassium e f f i c i e n c y r a t i o were a l s o more apparent under n a t u r a l c o n d i t i o n s . Potassium u t i l i z a t i o n e f f i c i e n c i e s under n a t u r a l c o n d i t i o n s g r e a t l y exceeded those observed under growth room c o n d i t i o n s (Table 52). For a l l the t r a i t s examined s i g n i f i c a n t environmental and genotype x environment e f f e c t s were observed (Tables 53 and 54). To b e t t e r i n v e s t i g a t e the genotype x environment i n t e r a c t i o n , c o r r e l a t i o n c o e f f i c i e n t s between performance i n the two environments were c a l c u l a t e d . Only the c o r r e l a t i o n c o e f f i c i e n t s f o r shoot weight proved to be s i g n i f i c a n t (Table 55). Therefore although a s i g n i f i c a n t genotype x environment i n t e r a c t i o n was observed f o r t h i s measure of e f f i c i e n c y , the ranking of the v a r i e t i e s i n the two environments was s t i l l f a i r l y c o n s i s t e n t . This f i n d i n g i s encouraging since i t i s very l i k e l y that shoot weight rather than the other i n d i c e s of u t i l i z a t i o n w i l l be used for s e l e c t i o n purposes. However, there s t i l l remains the very important question of the r e l a t i o n s h i p between measures of n u t r i e n t - u s e e f f i c i e n c y obtained at the vege t a t i v e stage and e f f i c i e n c y of n u t r i e n t use i n g r a i n production. Other s t u d i e s have a l s o shown that e f f i c i e n c y i n d i c e s are subject to environmental e f f e c t s (10, 68). However, i n these s t u d i e s only a few v a r i e t i e s were examined and there was no evidence of changes i n the ranking of v a r i e t i e s . Due to the importance of genotype x environment i n t e r a c t i o n s i n plant breeding (4, 36 ), the f i n d i n g s i n t h i s study thus pose an a d d i t i o n a l d i f f i c u l t y f o r the improvement of n u t r i e n t - u s e 129 Table 50. Shoot and root f r e s h weights of the 16 v a r i e t i e s when grown under p o t a s s i u m - l i m i t i n g c o n d i t i o n s i n the growth room and under n a t u r a l c o n d i t i o n s . Shoot weight (g/plant) Root weight (g/plant) V a r i e t y G. Room Nat. cdns. G. Room Nat. cdns. NP 52 1 .78 1 . .83 0. .73 1 , .96 Pb 8A 1 .71 2, .05 1 . .00 1 , .77 C 306 1 .90 2, .19 1 . .09 1 , .93 Pusa 4 1 .74 1 , .99 1 . .04 1 , .69 N a i n a r i 60 1 .67 2. .23 0, .85 1 , .72 Chapingo 53 1 .64 1 . .84 1 . .32 2 .92 P i t i c 62 1 .70 2. .23 1 , .07 1 .82 Penjamo 62 1 .36 1 , .78 1 , .02 1 .98 Sonora 64 1 .30 1 , .43 0. .77 1 .64 Jupateco 73 1 . 1 1 1 , .25 0, .75 1 .85 Pavon 76 1 .45 1 , .56 0, .96 1 .79 Tesia 79 1 .05 1 , .70 0, .62 1 .90 Yecora 70 1 .15 1 , .64 0, .78 1 .79 Arjun 1 .07 1 , .32 0, .78 1 .96 Moti 1 .43 1 , .23 0, .76 1 .14 UP 301 1 .09 1 , .39 0, ,90 1 .77 LSD (0.05) 0.24 0.27 0.22 0.51 Nat. cdns.: Na t u r a l c o n d i t i o n s G. room: Growth room 130 Table 51. Shoot and root potassium concentrations of the 16 v a r i e t i e s when grown i n the growth room and under n a t u r a l c o n d i t i o n s . V a r i e t y Shoot [K + ] (umol/g) Root [ K + ] (umol/g) G. room Nat. cdns. G. room Nat. cdns. NP 52 104 .9 84.6 38.7 20.7 Pb 8A 1 16 .8 79.1 43.7 24.5 C 306 109.2 85.5 41.7 26.2 Pusa 4 115.6 108.7 38.2 25. 1 N a i n a r i 60 129.4 91 .8 45.2 22.3 Chapingo 53 140.4 113.5 44. 1 22.5 P i t i c 62 104.4 76.5 33.5 22.7 Penjamo 62 151.0 110.5 53.7 30 . 8 Sonora 64 129.0 75. 1 40. 1 17.3 Jupateco 73 121.3 62.3 48.9 18.2 Pavon 76 1 10.4 58.3 44.3 15.3 Tesia 79 139.3 66.7 45.6 17.0 Yecora 70 129.0 62.6 40.5 15.3 Ar jun 125.0 58. 1 45.6 14.2 Moti 108. 1 51 . 9 47.2 14.0 UP 301 118 .8 53 . 8 40.4 13.7 LSD (0.05) 12.1 17.3 7.7 6.3 G. room: Growth room Nat. cdns.: Nat u r a l c o n d i t i o n s 131 Table 52. Potassium e f f i c i e n c y r a t i o s (KER) and u t i l i z a t i o n e f f i c i e n c i e s (KUE) of the 16 v a r i e t i e s when grown under p o t a s s i u m - l i m i t i n g c o n d i t i o n s i n the growth room and under n a t u r a l c o n d i t i o n s . KER (g/mmol) KUE (g^mmol) V a r i e t y G. room Nat cdns. G. room Nat. cdns. NP 52 9.5 12.2 16.9 22.3 Pb 8A 8.6 12.8 14.6 26.4 C 306 9.2 11.8 17.3 25.8 Pusa 4 8.7 9.3 15.1 18.5 N a i n a r i 60 7.7 10.9 12.9 24.3 Chapingo 53 7.1 8.9 1 1 .7 16.3 P i t i c 62 9.7 13.2 16.4 29.3 Penjamo 62 6.6 9.1 9.1 16.1 Sonora 64 7.8 13.8 10.1 19.7 Jupateco 73 8.3 16.3 9.2 20.2 Pavon 76 9.1 17.5 13.3 27.7 Tesia 7.2 15.1 7.6 25.7 Yecora 70 7.8 16.1 9.0 26.4 Ar jun 8.0 17.3 8.6 22.9 Moti 9.3 19.4 13.3 23.8 UP 301 8.5 18.7 9.2 26.3 LSD (0.05) 0.9 3.2 2.8 6.8 G. room: Growth room Nat. cdns.: Na t u r a l c o n d i t i o n s 132 Table 53. Analyses of v a r i a n c e , i n c l u d i n g expectations of mean squares, f o r root and shoot f r e s h weight per pla n t of the 16 v a r i e t i e s when grown i n the growth room and under under n a t u r a l c o n d i t i o n s . Source Mean squares DF Root weight Shoot weight Expectations Genotypes 15 0.333* Environments 1 21.612* G x E 15 0.120* Residual 64 0.055 0.542* 1.921* 0.071* 0.023 z z z CT-+ 3crge + 6<3~g 2 Z 2. cr + 3crge + 48cre 2 , 2 cr + 3<rge * S i g n i f i c a n t at the 5% l e v e l Table 54. Analyses of va r i a n c e , i n c l u d i n g expectations of mean squares, f o r potassium e f f i c i e n c y r a t i o (KER) and u t i l i z a t i o n e f f i c i e n c y (KUE) of the 16 v a r i e t i e s when grown i n the growth room and under n a t u r a l c o n d i t i o n s . Mean squares Source DF KER KUE Expectations Genotypes 15 21 . 845* 50 .537* 2 z 2 cr- + 3cr-ge + 6tyg Environments 1 750. 668* 2954 .820* 2 2. 2, c r + 3crge + 48o- e G x E 15 16. 115* 30 .726* c r + 3f5~ge Residual 64 2. 017 9 .705 * S i g n i f i c a n t at the 5% l e v e l 133 Table 55. C o r r e l a t i o n c o e f f i c i e n t s between root weights, shoot weights, potassium e f f i c i e n c y r a t i o s and u t i l i z a t i o n e f f i c i e n c i e s of the 16 v a r i e t i e s when grown i n the growth room and under n a t u r a l c o n d i t i o n s . Characters r Spearman's rho Root Wt.(GR):Root Wt.(NC) 0. 57 0. 18 Shoot Wt.(GR):Shoot Wt.(NC) 0. 78* 0. 62* KER(GR):KER(NC) 0. 31 0. 33 KUE(GR):KUE(NC) 0. 24 0. 19 * S i g n i f i c a n t at the 5% l e v e l GR: Growth room c o n d i t i o n s NC: Na t u r a l c o n d i t i o n s Table 56. Genotypic and phenotypic va r i a n c e s , and broad sense h e r i t a b i l i t i e s f or root and shoot weight per p l a n t , potassium e f f i c i e n c y r a t i o and u t i l i z a t i o n e f f i c i e n c y (KER and KUE r e s p e c t i v e l y ) . Variances Character Genotypic Phenotypic H e r i t a b i l i t y (%) Root Wt./plant 0.036 0.056 64.3 Shoot Wt./plant 0.079 0.090 87.8 KER 0.955 3.641 26.2 KUE 3.302 8.423 39.2 134 e f f i c i e n c y . However, the f u l l extent of t h i s problem cannot be app r e c i a t e d u n t i l the r e l a t i o n s h i p s between measures of n u t r i e n t - u s e e f f i c i e n c y at the vege t a t i v e stage and i n g r a i n production are examined. Despite the presence of s i g n i f i c a n t genotype x environment i n t e r a c t i o n s , the o v e r a l l analyses were used to obt a i n estimates of the phenotypic and genotypic variances as w e l l as h e r i t a b i l i t i e s on a l i n e mean basis (Table 56). H e r i t a b l i t i e s f o r potassium e f f i c i e n c y r a t i o and u t i l i z a t i o n e f f i c i e n c y were low whereas those for shoot and root weight per p l a n t were high. I t should be emphasized that these h e r i t a b i l i t i e s are based on r e p l i c a t e d p l o t s i n two environments. A l s o , two c r i t i c a l issues regarding these estimates should be noted. These are (1) that the experiments should i d e a l l y be conducted i n an adequate range of environments over a number of years, and (2) that the estimates of h e r i t a b i l i t y should be fr e e of any genotype x environment i n t e r a c t i o n s (36, 46). Dudley and M o l l (46) maintain that even i f the h e r i t a b i l i t y estimate i s to form the b a s i s of s e l e c t i o n i n one year and one environment, i t i s s t i l l necessary to use more than one year and one l o c a t i o n to estimate the components of v a r i a n c e . Presumably t h i s i s considered e s s e n t i a l since most t r a i t s e x h i b i t s i g n i f i c a n t genotype x environment i n t e r a c t i o n s . Therefore, f a i l u r e to take t h i s i n t o c o n s i d e r a t i o n would r e s u l t i n i n f l a t e d h e r i t a b i l i t y values which are not f r e e of the genotype x environment i n t e r a c t i o n component. Twelve v a r i e t i e s were grown to maturity under potassium-135 l i m i t i n g c o n d i t i o n s and t h e i r performance compared with measures of potassium u t i l i z a t i o n based on v e g e t a t i v e growth. The main o b j e c t i v e of t h i s study was to examine the r e l a t i o n s h i p between measures of potassium u t i l i z a t i o n at the vegetative stage and e f f i c i e n c y of potassium use i n g r a i n production. This issue i s of c r u c i a l importance i f s e l e c t i o n f o r n u t r i e n t - u s e e f f i c i e n c y i s to be undertaken at the v e g e t a t i v e stage. The twelve v a r i e t i e s grew s u c c e s s f u l l y to maturity and f a i l e d to e x h i b i t any potassium d e f i c i e n c y symptoms throughout t h e i r growth. U n l i k e i n other s t u d i e s i n which t a l l and dwarf v a r i e t i e s have been reported to produce s i m i l a r t o t a l biomass (84), s i g n i f i c a n t d i f f e r e n c e s were observed i n t h i s study (Table 57). Although the t a l l v a r i e t y C 306 had the highest biomass, some of the dwarf types had biomasses s i m i l a r to -or greater than those of the other t a l l v a r i e t i e s . S u r p r i s i n g l y the lowest biomass per p l a n t was observed i n the t a l l v a r i e t y Pb 8A, most probably due to i t s poor t i l l e r i n g . Harvest i n d i c e s g r e a t l y exceeded those reported i n other s t u d i e s (84). A l s o , the t a l l v a r i e t i e s d i d not c o n s i s t e n t l y e x h i b i t lower harvest i n d i c e s than the dwarf types. D i f f e r e n c e s i n potassium u t i l i z a t i o n f o r g r a i n production were greater than twofold (Table 57). The c o r r e l a t i o n c o e f f i c i e n t s between va r i o u s measures of potassium-use e f f i c i e n c y obtained at the v e g e t a t i v e stage and various measures of performance at the adult stage are shown i n Table 58. Only the negative rank c o r r e l a t i o n between shoot weight at three weeks and g r a i n weight per p l a n t proved to be s i g n i f i c a n t . Although the c o r r e l a t i o n s between shoot weight per 136 Table 57. Number of t i l l e r s per p l a n t , straw and g r a i n weight per p l a n t , t o t a l dry weight per p l a n t , harvest index (HI) and potassium u t i l i z a t i o n i n g r a i n production of the 12 v a r i e t i e s grown under n a t u r a l c o n d i t i o n s . Dry matter/plant (g) T i l l e r s / K u t i l i z a t i o n p l a n t Straw Grain T o t a l HI (%) (g grain/g K) NP 52 10. ,3 6. ,3 9. ,6 15. ,9 60. ,2 112. ,8 Pb 8A 8. ,7 7. ,4 4. , 1 1 1 . ,5 34. ,4 65. ,4 C 306 13. ,5 22. ,2 19. ,7 42. ,0 42. ,0 48. ,2 Pusa 4 9. ,0 8. .0 1 1 . ,8 19. ,7 59. ,3 59. , 1 N a i n a r i 60 1 1 . ,5 10. .6 16. ,7 27. .3 60. ,8 96. ,3 P i t i c 62 17. .5 16. .8 20. .3 37. . 1 54. .0 73. .0 Sonora 64 8. .2 4. .7 7. . 1 1 1 , .8 59. . 1 69. .2 Pavon 76 12. .0 9, . 1 17. .2 26, .3 64, .3 61 . 7 Tesia 79 13. .8 6, .2 13. .5 19, .6 68, .4 70. .3 Arjun 15. . 1 7, .7 20. .4 28, . 1 72, .3 83, .3 Moti 10, .3 4, .4 14, .7 15, .7 72, .2 73, .2 UP 301 13, .0 7, .3 16, .3 23, .6 68, .8 83, . 1 LSD (0.05) 4.3 4.7 9.0 12.6 6.6 28.5 137 Table 58. C o r r e l a t i o n c o e f f i c i e n t s between measures of potassium u t i l i z a t i o n based on veg e t a t i v e growth (under two c o n d i t i o n s ) and g r a i n production. E f f i c i e n c y measure p a i r s r Spearman's r Shoot weight(GR) :Total p l a n t weight 0. 24 0. 13 Shoot weight(NC) :Total p l a n t weight 0. 43 0. 35 Shoot weight(GR) :Grain weight/plant -0. 1 2 -0. 73* Shoot weight(NC) :Grain weight/plant 0. 03 -0. 80* KER (GR):GPKER -0. 05 -0. 08 KER (NC):GPKER 0. 02 0. 20 KUE (GR) .-GPKER -0. 09 -0. 30 KUE (NC):GPKER -0. 1 2 -0. 19 GPKER: Grain wei ght/plant -0. 07 0. 10 GR: Na t u r a l c o n d i t i o n s NC: Nat u r a l c o n d i t i o n s GPKER: Grain production potassium e f f i c i e n c y r a t i o 138 p l a n t and t o t a l weight per plant at maturity were p o s i t i v e , they were not s i g n i f i c a n t . The c o r r e l a t i o n s between potassium e f f i c i e n c y r a t i o for g r a i n production and both potassium e f f i c i e n c y r a t i o and u t i l i z a t i o n e f f i c i e n c y at three weeks were p a r t i c u l a r l y poor. These r e s u l t s i n d i c a t e that performance at the v e g e t a t i v e stage does not c o r r e l a t e w e l l with performance at the adult stage. Even when potassium-use e f f i c i e n c y at the vege t a t i v e stage was evaluated under c o n d i t i o n s s i m i l a r to those i n which the adult p l a n t s t u d i e s were conducted, the c o r r e l a t i o n s were s t i l l poor. Of p a r t i c u l a r concern i s the negative c o r r e l a t i o n between shoot weight and g r a i n weight per pl a n t since s e l e c t i o n i s most l i k e l y to be based on shoot weight per p l a n t . I t i s perhaps not too s u r p r i s i n g that t h i s c o r r e l a t i o n was found to be negative since although the t a l l v a r i e t i e s are g e n e r a l l y more vigorous i n the e a r l y stages of growth, they apportion l e s s of t h e i r dry matter to g r a i n . The relevance of these f i n d i n g s w i l l be discussed i n greater d e t a i l i n Chapter V. 139 V. GENERAL DISCUSSION I t i s now f a i r l y widely acknowledged that some attempt should be made to i n c l u d e p h y s i o l o g i c a l t r a i t s as s e l e c t i o n c r i t e r i a i n pla n t breeding programmmes (90, 116). Some researchers maintain that i f the u l t i m a t e o b j e c t i v e s of p l a n t improvement are b e t t e r understood i n terms of t h e i r u n d e r l y i n g p h y s i o l o g i c a l processes, then s e l e c t i o n on the b a s i s of these processes could be more e f f e c t i v e . S t i l l , there i s some debate as to whether s e l e c t i o n f o r p h y s i o l o g i c a l t r a i t s can r e a l l y make a s i g n i f i c a n t c o n t r i b u t i o n to p r a c t i c a l p l a n t breeding (51, 52, 109). With regard to mineral n u t r i t i o n there i s now i n c r e a s i n g i n t e r e s t i n the production of f e r t i l i z e r - e f f i c i e n t and low-input genotypes (11, 12, 16, 42, 44, 50, 63, 66, 73, 85, 90, 100, 102, 136). Researchers and a n a l y s t s maintain that d w i n d l i n g resources, i n c r e a s i n g f e r t i l i z e r c o s t s and concern over the negative e c o l o g i c a l e f f e c t of heavy f e r t i l i z e r a p p l i c a t i o n w i l l r e q u i r e that a more concerted e f f o r t be made to produce such genotypes. I f s u c c e s s f u l , t h i s endeavour could lead to the production of genotypes which are e i t h e r b e t t e r s u i t e d to n u t r i t i o n a l l y marginal c o n d i t i o n s or genotypes which r e q u i r e l e s s f e r t i l i z e r to produce y i e l d s which approach those obtained under high f e r t i l i t y c o n d i t i o n s . This approach could t h e r e f o r e lead to s u b s t a n t i a l savings i n f e r t i l i z e r costs and the expansion of crop production i n t o marginal areas. Opinions d i f f e r as to whether t h i s i s a f e a s i b l e or 140 worthwhile g o a l . The c o n s i d e r a b l e v a r i a b i l i t y observed for a number of t r a i t s governing e f f i c i e n t mineral n u t r i t i o n has l e d some researchers to express some optimism about the prospects f o r producing such genotypes (8, 20, 23, 41, 44, 50, 64, 66, 69, 72, 102, 134, 136). Vose (135, 136) b e l i e v e s that i t i s only the l a c k of sound genetic information that has impeded progress i n t h i s area. On the other hand, Arnon ( 5 ) , Borlaug (19) and F i s c h e r (57, 58) are somewhat p e s s i m i s t i c . Arnon ( 5 ) , without c i t i n g any examples, maintains that e f f o r t s undertaken to produce n u t r i e n t - e f f i c i e n t genotypes have l a r g e l y been u n s u c c e s s f u l . F i s c h e r (57, 58) contends that the y i e l d s obtained at n u t r i e n t l e v e l s under which s e l e c t i o n i s most l i k e l y to be e f f e c t i v e are too low to be considered economical. He t h e r e f o r e questions the v a l i d i t y of f i n d i n g s made under these c o n d i t i o n s . Borlaug (19) i n p a r t i c u l a r has attacked the advocates of t h i s approach, maintaining that increased food s u p p l i e s must' come from improved p r o d u c t i v i t y under high f e r t i l i t y c o n d i t i o n s . However, h i s comments seem rather misguided. Even the most ardent proponents f o r the production of n u t r i e n t - e f f i c i e n t genotypes do not b e l i e v e that high y i e l d s can be obtained from impoverished s o i l s simply by i n c r e a s i n g n u t r i e n t uptake and u t i l i z a t i o n . Rather, they maintain that improvement of these t r a i t s can lead to the production of genotypes which are e i t h e r b e t t e r s u i t e d to n u t r i t i o n a l l y marginal c o n d i t i o n s or which r e q u i r e l e s s f e r t i l i z e r to produce y i e l d s which approximate those obtained under high f e r t i l i t y c o n d i t i o n s . I t i s a l s o 141 argued that although n u t r i e n t - e f f i c i e n t genotypes w i l l probably give lower y i e l d s , the reduction i n f e r t i l i z e r c o s t s due to the c u l t i v a t i o n of such genotypes w i l l exceed the l o s s i n revenue r e s u l t i n g from lower y i e l d s . Graham (73) maintains that although breeding can lead to reduced requirements f o r some n u t r i e n t s and no need f o r the a p p l i c a t i o n of others, major emphasis should be placed on those n u t r i e n t s w i t h l a r g e s o i l reserves but poor a v a i l a b i l i t y . These would include i r o n , manganese, copper, z i n c and phosphate. Because few s o i l s can s u s t a i n high y i e l d s without the a p p l i c a t i o n of n i t r o g e n , he sees l i t t l e prospect f o r the improvement of the u s e - e f f i c i e n c y of t h i s n u t r i e n t . S t i l l , i t i s i n t e r e s t i n g to note that the improvement of nitrogen-use e f f i c i e n c y has been given s e r i o u s c o n s i d e r a t i o n i n some s t u d i e s (72, 95, 96, 102, 105). This study was undertaken to evaluate the extent of v a r i a t i o n f o r potassium and nit r o g e n uptake and u t i l i z a t i o n i n a number of wheat v a r i e t i e s and a l s o to address some issues of relevance to the improvement of these t r a i t s . These issues included the i n h e r i t a n c e of these t r a i t s and the d i f f i c u l t i e s that are l i k e l y to a r i s e due to (1) the methodology that i s used to measure ion f l u x e s and u t i l i z a t i o n , (2) ontogenetic v a r i a t i o n i n the expression of these t r a i t s , and (3) the growth stage at which n u t r i e n t u t i l i z a t i o n i s evaluated. Considerable v a r i a t i o n was observed f o r a l l the t r a i t s except potassium and nitrogen e f f i c i e n c y r a t i o . Due to the important negative feedback e f f e c t of root potassium 142 c o n c e n t r a t i o n on potassium i n f l u x , d i f f e r e n c e s i n short-term net potassium f l u x were examined i n r e l a t i o n to root potassium c o n c e n t r a t i o n . Although short-term f l u x e s were found to be n e g a t i v e l y c o r r e l a t e d with root potassium c o n c e n t r a t i o n (Table 7 ) , some of the d i f f e r e n c e s i n f l u x were not a s s o c i a t e d w i t h d i f f e r e n c e s i n root potassium c o n c e n t r a t i o n . These d i f f e r e n c e s i n f l u x must t h e r e f o r e be h e r i t a b l e . Because the r e g u l a t i o n of n i t r a t e i n f l u x i s much more complex (37, 39), d i f f e r e n c e s i n short-term net n i t r a t e f l u x were not examined i n r e l a t i o n to root n i t r a t e c o n c e n t r a t i o n . Therefore, some of the d i f f e r e n c e s i n n i t r a t e f l u x may be due to d i f f e r e n c e s i n root n i t r a t e c o n c e n t r a t i o n or some other f a c t o r ( s ) which regulates n i t r a t e i n f l u x . However, i t i s u n l i k e l y that the i n t e r n a l n u t r i e n t s t a t u s of the roots can account for the extent of v a r i a t i o n observed. I t i s th e r e f o r e safe to conclude that some of the v a r i a t i o n i n n i t r a t e f l u x i s a l s o h e r i t a b l e . To complement the s t u d i e s on v a r i a b i l i t y f o r these t r a i t s , , g e netic s t u d i e s were a l s o undertaken. Because e a r l y generation ( s i n g l e p l a n t ) s e l e c t i o n i s l i k e l y to be based on short-term net potassium uptake and shoot weight per p l a n t , the i m p l i c a t i o n s of the genetic s t u d i e s w i l l be discussed only with respect to these two t r a i t s . For short-term net potassium uptake both a d d i t i v e and dominance gene e f f e c t s were s i g n i f i c a n t (Tables 21 and 22) and narrow sense h e r i t a b i l i t i e s were rather low (Table 23). Therefore, i t would be more a d v i s a b l e to s e l e c t amongst f a m i l i e s rather than amongst s i n g l e p l a n t s f o r t h i s t r a i t . This approach 143 would a l s o enable i n f l u x k i n e t i c parameters to be used as s e l e c t i o n c r i t e r i a since the req u i r e d seed q u a n t i t i e s would then be a v a i l a b l e . Lindgren (91) a l s o obtained low narrow sense h e r i t a b i l i t i e s f o r phosphate uptake i n beans f u r t h e r i n d i c a t i n g that s e l e c t i o n f o r n u t r i e n t uptake should be made amongst f a m i l i e s . For shoot weight per pl a n t p r i m a r i l y a d d i t i v e e f f e c t s were important (Table 24). Unf o r t u n a t e l y estimates of narrow sense h e r i t a b i l i t y c o u l d not be obtained for two of the crosses and fo r the cross NP52 x N a i n a r i 60 the estimate i s questionable s i n c e i t exceeded the estimate of broad sense h e r i t a b i l i t y (Table 25). I t would probably be advi s a b l e to s e l e c t amongst f a m i l i e s rather than amongst s i n g l e p l a n t s f o r t h i s t r a i t s ince p l a n t weight i s subject to cons i d e r a b l e environmental v a r i a t i o n . As regards the other t r a i t s examined, namely e f f i c i e n c y r a t i o and u t i l i z a t i o n e f f i c i e n c y , s e l e c t i o n would have to be delayed u n t i l l a t e r generations when adequate seed q u a n t i t i e s are a v a i l a b l e . The s t u d i e s undertaken to examine v a r i a t i o n for potassium and n i t r o g e n uptake and u t i l i z a t i o n and the i n h e r i t a n c e of these t r a i t s thus i n d i c a t e that there are some prospects f o r the improvement of these t r a i t s . However, i t would be naive to evaluate the prospects f o r the improvement of nu t r i e n t - u s e e f f i c i e n c y by s u b t r a i t s e l e c t i o n simply on the b a s i s of the v a r i a b i l i t y observed and the f i n d i n g s of the genetic s t u d i e s . There are c l e a r l y a number of other issues which r e q u i r e c a r e f u l c o n s i d e r a t i o n as w e l l . These include the v a l i d i t y of the t r a i t s 144 s e l e c t e d f o r and the problems a s s o c i a t e d with p l a n t c u l t u r e and s e l e c t i o n . Plant c u l t u r e f o r the e v a l u a t i o n of the d e s i r e d p h y s i o l o g i c a l t r a i t s w i l l undoubtedly prove d i f f i c u l t i n a lar g e breeding programme. Two methods could be used. As has been done i n other s t u d i e s (25, 55, 64, 66, 68, 94) the p l a n t s could be grown s e p a r a t e l y and the l i m i t i n g n u t r i e n t provided only at the beginning of the growth p e r i o d . This i s the e a s i e r method but i t could prove very d i f f i c u l t i f p l a n t s of d i f f e r i n g m aturity are to be grown to the a d u l t stage. To date t h i s method has proved s u c c e s s f u l only f o r the e v a l u a t i o n of n u t r i e n t - use e f f i c i e n c y at the v e g e t a t i v e stage. A l t e r n a t i v e l y a system of maintained n u t r i e n t l i m i t a t i o n could be used as was done i n t h i s study. This method has the advantage that i t can be used to grow p l a n t s of d i f f e r i n g m a turity to the a d u l t stage. However, i f n u t r i e n t l e v e l s are to be maintained as was done i n t h i s study, i t i s h i g h l y u n l i k e l y t h i s method could be employed i n a breeding programme. Routine screening of l a r g e p o p u l a t i o n s would r e q u i r e that the system be automated such that n u t r i e n t l e v e l s are monitored and maintained by a computerized system. The important c o n s i d e r a t i o n would be whether the b e n e f i t s l i k e l y to accrue can j u s t i f y the cost of s e t t i n g up such a system. S e l e c t i o n f o r d i f f e r e n c e s i n the expression of p h y s i o l o g i c a l t r a i t s has proved to be a major o b s t a c l e to the e x p l o i t a t i o n of v a r i a b i l i t y f o r these t r a i t s . In general, techniques used to demonstrate p h y s i o l o g i c a l v a r i a b i l i t y i n s m a l l - s c a l e s t u d i e s are too tedious and time-consuming to be 145 used i n a breeding programme. To be u s e f u l , the s e l e c t i o n technique should be r e l i a b l e and a l s o allow f o r r a p i d screening of l a r g e p o p u l a t i o n s . For t r a i t s such as those examined i n t h i s study, a d d i t i o n a l d i f f i c u l t i e s could a r i s e due to ontogenetic v a r i a t i o n i n t h e i r e x p r e s s i o n . For n u t r i e n t uptake, the major issue i s whether to s e l e c t fo r short-term net f l u x or average net f l u x . Average net f l u x i s probably the p r e f e r r e d measure since i t represents uptake during growth. The r e s u l t s obtained i n t h i s study show that short-term net f l u x e s obtained by d e p l e t i o n of a s o l u t i o n much more concentrated than the growth s o l u t i o n are poorly c o r r e l a t e d with average net f l u x e s (Table 45). Hence, although v a r i e t a l ranking on the b a s i s of short-term net f l u x was f a i r l y c o n s i s t e n t (Table 42), i t i s questionable i f short-term, f l u x e s should be used f o r s e l e c t i o n purposes. I t would seem more ad v i s a b l e to base s e l e c t i o n on f l u x determinations made at an e x t e r n a l c o n c e n t r a t i o n i d e n t i c a l to that of the growth s o l u t i o n . For p r e l i m i n a r y screening of very l a r g e populations with respect to potassium uptake, the dye-reduction technique of Glass et a l . (71) c o u l d be used. I f s e l e c t i o n f o r u t i l i z a t i o n i s to be undertaken at the v e g e t a t i v e stage, i t should be based on shoot f r e s h weight since t h i s would enable the s e l e c t e d p l a n t s to be grown to m a t u r i t y . S e l e c t i o n f o r e f f i c i e n c y r a t i o and u t i l i z a t i o n e f f i c i e n c y could only be achieved i f s e l e c t i o n i s delayed u n t i l l a t e r generations. However, for p e r e n n i a l s p e c i e s , i n d i v i d u a l p l a n t s e l e c t i o n f o r e f f i c i e n c y r a t i o and u t i l i z a t i o n e f f i c i e n c y i s 146 p o s s i b l e . Chichester (30) has attempted to improve phosphate and n i t r o g e n u t i l i z a t i o n i n grass by s e l e c t i n g f o r both e f f i c i e n c y r a t i o and shoot weight. Further s t u d i e s await e v a l u a t i o n of the e f f e c t i v e n e s s of t h i s approach. Whether shoot weight at the v e g e t a t i v e stage can be adopted as a s e l e c t i o n c r i t e r i o n depends on i t s c o r r e l a t i o n with performance at the a d u l t stage and the c o n s i s t e n c y of v a r i e t a l ranking during growth. Both these issues were i n v e s t i g a t e d . Ranking of v a r i e t i e s was found to be c o n s i s t e n t over the f i r s t three weeks. Over the 4-5 week p e r i o d a few changes i n v a r i e t a l ranking were evident (Figures 5 and 6). Therefore i t i s u n l i k e l y that changes i n the ranking of v a r i e t i e s w i l l pose a problem f o r s e l e c t i o n . More i m p o r t a n t l y , shoot weight at three weeks was n e g a t i v e l y c o r r e l a t e d w i t h g r a i n weight per plant (Table 58). This f i n d i n g c a s t s some doubt on the s u i t a b i l i t y of t h i s t r a i t as a measure of n u t r i e n t - u s e e f f i c i e n c y f o r a crop i n which g r a i n i s the economic product. However, i t must be acknowledged that because the genotypes i n v e s t i g a t e d d i f f e r e d c o n s i d e r a b l y , t h i s probably served to obscure the r e l a t i o n s h i p between the t r a i t s examined. In p a r t i c u l a r , d i f f e r e n c e s i n harvest index most l i k e l y accounted f o r the negative c o r r e l a t i o n between shoot f r e s h weight and g r a i n y i e l d per p l a n t . I f the genotypes being compared are more s i m i l a r w i t h respect to harvest index, shoot f r e s h weight could be adopted as a u s e f u l index of n u t r i e n t - u s e e f f i c i e n c y . For the breeder i n t e r e s t e d i n improving n u t r i e n t - u s e e f f i c i e n c y there are e s s e n t i a l l y two o p t i o n s . A more h o l i s t i c 147 approach would e n t a i l growing the m a t e r i a l under n u t r i e n t -l i m i t i n g c o n d i t i o n s and then s e l e c t i n g those l i n e s or p l a n t s which perform best. P r e f e r a b l y s e l e c t i o n should be based on the a c t u a l economic product. A l t e r n a t i v e l y a r e d u c t i o n i s t or a n a l y t i c a l approach could be adopted whereby an attempt i s made to improve p h y s i o l o g i c a l t r a i t s which are considered important to improved n u t r i e n t - u s e e f f i c i e n c y . These would include l a r g e r r o o t s , greater uptake and improved u t i l i z a t i o n . The h o l i s t i c approach has proved most s u c c e s s f u l to date. Improvement i n the u s e - e f f i c i e n c y of i r o n has been achieved by s e l e c t i n g for the absence of d e f i c i e n c y symptoms under f i e l d or c o n t r o l l e d c o n d i t i o n s (56). Improved manganese and copper-use e f f i c i e n c y has been accomplished by s e l e c t i n g for a c t u a l y i e l d under f i e l d c o n d i t i o n s (73). The major d i f f i c u l t y encountered i n t h i s approach i s s i t e v a r i a b i l i t y and i n c o n s i s t e n c y of r e s u l t s from one year to another (56). For some n u t r i e n t s such as i r o n t h i s problem has been obviated by developing s o l u t i o n c u l t u r e techniques which can be used i n the greenhouse or growth room (56). Because i t has proved d i f f i c u l t to simulate manganese d e f i c i e n c y c o n d i t i o n s i n the greenhouse, s e l e c t i o n for e f f i c i e n t use of t h i s element has had to be r e s t r i c t e d to f i e l d s t u d i e s (73). I f s e l e c t i o n i s to be c a r r i e d out under f i e l d c o n d i t i o n s , one or s e v e r a l n u t r i e n t l e v e l s could be employed. Should one l e v e l be used, i t would be e s s e n t i a l that i t allow for adequate d i f f e r e n t i a t i o n between genotypes. Graham (73) maintains that s e l e c t i o n at one l e v e l may be counterproductive i f s e l e c t i o n 148 pressure i s too low or too high. Therefore he recommends that the p a i r e d p l o t technique be used and that s e l e c t i o n be based on r e l a t i v e y i e l d . The r e d u c t i o n i s t or a n a l y t i c a l approach i s more con t e n t i o u s . In general i t i s debatable whether s e l e c t i o n for s u b t r a i t s can r e a l l y make a s i g n i f i c a n t c o n t r i b u t i o n to p r a c t i c a l p l a n t breeding. To date l i t t l e success has been achieved by s e l e c t i n g f o r s u b t r a i t s . Two issues are of c r u c i a l importance to s u b t r a i t s e l e c t i o n . These are the a b i l i t y to s e l e c t e f f e c t i v e l y f o r the t r a i t and the c o r r e l a t i o n between the t r a i t and the u l t i m a t e o b j e c t i v e . C l e a r l y , s e l e c t i o n f o r n u t r i e n t uptake and u t i l i z a t i o n w i l l be d i f f i c u l t . A l s o , evidence obtained i n t h i s and other s t u d i e s (61) i n d i c a t e s that s e l e c t i o n f o r v e g e t a t i v e growth under c o n t r o l l e d c o n d i t i o n s may not r e s u l t i n improved g r a i n production under n u t r i e n t - l i m i t i n g c o n d i t i o n s . Therefore i t would be a d v i s a b l e to evaluate genotypes f o r improved n u t r i e n t -use e f f i c i e n c y on the b a s i s of the a c t u a l economic product. Although i t may be p o s s i b l e to produce n u t r i e n t - e f f i c i e n t genotypes simply by breeding f o r improved uptake, i n p r a c t i c e i t w i l l probably r e q u i r e that a number of t r a i t s be s e l e c t e d f o r . M o l l et a l . (102) maintain that i t may be p o s s i b l e to combine high uptake wi t h b e t t e r u t i l i z a t i o n by s e l e c t i n g f o r both t r a i t s at the same time. P e t t e r s s o n and Jensen (111) contend that i f nu t r i e n t - u s e e f f i c i e n c y i s to be improved, i t i s necessary that breeders s e l e c t for a number of t r a i t s such as root morphology and growth, ion uptake, ion t r a n s l o c a t i o n and u t i l i z a t i o n . I t 149 i s h i g h l y u n l i k e l y that breeders can be convinced to s e l e c t f o r so many t r a i t s . Therefore, f o r the foreseeable fu t u r e breeders are more l i k e l y to adopt an e m p i r i c a l rather than a n a l y t i c a l approach i n t h e i r attempts to produce n u t r i e n t - e f f i c i e n t genotypes. 150 VI. CONCLUSIONS The f o l l o w i n g conclusions can be made from t h i s study. 1. There i s considerable v a r i a t i o n f o r potassium and nitrogen uptake and u t i l i z a t i o n i n wheat which could be e x p l o i t e d i n a p l a n t breeding programme designed to improve f e r t i l i z e r - u s e e f f i c i e n c y . 2. Wheat v a r i e t i e s developed during d i f f e r e n t periods i n the h i s t o r y of wheat breeding d i f f e r s i g n i f i c a n t l y with respect to potassium and nitrogen uptake and u t i l i z a t i o n . However, the f i n d i n g s d i d not provide c o n c l u s i v e evidence to support the contention that s e l e c t i o n under high f e r t i l i t y c o n d i t i o n s has l e d to a reduction i n the a b i l i t y to acquire and u t i l i z e these n u t r i e n t s . 3. . Ontogenetic changes i n t r a i t expression are l i k e l y to a f f e c t s e l e c t i o n f o r average net potassium f l u x but not short-term net potassium f l u x and potassium u t i l i z a t i o n . 4. Due to the poor c o r r e l a t i o n between short-term and average net potassium f l u x e s , s e l e c t i o n f o r improved uptake should be based on f l u x e s obtained from s o l u t i o n s i d e n t i c a l i n c o n c e n t r a t i o n to the growth s o l u t i o n rather than on p e r t u r b a t i o n f l u x e s . 5. Because veget a t i v e measures of potassium u t i l i z a t i o n were found to be poorly c o r r e l a t e d with g r a i n production and potassium u s e - e f f i c i e n c y i n terms of g r a i n production, s e l e c t i o n for improved potassium u t i l i z a t i o n should be based on g r a i n production rather than the production of v e g e t a t i v e growth. 151 6. I f s e l e c t i o n for short-term net potassium f l u x and shoot weight per p l a n t i s to be undertaken, i t should be c a r r i e d out amongst f a m i l i e s rather than amongst s i n g l e p l a n t s . 152 GLOSSARY Short-term net f l u x : rate of n u t r i e n t uptake over a short time p e r i o d (30 or 60 minutes) measured by d e p l e t i o n of a s o l u t i o n c o n s i s t i n g of 200 uM potassium n i t r a t e plus 0.5 mM calcium sulphate. Average net f l u x : average rate of n u t r i e n t uptake over an extended p e r i o d of time during growth i n a s o l u t i o n of low n u t r i e n t c o n c e n t r a t i o n . E f f i c i e n c y r a t i o : amount of dry matter or g r a i n produced per u n i t of n u t r i e n t taken up by the p l a n t . U t i l i z a t i o n e f f i c i e n c y : amount of biomass produced per u n i t of t i s s u e n u t r i e n t c o n c e n t r a t i o n . 153 LITERATURE CITED 1. Abel , G. H. 1969. Inheritance of the c a p a c i t y f o r c h l o r i d e i n c l u s i o n and c h l o r i d e e x c l u s i o n by soybeans. Crop S c i . 9: 697-698. 2. A b r o l , Y. P., T. V. R. N a i r , V. Rajgopal, and S. K. Sinha. 1979. In v i t r o n i t r a t e reductase a c t i v i t y i n the l e a f blades of t a l l and dwarf wheat c u l t i v a r s . Plant P h y s i o l . Suppl. 63:48. 3. A b r o l , Y. P., P. A. Kumar, and T. V. R. N a i r . 1984. 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Excised r o o t s , p. 193-199, In: H a l l (eds.), Ion Transport i n North-Holland P u b l i s h i n g Co., 144. Zeven, A. C. and N. Ch. Zeven-Hissink. 1976. Genealogies of 14000 wheat v a r i e t i e s . I n t e r n a t i o n a l Maize and Wheat Improvement Centre (CIMMYT), E l Batan, Mexico. 166 Appendix 1. V a r i e t y Ar jun C 306 Chapingo 53 Jupateco 73 K-1 3 Kalvansona Pedigrees and height c a t e g o r i e s of v a r i e t i e s . Category TD, India T a l l , I n d i a Pedigree* LR 64/Sonora/LR 64A//Yaqui 5/N10B/ Lerma 52//2xLR Regent 1 974/3xCzechoslovakia//2xC591 3/819/C 281 T a l l , I n d i a SD, Mexico Lerma Rojo 64 SD, Mexico Moti NP 52 NP 718 N a i n a r i 60 Pb 8A Pb 9D Pusa 4 Pavon 76 Penjamo 62 P i t i c 62 Sonora 64 S i e t e Cerros Tesia 79 UP 301 Yaqui 50 Yaqui 54 Yecora 70 T a l l , Mexico Bonza S i b (Yaqui50/Kentana 48) DD, Mexico II-12300//LR 64/8156/3/Norteno 67 S e l e c t i o n , LV from United Provinces FKN/3/N10B/3/Gabo 55 Yaqui 50//N10B/3/Lerma 52/4/2xLR P611V-213/Yaktana 54//N10B//NP 852 Pedigree unknown NP 52/NP 165 TD, India T a l l , I n d i a T a l l , I n d i a T a l l , Mexico Supremo/Mentana//Gabo/3/Thatcher/ Queret/Kenya/Mentana/5/Gabo T a l l , I n d i a T a l l , I n d i a T a l l , I n d i a DD, Mexico S e l e c t i o n , LV from U t t a r Pradesh S e l e c t i o n , LV from U t t a r Pradesh Pedigree unknown Vicam 7l//Ciano 67 S i b / S i e t e C erros/ 3/Kalyansona/Bluebird FKN/3/N10B Yaktana 54//N1OB/26-1C Yaktana 54//N10B/2xLR 54 Penjamo 62 Sib/Gabo 55 Pedigree unknown Pedigree unknown T a l l , Mexico Newthatch/Marroqui 588//Yaqui 48 T a l l , Mexico Yaqui 48/Timstein//Kenya C9906 SD, Mexico SD, Mexico SD, Mexico SD, Mexico DD, Mexico TD, India DD, Mexico Ciano Sib/3/Sonora 64/Klein Rendidor 3/II 8156 167 Appendix 1 (continued) TI: T a l l Indian v a r i e t i e s TM: T a l l Mexicn v a r i e t i e s SD: Semidwarfs DD: Double dwarfs TD: T r i p l e dwarfs * Obtained from Zeven and Zeven-Hissink (144) 168 Appendix 2. Woolf-Augustinsson-Hofstee p l o t s f o r potassium i n f l u x k i n e t i c s i n the v a r i e t i e s NP 52 (•), C 306 (•), Moti ( A ) and Jupateco 73 (©). 12 1 10 1 CD 8 o E a. 6 INFLUX < 4 • \ 2 • • • 100 200 300 400 500 INFLUX/CK+]0 8 1 JZ 1 O) 6 —» o 1 4 O • >v INFLUX < 2 o * °( 3 200 400 600 INFLUX/CK+]0 800 169 Appendix 3. Woolf-Augustinsson-Hofstee p l o t s f o r potassium i n f l u x k i n e t i c s i n the v a r i e t i e s Pb 8A (•), Lerma Rojo 64 ( A ) , Arjun (O) and Tesia 79 (•). 170 Appendix 4. Woolf-Augustinsson-Hofstee p l o t s f o r n i t r a t e i n f l u x k i n e t i c s i n the v a r i e t i e s NP 52 (•), C 306 (A), Sonora 64 ( A ) and Pb 8A (•). 8r 200 12 -10 1 JZ 'cn 8 • "o X • \ \A i m § 2 n 1 • 0 50 100 150 FLUX/[N03-]o 200 250 171 Appendix 5. Woolf-Augustinsson-Hofstee p l o t s f o r n i t r a t e i n f l u x k i n e t i c s i n the v a r i e t i e s Jupateco 73 (•), Arjun ( A ) , Moti (•) and Yecora 70 ( A ) . 

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