{"http:\/\/dx.doi.org\/10.14288\/1.0093715":{"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool":[{"value":"Land and Food Systems, Faculty of","type":"literal","lang":"en"}],"http:\/\/www.europeana.eu\/schemas\/edm\/dataProvider":[{"value":"DSpace","type":"literal","lang":"en"}],"https:\/\/open.library.ubc.ca\/terms#degreeCampus":[{"value":"UBCV","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/creator":[{"value":"Li, Shin-Chai","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/issued":[{"value":"2010-02-08T22:36:08Z","type":"literal","lang":"en"},{"value":"1975","type":"literal","lang":"en"}],"http:\/\/vivoweb.org\/ontology\/core#relatedDegree":[{"value":"Doctor of Philosophy - PhD","type":"literal","lang":"en"}],"https:\/\/open.library.ubc.ca\/terms#degreeGrantor":[{"value":"University of British Columbia","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/description":[{"value":"It is desirable to develop tomato (Lycopersicon esculentum Mill.) cultivars which have the characteristics of earliness to fit the relatively short and cool growing season in Canada. Earliness was studied by parti-tioning the life cycle of the tomato plant into 7 component growth stages and using these as a basis for attempts to recombine quantitative genes which control the earliness of different stages from different parents to obtain progeny earlier than both parents.\r\nThe mode of inheritance of the earliness in the 7 growth component stages was studied with 3 approaches. First, a complete diallel cross experiments used 3 parental cultivars: Bonny Best, Immur Prior Beta and Cold Set. The progenies were grown under 2 temperature regimes (17.0-21.0\u00b0C and 10.0-13.0\u00b0C). The data for days required for each stage were analyzed first by the Hayman and Jinks method which estimated the following 4 genetic parameters; variation due to differences in additive and dominant gene action; asymmetry of positive and negative effects of genes; relative frequencies of dominant and recessive alleles; and 5 genetic estimators: average degree of dominance; proportion of dominant and recessive alleles; ratio of the total numbers of dominant to recessive genes in the parents; number of effective factors which exhibit some degree of dominance and the heritability.\r\nThe calculated genetic parameters and estimators differed in the 2 temperature regimes indicating there could be differences in gene action such as overdominant instead of partial dominant gene action depending on the temperature conditions. There were differences in heritabilities for the component stages, and some of the longer stages had potentially useful high heritabilities.\r\nThe data were also analyzed by the Griffing method which estimated the general combining ability and specific combining ability. The analyses showed that both the additive and dominant gene action had significant effects in most of the component stages, and in most cases, the additive variance was larger than the dominant variance.\r\nThe second approach employed reciprocal cross experiments with 2 parental cultivars, Bonny Best and Immur Prior Beta, and their reciprocal hybrids under the 2 temperature regimes in greenhouses and growth chambers. The nuclear and\/or cytoplasmic effect on the 7 growth component stages, net photosynthesis rate and leaf area were studied. There was some evidence that cytoplasmic effects were relatively important for some of these characteristics, and these effects were more noticeable in the cool regime.\r\nIn the third approach, field selection experiments on the earliness of 2 major stages were commenced in the F\u2083 of Bonny Best and Immur Prior Beta reciprocal cross populations. The mean values for both stages in the F\u2085 reciprocal populations were earlier than the 2 original parents indicating recombination of genes for earliness from parental cultivars. These results indicate that the methods which were used in these studies are a feasible way to increase the quantitative characteristic of earliness in the tomato.","type":"literal","lang":"en"}],"http:\/\/www.europeana.eu\/schemas\/edm\/aggregatedCHO":[{"value":"https:\/\/circle.library.ubc.ca\/rest\/handle\/2429\/19840?expand=metadata","type":"literal","lang":"en"}],"http:\/\/www.w3.org\/2009\/08\/skos-reference\/skos.html#note":[{"value":"GENETIC STUDIES OF EARLINESS AND GROWTH STAGES OF LYCOPERSICON ESCULENTUM MILL. BY SHIN-CHAI LI B.Sc., University of Taiwan, 1965 M.Sc., University of British Columbia, 1969 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOGT'OR OF PHILOSOPHY in the Department of Plant Science We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA MARCH 1975 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 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 Vancouver 8, Canada i i ABSTRACT I t i s desirable to develop tomato C Lycopersicon esculeritum M i l l . ) c u l t i v a r s which have the char a c t e r i s t i c s of earliness t o f i t the r e l a t i v e l y short and cool growing season i n Canada. Earliness was studied by p a r t i -t ioning the l i f e cycle of the tomato plant into 7 component growth stages and using these as a basis f o r attempts to recombine quantitative genes which control the earliness of d i f f e r e n t stages from d i f f e r e n t parents to obtain progeny e a r l i e r than both parents. The mode of inheritance of the earliness i n the 7 growth component stages was studied with 3 approaches. 'First, a complete d i a l l e l cross experiments'' used 3 parental c u l t i v a r s : Bonny Best, Immur P r i o r Beta and Cold Set. The progenies were grown under 2 temperature regimes (17.0-21.0\u00b0C and 10.0-13.0\u00b0C). The data f o r days required f o r each stage were analyzed f i r s t by the Hayman and Jinks method which estimated the following 4 genetic parameters; v a r i a t i o n due to differences i n additive and donrinant gene action; asymmetry of pos i t i v e and negative effects of genes; r e l a t i v e frequencies of dominant and recessive a l l e l e s ; and 5 genetic estimators: average degree of donrinance; proportion of dominant and recessive a l l e l e s ; r a t i o of the t o t a l numbers of dominant to recessive genes i n the parents; number of ef f e c t i v e factors which exhi b i t some degree of dativinance and the h e r i t a b i l i t y . The calculated genetic parameters and estimators d i f f e r e d i n the 2 tenperature regimes in d i c a t i n g there could be differences i n gene action such as overdominant instead of p a r t i a l dominant gene action depending on i i i the temperature conditions. There were differences i n h e r i t a b i l i t i e s f o r the component stages, and some of the longer stages had p o t e n t i a l l y useful high h e r i t a b i l i t i e s . The data were also analyzed by the G r i f f i n g method which estimated the general combining a b i l i t y and s p e c i f i c combining a b i l i t y . The analyses showed that both the additive and dominant gene action had s i g n i f i c a n t effects i n most of the component stages, and i n most cases, the additive variance was larger than the dominant variance. The second approach employed re c i p r o c a l cross experiments with 2 parental c u l t i v a r s , Bonny Best and Immur P r i o r Beta, and t h e i r r e c i p r o c a l hybrids under the 2 temperature regimes i n greenhouses and growth chambers. The nuclear and\/or cytoplasmic effect on the 7 growth component stages, net photosynthesis rate and leaf area were studied. There was some evidence that cytoplasmic effects were r e l a t i v e l y important f o r some of these c h a r a c t e r i s t i c s , and these effects were more noticeable i n the cool regime. In the t h i r d approach, f i e l d selection experiments on the ,earliness of 2 major stages were commenced i n the F^ of Bonny Best and Immur P r i o r Beta re c i p r o c a l cross populations. The mean values f o r both stages i n the F^ r e c i -procal populations were e a r l i e r than the 2 o r i g i n a l parents indicating recombination of genes f o r earliness from parental c u l t i v a r s . These r e s u l t s indicate that the methods which were used i n these studies are a fea s i b l e way to increase the quantitative c h a r a c t e r i s t i c of earliness i n the tomato. i v TABLE OF CONTENTS page-INTRODUCTION ' \u2022 1 LITERATURE REVIEW ...... .... \u2022 \u2022 . 3 A. D i a l l e l Crosses \u2022 3 B. 'Reciprocal Crosses ... 5 C. Selection In Plant Breeding . \u2022 7 D. Growth Component Stages And Temperature Effects \u2022. 10 E. Genetic Analysis Of Growth And Earliness Of Tomato 26 MATERIALS AND METHODS ................... \u2022 \u2022 ... 29 MATERIALS \u2022 . ' ' \u2022 \u2022 29 METHODS . ............ 31 A. Greenhouse Experiments 31 '.B.- Growth Chamber Experiments 33 C. F i e l d Experiments 31+ STATISTICAL METHODS \u2022 37 A. Analyses Of Data From The D i a l l e l Crosses 37 B. Analyses Of Data From The Reciprocal Crosses \u2022 42 C. Analyses Of. Data From The F i e l d Experiments '. 44 EXPERIMENTAL RESULTS .... 45 D i a l l e l Cross Experiments 45 Reciprocal Cross Experiments 88 F i e l d Experiments 99 DISCUSSION .- ........ '. -106 D i a l l e l Cross Experiments 106 Reciprocal Cross Experiments 117 F i e l d Experiments .; ..120 SUMMARY ' ' 124 LITERATURE CITED \u2022 .\u2022 127 APPENDIX. . .... ' 144 V LIST OF TABLES Table P a\u00a7 e 38 1. The second degree stat i s t i c s for a d i a l l e l set (Mather and Jinks, 1971). .2. Analysis of variance for combining a b i l i t y giving expectation of mean squares for the assumption of a fixed model. M-1 3. Mean number of days required for each of the 7 stages i n the d i a l l e l cross tested i n warm and cool temperature.regimes i n greenhouse experiment I. 46 4. Calculated mean values of V and W for the 7 stages i n the d i a l l e l cross tested i n warm and cool regimes i n greenhouse experiment I. 47 5. Uniformity test of. W -V values by analyses of variance for 48 a l l the characters investigated i n the d i a l l e l cross experiments. 6. Correlation coefficient between parental values (y ) and W +V for a l l characters investigated i n the d i a l l e l cross experiment s. 52 7. Mean number of days required for stages 5 and 6 i n the d i a l l e l cross tested i n warm and cool regimes in greenhouse experiment I I . 60 60 8. Calculated mean values of V and W for stages 5 and 6 i n the d i a l l e l cross tested i n warm and cool regimes in greenhouse experiment I I . 9. Mean number of days required per.plastochron i n the d i a l l e l cross tested i n warm and cool regimes i n greenhouse experiment I I . 63 10. Calculated mean values of V and W for the days required per plastochron i n the d i a l l e l cross tested i n warm and cool regimes in greenhouse experiment I I . 63 11. Mean f r u i t weight (g) and f r u i t diameter (mm) i n the d i a l l e l cross tested i n warm and cool regimes i n greenhouse experiment I I . 65 12. Calculated mean values of V and W for the f r u i t weight and r r f r u i t diameter m the d i a l l e l cross tested m warm and cool regimes i n greenhouse experiment I I . 65 v i 69 69 73 73 13. Means and standard deviations f o r the d i a l l e l cross parameters derived from the data on days required f o r 7 growth stages i n the warm regime of the greenhouse experiment I . 14. The d i a l l e l cross estimators f o r the data of the warm regime of the greenhouse experiment I . 15. Means and standard deviations f o r the d i a l l e l cross parameters derived from the data on days required f o r 7 growth stages i n the cool regime of the .greenhouse experiment I . 16. The d i a l l e l cross estimators from the data of the cool regime of the greenhouse experiment I . 17. Means and standard deviations f o r the d i a l l e l cross parameters and estimators from warm and cool regimes i n greenhouse expe-riment I I . 77 18. Means and standard deviations f o r the d i a l l e l cross parameters and estimators from warm and cool.regimes\u2022for days required per plastochron. 19. Means and standard deviations f o r the d i a l l e l cross parameters and estimators f o r warm and cool regimes f o r f r u i t weight and f r u i t diameter. 20. Mean squares f o r general (G.C.A.) and s p e c i f i c (S.C.A.) combin-ing a b i l i t y f o r the growth component stages i n warm and cool regimes. 21. Mean squares f o r general (G.C.A.) and s p e c i f i c (S.C.A.) combin-ing a b i l i t y f o r the stages 5 and 6 a f t e r hand-pollination treatment i n warm and cool regimes-. 22. Mean squares f o r general (G.C.A.) and s p e c i f i c (S.C.A.) confin-ing a b i l i t y effects f o r days required per plastochron i n warm and cool regimes. 23. Mean squares f o r general (G.C.A.) and s p e c i f i c (S.C.A.) combin-ing a b i l i t y effects f o r f r u i t weight and diameter i n warm and cool regimes. 24. Net photosynthesis rate and leaf area i n growth chamber expe-riment I i n warm regime. 25. Net photosynthesis rate and l e a f area i n growth chamber expe-riment I i n cool regime. 79 79 82 82 84 84 86 87 v i i 26. The non-orthognal comparisons f o r the seven growth component stages i n the recipr o c a l cross experiment I under warm and cool regimes. 89 27. The non-orthognal comparisons f o r the net photosynthesis rate i n the recipr o c a l cross experiment I I under warm and cool regimes. 91 28. The non-orthognal comparisons f o r the l e a f area i n the r e c i -procal cross experiment I I under warm and cool regimes. 96 29. Mean days required f o r stages A and C i n the f i e l d experiment I , part 1. 99 30. The mean number of days required f o r stages A and C i n the f i e l d experiment I , part 2. 100 31. Means, h e r i t a b i l i t y , selection progress and genetic progress i n F^ generations: 101 103 32. Mean days required f o r selections made f o r stages A and C i n the Fj- of the f i e l d experiment I I I . 33. Summary of the f i e l d experiments, mean days required f o r stage A. 105 34. Summary of the f i e l d experiments, mean days required f o r stage C. 105 LIST OF FIGURES Figure 1. (V ,W ) graph f o r stage 1, greenhouse experiment I warm regime. 2. CV ,W ) graph f o r stage 2, greenhouse experiment I warm regime. 3. (Vr,W ) graph f o r stage 3, greenhouse experiment I warm regime. 4. (V \u00bbW ) graph f o r stage 4, greenhouse experiment I warm regime. 5. CV ,W ) graph f o r stage 5, greenhouse experiment I warm regime. 6-i' (V ,W ) graph f o r stage 6, greenhouse experiment I warm regime. 7. CV ,W ) graph f o r stage 7, greenhouse experiment I warm regime. 8. CV \u00bbW ) graph f o r stage 1, greenhouse experiment I cool regime. .9. CV Wp) graph f o r stage 2, greenhouse experiment I cool regime. 10. CVr,Wr) graph f o r stage 3, greenhouse experiment I cool regime. 11. CV^jWp) graph f o r stage 4, greenhouse experiment I cool regime. 12. CV jW^) graph f o r stage 5, greenhouse,experiment I cool regime. 13. CV ,W ) graph f o r stage 6, greenhouse experiment I cool regime. 14. CV ,W^,) graph, f o r stage 7, greenhouse experiment I cool regime. (V ,W ) graph for stage 5, greenhouse experiemnt I I , warm regime. (V ,W ) graph for stage 6, greenhouse experiment I I , warm regime. (V ,W ) graph for stage 5, greenhouse experiment I I , cool regime'. (V ,W ) graph for stage 6, greenhouse experiment I I , cool regime. (V ,W ) graph for days required per plastochron,.greenhouse experiment I I , warm regime. (V ,W ) graph for days required per plastochron, greenhouse experiment I I , cool regime. CV ,Wr) graph for f r u i t weight, greenhouse experiment I I , warm regime. (V ,W ) graph for f r u i t weight,greenhouse experiment I I , cool regime.' CV ,W ) graph for fruit\u2022:diameter, greenhouse experiment I I , warm regime. (V ,W ) graph for f r u i t diameter, greenhouse experiment I I , cool regime. Net. photosynthesis rate for each plastochron of four lines i n the warm regime. Net photosynthesis rate for each plastochron of four lines i n the cool regime. Leaf area at- each plastochron among the lines i n the warm regime. Leaf area at each plastochron among the lines i n the cool regime. X ACKNOWLEDGEMENT I wish to express my sincere thanks to the following persons, whose assistance i n the preparation of t h i s thesis has contributed, s i g n i f i c a n t l y to whatever merits i t may have. To Dr. C.A.Hornby, Associate Professor of Plant Science, who not only suggested.the topic f o r t h i s thesis but also spent many hours reviewing the manuscript. Moreover, during a l l phases of my. graduate study, he has given guidance and valuable personal assistance\/ To Professors V.C.Brinks., K.Cole, G.W.Eaton, C.W.Roberts and V.C. Runeckles, Chairman of the thesis committee, thanks are expressed f o r taking the time to review t h i s work and f o r o f f e r i n g many h e l p f u l suggestions. F i n a l l y , t o my wife, Rose, whose love and confidence contributed to the timely completion of t h i s work. As a small token of my gratitude .for her devotion, I dedicate t h i s study to my. wife. INTRODUCTION The tomato (Lycopersicon esculentum .Mill.) i s one of the most important vegetable crops i n North America. This crop i s strongly thermoperiodic i n i t s environmental response (Went, 1957) and i s not w e l l adapted f o r short and frequently cool growing seasons i n Canada, therefore fa s t e r growing and e a r l i e r crops tolerant to cool temper-atures are a primary r e q u i s i t e i n the production of Canadian tomatoes. Breeding f o r increased earliness and cool temperature tolerance has been done f o r many years, but further improvement f o r both characteristics i s needed i n order to have an expanding tomato production program i n Canada. Powers et a l . (1950) studied tomato earliness by p a r t i t i o n -ing the l i f e cycle into 3 stages: a) f i r s t stage: seeding to f i r s t bloom; b) second stage: f i r s t bloom to f i r s t f r u i t set and c) t h i r d stage: f i r s t f r u i t set to f i r s t r i p e f r u i t . They proposed that re-combination of early stages could r e s u l t i n e a r l i e r c u l t i v a r s . These designated f i r s t and t h i r d stages were r e l a t i v e l y long and the genetic mechanisms which controlled these stages s t i l l need to be c l a r i f i e d . For t h i s study, the l i f e cycle of 3 c u l t i v a r s : Bonny Best, Immur P r i o r Beta and Cold Set was further partitioned i n t o 7 stages: 1) seeding to ge:mfeation;':2>) germination fo f i r s t true l e a f ; 3) f i r s t true l e a f to flower bud formation; M-) flower bud formation to f i r s t flower; 5) f i r s t flower to f i r s t f r u i t set; 6) f i r s t f r u i t set to color change; 7) color change to ripening. The objectives;;of the present experiments were 1) to evaluate 1 the ,7 growth component stages using the d i a l l e l ' cross technique to estimate gene action, h e r i t a b i l i t y and numbers of genes^ associated with each stage; 2) to use r e c i p r o c a l crosses to ascertain whether any differences could be attributed to cytoplasmic e f f e c t s ; 3) to contrast warm and cool temperature regimes inathe genetics studies i n the d i a l l e l and r e c i p r o c a l cross experiments and 4) to u t i l i z e the genetic knowledge i n a f i e l d selection program f o r earliness recombinations i n the t h i r d to f i f t h generations. 2 LITERATURE REVIEW A. D i a l l e l Crosses Jinks and Hayman (1953) and Hayman (1954), based on methods of Mather (1949), and using d i a l l e l crossing, showed how variances and covariances among pure l i n e s could be used to provide estimates of the o v e r a l l degree of dominance i n the parents, an estimate of h e r i t a b i l i t y and other genetic parameters. Accordingly, the d i a l l e l cross tech-nique has been widely used by plant breeders as a method f o r studying continuous v a r i a t i o n . Johnson (1963) pointed out that the d i a l l e l cross has 2 main advantages: a) experimentally, i t i s a systematic approach, and b) a n a l y t i c a l l y , i t has a genetic evaluation that i s .-, p r a c t i c a l f o r i d e n t i f y i n g the I'erossesiwith the best selection p o t e n t i a l i n early generations. G r i f f i n g (1956a) showed how the d i a l l e l analysis provides information about the variance of general combining a b i l i t y (a|).' and s p e c i f i c combining a b i l i t y (a*). G r i f f i n g (1956b) demonstrated that when a set of inbred l i n e s i s used i n a d i a l l e l crossing system, a genetic interpretation i n terms of quantitative inheritance i s made possible by the fact that the analysis i s r e a l l y a 'gamete' combining a b i l i t y analysis. Thus i n the d i a l l e l s t a t i s t i c a l analysis, the method may regard the genotypic e f f e c t of any i n d i v i d u a l as the summation of effects contributed by each gamete ( i . e . set of genes i n the gamete) and the inte r a c t i o n of gametes ( i . e . the interaction of the genes i n one gamete with those i n the other). Kempthorriie (1956) c r i t i c i z e d the Jinks-Hayman analysis on the basis that \"the d i a l l e l cross must be interpreted i n terms of some population which has given r i s e to the homozygous parents i n inbreeding. I f such a population does not e x i s t then the whole analysis i s l i k e l y to lead nowhere, and also one may question the value of estimating genetic variance, un-less the estimated quantities are measures of the character-i s t i c of a d e f i n i t e population\". Since the parents of s e l f - p o l l i n a t e d crops w i l l usually not have been derived by inbreeding from the d e f i n i t e population, Kempthorne e v i -dently considers that the Jinks-Hayman type of analysis of d i a l l e l crosses has l i t t l e p r a c t i c a l value as an a i d i n the improvement of s e l f - p o l l i n a t e d crops. Hayman (1957, 1958 and 1960) has considered these c r i t i c i s m s and has discussed some additional aspects of the theory by removing the r e s t r i c t i o n that the inbred l i n e s must be f i x e d . Gilbert (1958) has evaluated the d i a l l e l cross, and pointed out that t h i s technique does give more information than that obtained from the parents only: the d i a l l e l analysis provides additional information on dominance and recessive r e l a t i o n s , on genie i n t e r a c t i o n , and on probable linkage associations. The use of the d i a l l e l analysis to study quantitatively i n -herited characteristics of crops has received considerable attention during the l a s t 20 years. Many investigators have applied the Jinks-Hayman and\/or G r i f f i n g approaches on various crops, including snap beans (Dickson, 1967); cotton (Verhalen et a l . , 1971; Al-Rarvi and Kohel, 1970); tobacco (Jinks, 1954; P o v i l a i t i s ' , :> 1966; Legg et a l . , 1970; Matzinger et a l . , 1971); ryegrass (Lewis, 1970); forage crops (England, 1968; Fejer, 1971); weeds (Williams, 1962); maize (Eberhart et a l . , 1964; Poneleit and Bauman, 1970; Rosenbrood and Ankrew, 1971); cabbage (Chiang, 1969); wheat ( A l l a r d , 1962; Kronstad and Foote, 1964; 4 Hsu and Sosulski, 1969; Bhatt, 1971); barley (Johnson and Aksel, 1959); f l a x (Shehata and Comstock, 1971); linseed (Ahand and Murty, 1969). In tomato, the d i a l l e l cross analysis has been applied to many c h a r a c t e r i s t i c s , such as locule number (Ahuja, 1968; Andrasfalvy, 1971); f r u i t s ize (Horner and Lana, 1956; K h e i r a l l a and Whittington, 1962; Peat, 1963; Khalf-Allah, 1970; Andrasfalvy,, 1971); y i e l d (Horner and Lana, 1956) and soluble so l i d s i n f r u i t (Stoner and Thompson, 1966). B. Reciprocal Crosses In h i s book \"Extrachromoscmal Inheritance\", Jinks (1964) defined reci p r o c a l crosses as crosses i n which the sources of male and female gametes are reversed. When parental l i n e s d i f f e r only by chromo-somal genes, i t i s generally unimportant whether these genes go i n t o male or female gametes; the progeny of rec i p r o c a l crosses between such parental\/lines are genetically i d e n t i c a l . However, differences i n cer-t a i n quantitative characters between recipr o c a l crosses do a r i s e . Some examples of such characters are: o i l and f a t t y acid contents, grain y i e l d , maturity, plant and ear heights, and number of ears per plant i n maize (Bhat and Dhawan,197l; Garwood et a l . .,1970); flowering time and plant height i n Nicotiana r u s t i c a (Jinks et al.,1972); seed protein content i n soybeans (Singh and Hadley ,19.72); i n tomato, seed germination ( E l Hassan,1972); f r u i t s i z e (Halsted 1918, Cram 1952; Shumaker e t _ a l . .,1970); early maturity ( L i and Hornby, 1972; Shumaker et al.1970); early y i e l d (Driver,1937; Meyer and Peacock,1941; Moore and Qirrence,1950; Cram,1952;.Shumaker et al.,1970). The e a r l i e s t work on rec i p r o c a l breeding i n tomatoes was reported by Halsted (1918) on f r u i t s i z e . He concluded that i f a 5 small f r u i t c u l t i v a r was used as a female parent, the Yi produced smaller f r u i t , whereas i f the female parent was the l a r g e - f r u i t c u l t -i v a r , the F x produced larger .fruit., Moore and Currence (1950) studied 21 pairs of re c i p r o c a l hybrids i n tomatoes. They found that 6 pairs showed s i g n i f i c a n t differences between reciprocals i n early y i e l d , whereas f r u i t s ize and t o t a l y i e l d d i f f e r e d s i g n i f i c a n t l y i n thir t e e n and three pairs respectively. Driver (1937) and Meyer and Peacock (194-1) demonstrated differences between pairs of reciprocals f o r e a r l i -ness and t o t a l y i e l d i n Fi hybrid tomatoes. Cram (1952) claimed that the differences between tomato r e c i p r o c a l hybrids resulted from some maternal or cytoplasmic influence. E l Hassan (1972) reported that the re c i p r o c a l differences were found between Fi and F2 generations, i n tomato, f o r sprouting at 10.0\u00b0C.but not at 35.0\u00b0C. He concluded that the r e c i p r o c a l differences were attributable to the ^ contribution of the embryo genotype, maternal effects and i n t e r a c t i o n of maternal genotype and cytoplasmic e f f e c t s . L i and Hornby (1972) partitioned the tomato l i f e cycle i n t o 3 growth component stages under 2 d i f f e r e n t temperature regimes, they found that the days required to complete each of the growth component stages i n r e c i p r o c a l hybrids responded d i f f e r e n t l y . \u2022P. Evidence f o r cytoplasmic inheritance has been reported f o r di f f e r e n t plants by many workers including Ashri (1964), Beale (1966), Granick (1965), Katsuo and Mizushima (1958), Koopmans (1959), Michaelis (1954) and Sager (1965). Bhat and'Dhawan (1970, 1971), Brown (1961), Fleming et a l . (I960) and Singh (1965, 1966), working with maize-y,;;have shown that the expression of some polygenically inherited t r a i t s may be governed by the cytoplasm. 6 Jinks et a l . (1972) reported that there are 2 kinds of d i f -ferences between re c i p r o c a l crosses, transient and persistent. These may be maternal or paternal effects. Differences i n the maternal environment can give r i s e to transient r e c i p r o c a l differences. Such differences are known i n the animal kingdom where they ' 'were traced to differences i n the maternal genotypes (Mather and Ji n k s , 1971). Per-sist e n t r e c i p r o c a l deferences; usually arise through unequal contrib-. utions of cytoplasmic determinants from the female and male gametes to the zygotes. Such differences are prevalent i n the plant kingdom. C. Selection In Plant Breeding The hi s t o r y of crops has been influencecl considerably by man's augmentation of selection. I t was understood that many crop characteristics were being modified by selection. Walker i n h i s 1969 review, stated that there were only three basic factors of selection even when the genetic s i t u a t i o n i s highly complex. F i r s t , selection operates because'^-some individuals are favoured i n reproduction at the expense of others; secondly, selection acts through heritable differences; and t h i r d l y , selection works_ upon va r i a t i o n already present i n the organism. Mather (1953) summarized the effects of selection on a population as being d i r e c t i o n a l s t a b i -l i z i n g or disruptive. Many characteristics such as y i e l d and earliness are easy to measure, but they are the products of interactions at both the genetic and environmental l e v e l s . These characteristics have been considered to be b a s i c a l l y controlled by genes with small e f f e c t s , which may be modified by environmental f l u c t u a t i o n and subsequently 7 the data lead to variable estimates of h e r i t a b i l i t y . Hazel and Lush (1942) showed.that selection f o r a t o t a l score i s much more e f f i c i e n t than selection f o r one t r a i t at a time. They also showed that selec-t i o n f o r several t r a i t s by using indepenent c u l l i n g l e v els f o r each i s more e f f i c i e n t than random selection f o r each t r a i t one at a time. In contrast, Mather (1960) proposed that the selection procedure begin with the p a r t i t i o n i n g of complex char a c t e r i s t i c s i n t o subunits (com-ponent analysis) and, with the use of biometrical genetics, modify the selection procedure as required. The best r e s u l t s from component analysis have been achieved when subunits act i n m u l t i p l i c a t i v e fashion; f o r instance, the y i e l d of the tomato plant can be expressed i n terms of f r u i t number and f r u i t s i z e ( G i l b e r t , 1961). S i m i l a r l y , Powers et a l . (1950) partitioned the tomato l i f e cycle i n t o 3 major component stages: 1) seeding to f i r s t flower, 2) f i r s t flower to f i r s t f r u i t set, and 3) f i r s t f r u i t set to f i r s t f r u i t ripening. They found l i t t l e evidence, that these subunits were determined by a s u f f i c i e n t l y small number of l o c i to permit simple Mendelian analysis. In reviewing t h e i r data, i t appeared that the biometrical t e s t sometimes showed that the subunits could be considered under more simple control than the complex characteristics of t o t a l y i e l d and earliness. Peirce and Currence (1959) reported on the r e s u l t s of selec-t i o n f o r 3 quantitative characters: earliness, y i e l d and f r u i t s i z e i n segregating populations of tomato plants. Their data showed1that-one generation of selection resulted i n a considerable gain i n f r u i t s i z e , a s i g n i f i c a n t increase i n y i e l d and l i t t l e change i n earliness. As expected the estimates of h e r i t a b i l i t y f o r earliness were low where-as the other two characteristics had higher h e r i t a b i l i t y values. 8 One major selection system developed to maintain a higher l e v e l of genetic v a r i a b i l i t y w i t h i n the breeding population i s re-current selection. This system has been proposed as a promising method f o r e f f e c t i n g stepwise changes i n gene frequency within a population as opposed to the development of inbred l i n e s which gave homozygosity under continuous s e l f - p o l l i n a t i o n . Comparative studies conducted by Comstock et a l . (1949), Lonquist and M c G i l l (1956), Sprague et a l . (1952) have demonstrated the superiority of recurrent selection over selection within s e l f - f e r t i l i z e d progenies. The rapid approach to-=~ ward homozygosity apparently did not allow adequate Opportunity f o r selection; therefore, A l l a r d (1960) suggested that some less intense form of inbreeding, such as sib-mating might a i d i n the selection of superior genotypes from a given foundation population. Khalf-Allah and Peirce (1964) applied t h i s method i n tomato and found that the progenies developed by sib-mating generally maintained higher genetic v a r i a b i l i t y f o r f r u i t s i z e , earliness and t o t a l y i e l d than did s e l f p o l l i n a t e d selections. Recurrent selection has also been applied to improve the s p e c i f i c combining a b i l i t y of breeding l i n e s i n many other crops, especially i n maize ( H u l l , 1945; Horner et a l . , 1972). The d i f f i c u l t y a r i s i n g from selection f o r a single t r a i t i s the genetic and cenvironmerital c o r r e l a t i o n with other t r a i t s , but t h i s can be p a r t i a l l y resolved by the use of a selection index. Such an index has been widely used by the animal breeders, but has been l i t t l e used by the plant breeders. Andrus and Bonn (1967) used an index i n a mass selection program with muskmelon. This index was a simple ' scoring method with equivalent economic weight attached to each char-acter. Plants with the largest t o t a l score or highest index were selected. Peirce (1968) reviewed selection procedures and the problems 9 involved. He noted that the estimates of parameters used to construct an-index are usually d i f f e r e n t f o r each c u l t i v a r population i n a breeding program, and these estimates, p a r t i c u l a r l y of genetic corre-l a t i o n s , are subject to considerable error. He states that* \"The concept of selection by index i s a viable one and should not be discarded\". He also stated that \"An index i s p a r t i c u l a r l y suited t o those crops i n which value i s determined by r e a d i l y measureable attr i b u t e s . And f o r those measureable characters contributing to the balanced genotype, affected by d i f f i c u l t c orrelations, an index may help\". Another aspect that must be considered by the plant breeders as affecting selection i s the magnitude of the genotype\/environment interaction. A l l a r d (196M-) summarized t h i s problem as follows: \"The genotype and environment i n t e r a c t i o n i s always a com-ponent of va r i a t i o n . Interactions, such as variety x lo c a t i o n , variety x treatment are frequently predictable, and one can usually breed plants that w i l l excel i n a s p e c i f i c envir-onment. The variety x year effects are not predictable, and the breeders must attempt to minimize the impact of such inte r a c t i o n by testiingy. v a r i e t i e s over a series of years and locations\". Further emphasis on t h i s i n t e r a c t i o n was expressed by Cornst6ck and Mo l l (1963) as follows: \"Because genetic facts are infe r r e d from observations on phenotype, because selection i s based on phenotype and becaused there .is a pot e n t i a l contribution of genotype and environment int e r a c t i o n effects on the phenotype of a l l quantitative characters; genotype x environment i s i n some way involved i n most problems of quantitative genetics and many problems of plant breeding, therefore, a l l of i t s poss-i b l e implications deserve attention.\" D. Growth Component Stages And Temperature Effects 1. Stage 1: From Seeding to Gernrination In e a r l i e r studies, v a r i a t i o n i n the rate of seed germination 10 at d i f f e r e n t temperatures has been observed in;;many vegetable crops. Kotowski (1926) reported that speed of germination f o r 17 d i f f e r e n t kinds of vegetables increased as the temperature rose. The optimum temperature f o r tomato was 18.0\u00b0C and the nuxiimum was between 11.0\u00b0C and 18.0\u00b0C. Went (1957) found the time required f o r tomato seed ger-mination depended greatly on temperature, and the lower the temper-ature then the longer the time required f o r gernrination. Whittington et a l . (1965) reported that time f o r germination showed a genetic com-ponent, but the relationships between d i f f e r e n t genotypes was much influenced by environmental factors. The eff e c t of temperature on seed germination was highly s i g n i f i c a n t , and the time required f o r germination being greatest at the lower temperatures. Whittington and F i e r l i n g e r (1972) indicated the inheritance of time to germination of tomato seed was largely additive and-closely related to seed s i z e . Pollack and Larson (1956) indicated that speed of tomato seed germ-in a t i o n depended primarily upon environmental f a c t o r s , and that with-i n one c u l t i v a r seed s i z e has l i t t l e or no effect. The existence of genetic differences i n the ca p a b i l i t y of tomato seed to germinate at low temperature has been mentioned by various investigators. Smith and M i l l e t t (1964) reported that s i g -n i f i c a n t differences were observed among 10 v a r i e t i e s at constant temperatures of 15.0\u00b0C and 10.0\u00b0C but not at 20.0\u00b0C. Kemp (1968) reported that the a b i l i t y of some tomato c u l t i v a r s , such as 'Earlinorth' and 'Rocket', to germinate at low temperatures may be inher i t e d ; and at 10.0\u00b0C or lower, the percentages of germination of a l l c u l t i v a r s was reduced s i g n i f i c a n t l y . Berry (1969) reported differences i n germ-ina t i o n response at 35.0\u00b0C and the existence of a heritable association 11 between high and lew temperature response. E l Hassan (1972) reported that sprouting at 10.0\u00b0C, germination percentage at 35.0\u00b0C, and rate of germination at 35.0\u00b0C are inherited characters and controlled by at least 3, 2 and 1 gene(s) respectively. He also reported a high corv r e l a t i o n between germination at low and high temperatures and the probable existence of 2 different genetic systems which are recombinable. Cannon et a l . (1973) reported the a b i l i t y of tomato l i n e PI 341988 to germinate at 10.09C i s controlled by a recessive gene ( l t g ) . E l Sayed andj\u00a9&pii (1973) pointed out that germination of tomato seed needs at least the accumulation of 160 d a i l y heat un i t s . They found the c h a r a c t e r i s t i c of germination at low temperature f o r the Fr::and F2 progenies was intermediate between t h e i r contrasting parents. In h e r i t -ance was found to be quantitative and an estimate of 24 gene pairs d i f f e r e n t i a t e d the parents f o r germination. There was strong evidence f o r additive gene action although dominance and epistasis were not ruled out. They also indicated that the same gene system appears to control emergence of seeds at both low (10.0\u00b0C) and high (20.0\u00b0C) temperatures with a h e r i t a b i l i t y of 25-40% and selection f o r emergence at low temperature could be achieved at high temperature. Phatak (1970) indicated that the seed from plants selected f o r normal germ-ina t i o n at 10.0\u00b0C night and 12.0\u00b0C day showed a d e f i n i t e improvement i n cold germinating a b i l i t y . 2. Stage 2: From Germination to F i r s t -Shme Leaf Appearance Variation i n growth of the seedling could be expected to be influenced by i n i t i a l embryo s i z e (Ashby 1930, 1937).- However, East (1936), Luckwill (1939) and Hatcher (1940) found that some tomatoes which showed heterosis f o r early seedling growth did not have any 12 apparent difference i n embryo s i z e and concluded that the s i z e of the embryo was not the index of heterosis. Whaley (1939) made a study of growth rates of the parents and hybrids i n two Lycopersicon species crosses showing heterosis. In both crosses the hybrids grew fas t e r than either parent i n the early post-embryonic stage, he also noted \u2022. that heterosis was not always accompanied by the possession of a larger embryo i n the hybrid. In a second paper (1939) he presented evidence showing that there was no relationship either i n the embryo or during development, between the volume of the a p i c a l meristem and heterosis. Whittington et a l . (1965) using hybrids from L. esculentum and L. pimpinellifolium found that the hybrid hypocotyl although i t s emergence was delayed by l a t e r germination, came to exceed i n length that of L. pimpinellifolium. Since hypocotyl extension i n tomatoes i n the dark i s by c e l l elongation rather than by c e l l d i v i s i o n , i t i s l i k e l y that t h i s r e s u l t i s due to an enhanced rate of extension of i n d i v i d u a l c e l l s i n the hybrids.\u2022 I t was thought that the s i g n i f i c a n t difference between the parent and hybrid was due to the greater c e l l number i n the hybrid hypocotyl. ' 3. Stage 3: From F i r s t True Leaf to Flower Bud Appearance (A) Leaf Development Throughout the h i s t o r y of research on crop plants many workers have sought to f i n d some observation or system of measurements that would accurately r e f l e c t the growth response caused by the environ-mental factors, f o r instance, flu c t u a t i o n of temperature has been evaluated i n various ways with respect to the effects on plant growth such as plant height, le a f area, phenological development, etc. As early as 1735, Reaumur attempted to correlate changes i n temperature 13 with plant development. Since then, the resultant correlations of growth and temperature data were developed. Went (1944, 1945), Verkerk (1955), Lewis (1953), Calvert 0-9SB\", 1959) have demonstrated that the early development of the tomato i s affected by the temperature and l i g h t i n t e n s i t y during the f i r s t few weeks from germination. Calvert (1957, 1959) has shown that the number of leaves formed between the cotyledons and the''first inflorescence, increases with temperature but decreases with l i g h t i n t e n s i t y . Hussey (1963) reported that temper-ature had a greater e f f e c t on l e a f growth than on l e a f number; however, more leaves were formed before flowering at 25.0\u00b0C than at 15.0\u00b0C. He also observed the effects of high temperature i n delaying the en-largement of the apex and of increasing the number of leaves produced before flowering. The day and night temperature requirements f o r the tomato were iinVe^stigatedd by Went (1944) who^ ' \u2022 found that optimal growth occurs when the temperature during the dark period i s lower than that during the d a i l y l i g h t period. This kind of temperature response, he termed thermoperiodicity. Hussey (1965) indicated that the average day temp-erature affected l e a f growth one and h a l f times as much as night . temperature. To establish the process which controls the growth of tomato plants i s of some i n t e r e s t , because i t may a s s i s t the plant breeder i n choosing the d i r e c t i o n f o r developing improved -'cultivars \u2022 Went (1944) studied the correlation between various physiological processes and growth i n the tomato plant. He found the elongation rate of tomato stems decreased sharply during the day, and photosynthesis reached i t s optimum near 10,764 lux and was only s l i g h t l y lower at 18.0\u00b0C 14 than at 26.5\u00b0C, but was s i g n i f i c a n t l y lower at 8.0\u00b0C. Translocation of sugars was low at 26.5\u00b0C, and steadily increased as the temperature decreased to 8.0\u00b0C. (B) Plastochron In developmental studies one can usually r e l a t e only the simplest aspects of the developing organism or organ to time d i r e c t l y . The term 'plastochron' proposed by Askenasy (1880) has gained f a i r l y wide usage (Esau, 1953). She defined plastochron as:^ \"The period between i n i t i a t i o n of successive leaves i n the shoot of a higher plant which appear p e r i o d i c a l l y \" . When successive plastochrons are equal i n duration, the plastochron may be made to serve as the unit of a developmental scale. Ericksron and M i c n e l i n i (1957) defined a plastochron as the time i n -t e r v a l between i n i t i a t i o n of two successive leaves. Thus the plasto-chron might be more broadly defined as the i n t e r v a l between corres-ponding stages of development of successive leaves, and one might choose i n i t i a t i o n , maturity or any intermediate stage of development as the stage of reference. (C) Photosynthesis The y i e l d of each a g r i c u l t u r a l crop i s d i r e c t l y affected by the rate and production of photosynthesis. The production and the rate of photosynthesis are affected by the s o i l and c l i m a t i c condi-t i o n s , especially the l a t t e r ; f o r example, l i g h t (Porter, 1937; T a i l i n g , 1961; Hesketh and Moss, 1963; Hesketh and Baker, 1967; Peat, 1970; Scott et a l . , 1970); temperature (Wassink, 1945; Kramer andKerzlowski, 1960; Alberda, 1969; Hew et a l . , 1969; Machold, 1969; Treharne and Eagles, 1970); C0 2 concentration (Gaastra-a, 1962; Brun and Cooper, 15 1967; Bishop and Whittingham, 1968). In spite of the importance of photosynthesis, no serious attempt was made u n t i l recently to establish the genetic v a r i a b i l i t y i n photosynthetic e f f i c i e n c y among crop< plants. A plant breeder must understand thoroughly the masking effect of the various factors (both external and internal) regulating photosynthetic rates and in^.turn obscuring the genetic p o t e n t i a l i t y of t h i s character i n crop improve-ment programs. The evidence f o r genetic v a r i a b i l i t y of photosynthetic e f f i c i e n c y among species has been demonstrated i n numerous studies. Hesketh (1963) and Hiesey and Milner (1965) reported differences i n photosynthesis, amongg species such as Ricinus communis L., Helianthus annus L., Zea mays L.,-^Dactylis glomerata L., Trifolium pratense L., Acer saccharum Marsh., and Quercus rubra L. Differences f o r photosynthetic rate have been shown amonggcultivars within a species as ;inethe case of r i c e (Noguti, 1941); barley (Ekdahl, 1944); wheat (Asana and'.Kani, 1950); cotton (Muramoto et a l . , 1965); blueberry (Forsyth and H a l l , 1965); sugarcane ( I r v i n e , 1967); oats (Jennings and Shibles, 1968; Lawes and Treharne, 1971);;s\u00a9rghum (Eastin and S u l l i v a n , 1969); a l f a l f a (Eearoeei et a l . ,1969); bean (Wallace and Munger, 1966); maize (Duncan and Hesketh, 1968; Garg et a l . , 1969); tobacco ( Z e l i t c h and Day, 1973). In tomato, Stambera and Petrikova (1970) found a difference i n photosynthetic rate between determinate and indeterminate tomato vari e t i e s , and they also found that the high e f f i c i e n c y of the a s s i m i l -ative apparatus can be observed i n the period from the beginning of flowering t i l l the beginning of f r u i t formation. Breznev and Tagmazjav (1969) reported that i n the majority of hybrids, photosynthetic act-i v i t y during bud formation and flowering was higher than i n the 16 parental v a r i e t i e s and that the hybrids were superior i n y i e l d . Kirk and Tilney-Bassett (1967) indicated that there was the p o s s i b i l i t y of genetic control of formation of photosynthetic apparatus i n the plas-t i d , which apparently influenced the photosynthetic rate among the c u l t i v a r s . They also discussed a number of instances of mutations i n nuclear genes which might possibly be regulator genes, as f o r example, the green-flesh and the lutescent mutations i n tomato. Went (1957) pointed out that under normal f i e l d conditions young tomatoes probably lose less than 10 percent of t h e i r photosyn-thates i n r e s p i r a t i o n , the remaining 90% going i n t o the building of the tomato plant and f r u i t growth. Evans (1969) was of the opinion that photosynthetic rate constituted the primary l i m i t a t i o n to productivity i n tomato under most conditions. Donald (1962) expressed the opinion that plant breeders have been paying i n s u f f i c i e n t attention to photo-synthesis as a basic process affecting crop y i e l d . Also he pointed out that plant form or habit can affect photosynthetic gain. Moss (1969). indicated that breeding f o r photosynthetic e f f i c i e n c y requires the i d e n t i f i c a t i o n of desirable parental stocks. Non-genetic v a r i -a b i l i t y on photosynthetic measurements i s important. When measuring the photospiitihetdiG:: r a t e , one has to consider the environmental effects and t r y to control t h i s v a r i a t i o n . Kristoffersen (1963) pointed out that the net photosynthesis i n tomato was so greatly affected by en-vironmental f l u c t u a t i o n during the time periods used to make the measure-ments, that the net photosynthesis rate from such procedures were i n -e f f i c i e n t f o r i d e n t i f y i n g parental l i n e s with the genotypes f o r high net photosynthesis rates. 17-17 (D) Flower I n i t i a t i o n There are several reports about the influence of temperature and l i g h t on f l o r a l i n i t i a t i o n i n the tomato. Went (1941) reported : that the optima of normal day temperature and lower night temperature did not materially increase or decrease the number of flowers i n i t i -ated per inflorescence. Phatak (1966) compared two regimes, 15.5\u00b0C to 18.5\u00b0C and 18.5\u00b0C to 21.1\u00b0C during the period from the seedling to the appearance of the f i r s t inflorescence, and reported that the num-ber of flowers was s i g n i f i c a n t l y increased under the cooler regimes. Lewis (1959) reported that temperature was the main factor which af-fected the number of flowers i n a tomato inflorescence. He also i n -dicated that alternation of warm days and cool nights, and vice versa, as opposed to a uniform temperature, had no e f f e c t on flower number i n plants grown under natural l i g h t , but both temperature combinations had a depressing effect on flower \/.production under a r t i f i c i a l l i g h t . Wittwer and Teubner (1956) and Calvert (1958) reported that e a r l i e s t flowering was i n i t i a t e d when the day and night temperatures were equal. Lake (1965) suggested that various plant processes such as vegetative growth, flower i n i t i a t i o n , f l o r a l growth and f r u i t growth may have dif f e r e n t temperature requirements. 4. Stage 4: From Flower Bud Appearance to F i r s t Flowering Wittwer and Aung (1969) reviewed the development of the tomato flower and indicated that a small protuberance of meristematic tissue develops from the pedicel of the preceding flower. The portion of t h i s pedicel posterior to the protuberance becomes part of the peduncle. The meristematic protuberance o r - a x i l -fortsbhelfirst flower of the c l u s t e r originates i n the a x i l of the le a f . The pedicel which 18 supports a single flower, as w e l l as the peduncle from which i t a r i s e s , i s composed of a rather thick cortex, a r i n g of vascular tissue and a central portion of p i t h tissue (Cooper, 192-7). Smith (1935) s i m i l a r l y observed that the protuberance of the f i r s t flower of the inflorescence arose i n the a x i l of the lea f . The succeeding flowers of the c l u s t e r each a r i s e from s i m i l a r protuberances which grow out from the pedicels of the preceding flower. There are reports about the environmental effects of temp-erature on flower development. Z i e l i n s k i (1948) reported that low temp-erature environment (7?28GCand 12.8\u00b0C) influenced perianth develop-ment i n the tomato, r e s u l t i n g i n f a s c i a t i o n of perianth components, and frequently i n adhesion of stamens to the c o r o l l a or calyx and and cohesion of the an t h e r i d i a l filaments. Rudimentary anther sacs with aborted pollen occurred frequently. Rick (1946) observed that under cool temperature, tomato flowers often drop without setting f r u i t , and one of the main reasons may be abortion of the p i s t i l . 5. Stage 5: From F i r s t Flower to F r u i t Set Although the days required f o r t h i s stage are r e l a t i v e l y few, there are several developmental processes which occur during t h i s stage. Besides the existence of viable pollen i n the anthers, there i s the need f o r transfer of pollen from the anthers to the stigma, pollen germination, pollen tube growth, f e r t i l i z a t i o n and early f r u i t development. A comprehensive study of factors a f f e c t i n g sporogenesis and the development of pollen grains was made by Hewlett (1936). Using c y t o l o g i c a l techniques he found that under conditions of severe car-bohydrate deficiency, sporogenous tissue i n some anthers f a i l e d to 19 reach meiotic d i v i s i o n . In addition to t h i s early e f f e c t , degener-ation of mature pollen grains was also a frequent occurrence (Calvert, 1964). Anthers which were subnormal i n s i z e and were not the normal deep yellow color invariably contained only s t e r i l e pollen grains. Went (1957) indicated that abnormal pollen was produced when temper-atures were lower than 13\u00b0C, and he considered t h i s to be the major factor causing unfruitfulness i n tomatoes grown at low night temper-atures. On the other hand, pollen can be produced normally, but may not be released from the anthers due to morphological abnormalities. Larson and Paur (1948) studied t h i s functional male-sterile tomato, and reported that the connate form of the petals resulted i n consid-erable c o n s t r i c t i o n of the anthers and tended to hold them i n close contact with the p i s t i l , thus preventing rupture of the stromium and the subsequent release of the pollen. The p o s i t i o n of the stigma within the anther tube and the i n t e r n a l dehiscence of the anthers favors a high degree of s e l f - p o l -l i n a t i o n . A number of workers have observed that with certain c u l t -ivars i n certain environments, the stigma may project beyond the open-ing of the anther tube, (White, 1918; Bouquet, 1919; Smith, 1935). More recently Williams CESSiDl) observed that both day length and temp-erature affected the rationof carpel length to stamen length. He also observed the degree of unfruitfulness l i k e l y to r e s u l t from s t i g -ma-'exsertion, f o r example, one c u l t i v a r which had a carpel length\/,;'' stamen length r a t i o ^ o f 1.12 set only 16.2% of flowers, whereas another c u l t i v a r with a r a t i o n of 0:96 set 60% of the flowers. The time of dehiscence and the period during which the stigma remains receptive are c r i t i c a l factors i n the p o l l i n a t i o n and 20 f e r t i l i z a t i o n of inbreeding species such as the tomato. Smith (1935) stated that i n summer the c o r o l l a remained open and the stigma receptive f o r about 4 days. Judkins (1940) found the stigma to be receptive about 2 days before anthesis, and a period of 2-3 days usually elapsed be-tween p o l l i n a t i o n and f e r t i l i z a t i o n at normal greenhouse temperatures (16.0i'20.0\u00b0C). Koot and Ravestijn (1963) found the r e c e p t i v i t y of the stigma to be adversely affected by dry sunny weather, but i n d u l l humid weather l i t t l e pollen was liberated from the anthers. The r e c e p t i v i t y of the stigma and the a b i l i t y of pollen t o germinate appears to be strongly influenced by temperature. Exper-iments i n which pollen was germinated at 4- temperatures, namely 10.0\u00b0, 21.1\u00b0, 29.4\u00b0 and 32.8\u00b0C were reported by Smith (1935) and Smith and Cochran (1935). They found that pollen remained in a c t i v e f o r several hours a f t e r being deposited on the stigma. At 21.1\u00b0 and 29.4\u00b0C short tubes formed a f t e r 6 hours, but at 32.8\u00b0C only 0.1% of the pollen had germinated during the f i r s t 12 hours and only 3.9% a f t e r 84 hours. Germination was best at 29.4\u00b0C but only s l i g h t l y better than 21.1\u00b0C. Koot and Ravestijn (1963) assessed the degree of f e r t i l i z a t i o n by the percentage of pollen grains germinating on the stigma 2 hours a f t e r p o l l i n a t i o n . : : They found that both the degree and speed of germination were largely dependent on temperature. Dempsey (1969) reported tomato pollen germination occurred a f t e r 40 minutes at 35.0\u00b0C, and at 5.0\u00b0C the time was increased t o 20 hours. Hornby and Charles (1962) r e -ported \"fe^t the need f o r a nanimum si z e of pollen application, and noted c u l t i v a r differences i n the minima. Afte r germination of the pollen grain, growth of the po l -l e n tube through the s t y l e i s the most important part of the sequence 21 of events during the progamic phase of f e r t i l i z a t i o n . Tube growth i s concerned with protein synthesis, formation of w a l l material, as w e l l as oriented growth toward the micropyle of the embryo sac. For external factors, temperature was found to have a marked effect on the genirination percentage of pollen as w e l l as on the rate of pollen \u2022 tube growth. The maximum rate of pollen tube growth occurred at 21.1\u00b0C with 29.4\u00b0, 10.0\u00b0 and 32.0\u00b0 ranging i n decreasing order (Smith and Cochran, 1935). P r e i l and Reimann-Philipp (1969) reported that the pollen tubes reached the ovary i n about 12 hours at 20.0-25.0\u00b0C and i n 48 hours at 10.0\u00b0C. Temporary low temperature (0\u00b0-2.0\u00b0C\/15 hours) did not in j u r e the pollen tubes and they began to grow again when the temperature had r i s e n . Judkins (1940) reported the time involved i n pollen tube growth appears to increase during the f a l l and winter when l i g h t i s of low i n t e n s i t y . Dempsey (1969) stated that the ex-tensive pollen tube growth only occurred i n the 10.0-35.0\u00b0C range. At 37.0\u00b0C pollen tubes grew abnormally and l a t e r ceased growth while i n the s t y l e . He concluded that growth was inversely related to temp-erature because pollen tubes entered the micropyles 7 hours a f t e r p o l l i n a t i o n at 35.0\u00b0C but required 34 hours at 10.0\u00b0C. The sequence of events between p o l l i n a t i o n and*'fertilization was ca r e f u l l y observed and reported by Smith (1935). About 50 hours a f t e r pollen-.:reached the stigma, one of the male nuclei fused with the polar n u c l e i , the other fusing with the egg.. Af t e r f e r t i l i z a t i o n the zygote did not begin d i v i s i o n f o r 36 to 48 hours. The embryo sac greatly enlarged i n the meantime. The primary endosperm nucleus, began d i v i s i o n i n advance of the embryo. At 66 hours a f t e r p o l l i n -ation , when the zygote was s t i l l a single c e l l , the endosperm 22 consisted of 8 c e l l s with d e f i n i t e walls separating them. 6. Stage 6: From F i r s t F r u i t Set to F i r s t Change of F r u i t Color There has been considerable discussion and speculation on the general problem of the f r u i t s e t t i n g and the development of young f r u i t i n r e l a t i o n t o the growth of the plant and d i f f e r e n t factors of the environment. Shan'gina (1961) stated that r e l a t i v e l y poor f r u i t set on the lower truss of - the tomato may be attributed to the small storage reserves in- plants grown under the poor l i g h t conditions of early spring. Such- n u t r i t i o n a l deficiencies have been suggested as the possible cause of f a i l u r e or poor set f o r the f i r s t i n f l o r e s -censes to produce f r u i t i n tomato a f t e r transplanting (White, 1930; Rick, 1946; Leopold and Scott, 1952). Murneek (1939) pointed out that food reserves are of great importance i n the i n i t i a t i o n and devel-opment of the reproductive phase i n tomato plants. Regarding the environmental e f f e c t s , Went (1944) reported that i n the f i r s t and second c l u s t e r s , f r u i t set was abundant only when the night temperatures were between 10.0\u00b0 and 20.0\u00b0C; and with lower or higher night temperatures, f r u i t i n g was reduced or even ab-sent. Lake (1965) studied the temperature ef f e c t on f r u i t s e t t i n g , and claimed the day temperature appeared more important than the night temperature. Robinson et a l . (1965) reported that cold temperature appeared to affect f r u i t setting of tomato primarily through i t s i n -fluence on microsporogenesis. They also reported that high temper-ature had a s i m i l a r effect.^ suggesting that the same genetic system determined f r u i t setting response to either high or low temperatures. This cool temperature effect on f r u i t set was also reported by Learner and Wittwer (1953), Calvert (1958), Wedding and Vines (1959), Schaible 23 (1962), Curme (1962) and Lake (.1967). ' Most v a r i e t i e s of tomatoes w i l l produce parthenocarpic f r u i t at a r e l a t i v e l y low temperature, but not at r e l a t i v e l y warm temper-ature. Osborne and Went (1953) found parthenocarpic f r u i t at a low temperature with a high l i g h t i n t e n s i t y . Daubeny (1955) found that poor pollen germination and\/or growth may explain the parthenocarpic f r u i t produced by tomato cul\u00b1\u00a3\\%>tBonny Best at the cool temperature (10.0\u00b0 to 12.8\u00b0C) despite hand p o l l i n a t i o n . Leopold and Scott (1952) pointed out that tomato f r u i t set was strongly and quantitatively dependent upon the presence of mat-ure leaves. Darkened mature leaves were less e f f e c t i v e than l i g h t e r ones f o r promoting f r u i t set. . Agreement has not been reached as to the stage of develop-ment at which mitosis a c t u a l l y ceases i n the developing f r u i t . Smith and Cochran (1935) reported that c e l l d i v i s i o n proceeded a c t i v e l y i n the f r u i t f l e s h f o r approximately 2 weeks a f t e r p o l l i n a t i o n . Hough-t a l i n g (1935) as w e l l as Gustafson and Houghtaling (1935) concluded that f r u i t growth a f t e r p o l l i n a t i o n was a r e s u l t of c e l l enlargement only. MacArthur and Butler (1938) reported that ovary growth was e n t i r e l y by c e l l d i v i s i o n p r i o r to p o l l i n a t i o n , and that subsequent growth was c h i e f l y by c e l l expansion, c e l l d i v i s i o n being atfrninor factor that just s u f f i c e d to maintain the tissue containing non^ex-panding epidermal c e l l s . Groth (1910) had previously reported that young and mature f r u i t s contained the same number of epidermal c e l l s , and that mitosis played l i t t l e part i n the enlargement of the tomato f r u i t skin. Clendenning (1948) reported that growth of the f r u i t i n -cludes a phase of residual m i t o t i c a c t i v i t y that :;.pers'istsf-:c.for 24 approximately 1 week a f t e r setting. There i s a relationship between f r u i t p o s i t i o n within the truss and f r u i t growth. Beadle (1937) considering the f i r s t 6 f r u i t s i n the trusses of c u l t i v a r Kondine Red, found that the nearer the f r u i t was to the main stem then the shorter was the maturation period. Similar reports were made by Kidson and Stanton (1935), Kerr (1955) and Cooper (1959). There are also some relationships between growth rate, s i z e of f r u i t and other physiological characters. Cooper (1959) pointed out that f r u i t s which begin to swell r a p i d l y at the beginning of f r u i t development have a shorter maturation period than those f r u i t s which have a period of i n i t i a l lag before rapid growth begins. Gustafson and Stoldt (1936) pointed out that increasing the leaf area, can r e -s u l t i n the si z e of f r u i t being increased a f t e r the time of set t i n g . Clendenning (1942) reported that the growth of f r u i t was found to be associated with an absolute increase i n r e s p i r a t i o n crate. 7. Stage 7: From F i r s t Change i n F r u i t Color to F r u i t Ripening Color changes i n tomato f r u i t are the most obvious signs of ripening. These changes are primarily due to degradation of the chlor-ophylls and the synthesis of carotenoid pigments. Duggar (1913) and Sando (1920) reported that normal temperature and oxygen supply were the essential requirements f o r f r u i t ripening. High temperatures over 32.0\u00b0C and low temperatures under 10.0\u00b0C were reported to delay or even h a l t the ripening (Tomes, 1962; Pharr and Kattan, 1971; Walkof, 1962). Additional to the color changes i n ripening f r u i t , Pattersen (.1970) emphasized two major changes: 1) t e x t u r a l changes r e s u l t i n g 25 from environment and c u l t u r a l practices that a f f e c t c e l l morphology during growth; and 2) f l a v o r changes i n which there i s a perception of a combination of sweetness, a c i d i t y and astringency i n conjunction . with the odorous v o l a t i l e s . E. Genetic Analysis Of Growth And Earliness Of Tomato Investigations on si z e and shape i n the development of plant organs have given-further ins i g h t i n t o the more fundamental aspects of t h e i r inheritance. K h e i r a l l a and Whittington ( 1962) and Mallah et a l . (1970) pointed out that s i g n i f i c a n t differences i n growth rates were found between c u l t i v a r s and between the r e c i p r o c a l i n t e r - s p e c i f i c hybrids, and that l a t e r t h i s growth rate was found to be inherited ad-a d i t i v e l y with a large dominance component (Peat and whittington, 1 9 6 3 ) . K h e i r a l l a ( 1961) reported that delayed germination of L. frlnfeine-I-li- folium x L. esculentum r e l a t i v e to L. pimpinellifolium may allow a r e l a t i v e l y greater translocation of reserves to the shoot of the hy-b r i d . The growth rate of the hypocotyl i n t h i s hybrid was found to be higher f o r a l i m i t e d period p r i o r to emergence. This may be an explanation f o r the \"undefined biochemical super i o r i t y \" which Lewis Q!9j5}3>) suggested resulted i n the hybrid having a shorter \"lag phase\" i n the attainment of i t s growth rate. Luckwill (.MW) and K h e i r a l l and Whittington (1962) comparing hybrids and t h e i r parents reported that the hybrids had a larger le a f area which was related to a greater f r u i t y i e l d . Whaley (1939) pointed out that the leaves of hybrids were intermediate i n s i z e between par-ents and tended to be greater than the mean of the parents. Mallah et a l . (1970) reported that a dominant gene actioniwas found i n the 26 inheritance of le a f area, whereas f o r f r u i t s i z e both dominant and additive gene action were present. Whaley (1939) reported that the s i z e of flower i n tomato hybrids was intermediate between those of the parents. Somewhat sim-i l a r r esults were reported by Williams (1959), who found that none of the tomato hybrids exceeded the better parent f o r such char a c t e r i s t i c s as number of flowers, f r u i t s i z e and number of f r u i t s ; with the one exception of y i e l d per plant. The study of earliness led Powers and Eyi>h (194-1) to part-i t i o n the following 3 stages of the l i f e cycle, 1) seeding to f i r s t bloom; 2) f i r s t bloom to f i r s t f r u i t set and 3) f i r s t f r u i t set to f i r s t r i p e f r u i t . Later Powers et a l . (1950) concluded from the use of 2 parentadiscultivars and t h e i r hybrids that the f i r s t 2 stages' were each controlled by 3, and the t h i r d stage by t>2o major gene p a i r s . Honma et a l . (1963) reported that only 1 major gene p a i r controlled the f i r s t growth stage. Burdick (1954) reported that the time of flowering f o r hy-brids was approximately intermediate between the parents. Similar res u l t s were also reported by Williams (1959) and Young (1966). The opinions about the genetic mechanisms c o n t r o l l i n g com-ponent stages are varied. Corbeil (1965) found that early maturity genes were completely dominant to t h e i r l a t e phase a l l e l e s i n the second and t h i r d stages and p a r t i a l l y dominant i n the f i r s t stage:.' Peat and Whittington (1965) and Mallah et a l . (1970) found additive gene action with various degrees of dominant gene action f o r the f i r s t stage. Young (1966) claimed that dominant gene action f o r the f i r s t stage was lacking. Burdick (1954) stated the following: \"The maturity genes of both parents appear to be expres-sing themselves, at d i f f e r e n t stages i n seme hybrids. This would support the view that dominance i s a r e l a t i v e phenomenon, depending on the stage of development and the environmental circumstances under which i t i s measured, and that the excellence of hybrids may be a t t r i b u t a b l e to the co-expression of the a l l e l e s from both parents, made possible by the existence of dominance along with ontogenetic and environment gradients.\" Burdick's idea was. supported by L i and Hornby (1972) who showed that certain hybrids exhibited earliness heterosis under a cool temper- ' \\ ature environment (10.0\u00b0-12.0\u00b0C) but responded intermediately bet-ween parents under normal culture temperature conditions (19.0\u00b0-21.0\u00b0C). A number of workers have reported an association between earliness and certain other tomato characters. Alpat'ev (1957), Daubeny (1959) and Yeager and Meader (1937) reported that selection based on early flowering was the most e f f i c i e n t method i s o l a t i n g early tomato segregates. Bernier and Ferguson (1962) studied the relationships of developmental characters of the tomato with e a r l i -ness, and they found that the days to f i r s t flower (Stage 1) were negatively correlated with earliness (Stages 1, 2 and 3) f o r the c u l t i v a r s 'Imun P r i o r ' and 'Early Lethbridge'. Days required f o r Stage 3 were not correlated with earliness except f o r the c u l t i v a r s , E a r l i n o r t h , and 'Early Lethbridge', therefore they concluded that Stage 3 cannot be regarded as a good index of earliness. 28 MTERIALS AND METHODS MATERIALS Three true breeding tomato c u l t i v a r s which were used as parental l i n e s , and a l l possible combinations of t h e i r crosses were evaluated. The parental l i n e s were Bonny Best (B), Cold Set (C) and Immur P r i o r Beta ( I ) . They have the following h i s t o r y and character-i s t i c s . 1. Bonny Best (B) According to Boswell (1933) t h i s c u l t i v a r was introduced by the firm of Johnson and Stokes df Philadelphia, U.S.A. i n 1908. I t l i s very w e l l known on the North American continent. B has i n -determinate growth habit with round, fleshy and uniform colored f r u i t s . Boswell (1933) pointed out that maturation of B f r u i t was delayed ' considerably under cool temperatures or other unfavorable conditions. Ty p i c a l l y , there are 4 or 5 flowers per clus t e r with 2 or 3 f r u i t s being set per clust e r . This c u l t i v a r was used because i n the past years a considerable amount of research has been done, i n which t h i s popular c u l t i v a r was the t e s t plant. 2. Cold Set (C) I t i s a e r e l i t i v e l y new tomato c u l t i v a r f o r d i r e c t seeding, developed by Professor T. 0. Graham, at the University of Guelph, Ontario, Canada and released i n 1962. I t came from a cross between F i r e b a l l and F i l i p i n o #2. Both of C's parents are tolerant to Very warm 29 and cold temperal^jres. Young (1963) reported that i t i s resistant to cold temperature, and w i l l set f r u i t at a night temperature of 7.2\u00b0C. This cultivar can set i t s flowers under both cold and warm conditions. I t also has indeterminate growth, and uniformly colord f r u i t of medium size. \u2022 3. Immur Prior Beta (I) The origin of this cultivar i s not known. Curme (1968) and Reynard (1968) believed that this cultivar was developed by Dr. A. K a l l i o , University of Alaska art Fairbanks, Alaska, U.S.A., how-ever Kallio (1968) said he obtained the seed i n 1951 from the Hort-icultrure Department of the University of North Dakota, U.S.A., and he also thought that this cultivar might have come from Europe. This cultivar has the potato leaf t r a i t . I t i s indeterminate i n growth habit, and i s very tolerant to low temp.er.atures (e.g. 10.0\u00b0C-12.0\u00b0C) for f r u i t set and vine growth. The f r u i t i s relatively small (60-90g) with flattened globe shape, somewhat angular with green shoulders. Dirikel (1966) stated that this cultivar i s one of the best for summer production i n heated glass houses i n the Alaska latitudes. The three parental lines were crossed i n a l l possible com-binations, thus there were six Fi hybrids. For convenience, these . six d i a l l e l cross hybrids were abbreviated with the female parent indicated f i r s t as follows: Bxl, (BI); IxB, (IB); BxC, (BC); CxB, (CB); Cxi, (CI); and IxC, (IC). 30 30 METHODS A. Greenhouse Experiments 1. Experiment I A d i a l l e l cross experiment employing the 3 parental and 6 Fi hybrids was conducted i n the winter of 1969!-1970 to observe growth stages under ' &2o temperature regimes. One greenhouse was kept i n the optimum range of 17.0\u00b0C-21.0\u00b0C and was considered to be the warm regime, i n contrast to the second house which was kept i n the 10.0\u00b0-13.0\u00b0C range and considered to be the cool regime. Seeds were sown on October 20 i n each of the 2 greenhouses. Seedlings were pricked out 2 weeks later and set i n 5 x 5 cm veneer bands i n f l a t s . Temperatures i n the 2 houses were recorded on ther-mographs throughout the experiment (Table 2 in Appendix). On Nov-ember 30, the plants were placed i n the s o i l beds i n 2 greenhouses. The plants were 50 cm apart within the row and 4-5 cm between the rows. Supplementary light was provided by 4 300-watt fluorescent tubes installed i n pairs over the s o i l beds to ensure a 14-hour photo-period. Pollination was allowed to occur naturally. A randomized block design was used with 4 blocks of 1-plant per plot for each of the 9 lines (see Table 1, Appendix). Earliness was recorded as the number of days required for each of the following: Stage 1: seeding to germination - germination was recorded when 50% of the t o t a l of 50 seeds per line had emerged and ex-panded their cotyledons to a horizontal level. Stage 2*:i\\ germination to f i r s t true leaf emergence - which was 31 considered t o be when the f i r s t true l e a f had reached a length of 10mm. Stage 3: f i r s t true l e a f to flower bud emergence. Stage 4: flower bud emergence to f i r s t flowering - the flower was considered open when the c o r o l l a was bright yellow and had begun to r e f l e x . Stage 5: f i r s t flowering to f i r s t f r u i t set - which was considered to be when the f i r s t f r u i t had reached a diameter of 5mm. Stage 6: f i r s t f r u i t set to f r u i t changing color - when the f i r s t orange-pink color was shown at the blossom end. Stage 7: f r u i t changing color to f r u i t ripening - when the color hadd changed to red, the f r u i t was .considered to be r i p e . In Stage 3, the i n t e r v a l between f i r s t true l e a f t o flower bud emergence was subdivided i n t o plastochron units. The f i r s t plasto-chron was considered to be the age when the plant's f i r s t l e a f had reached the length of 10mm. When the second l e a f reached the'length of 10mm, i t was considered to be plastochron two, and so on. The number of days were also recorded f o r the in t e r v a l s between plasto-chrons. 2. Experiment I I The second experiment was done i n the winter of 1970-1971 and the purpose of t h i s experiment was to further the study of Stages 5 and 6 by using controlled p o l l i n a t i o n procedures to ensure that a l l the l i n e s had a uniform s t a r t i n g point f o r t h e i r f r u i t development. The flowers were emasculated 1 day before anthesis by taking away petals and anthers with a p a i r of tweezers. Pollen was collected 32 on microscope slides, and transferred to the stigmas with a needle. The date of hand pollination was considered as the f i r s t day of Stage 5. The second and t h i r d flower of the second cluster were used for this experiment. When the f r u i t reached 5mm diameter, i t was considered as the f i r s t day Stage 6. When ripe, the individual fruits were weighed and measured for diameter. The management regimes including temperature differentials for this experiment were similar to those i n the f i r s t experiment. Seeds of the 9 lines.were sown on Novemberr- 1, and the plants were set i n the s o i l beds on December 12. The same design was employed as i n Experiment I with a new randomization (see Table 3, Appendix). 3. Experiment I I I . This experiment used a larger population size but had to be limited to the two more promising parental cultivars, B and I, and their reciprocal hybrids. The management regimes including temp-erature'were similar to those i n the f i r s t 2 experiments. Seeds of the 4 lines B, I and their reciprocal hybrids were sown on Oct-ober 29, 1971. Plants were set on the s o i l beds on December 9 and a randomized block design was arranged with 10 blocks of the 4 lines. There was 1-plant per plot (see Table 5, Appendix). The same data were collected as i n Experiment I. B. Growth Chamber Experiments. 1. Experiment I This experiment was conducted to contrast the response of the plant materials at the cool temperature of 12.0\u00b0C with the more optimum one of 21.0\u00b0C. Seeds of 3 parental lines and their 6 d i a l l e l 33 hybrids f o r a t o t a l of 9 li n e s were sown on May 11, 1970. Seedlings were pricked out and set i n 7x7 cm p l a s t i c pots and placed i n growth chambers u n t i l the eighth plastochron stage was reached when the ex-periment was terminated. There was only one r e p l i c a t i o n per l i n e per plastochron. The plants were s h i f t e d around within the chambers every other day to minimize the environmental effects. Data were collected f o r plastochron ages s t a r t i n g from the 4th to 8th i n c l u s i v e l y . Plants were watered at 9:00 a.m. and net photosynthesis rate was measured at 10:30 a.m. An L\/B Infrared Analyzer (Beckman model 15A) was used. The leaf area was measured i n an a i r f l o w planimeter. 2. Experiment I I This experiment used a larger population s i z e than i n Ex-periment I , but was l i m i t e d to the more promising parental c u l t i v a r s B and I , and t h e i r r e c i p r o c a l hybrids. Plants of the 4 l i n e s were arranged at random i n the growth chamber with 4 re p l i c a t i o n s f o r each plastochron. Seeds were sown on May 1, 1971 and the management was s i m i l a r to that i n Experiment I , and s i m i l a r data were collected on the 4th to 8th plastochrons i n c l u s i v e . C. F i e l d Experiments 1. Experiment I This experiment was conducted i n 2 parts i n f i e l d plots ,at The University of B r i t i s h Columbia i n the summer of 1971. The f i r s t part comprised B and I and t h e i r r e c i p r o c a l r crosses, f o r a t o t a l of 8 l i n e s (B, I , B l , .IB, BIxI, IBxI, BIxB, IBxB). Twelve plants per l i n e were used. The seeds were sown on A p r i l , 17,..and 34 transplanted to the f i e l d on May 10. This planting was about 1 to 2 weeks e a r l i e r than gardeners would set out plants, and i t was ex-pected that the plants would be under test to ascertain whether the plants could set f r u i t i n the less than optimum growing conditions. The data were recorded f o r t h i s and subsequent f i e l d ex-periments on i n d i v i d u a l plants as number of days required f o r each of the following stages: Stage A;, seeding to f i r s t flowering - the flower was considered open when the c o r o l l a was bright yellow and had begun to r e f l e x . Stage B: f i r s t flowering t o f i r s t f r u i t set - the f r u i t was consid-ered set when the diameter reached 5mm. Stage C: f i r s t f r u i t set to f r u i t ripening - a f r u i t was considered r i p e when the f r u i t color changed to red. SinceeStage B i s very short r e l a t i v e t o Stages A and C, i t was assumed that Stage B may not be as important as Stages A and C i n breeding f o r earliness, therefore Stage B was not considered f o r further study. The second part was used to observe the segregation of F 2 and F 3 from IB and BI recipr o c a l crosses, and ad d i t i o n a l l y to do selection among the F 3 plants. The selection was f o r earliness and tolerance of early spring cool temperatures. There were 6 and 11 plants selected i n the IB and BI l i n e s respectively. The selection c r i t e r i a i n t h i s 2nd part of the experiment were f o r segregates which were e a r l i e r than both parents, B and I , i n Stages, A cv and\/or Stage C. 2. Experiment I I The selected plants from the F 3 generation of re c i p r o c a l 35 populations IB and BI were reproduced and evaluated. Thus there was the F^;. for 6 lines from IB selection and 11 lines from the BI selection plus two parents I and B, to give a t o t a l of 19 lines i n this experiment. Seeds were sown on March 30, 1972 and transplanted to the f i e l d on May 15. There were 5 plants per plot, 19 plots per block and to t a l of 5 blocks. The experimental design of the random-ized complete block i s shown i n Table 8 of the Appendix. 3. Experiment I I I This f i e l d experiment was conducted i n two parts. In the f i r s t part, seeds from the earliest 10% of the F i* of the IB and BI lines, which were pedigree selected i n Experiment I I , were used i n a simulated mass selection programme. Equal amounts of seed from, the earliest 15 plants selected i n the F i t of the IB line were mixed and a sample of the mixture was used to grow 125 plants which was the F 5 of the IB line. Similarly, seeds from 25 plants of the Fit of the BI line were mixed, and 250 plants were grown to provide the F 5 of the BI line. In the. second part, selected individual plants for e a r l i -ness were compared to the individual plants selected for lateness in the F i t generation. There were 6 plants from the F4 generation selected for earliness and 2 plants selected for lateness. These represented the extremes i n the F i t population. Seeds were sown on March 30, 1973 and transplanted to the f i e l d on May 11. Plants were arranged i n special blocks as shown i n Table 9 of the Appendix. Data for Stages A, B and C were collected as i n Experiment I. 36 STATTSTTCAL METHODS A. Analyses Of Data From The D i a l l e l Crosses Hayman (1954a; 1954b); Jinks (1954); Jinks and Hayman (1953) developed the analysis for the Fi generation of a d i a l l e l cross. The theory for their method can be divided into 2 parts. The f i r s t part proposes a p i c t o r i a l presentation i n which Jinks (1954) stated that \"the covariance of array means on the common parent of the array gives the array covariance (W )\". The Wr values for each array were plotted against the variance of the array (V ). In order for the basic assumptions for this analysis to be met, these points should l i e along a line of unit slope and within a parabola defined as .\"Wr2= V x variance of parents\". The position of the line gives an estimate of the degree of dominance. When the interception i s through the origin, complete dominance i s concluded. The intercep-tion above or below the origin indicates p a r t i a l dominance and over-dominance respectively. The-second part proposed a numerical analysis (Table 1) in which the variances and covariances available from the d i a l l e l table were defined i n terms of the components D, H l s H 2, F and E ( f i r s t designated by Mather, 1949), where D was the weighted com-ponent of variationndue to differences i n additive gene effects, Hj was the weighted components due to dominance, H 2 indicated the asymmetry of positive and negative effects of genes, F was a com-ponent due to the relative frequencies of dominant and recessive 37 TABLE 1. The second degree s t a t i s t i c s f o r a d i a l l e l set. (Mather and Jin k s , 1971) S t a t i s t i c s Model V . p D + E V r \u2022 h\u00a3) + J^ Hx -hF + 5\/9 E W r %D -%F + 1\/9:^ E V-r hp + -\"*H2 + 5\/81 E Hi = 4 V + V - 4 W - ^ 2\u00b1i-\u00a3 E r p r n H-2 = 4 V - M-V- + 2 ( n 2 u 1 ) E r r n z F = 2 V - 4 W - 2 ( n \" 2 ) E p r n V r the variance of an array W r parent-offspring covariance of members of the same array W\" r mean of Wr V r mean of Vj-V P variance of parents V-r the variance of array means E environment effect, derived from the block interactions of the family-.means (from analysis of variance of d i a l l e l table), i t has the same value for each block;V D the weighted component of variaffeionhdue to differences -in additive gene effects Hi the weighted components due to dominance Hjj. the asymmetry of positive and negative effects of genes F the relative frequencies of dominant and recessive alleles 38' a l l e l e s , (being p o s i t i v e when dominant a l l e l e s are more frequent, and negative when recessive a l l e l e s are the more frequent), and E was the component due to environmental error. Additional informa-t i o n may be gained: D