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Breeding system, genetic variability, and response to selection in Plectritis (Valerianaceae) 1981

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BREEDING SYSTEM, GENETIC VARIABILITY, AND RESPONSE TO SELECTION IN PLECTRITIS (VALERIANACEAE) by CHARLES KENNETH CAREY B.Sc.,.The University of B r i t i s h Columbia, 1976 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES (Department of Botany) We accept t h i s thesis as conforming . to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1981 - (c) Charles Kenneth Carey, 1981 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I further agree that permission for extensive copying of t h i s thesis for s c h o l a r l y purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or pu b l i c a t i o n of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Botany The University of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date July 20, 1981 - i i Abstract P l e c t r i t i s congesta and P. brachystemon are two very c l o s e l y r e l a t e d species which grow sympatrlcally, and d i f f e r i n t h e i r : breeding system, some associated morphological.(floral) characters, and isozyme phenotypes. P l e c t r i t i s congesta i s approximately 70% outcrossed i n nature, while P. brachystemon i s less than 3% outcrossed i n natural populations. Theory would predict that, a l l other things being equal, the outcrossed species would be more v a r i a b l e g e n e t i c a l l y than the s e l f e d species. Since s e l e c t i o n acts on genetic v a r i a b i l i t y , the two species could be expected to respond d i f f e r e n t l y to i t . Six generations of plants of both species were grown under co n t r o l l e d conditions, and measured for a number of characters. Control and treatment ( s e l e c t i o n f o r t a l l and short height, and for early and l a t e anthesis) populations were maintained. Two sets of P. congesta populations were maintained, one outcrossed (approximately 65%) and one s e l f e d (outcrossed approximately 15%); the P^ brachystemon populations were n a t u r a l l y s e l f - p o l l i n a t i n g . Selection pressure i n the experiment was approximately 90%; 20 of the 200 plants i n any population were selected to form the next - generation, on the basis of height or flowering time i n the treatment populations, and at random i n the control populations. The P^ congesta populations responded to divergent s e l e c t i o n f o r height at anthesis, i n d i c a t i n g that genetic v a r i a b i l i t y f o r t h i s character was present i n the populations. The outcrossed l i n e s , PCO, diverged 66% or 148 mm from the control l i n e ; the s e l f e d l i n e s , PCS, diverged 78% or 175 mm. There were no s i g n i f i c a n t differences between the outcrossed and s e l f e d P. congesta l i n e s over the course of the experiment. Two estimates of narrow sense h e r i t a b i l i t y - r e a l i s e d h e r i t a b i l i t y (b^) and parent-offspring 2 : regression (h ) - quantified t h i s genetic v a r i a b i l i t y : i n PCO b^ = 0.53, - i i i 2 2 h = 0.45: i n PCS b = 0.58, h = 0.44. There was a decline i n the c phenotypic variance for height at anthesis i n the 'P_ corigesta l i n e s selected f o r t h i s character. In contrast, the P. brachystemon populations did not respond to s e l e c t i o n f o r height at anthesis, and appear to have no detectable genetic v a r i a b i l i t y f o r t h i s character. Both species appear to have s i g n i f i c a n t genetic v a r i a b i l i t y f o r flowering time, as both responded to divergent s e l e c t i o n f o r t h i s character. The PCO l i n e s diverged 33.5% or 31.8 days from the control l i n e , the PCS l i n e s diverged 28.7% or 27.3 days, and the P. brachystemon lines>"PBS,- diverged 18.5% or 21.5 days. According to the h e r i t a b i l i t y estimates, P. congesta i s more v a r i a b l e g e n e t i c a l l y : i n the PCO l i n e s b c =0.77, h 2 = 0.60; i n PCS b = 0.75, h 2 = 0.72; while i n PBS b = 0.49, and h 2 = 0.42. There c ' c was a decline i n the phenotypic variance for flowering time i n a l l three species groups. Of the other measured but unselected characters - number of days to emergence, number of nodes at anthesis, number of primary branches at anthesis, and f r u i t production - some responded to the s e l e c t i o n pressure with divergence, notably those characters which were correlated with the selected characters (for example, number of nodes at anthesis, correlated with flowering time). With others there was no change which could be a t t r i b u t e d to the s e l e c t i o n procedure. There was no evidence from two q u a l i t a t i v e characters - f r u i t wing phenotype and f r u i t pubescence pattern phenotype - f o r any response to s e l e c t i o n ; dispersion i n both characters was not s i g n i f i c a n t l y d i f f e r e n t from that expected to r e s u l t from random d r i f t . The r e l a t i v e l y high increase i n aberrant characters i n the P. congesta l i n e s compared to the P. brachystemon l i n e s i s probably i n d i c a t i v e of inbreeding depression i n the normally outcrossed P. congesta. <•,.' - i v I t appears that despite the differ e n c e i n breeding system, the two P l e c t r i t i s species are able to maintain v a r i a b i l i t y by s i m i l a r processes (genetic) i n some characters, as i n flowering time, and by d i f f e r e n t processes (genetic i n P. congesta, phenotypic i n P_. brachystemon) i n other characters, as i n height at anthesis. Thus one quantitative character, height at anthesis, follows the pattern predicted by the breeding system d i f f e r e n c e , with the outcrossed P. congesta being much more v a r i a b l e g e n e t i c a l l y than the s e l f e d P_ brachystemon. This agrees with the l e v e l s of v a r i a b i l i t y observed by Layton (1980) i n e l e c t r o p h o r e t i c a l l y detectable isozymes, and observed by Ganders and Maze (unpublished) i n m e t r i c a l f r u i t characters. The other quantitative character, flowering time, shows considerable genetic variance i n the populations of the se l f e d P^ brachystemon, though l e s s than i n the populations of P_ congesta. The maintenance of such r e l a t i v e l y high l e v e l s of genetic v a r i a b i l i t y i n the face of the strong inbreeding pressures which must be present i n P_̂_ brachystemon populations i s c e r t a i n l y adaptive, and probably comes about through occasional outcrossing and multiniche s e l e c t i o n f o r v a r i a b i l i t y among the segregating l i n e s . - V Table of Contents Abstract i i L i s t of Tables x L i s t of Figures x i Acknowledgements xv Introduction 1 Breeding system and genetic v a r i a b i l i t y 2 Th e o r e t i c a l considerations 2 Experimental evidence ..... 6 Monogenic t r a i t s 7 Quantitative t r a i t s 9 Genetic v a r i a b i l i t y and the response to s e l e c t i o n ..... 12 Th e o r e t i c a l considerations 12 Experimental evidence 14 Breeding system and the response to s e l e c t i o n 16 Th e o r e t i c a l considerations 16 Experimental evidence 17 Outcrossed taxa 18 Inbreeding taxa ..... 19 Breeding system, genetic v a r i a b i l i t y , and the response to s e l e c t i o n i n P l e c t r i t i s 21 Materials and methods 23 Source populations 23 Growing conditions 25 Measurements .. 25 - v i Breeding procedure 29 Sele c t i o n procedure ..... 32 Base population ..... 33 F i r s t cycle of s e l e c t i o n 33 Subsequent cycles of s e l e c t i o n 33 Progeny te s t and outcrossing rates i n P_j_ congesta 35 Data treatment and analyses 35 M e t r i c a l characters 36 Descriptive s t a t i s t i c s 36 Comparisons between d i s t r i b u t i o n s 38 Correlations 38 H e r i t a b i l i t y estimates 38 Variance within populations 39 Other characters 39 Results 40 Breeding systems i n P l e c t r i t i s congesta and P. brachystemon ..... 40 Outcrossing rates i n the source populations ( M i l l H i l l Pk. , 1977) 40 Outcrossing rates i n the experimental populations 40 C h a r a c t e r i s t i c s of the base populations 41 Descriptive s t a t i s t i c s of the m e t r i c a l (quantitative) characters 41 Frequencies of q u a l i t a t i v e characters 44 Response to s e l e c t i o n of the selected characters 44 Height at anthesis 44 Means 44 - v i i Estimates of v a r i a b i l i t y 57 Variances 57 H e r i t a b i l i t i e s ..... 60 Components of variance 63 Other changes i n d i s t r i b u t i o n ..... 64 Days to anthesis (flowering time) 64 Means 64 Estimates of v a r i a b i l i t y 67 Variances 67 H e r i t a b i l i t i e s 67 Components of variance 70 Other changes i n d i s t r i b u t i o n ..... 70 Changes i n the unselected characters during the experiment 71 Means 71 Days to emergence 71 Height at anthesis ( i n l i n e s selected f o r flowering time) 71 Nodes at anthesis 74 Primary branches at anthesis 74 Flowering time ( i n l i n e s selected f o r height at anthesis) 79 F r u i t production 79 Estimates of v a r i a b i l i t y 84 Variances 84 H e r i t a b i l i t i e s 84 Components of variance 89 Other changes i n d i s t r i b u t i o n 89 - v i i i The e f f e c t s of s e l e c t i o n on cor r e l a t i o n s among the measured characters 92 The c o r r e l a t i o n between height at anthesis and flowering time, the characters under s e l e c t i o n ..... 92 Other c o r r e l a t i o n s 92 Changes i n q u a l i t a t i v e characters ..... 124 Winged and wingless plant frequencies 124 Pubescence patterns 125 Aberrant characters 125 Comparisons between the i n t e r n a l control populations and the source populations ..... 125 Quantitative characters 127 P l e c t r i t i s congesta 127 P l e c t r i t i s brachystemon 127 Correlations 130 Summary of r e s u l t s 132 Discussion ..... 136 The experimental species 136 Genetic v a r i a b i l i t y and the response to s e l e c t i o n ..... 136 Direc t responses 136 P l e c t r i t i s congesta outcrossed versus P. congesta s e l f e d 136 P l e c t r i t i s congesta versus P^ brachystemon ..... 137 Height at anthesis 137 Flowering time ..... 139 Confounding phenomena 140 Indi r e c t responses to s e l e c t i o n ..... 142 - i x Unselected characters 142 Other s e l e c t i o n studies 144 Independent estimates of genetic v a r i a b i l i t y i n P l e c t r i t i s 146 The e f f e c t s of breeding system on the population genetic structure of P l e c t r i t i s 149 P l e c t r i t i s brachystemon 150 P l e c t r i t i s congesta 156 L i t e r a t u r e c i t e d 163 Appendix 1: Between family/within family variance r a t i o s i n experimental populations 169 Appendix 2: C o e f f i c i e n t s of v a r i a t i o n , unselected characters ..... 172 - X L i s t of Tables Table T i t l e Page I Growing conditions 26 II Estimates of outcrossing rates i n the experimental 42 populations I I I Measured characters, base populations 43 IV Realised h e r i t a b i l i t y , c alculated using the method 61 of H i l l (1972) V H e r i t a b i l i t y , from parent-offspring regressions 62 VI H e r i t a b i l i t i e s from parent-offspring regressions, 90 unselected characters VII Frequencies of aberrant i n d i v i d u a l s 126 VIII Measured characters: G,. source populations 128 compared with G^ control populations IX Correlations i n the G,. source populations 131 - x i L i s t of Figures Figure T i t l e Page 1. Source P l e c t r i t i s populations: M i l l H i l l Pk., 24 June 1977 2 Morphology of P l e c t r i t i s 28 3 P l e c t r i t i s f r u i t wing phenotypes 30 4 F r u i t pubescence phenotypes i n winged P l e c t r i t i s 31 congesta f r u i t s 5 Experimental populations maintained through 5 34 generations of s e l e c t i o n , G^ to G,. 6 An example of data transformation procedure used 37 on m e t r i c a l characters 7 Frequency of various pubescence types i n the 46 experimental populations a. PCO populations, type 0 b. PCO populations, type 1 c. PCO populations, type 2 8 Frequency of various pubescence types i n the 48 experimental populations a. PCO populations, type 3 b. PCO populations, type 4 c. PCO populations, type 5 9 Frequency of various pubescence types i n the 50 experimental populations a. PCS populations, type 0 b. PCS populations, type 1 c. PCS populations, type 2 10 Frequency of various pubescence types i n the 52 experimental populations a. PCS populations, type 3 b. PCS populations, type 4 c. PCS populations, type 5 11 Frequency of wingless f r u i t e d plants i n the 54 experimental populations a. PCO populations b. PCS populations 12 Mean height at anthesis i n populations selected f o r height at anthesis. 56 - x i i Figure T i t l e Page 13 C o e f f i c i e n t s of v a r i a t i o n f o r height at anthesis 59 i n populations selected f o r height at anthesis 14 Mean number of days to anthesis (flowering time) 66 i n populations selected f o r flowering time 15 C o e f f i c i e n t s of v a r i a t i o n for, days to anthesis i n 69 populations selected f o r flowering time 16 Mean number of days to emergence i n various 73 populations a. Populations selected f o r flowering time b. Populations selected f o r height at anthesis 17 a. Mean height at anthesis i n populations 76 selected f o r flowering time b. Mean number of days to anthesis i n populations selected f o r height at anthesis 18 Mean number of nodes at anthesis i n various 78 populations a. Populations selected f o r flowering time b. Populations selected f o r height at anthesis 19 Mean number of primary branches at anthesis 81 i n various populations a. Populations selected f o r flowering time b. Populations selected f o r height at anthesis 20 Mean f r u i t production i n various populations 83 a. Populations selected f o r flowering time b. Populations selected f o r height at anthesis 21 C o e f f i c i e n t s of v a r i a t i o n f o r number of days to 86 emergence i n the experimental populations a. PCO b. PCS c. 'PBS 22 C o e f f i c i e n t s of v a r i a t i o n f o r number of nodes at 88 anthesis i n the experimental populations a. PCO b. PCS c. PBS 23 Correlations between height at anthesis and flowering 94 time a. PCO populations b. PCS populations c. PBS populations - x i i i Figure T i t l e Page 24 Correlations between height at anthesis and 96 number of primary branches at anthesis a. PCO populations b. PCS populations c. PBS populations 25 Correlations between number of nodes at anthesis 98 and number of primary branches at anthesis a. PCO populations b. PCS populations c. PBS populations 26 Correlations between height at anthesis and f r u i t 100 production a. PCO populations b. PCS populations c. PBS populations 27 Correlations between number of days to emergence 103 and height at anthesis a. PCO populations b. PCS populations c. PBS populations 28 Correlations between number of days to emergence 105 and number of nodes at anthesis a. PCO populations b. PCS populations c. PBS populations 29 Correlations between number of nodes at anthesis 107 and f r u i t production a. PCO populations b. PCS populations c. PBS populations 30 Correlations between number of primary branches at 109 anthesis and flowering time a. PCO populations b. PCS populations c. PBS populations 31 Correlations between number of days to emergence 111 and number of primary branches at anthesis a. PCO populations b. PCS populations c. PBS populations 32 Correlations between number of days to emergence 113 and f r u i t production a. PCO populations b. PCS populations c. PBS populations T i t l e C orrelations between flowering time and f r u i t production a. PCO populations b. PCS populations c. PBS populations Correlations between days to emergence and flowering time a. PCO populations b. PCS populations c. PBS populations Correlations between number of nodes at anthesis and flowering time a. PCO populations b. PCS populations c. PBS populations Correlations between number of primary branches at anthesis and f r u i t production a. PCO populations b. PCS populations c. PBS populations Correlations between height at anthesis and number of nodes at anthesis a. PCO populations b. PCS populations c. PBS populations - XV Acknowledgements 1 am deeply g r a t e f u l to my supervisor, Dr. Fred Ganders, for introducing me to P l e c t r i t i s , a genus of t r u l y endless i n t e r e s t . His knowledge and advice, i n t e r e s t and encouragement, and h i s willingness to discuss any aspect of the p r o j e c t , large or small, have added immeasurably to the q u a l i t y of the r e s u l t . I thank the members of my thesis committee, Dr. Tony G r i f f i t h s and Dr. Gary B r a d f i e l d , f o r t h e i r patience and advice. Their c a r e f u l and constructive c r i t i c i s m throughout have helped me to d i r e c t the research to best advantage, and to c l a r i f y and round out i t s presentation. I am g r a t e f u l to the members of the Department of .^Botany at U.B.C., whose combined excellence has i n s t r u c t e d and i n s p i r e d me. I thank the Natural Sciences and Engineering Research Council of Canada for f i n a n c i a l support i n the form of Post-graduate Scholarships and through grants to Dr. Ganders. This work would not have been the same without the patience and support of my wife, A l i c e , who kept me cheerful and o p t i m i s t i c through the more d i f f i c u l t moments, and shared my happiness when.things went w e l l . - 1 Breeding system, genetic v a r i a b i l i t y , , and response to s e l e c t i o n i n P l e c t r i t i s (Valerianaceae). Introduction Genetic v a r i a b i l i t y i n various organisms has been a major object of study since the rediscovery of Mendel's laws of inheritance and t h e i r synthesis with Darwin's theory of evolution by natural s e l e c t i o n . The kind of questions to which answers are sought include questions about the extent to which v a r i a b i l i t y i s present i n i n d i v i d u a l s , populations,.or taxa; about the ways i n which v a r i a b i l i t y i s generated, maintained, or l o s t ; and about the e f f e c t which v a r i a b i l i t y may. have on the f i t n e s s or s u r v i v a l of an i n d i v i d u a l , population, or taxon. This study deals with the following questions about.genetic v a r i a b i l i t y . F i r s t , how has the amount of genetic v a r i a b i l i t y underlying the expression of q u a n t i t a t i v e l y i n h e r i t e d characters i n a population of plants been affected by the breeding system of that population? Second, i f the breeding system has affected the amount or nature of genetic v a r i a b i l i t y , can t h i s e f f e c t be detected by observing the response to s e l e c t i o n i n two taxa between which the major b i o l o g i c a l difference i s i n t h e i r breeding system? F i n a l l y , how does the genetic v a r i a b i l i t y present i n q u a n t i t a t i v e l y i n h e r i t e d characters compare to that of other (monogenic) characters, both within and between taxa with d i f f e r e n t breeding systems? To combine the questions i n more concrete terms., i s a population of inbreeding plants more or less v a r i a b l e g e n e t i c a l l y than a population of "otherwise i d e n t i c a l " outbreeding plants with respect to q u a n t i t a t i v e l y i n h e r i t e d characters, does i t respond more or les s quickly to s e l e c t i o n pressures on these - 2 characters, and does the genetic v a r i a b i l i t y , .in multigenic characters follow the same patterns as v a r i a b i l i t y i n monogenic characters? Both t h e o r e t i c a l predictions and experimental evidence have provided some answers to a l l three of these questions.. Differences i n genetic v a r i a b i l i t y between plant species of.varied.breeding systems have been studied by population b i o l o g i s t s ; i n most cases the characters studied have been monogenic rather than q u a n t i t a t i v e l y i n h e r i t e d . Differences i n response to s e l e c t i o n are of v i t a l i n t e r e s t to plant breeders;, i n most of t h e i r studies the goals have not included assessing the e f f e c t s of the breeding systems of the plants involved, or more p a r t i c u l a r l y comparing species of d i f f e r i n g breeding system. There i s a place (not to say a gap) to be f i l l e d by s e l e c t i o n studies of q u a n t i t a t i v e l y i n h e r i t e d characters i n natural populations; i t i s to be.hoped that such studies w i l l add to what i s known about breeding systems, g e n e t i c . v a r i a b i l i t y , response to s e l e c t i o n , and the in t e r a c t i o n s among the three. Breeding system and genetic v a r i a b i l i t y T h e o retical considerations A f i r s t step i n answering questions about genetic v a r i a b i l i t y i s ne c e s s a r i l y the d e f i n i t i o n of some of the terms. G e n e t i c . v a r i a b i l i t y i s a broad term which can lead to some confusion i f loosely.applied. I t encompasses a number of parameters i n any.population, including-the numbers and frequencies of a l l e l e s at various gene l o c i , the numbers and frequencies of various genotypes, and the d i s t r i b u t i o n of genotypic components,of the t o t a l phenotypic variance for various characters. Although these parameters are not independent, they can be divided into two groups on the basis of - 3 whether or not they are subject -to s e l e c t i o n d i r e c t l y . The f i r s t group I w i l l c a l l the p o t e n t i a l components of .the genetic v a r i a b i l i t y i n a population. In the simplest genetic sense,.a gene locus i s v a r i a b l e (polymorphic) i f more than one a l l e l e occurs at i t . For any population the number and frequencies of a l l e l e s at various l o c i can t h e o r e t i c a l l y be observed. These a l l e l e s w i l l be combined to form the genotype of an i n d i v i d u a l . The number and frequencies of various genotypes i n any population can also be o b s e r v e d - t h e o r e t i c a l l y . Various indices can be derived from these types of observations; some examples which are commonly used i n studies of r e a l populations are the number or percentage of l o c i which are observed to be polymorphic, and the number of a l l e l e s per polymorphic locus. In addition,.the frequencies of genotypes expected i n a population behaving according to p a r t i c u l a r assumptions can.be .calculated. Most often the assumptions are those leading to Hardy-Weinberg ..equilibrium i n a t h e o r e t i c a l population. The populations under study may not be behaving according to the.assumptions by which the genotype frequencies have been derived. For example, i f at a p a r t i c u l a r locus a population has two a l l e l e s , and A^, then t h e o r e t i c a l l y there are three genotypes - poss i b l e . An actual population may i n f a c t be missing any one of the three genotypes (or even both'homozygous genotypes), and be l e s s v a r i a b l e i n f a c t than i t appears i n theory. Many studies of t h i s type of genetic v a r i a b i l i t y c a l c u l a t e genotype frequencies rather than observing them i n populations. Since a l l e l e s and genotypes are not selected d i r e c t l y but rather through t h e i r expression i n phenotypes, i t should be kept i n mind that i n d i c e s which compare populations on t h i s basis may not be assessing the genetic v a r i a b i l i t y a v a i l a b l e for s e l e c t i o n . This has been a p a r t i c u l a r problem i n studies dealing with isoenzymes; the s e l e c t i v e values of - 4 p a r t i c u l a r isoenzyme phenotypes are f o r the most part unknown.. I . w i l l r e f e r to-these estimates.of potential.genetic v a r i a b i l i t y .as. estimates of g e n e t i c . d i v e r s i t y (a term.which.has a more s p e c i f i c a p p l i c a t i o n i n some of the l i t e r a t u r e of population genetics). I f the contribution of various genotypes to the genotypic component of the t o t a l phenotypic variance for a p a r t i c u l a r character can be assigned a r b i t r a r i l y or determined by experiment, then one i s dealing with the second group of parameters, which I w i l l c a l l the r e a l i s e d components of the genetic v a r i a b i l i t y . For any character a p a r t i c u l a r phenotype can be assigned a numerical value, be i t a f i t n e s s value or an actual measurement (height, weight, e t c . ) , and the d i s t r i b u t i o n of these values i n a population w i l l have.a mean and a variance. The genotypic component of t h i s t o t a l phenotypic variance i s referred to as the genetic variance, and i t i s upon t h i s variance that s e l e c t i o n may act. The e f f e c t of breeding system on the p o t e n t i a l genetic v a r i a b i l i t y , or genetic d i v e r s i t y , can be predicted in.theory i f a number of assumptions are invoked. I f two populations are i n i t i a l l y i d e n t i c a l i n a l l respects, that i s , contain equal numbers and frequencies of genotypes, and are otherwise i n Hardy-Weinberg equilibrium, then breeding system differences w i l l a f f e c t them i n the following way. .The frequency of heterozygous i n d i v i d u a l s at a p a r t i c u l a r locus, and i n consequence the t o t a l number of genotypes, w i l l quickly decline i n the inbreeding or autogamous population compared to the random mating population. However, the t o t a l number and frequencies of a l l e l e s , the percentage of l o c i which are polymorphic, and the number of a l l e l e s per. polymorphic, locus w i l l remain the same, as w i l l , the genotype frequencies expected under Hardy-Weinberg, equilibrium. I f the equilibrium assumptions are relaxed, and r e a l i s t i c and f i n i t e - 5 population'size and selection, are a f f e c t i n g ..the populations, random d r i f t and s e l e c t i o n will.reduce..the.total number:of a l l e l e s i n the s e l f i n g population f a s t e r than i n the outcrossed one,, and.genetic d i v e r s i t y as measured by the percentage of l o c i polymorphic, the number of a l l e l e s per polymorphic locus, and.the expected.frequency of heterozygotes at equilibrium w i l l thus be reduced i n the s e l f e r r e l a t i v e to the outcrossed population. The degree o f . d i f f e r e n c e i n genetic d i v e r s i t y between the two populations of d i f f e r e n t breeding system w i l l depend on the d i f f e r e n c e i n t h e i r rates of inbreeding, the e f f e c t i v e population s i z e , and rates of s e l e c t i o n . The e f f e c t of the breeding system on the r e a l i s e d g e n e t i c . v a r i a b i l i t y or genetic variance can also be predicted i n theory, again subject to a number of s i m p l i f y i n g assumptions.. If we s t a r t with the same two populations as mentioned above, w i t h , i d e n t i c a l genotypic structure under Hardy-Weinberg equilibrium, then breeding system differences w i l l have the following e f f e c t s . If • the environmental component of the .total phenotypic variance i n t h i s case i s taken to be zero, then the genotypic values are contributing a l l of the phenotypic v a r i a b i l i t y . With s e l f i n g , as heterozygous genotypes are l o s t from.the population the variance of the phenotypic values w i l l increase r e l a t i v e to a random mating population. Thus inbreeding on i t s own w i l l increase genetic variance. . I f we again relax the equilibrium assumptions by assuming r e a l i s t i c f i n i t e populations on which s e l e c t i o n i s acting, then the t h e o r e t i c a l p r e d i c t i o n becomes rather problematical. The r e l a t i v e l y larger loss of a l l e l e s due'to random d r i f t and s e l e c t i o n i n f i n i t e populations of s e l f e r s w i l l tend.to reduce the genetic variance. Simultaneously, inbreeding.will increase the genetic variance r e l a t i v e to a random mating population. The - 6 e f f e c t s on g e n e t i c v a r i a n c e o f i n b r e e d i n g and random d r i f t / s e l e c t i o n w i l l be i n o p p o s i t e d i r e c t i o n s , and t h e n e t e f f e c t cannot be g e n e r a l i z e d . Lande Q.977) has p r o p o s e d a model w h i c h i n d i c a t e s t h a t i f the p o p u l a t i o n s a r e l a r g e C i n f i n i t e ) , b u t w i t h s e l e c t i o n and m u t a t i o n a c t i n g , t h e n t h e b r e e d i n g s y s t e m w i l l have no e f f e c t on the amount o f a d d i t i v e g e n e t i c v a r i a n c e m a i n t a i n e d . To summarize, such t h e o r e t i c a l t r e a t m e n t s of r e a l i s t i c p o p u l a t i o n s ( w i t h o u t e x t e n s i v e s i m p l i f y i n g a s s u m p t i o n s ) as a r e a v a i l a b l e s h o u l d be g e n e r a l i z e d w i t h c a u t i o n . N e v e r t h e l e s s , compared t o random m a t i n g , s e l f i n g i n f i n i t e p o p u l a t i o n s i s l i k e l y , t o l e a d t o a l o s s of g e n e t i c d i v e r s i t y , and w h e t h e r t h i s i s accompanied by a n e t r e d u c t i o n i n g e n e t i c v a r i a n c e w i l l depend on f a c t o r s u n r e l a t e d t o t h e b r e e d i n g s y s t e m , s u c h as p o p u l a t i o n s i z e and s e l e c t i o n p r e s s u r e s . E x p e r i m e n t a l e v i d e n c e V a r i a b i l i t y has been s t u d i e d i n p o p u l a t i o n s o f many p l a n t s p e c i e s , b o t h n a t u r a l and d o m e s t i c a t e d . D i s c o n t i n u i t i e s i n v a r i a t i o n p a t t e r n s between t a x a f o r m t h e b a s i s f o r taxonomic s t u d i e s ; g e n e t i c v a r i a b i l i t y i s t h e s o u r c e o f improvement by p l a n t b r e e d e r s i n e c o n o m i c a l l y i m p o r t a n t s p e c i e s ; and t h e i n t e r a c t i o n o f g e n e t i c v a r i a t i o n and n a t u r a l s e l e c t i o n i s t h e ' o b j e c t o f e v o l u t i o n a r y s t u d i e s . S t u d i e s s p e c i f i c a l l y i s o l a t i n g b r e e d i n g s y s t e m and g e n e t i c v a r i a b i l i t y a r e l i m i t e d , and c o mparisons between c l o s e l y r e l a t e d s p e c i e s d i f f e r i n g i n b r e e d i n g s y s t e m a r e as y e t v e r y few. The e x p e r i m e n t a l e v i d e n c e r e l a t i n g b r e e d i n g s y s t e m and g e n e t i c v a r i a b i l i t y can be d i v i d e d i n t o two groups i n w h i c h t h e e s t i m a t e s of g e n e t i c v a r i a b i l i t y r o u g h l y p a r a l l e l t h o s e o u t l i n e d e a r l i e r as g e n e t i c d i v e r s i t y and g e n e t i c v a r i a n c e . The f i r s t group c o n s i s t s o f e v i d e n c e f r o m monogenic o r s i n g l e l o c u s t r a i t s , whose q u a l i t a t i v e n a t u r e makes assignment o f s p e c i f i c p h e n o t y p i c v a l u e s , and t h u s p o p u l a t i o n p a r a m e t e r s s u c h as mean v a l u e and v a r i a n c e , d i f f i c u l t . I n some c a s e s f i t n e s s v a l u e s have been e s t i m a t e d e x p e r i m e n t a l l y , b u t f o r t h e most p a r t t h e e x p e r i m e n t a l e v i d e n c e i s i n the f o r m o f e s t i m a t e s of g e n e t i c d i v e r s i t y s u c h as a l l e l e and genotype f r e q u e n c i e s , and i n d i c e s s u c h as the p e r c e n t a g e of l o c i p o l y m o r p h i c and number o f a l l e l e s p e r p o l y m o r p h i c l o c u s . The second group c o n s i s t s o f e v i d e n c e f r o m c h a r a c t e r s w h i c h a r e known o r assumed t o be m u l t i g e n i c , o r q u a n t i t a t i v e l y i n h e r i t e d . F o r t h e s e c h a r a c t e r s t h e e s t i m a t e s a r e a p p r o x i m a t e l y e s t i m a t e s o f g e n e t i c v a r i a n c e , a l t h o u g h as w i l l be seen t h e y may r e q u i r e f a i r l y e l a b o r a t e e x p e r i m e n t a l d e s i g n s t o e l i m i n a t e e n v i r o n m e n t a l components o f the v a r i a n c e and o b t a i n more e x a c t e s t i m a t e s o f t h e g e n e t i c v a r i a n c e . Monogenic t r a i t s Because o f the ease w i t h w h i c h r e l a t i v e l y l a r g e numbers o f c h a r a c t e r s can be s t u d i e d , the b u l k , o f s t u d i e s a l l o w i n g a c o m p a r i s o n o f b r e e d i n g s y s t e m and g e n e t i c v a r i a b i l i t y i n monogenic c h a r a c t e r s i n v o l v e e l e c t r o p h o r - e t i c a l l y d e t e c t a b l e enzyme v a r i a t i o n . H a m rick e t a l . (1979) have r e v i e w e d the i sozyme d a t a r e c e n t l y , r e l a t i n g l e v e l s o f e l e c t r o p h o r e t i c v a r i a t i o n C g e n e t i c d i v e r s i t y ) and l i f e h i s t o r y c h a r a c t e r i s t i c s i n a l a r g e number o f p l a n t s p e c i e s . They r e p o r t t h a t f o r t h r e e i n d i c e s of d i v e r s i t y - p e r c e n t a g e o f l o c i p o l y m o r p h i c , number o f a l l e l e s p e r p o l y m o r p h i c l o c u s , and a p o l y m o r p h i c i n d e x C f r e q u e n c y o f h e t e r o z y g o t e s e x p e c t e d under Hardy-- Weinberg e q u i l i b r i u m ) - 36 p r i m a r i l y o u t c r o s s e d s p e c i e s showed more d i v e r s i t y t h a n 33 p r i m a r i l y s e l f e d s p e c i e s . F o r t h e most p a r t t h e s e d a t a combine - 8 r e l a t i v e l y u n r e l a t e d t a x a i n each b r e e d i n g s y s t e m group, b u t t h e r e a r e some comparisons w h i c h may be n o t e d . F o r example, groups of c o n g e n e r i c s p e c i e s i n w h i c h l e v e l s o f g e n e t i c d i v e r s i t y have been c o n f i r m e d t o be h i g h e r i n the o u t c r o s s e d s p e c i e s t h a n i n t h e s e l f e d s p e c i e s i n c l u d e : L i mnanthes a l b a ( o u t c r o s s e d ) and L. f l o c c o s a ( s e l f e d ) CBrown and J a i n , " 1 9 7 9 ) ; C l a r k i a r u b i c u n d a, C. amoena ( o u t c r o s s e d ) , and C_. f r a r i c i s c a n a ( s e l f e d ) ( G o t t l i e b , 19 73) ; Gaura s u f f u l t a ( o u t c r o s s e d ) and Gy t r i a r i g u l a t a ( s e l f e d ) ( L e v i n , 1975) ; P h l o x d r u m i i i o n d i i , P_.̂  r o e m a r j a n a ( o u t c r o s s e d ) , and P_j_ c u s p i d a t a ( s e l f e d ) (Le-yin, 1 9 7 8 ) ; L e a v e n w o r t h i a a l a b a r n i c a , L. c r a s s a , L. s t y l o s a ( o u t c r o s s e d ) , L. u r i i f l o r a , \'h. e x j g u a , "and L. t o r u l o s a ( s e l f e d ) ( S o l b r i g , 1972) ; L y c o p e r s i c o n p i m p i n e l l j f o l i u m ( o u t c r o s s e d ) ( R i c k e t a l . , 1977) and L. p a r v i f l o r u m ( s e l f e d ) ( R i c k and Fobes, 1975). A t t h e c o n s p e c i f i c l e v e l , p o p u l a t i o n s o f L y c o p e r s i c o n p i m p i n e l l j f o l i u m v a r y i n b r e e d i n g s y s t e m from r e l a t i v e l y o u t c r o s s e d t o r e l a t i v e l y s e l f e d , and t h e more h i g h l y o u t c r o s s e d p o p u l a t i o n s have h i g h e r l e v e l s o f g e n e t i c d i v e r s i t y ( R i c k e t a l . , 1 9 7 7 ) . • L n O e n o t h e r a , E l l s t r a n d and L e v i n (1980) found t h a t t h e r e was a s i g n i f i c a n t d i f f e r e n c e i n gene d i v e r s i t y between t h e more d i v e r s e , o u t c r o s s e d 0. g r a n d i s and the s e l f e d 0. me x i c a n a . A t h i r d s p e c i e s , 0. 1 a c i n i a t a , w h i c h i s h i g h l y i n b r e d b u t a permanent t r a n s l o c a t i o n h e t e r o z y g o t e , has r e l a t i v e l y h i g h d i v e r s i t y , n o t s i g n i f i c a n t l y d i f f e r e n t f r o m 0. g r a n d i s . Of p a r t i c u l a r i n t e r e s t i s the s t u d y o f t h e two c l o s e l y r e l a t e d s p e c i e s P l e c t r i t i s c o n g e s t a and P_j_ b r a c h y s t e m o n , w h i c h i n d i c a t e d t h a t t h e o u t c r o s s e d P_̂_ c o n g e s t a has much h i g h e r l e v e l s o f g e n e t i c d i v e r s i t y as i n d i c a t e d by isozyme d a t a t h a n t h e s e l f e d P. b r a c h y s t e m o n ( L a y t o n , 1980). There a r e few e r s t u d i e s o f o t h e r t y p e s o f monogenic c h a r a c t e r s , p a r t i c u l a r l y i n c l o s e l y r e l a t e d t a x a o f d i f f e r e n t b r e e d i n g s y s t e m s . J a i n and M a r s h a l l (1967) found t h a t Avena f a t u a , w h i c h has a s l i g h f l y h i g h e r - 9 o u t c r o s s i n g r a t e t h a n i t s r e l a t i v e A. b a f b a t a , was p o l y m o r p h i c a t t h r e e m o r p h o l o g i c a l l y e x p r e s s e d l o c i , w h i l e A. b a r b a t a was monomorphic a t t h e same l o c i . However, w h i l e t h e r e i s a s l i g h t d i f f e r e n c e i n b r e e d i n g s y s t e m between them, b o t h Avena s p e c i e s a r e r e l a t i v e l y h i g h l y s e l f e d . I n o u t c r o s s e d P l e c t r i t i s c o n g e s t a , p o p u l a t i o n s p o l y m o r p h i c f o r a monogenic f r u i t w i n g c h a r a c t e r a r e much more common C30 p o p u l a t i o n s p o l y m o r p h i c o f 32 s t u d i e d ) t h a n i n s e l f e d P. brac h y s t e m o n C3 o f 11 p o p u l a t i o n s ) (Ganders e t a l . , 1977b; Carey and Ganders, 1980) . I n L y c o p e r s i c o n p i m p i n e l l i f o l i u m , R i c k e t a l . CL977) f o u n d t h a t two monogenic m o r p h o l o g i c a l c h a r a c t e r s showed t h e i r h i g h e s t l e v e l s o f p o l y m o r p h i s m i n p o p u l a t i o n s w i t h t h e h i g h e s t o u t c r o s s i n g r a t e s and were monomorphic i n p o p u l a t i o n s w h i c h were r e l a t i v e l y h i g h l y s e l f e d . A l l o f t h e e v i d e n c e from monogenic t r a i t s s u g g e s t s t h a t s e l f i n g r educes t h e g e n e t i c d i v e r s i t y r e l a t i v e t o a comparable o u t c r o s s e d p o p u l a t i o n (most o f t h i s e v i d e n c e comes f r o m isozyme l o c i , w h i c h may or may n o t be r e p r e s e n t a t i v e o f a l l l o c i ) . T h i s i s i n agreement w i t h t h e t h e o r e t i c a l p r e d i c t i o n s . Q u a n t i t a t i v e t r a i t s D a t a on the g e n e t i c v a r i a b i l i t y o f m u l t i g e n i c o r q u a n t i t a t i v e c h a r a c t e r s i n s e l f e d o r o u t c r o s s e d s p e c i e s a r e l e s s s t r a i g h t f o r w a r d t h a n t h o s e on monogenic t r a i t s . F i r s t , many o f t h e s e c h a r a c t e r s a r e assumed, r a t h e r t h a n known, t o be m u l t i g e n i c . They might more a c c u r a t e l y be termed m e t r i c a l o r c o n t i n u o u s l y d i s t r i b u t e d t r a i t s . Second, t h e s e c h a r a c t e r s a r e i n v a r i a b l y confounded by an e n v i r o n m e n t a l component w h i c h may be d i f f i c u l t t o remove e x c e p t i n l a r g e s c a l e , c a r e f u l l y d e s i g n e d e x p e r i m e n t s . T h i r d , e s t i m a t e s o f g e n e t i c v a r i a b i l i t y f r o m t h e s e c h a r a c t e r s a r e f u r t h e r removed f r o m t h e genome t h a n t h o s e f r o m monogenic c h a r a c t e r s ; t h a t i s , a l l e l e f r e q u e n c i e s , r 10 p o l y m o r p h i c l o c i , and r a t e s o f h e t e r o z y g o s i t y a r e r a r e l y d i s c e r n i b l e d i r e c t l y f r o m measurements of t h e s e c h a r a c t e r s u n l e s s e x t e n s i v e g e n e t i c s t u d y has been done. F o r t h e s e r e a s o n s a r e v i e w w h i c h b r i n g s t o g e t h e r d a t a on v a r i o u s t a x a f r o m many s t u d i e s , s u c h as t h a t o f Hamrick e t a l . • C1979) f o r isozyme d a t a , i s n o t f e a s i b l e , as t h e r e i s l i t t l e a s s u r a n c e t h a t the measurements o f g e n e t i c v a r i a b i l i t y f rom a wide v a r i e t y o f m e t r i c a l c h a r a c t e r s under d i f f e r e n t e x p e r i m e n t a l d e s i g n s can v a l i d l y be compared. F i n a l l y , as w i t h monogenic t r a i t s , t h e r e have been o n l y a l i m i t e d number o f s t u d i e s o f c l o s e l y r e l a t e d t a x a w i t h . ' d i f f e r e n t - b r e e d i n g . - s y s t e m s . I w i l l examine a few of t h e s e a t t h i s p o i n t . I n most cases the v a r i a b i l i t y t h a t has been measured has n o t been p a r t i t i o n e d i n t o g e n e t i c and e n v i r o n m e n t a l components, and t h e a c t u a l measurements a r e o f p h e n o t y p i c v a r i a n c e , f r o m w h i c h e s t i m a t e s o f t h e g e n e t i c v a r i a b i l i t y have been e x t r a p o l a t e d , I w i l l r e f e r t o i t as g e n e t i c v a r i a b i l i t y , a l t h o u g h one may hope t h a t g e n e t i c v a r i a n c e i s b e i n g e s t i m a t e d a p p r o x i m a t e l y . I n some c a s e s no s i g n i f i c a n t d i f f e r e n c e between t a x a w i t h d i f f e r e n t b r e e d i n g systems was f o u n d . Brown and J a i n (1979) s t u d i e d 15 q u a n t i t a t i v e c h a r a c t e r s i n Limrianthes a l b a ( o u t c r o s s e d ) and L. f l o c c o s a ( s e l f e d ) and c o n c l u d e d t h a t b o t h t h e t o t a l amount o f g e n e t i c v a r i a b i l i t y and t h e p a r t i t i o n i n g o f t h e v a r i a b i l i t y w i t h i n t h e t a x a ( t h a t i s , w i t h i n and between p o p u l a t i o n s o f t h e t a x a ) were n o t s i g n i f i c a n t l y d i f f e r e n t between them. T h i s i s i n c o n t r a s t t o the s i t u a t i o n found i n the i s o z y m e s i n t h e s e two s p e c i e s , d e s c r i b e d above ( p . 9 ) . S t u d y i n g t h e L u p i n u s nanus g r o u p , w h i c h i n c l u d e d f o u r L. nanus s u b s p e c i e s and two o t h e r s p e c i e s w i t h o u t c r o s s i n g r a t e s between 0 and 100%, H a r d i n g e t a l . (1974) found no c o r r e l a t i o n between t h e o u t c r o s s i n g r a t e and the amount o f g e n e t i c v a r i a b i l i t y ( i n t h i s case e s t i m a t e d g e n e t i c v a r i a n c e ) f o r s i x q u a n t i t a t i v e c h a r a c t e r s . I n t h r e e - 11 g r a s s s p e c i e s j Fe.sttj.ca m i c f o s t a c h y s C c o m p l e t e l y • s e l f ed) , Averia f a t u a ( h i g h l y s e l f e d ) , and L o l i u m m t i l t i f l o r u m (.outcrossed) , Kannenberg and A l l a r d (1967) f o u n d no d i f f e r e n c e among t h e t h r e e s p e c i e s i n g e n e t i c v a r i a n c e f o r t h r e e q u a n t i t a t i v e c h a r a c t e r s . I n some cases t h e more h i g h l y o u t c r o s s e d s p e c i e s appears t o be more v a r i a b l e . I n L y c o p e r s i c o n p i m p i n e l l i f o l i u m R i c k e t a l . (1977) n o t e d t h a t s e v e r a l q u a n t i t a t i v e c h a r a c t e r s showed maximum v a r i a b i l i t y i n g e o g r a p h i c a r e a s w h i c h c o i n c i d e d w i t h maximum isozyme d i v e r s i t y and maximum o u t c r o s s i n g r a t e , and minimum v a r i a b i l i t y i n a r e a s w i t h minimum o u t c r o s s i n g r a t e s ; t h e s e o b s e r v a t i o n s were u n f o r t u n a t e l y n o t b a s e d on a c t u a l measurements o f the c h a r a c t e r s c o n c e r n e d . S t r i d . ' ( 1 9 70) n o t e d t h a t p o p u l a t i o n s o f N i g e l l a d e g e n i i . an o u t c r o s s e d s p e c i e s , showed more v a r i a b i l i t y i n f l o w e r i n g time and p e r c e n t a g e of good p o l l e n t h a n N. d O e r f l e r i , a s e l f e d s p e c i e s , b u t a g a i n no measurements o f t h e c h a r a c t e r s have been r e p o r t e d . I n S t e p h a n o m e r i a e x j g u a s s p . c o r o n a r i a , an o u t c r o s s e d s p e c i e s , and i t s o b l i g a t e l y s e l f e d d e r i v a t i v e S. m a l h e u r e n s i s , G o t t l i e b (1977) measured 33 q u a n t i t a t i v e t r a i t s and f ound 90% o f them t o be more v a r i a b l e i n the o u t c r o s s e r . These d a t a must, however, be v i e w e d k e e p i n g i n mind t h a t m a l h e u r e n s i s i s a r e c e n t l y e v o l v e d t a x o n whose p o p u l a t i o n g e n e t i c s t r u c t u r e i s p r o b a b l y s t i l l e x t e n s i v e l y s u b j e c t t o phenomena s u c h as t h e f o u n d e r e f f e c t , w h i c h a l s o l i m i t g e n e t i c v a r i a b i l i t y . I n Ayena f a t u a and A. b arb a t a J a i n and M a r s h a l l (1967) s t u d i e d 3 q u a n t i t a t i v e c h a r a c t e r s and f ound more g e n e t i c v a r i a n c e i n t h e " o u t c r o s s e d " A. f a t u a t h a n i n A. b a r b a t a , b u t as n o t e d above, b o t h s p e c i e s are a c t u a l l y h i g h l y s e l f e d , and t h e c o m p a r i s o n i s l e s s u s e f u l . i n t h i s i n s t a n c e . Rogers(1971) f o u n d i n P a p a y e r rhoeas ( o u t c r o s s e d ) , P. dubium, and P. l e c o q l i ( s e l f e d ) t h a t the o u t c r o s s e d s p e c i e s showed more w i t h i n p o p u l a t i o n v a r i a b i l i t y t h a n between p o p u l a t i o n v a r i a b i l i t y f o r two q u a n t i t a t i v e c h a r a c t e r s , and t h a t t h e s e l f e d s p e c i e s showed the r e v e r s e , t h a t i s l e s s - 12 w i t h i n p o p u l a t i o n v a r i a b i l i t y and more between p o p u l a t i o n s . I t i s u n c l e a r w h e t h e r t h e o v e r a l l v a r i a b i l i t y was g r e a t e r w i t h i n t h e o u t c r o s s e d t h a n w i t h i n t h e s e l f e d s p e c i e s . B a k e r (1953) s t u d i e d a s i m i l a r s i t u a t i o n i n A r m e r i a , l o o k i n g a t s e v e r a l q u a n t i t a t i v e c h a r a c t e r s i n A. m a r i t i m a s s p . m a r i t i m a ( s e l f i n c o m p a t i b l e ) and'A: m a r i t i m a s s p . c a l i f o r n i c a ( s e l f c o m p a t i b l e but more o r l e s s o u t c r o s s e d ) where he found t h a t t h e f o r m e r , more h i g h l y o u t c r o s s e d .taxon was more v a r i a b l e w i t h i n t h a n between p o p u l a t i o n s , and the l a t t e r , more h i g h l y s e l f e d t a x o n more v a r i a b l e between t h a n w i t h i n p o p u l a t i o n s . I n a d d i t i o n , he found t h a t A . . m a r i t i m a s s p . m a r i t i m a showed more g e n e t i c v a r i a b i l i t y i n t o t o t h a n A. m a r i t i m a s s p . c a l i f o r n i c a . I n P l e c t r i t i s c o n g e s t a and P. b r a c h y s t e m o n , a s t u d y o f a number o f m o r p h o m e t r i c f r u i t c h a r a c t e r s by Ganders and Maze ( u n p u b l i s h e d ) showed t h e o u t c r o s s e d P. c o n g e s t a t o be more v a r i a b l e t h a n t h e s e l f e d P. b r a c h y s t e m o n . F i n a l l y t h e r e a r e cases where t h e s e l f e d t a x o n i s a p p a r e n t l y more v a r i a b l e t h a n i t s o u t c r o s s e d r e l a t i v e . H i l l e l e t a l . (1973) s t u d i e d 36 q u a n t i t a t i v e c h a r a c t e r s i n T r i t i c u m s p e l t o i d e s , ( o u t c r o s s e d ) and T. l o n g i s s i m u m ( s e l f e d ) and c o n c l u d e d t h a t t h e s e l f e d s p e c i e s showed g r e a t e r g e n e t i c v a r i a b i l i t y w i t h i n f a m i l i e s and w i t h i n and between p o p u l a t i o n s t h a n the o u t c r o s s e d s p e c i e s . The o v e r a l l i m p r e s s i o n from t h e e v i d e n c e of g e n e t i c v a r i a b i l i t y i n q u a n t i t a t i v e c h a r a c t e r s i s t h a t t h e e f f e c t o f a p a r t i c u l a r b r e e d i n g s y s t e m i s i n f a c t d i f f i c u l t t o p r e d i c t . S i n c e i n most o f the cases p r e s e n t e d h e r e the e s t i m a t e o f g e n e t i c v a r i a n c e i s n o t an a c c u r a t e one, i t i s p o s s i b l e t h a t d i f f e r e n c e s i n the e n v i r o n m e n t a l component o f the t o t a l v a r i a n c e may be a f f e c t i n g the c o m p a r i s o n . G e n e t i c v a r i a b i l i t y and t h e r e s p o n s e t o d i r e c t i o n a l s e l e c t i o n T h e o r e t i c a l c o n s i d e r a t i o n s - 13 Can the r e s p o n s e t o s e l e c t i o n f o r a p a r t i c u l a r c h a r a c t e r be p r e d i c t e d b y an i n d e p e n d e n t e s t i m a t e o f g e n e t i c v a r i a b i l i t y ? A g a i n , as w i t h the f i r s t q u e s t i o n , i t i s n e c e s s a r y at the o u t s e t t o d e f i n e some terms. S e l e c t i o n i s any p r o c e s s i n a p o p u l a t i o n w h i c h d i v i d e s t h o s e i n d i v i d u a l s s u r v i v i n g t o r e p r o d u c e f r o m t h o s e w h i c h do n o t s u r v i v e t o r e p r o d u c e i n Some way o t h e r t h a n randomly. D i r e c t i o n a l s e l e c t i o n f o r a c h a r a c t e r i s the d i f f e r e n t i a l s u r v i v a l o f i n d i v i d u a l s whose p h e n o t y p i c e x p r e s s i o n f o r t h a t c h a r a c t e r i s d i f f e r e n t f r o m t h e p o p u l a t i o n mean i n one d i r e c t i o n . Response t o s e l e c t i o n i s f u n d a m e n t a l l y any change i n t h e g e n e t i c s t r u c t u r e o f a p o p u l a t i o n w h i c h can be a t t r i b u t e d t o s e l e c t i o n p r e s s u r e . S e l e c t i o n a c t s on p h e n o t y p e s , b u t the d i r e c t r e s p o n s e t o s e l e c t i o n , i f any, t a k e s p l a c e i n t h e genotypes i n a p o p u l a t i o n . I t i s because g e n o t y p i c changes i n a p o p u l a t i o n a r e r e f l e c t e d i n the t o t a l p o p u l a t i o n phenotype t h a t s e l e c t i o n r e s p o n s e s can be o b s e r v e d , and i n t h e case o f l o n g term s e l e c t i o n , t h a t the s e l e c t i o n p r o c e s s can c o n t i n u e . These r e s p o n s e s a r e u s u a l l y o b s e r v e d as changes i n p o p u l a t i o n mean and v a r i a n c e f o r thos e c h a r a c t e r s w h i c h a re q u a n t i t a t i v e l y i n h e r i t e d , o r as changes i n a l l e l e o r genotype f r e q u e n c i e s f o r c h a r a c t e r s whose genotype i s d i r e c t l y o b s e r v a b l e i n the phenotype o f an i n d i v i d u a l . F i s h e r ' s f u n d a m e n t a l theorem o f n a t u r a l s e l e c t i o n s t a t e s t h a t the r e s p o n s e t o s e l e c t i o n f o r a c h a r a c t e r i n a p o p u l a t i o n i s d i r e c t l y p r o p o r t i o n a l t o the g e n e t i c v a r i a n c e f o r t h a t c h a r a c t e r i n t h e p o p u l a t i o n . Of i n t e r e s t a t t h i s p o i n t i s t h e p r e d i c t i o n o f r e s p o n s e t o s e l e c t i o n f o r a c h a r a c t e r on t h e b a s i s o f e s t i m a t e s o f g e n e t i c v a r i a b i l i t y i n i n d e p e n d e n t c h a r a c t e r s . T h i s i s n o t p o s s i b l e i n t h e o r y u n l e s s some a s s u m p t i o n s a r e made about t h e e x t e n t t o w h i c h p a r t i c u l a r c h a r a c t e r s a r e r e p r e s e n t a t i v e o f the genome as a whole. We c o u l d assume t h a t c h a r a c t e r s f o r w h i c h we have e s t i m a t e s o f g e n e t i c V v a r i a b i l i t y a r e c o m p l e t e l y r e p r e s e n t a t i v e o f c h a r a c t e r s w h i c h m i g h t be - 14 s u b j e c t t o s e l e c t i o n . The success- o f t h e p r e d i c t i o n i n t h i s case w i l l depend once a g a i n on whether our e s t i m a t e i s o f g e n e t i c d i v e r s i t y o r o f g e n e t i c v a r i a n c e . ' As o u t l i n e d e a r l i e r , e s t i m a t e s o f g e n e t i c d i v e r s i t y do n o t n e c e s s a r i l y measure v a r i a b i l i t y w h i c h i s a v a i l a b l e f o r s e l e c t i o n t o a c t upon, whereas g e n e t i c v a r i a n c e e s t i m a t e s do. > Even g e n e t i c v a r i a n c e e s t i m a t e s n e g l e c t the e n v i r o n m e n t a l component, w h i c h may be so l a r g e a component o f the t o t a l p h e n o t y p i c v a r i a b i l i t y upon w h i c h s e l e c t i o n a c t s d i r e c t l y as t o confound any p r e d i c t i o n . A r i g o r o u s t h e o r e t i c a l t r e a t m e n t o f t h e q u e s t i o n has n o t y e t been p r o d u c e d . N e v e r t h e l e s s , a l l other.<things B e i n g e q u a l ( r a t e .of s e l e c t i o n , p o p u l a t i o n s i z e , b r e e d i n g s y s t e m ) , a p o p u l a t i o n w h i c h has more g e n e t i c d i v e r s i t y would be e x p e c t e d i n g e n e r a l t o a l s o have g r e a t e r g e n e t i c v a r i a n c e , and t o r e s p o n d f a s t e r t o s e l e c t i o n t h a n one w i t h l e s s g e n e t i c d i v e r s i t y . S i m i l a r l y , a p o p u l a t i o n w h i c h has g r e a t e r g e n e t i c v a r i a n c e i n some c h a r a c t e r s c o u l d be p r e d i c t e d t o have g r e a t e r g e n e t i c v a r i a n c e i n o t h e r f c h a r a c t e r s , w h i c h when s e l e c t e d w o u l d show a g r e a t e r r e s p o n s e . E x p e r i m e n t a l e v i d e n c e There i s ample e v i d e n c e f o r r e s p o n s e t o a r t i f i c i a l s e l e c t i o n i n a b r o a d sense i n many o r g a n i s m s . The d o m e s t i c a t i o n of hundreds of p l a n t and a n i m a l s p e c i e s f o r human p u r p o s e s has i n a l m o s t e v e r y case i n v o l v e d changes i n what are now t h e d o m e s t i c t a x a , sometimes t o t h e p o i n t where f e r a l r e l a t i v e s are unknown o r so d i f f e r e n t f r o m t h e i r d o m e s t i c a t e d d e r i v a t i v e s as t o make the o r i g i n s o f t h e l a t t e r e x t r e m e l y d i f f i c u l t t o t r a c e . U n f o r t u n a t e l y , t h e s e l e c t i o n i n v o l v e d i n t h e s e , o f t e n p r e h i s t o r i c , d o m e s t i c a t i o n s has n o t been documented i n a manner t o make t h e m . u s e f u l i n - 15 t h i s s t u d y . A r t i f i c i a l s e l e c t i o n , t h a t i s s e l e c t i o n under t h e c o n t r o l o f humans, s h o u l d be c o n s i d e r e d as two s e p a r a t e k i n d s o f p r o c e s s . The f i r s t i s an a t t e m p t t o d u p l i c a t e the p r o c e s s e s of n a t u r a l s e l e c t i o n , u s u a l l y i n o r d e r t o u n d e r s t a n d what i s g o i n g on i n n a t u r e , and i n v o l v e s s e l e c t i n g i n d i v i d u a l s by t h e i r phenotype i n one g e n e r a t i o n (mass s e l e c t i o n ) , b r e e d i n g them i n some n a t u r a l m a t i n g s y s t e m , and f o r m i n g the subsequent g e n e r a t i o n f r o m t h e i r p rogeny. The second t y p e of a r t i f i c i a l s e l e c t i o n i s e c o n o m i c a l l y m o t i v a t e d and aimed at p r o d u c i n g p a r t i c u l a r s u p e r i o r genotypes o r p o p u l a t i o n s o f genotypes i n c r o p p l a n t s and a n i m a l s i n t h e f a s t e s t and most e c o n o m i c a l way. I n d i v i d u a l o r mass s e l e c t i o n i s o n l y one o f many s e l e c t i o n schemes w h i c h may be u s e d , i n c o m b i n a t i o n w i t h c a r e f u l b r e e d i n g programs, t o i s o l a t e t h a t p o r t i o n o f t h e a v a i l a b l e g e n e t i c v a r i a b i l i t y w h i c h r e p r e s e n t s the s u p e r i o r g e n o t y p e ( s ) . S p e c i a l b r e e d i n g t e c h n i q u e s ( d i a l l e l c r o s s e s , i n b r e e d i n g , s i b m a t i n g s , back c r o s s e s , e t c . ) and s e l e c t i o n r egimes ( r e c u r r e n t s e l e c t i o n , progeny t e s t i n g , e t c . ) a r e u s u a l l y employed t o i n c r e a s e s e l e c t a b l e v a r i a t i o n and speed up s e l e c t i o n f o r economic r e a s o n s - a r t i f i c i a l s e l e c t i o n w h i c h a p p r o x i m a t e s n a t u r a l s e l e c t i o n i s o f t e n a r e l a t i v e l y s l o w e r p r o c e s s . The two t y p e s o f a r t i f i c i a l s e l e c t i o n a r e n o t m u t u a l l y e x c l u s i v e , t h a t i s v a l u a b l e i n f o r m a t i o n about n a t u r a l s e l e c t i o n can be o b t a i n e d f r o m p l a n t and a n i m a l b r e e d i n g s t u d i e s , and r e l a t i v e l y n a t u r a l s e l e c t i o n schemes may produce e c o n o m i c a l l y v a l u a b l e r e s u l t s i n some c a s e s . To h e l p answer t h e q u e s t i o n s about s e l e c t i o n , g e n e t i c v a r i a b i l i t y , and b r e e d i n g s y s t e m as p o s e d , t h e e v i d e n c e we r e q u i r e s h o u l d i d e a l l y come fr o m s e l e c t i o n e x p e r i m e n t s where t h e r e i s an i n d e p e n d e n t e s t i m a t e o f g e n e t i c v a r i a b i l i t y f o r the o r g a n i s m , where t h e o r g a n i s m s t u d i e d has a known b r e e d i n g s y s t e m , and where the i n i t i a l p o p u l a t i o n s under s e l e c t i o n have n o t been - 1 6 b r e d t o change t h e i r n a t u r a l l e v e l s o f y a r l a b i l i t y , f o r example by I n b r e e d i n g an o u t c r o s s e d s p e c i e s o r c r o s s i n g a s e l f e d s p e c i e s . I n a d d i t i o n , f o r t h e p u r p o s e s o f c o m p a r i s o n t o t h e s t u d y u n d e r t a k e n h e r e , t h e s e l e c t i o n method s h o u l d be comparable (mass s e l e c t i o n ) . I have been a b l e t o f i n d o n l y one e x p e r i m e n t where s e l e c t i o n f o r a c h a r a c t e r has been p e r f o r m e d on two t a x a f o r w h i c h e s t i m a t e s o f g e n e t i c d i v e r s i t y o r v a r i a n c e f r o m an i n d e p e n d e n t s o u r c e a r e a v a i l a b l e . J a i n and M a r s h a l l (1970) s e l e c t e d f o r two extremes of h e a d i n g d a t e and seed s i z e i n Avena f a t u a and A. b a r b a t a . These a r e two s p e c i e s f o r w h i c h measurements o f g e n e t i c d i v e r s i t y from i s o z y m e s ( M a r s h a l l and J a i n , 1969) and g e n e t i c v a r i a n c e i n o t h e r c h a r a c t e r s ( J a i n and M a r s h a l l , 1967) a r e a v a i l a b l e , and i n b o t h c a s e s A. f a t u a has been shown t o be t h e more v a r i a b l e s p e c i e s . A. f a t u a responded b e t t e r t o s e l e c t i o n f o r b o t h c h a r a c t e r s , and t h i s r e s u l t a g r e es w i t h t h e p r e d i c t i o n b a s e d on t h e i n d e p e n d e n t e s t i m a t e o f g e n e t i c v a r i a b i l i t y . S e l e c t i o n r e s p o n s e i s s u f f i c i e n t l y u b i q u i t o u s t h a t c a r e f u l c o mparisons s u c h as t h i s a re t h e o n l y ones o f r e a l v a l u e i n a n s w e r i n g t h i s q u e s t i o n . B r e e d i n g s y s t e m and t h e r e s p o n s e t o s e l e c t i o n T h e o r e t i c a l c o n s i d e r a t i o n s Can the r e s p o n s e t o s e l e c t i o n f o r a p a r t i c u l a r c h a r a c t e r be p r e d i c t e d by t h e b r e e d i n g s y s t e m of t h e o r g a n i s m b e i n g s e l e c t e d ? B r e e d i n g s y s t e m can o n l y a f f e c t the r e s p o n s e t o s e l e c t i o n t h r o u g h i t s e f f e c t on t h e g e n e t i c v a r i a n c e p r e s e n t i n the p o p u l a t i o n . As we have seen i n t h e d i s c u s s i o n o u t l i n e d e a r l i e r , t h e e f f e c t o f b r e e d i n g s y s t e m on g e n e t i c v a r i a n c e i s d i f f i c u l t t o p r e d i c t i n t h e o r y , b u t t h e e v i d e n c e i n d i c a t e s t h a t s e l f e d t a x a c o n t a i n l e s s g e n e t i c d i v e r s i t y t h a n o u t c r o s s e d t a x a . The e v i d e n c e f o r d i f f e r e n c e s i n g e n e t i c v a r i a n c e between p o p u l a t i o n s w i t h d i f f e r e n t b r e e d i n g s ystems i s e q u i v o c a l . " I n b r e e d i n g i n an i n f i n i t e l y l a r g e p o p u l a t i o n w i l l i n c r e a s e t h e g e n e t i c v a r i a n c e r e l a t i v e t o an o u t c r o s s e d p o p u l a t i o n , and r e s p o n s e t o d i r e c t i o n a l s e l e c t i o n w i l l t hus t h e o r e t i c a l l y be f a s t e r i n i t i a l l y . However, g e n e t i c v a r i a n c e w i l l t h e o r e t i c a l l y be d e p l e t e d more q u i c k l y i n the i n b r e d p o p u l a t i o n , and s e l e c t i o n r e s p o n s e w i l l cease e a r l i e r ( t h e s e l e c t i o n l i m i t h a v i n g been r e a c h e d ) . I f i n a f i n i t e p o p u l a t i o n the s e l e c t i o n p r e s s u r e i s heavy enough, i t i s p o s s i b l e t h a t t h e s e l e c t i o n l i m i t may be f a r t h e r f r o m th e mean o f t h e o r i g i n a l p o p u l a t i o n i n an o u t c r o s s e d p o p u l a t i o n t h a n i n an i n b r e d one, as l o s s o f a l l e l e s t h r o u g h homozygosis and random d r i f t i n the i n b r e e d e r i n e a r l y g e n e r a t i o n s may p r e v e n t s e l e c t i o n o f t h e o p t i m a l genotype. E x p e r i m e n t a l e v i d e n c e The e v i d e n c e r e q u i r e d t o d i s t i n g u i s h the e f f e c t o f b r e e d i n g systems on the r e s p o n s e t o s e l e c t i o n s h o u l d i d e a l l y come f r o m t h e same type o f e x p e r i m e n t s as o u t l i n e d e a r l i e r under g e n e t i c v a r i a b i l i t y and r e s p o n s e t o s e l e c t i o n ( p . 1 5 ) . The a v a i l a b l e e v i d e n c e comes m o s t l y f r o m p l a n t b r e e d i n g s t u d i e s , and has t h e a t t e n d a n t s h o r t c o m i n g s i n t h i s c o n t e x t . Most o f t h e " p o p u l a t i o n s " b e i n g s e l e c t e d a r e n o t r e p r e s e n t a t i v e o f a n a t u r a l p o p u l a t i o n I n terms o f l e v e l s o f g e n e t i c v a r i a b i l i t y ; t h a t i s , even s p e c i e s w h i c h have an o u t c r o s s e d breeding s y s t e m have u s u a l l y been i n b r e d , o f t e n h i g h l y i n b r e d , and n a t u r a l l y s e l f e d s p e c i e s may have been o u t c r o s s e d a number of ways t o i n c r e a s e v a r i a b i l i t y . Most w e l l documented e v i d e n c e o f r e s p o n s e t o s e l e c t i o n i n p l a n t s comes from p l a n t b r e e d i n g s t u d i e s w h i c h use some regime of s e l e c t i o n o t h e r t h a n mass s e l e c t i o n . And, of c o u r s e , c o mparisons between r- 18 c l o s e l y r e l a t e d t a x a of d i f f e r e n t b r e e d i n g systems- a r e s c a r c e , so one i s f o r c e d t o d e a l w i t h e x p e r i m e n t s on p l a n t s w i t h p a r t i c u l a r b r e e d i n g systems as a group. O u t c r o s s e d t a x a The b e s t example o f l o n g t e r m mass s e l e c t i o n i n an o u t c r o s s e d t a x o n i s the 70 g e n e r a t i o n e x p e r i m e n t s e l e c t i n g f o r o i l and p r o t e i n c o n c e n t r a t i o n i n Zea mays, summarized by Dudley e t a l . ( 1 9 7 4 ) . The f o u r p o p u l a t i o n s s e l e c t e d f o r extremes i n c o n c e n t r a t i o n have c o n t i n u e d t o show a s i g n i f i c a n t r e s p o n s e f o r 70 g e n e r a t i o n s , w i t h the means o f the h i g h p r o t e i n , low p r o t e i n , h i g h o i l , and low o i l s t r a i n s i n g e n e r a t i o n 70 b e i n g r e s p e c t i v e l y 215%, 23%, 341%, and 14% o f the means o f t h e o r i g i n a l p o p u l a t i o n . Zea mays has a l s o been s u c c e s s f u l l y s e l e c t e d f o r i n c r e a s e d p r o f l i c a c y (24% i n 6 c y c l e s o f s e l e c t i o n ) and g r a i n y i e l d ( 1 8 % i n 6 c y c l e s ) ( A r b o l e d a - R i v e r a and Compton, 1 9 7 4 ) , i n c r e a s e d y i e l d ( 2 0 % i n 4 c y c l e s ) ( G a r d n e r , 1 9 6 1 ) , i n c r e a s e d earworm r e s i s t a n c e C28% i n 10 c y c l e s ) (Zuber e t a l . , 1 971), i n c r e a s e d c o l d g e r m i n a t i o n (36% i n 4 c y c l e s ) ( M c C o n n e l l and G a r d n e r , 1979), and i n c r e a s e d and d e c r e a s e d e a r l e n g t h ( C o r t e z - M e n d o z a and H a l l a u e r , 1979). A n o t h e r o u t c r o s s e d s p e c i e s w h i c h has been the s u b j e c t of s u c c e s s f u l mass s e l e c t i o n e x p e r i m e n t s i s Medicago s a t i v a . Response has been o b s e r v e d t o s e l e c t i o n f o r i n c r e a s e d r e s i s t a n c e t o b a c t e r i a l w i l t ( 3 8 % i n 4 c y c l e s ) ( B a r n e s e t a l . , " 1 9 7 1), i n c r e a s e d s e l f - s t e r i l i t y ( 7 7 % i n 2 c y c l e s ) and s e l f - f e r t i l i t y ( 1 0 3 % i n 2 c y c l e s ) ( B u s b i c e e t a l . , 1 9 7 5 ) , ( 7 3 % i n 3 c y c l e s ) ( V i l l e g a s e t a l . / 1 9 7 1 ) , r e s i s t a n c e t o a n t h r a c n o s e ( 6 7 % i n 3 c y c l e s ) ( D e v i n e e t a l . , 1 9 7 1 ) , and i n c r e a s e d (300% i n 2-3 c y c l e s ) and d e c r e a s e d (66% i n 2^5 c y c l e s ) s a p o n i n l e v e l s ( P e d e r s e n e t a l . j 1973). - 19 I n Ipomoea b a t a t a s mass s e l e c t i o n has produced r e s p o n s e i n terms o f d e c r e a s e d o x i d a t i o n o f the r o o t f l e s - h ( J o n e s , 1 9 7 2 ) and changes i n a complex composed of a number o f e c o n o m i c a l l y v a l u a b l e c h a r a c t e r s Clones e t a l . , 1 9 7 6 ) . I n A g r o p y r o h d e s e f t o r u m S c h a a f ( 1 9 6 8 ) has s u c c e s s f u l l y s e l e c t e d f o r extremes o f seed s i z e (+7% i n one c y c l e ) and i n c r e a s e d s e e d y i e l d . B r a s s i c a h j r t a ( S i n a p i s a l b a ) has been s e l e c t e d f o r extremes o f o i l c o n t e n t (+16%, - 1 4 % i n 8 c y c l e s ) ( O l s s o n and A n d e r s s o n , 1 9 6 3 ) . Extremes o f f l o w e r i n g t i m e were s u c c e s s f u l l y s e l e c t e d i n B r a s s i c a c a m p e s t r i s v a r . brown s a r s o n by d i r e c t i o n a l s e l e c t i o n ( + 0 . 3 % , - 1 0 % i n 3 c y c l e s ) ( M u r t y e t a l . , 1 9 7 2 ) . B e t a v u l g a r i s has been s e l e c t e d f o r extremes o f d r y m a t t e r c o n t e n t i n the r o o t (+35%, - 4 0 % i n 1 3 c y c l e s ) ( J o s e f s s o n , 1 9 6 3 ) . Limnanthes a l b a has responded t o two c y c l e s o f s e l e c t i o n f o r f l o w e r i n g t i m e ( +13%, ?.11%) ( J a i n , 1 9 7 9 ) . T h i s i s one s i t u a t i o n where a c l o s e l y r e l a t e d i n b r e e d i n g s p e c i e s ( L . f l o c c o s a ) e x i s t s and has been s t u d i e d f o r l e v e l s o f g e n e t i c v a r i a b i l i t y , b u t u n f o r t u n a t e l y no s e l e c t i o n e x p e r i m e n t s have been done on i t y e t . I n b r e e d i n g t a x a There a r e a number o f s t u d i e s o f r e s p o n s e t o mass s e l e c t i o n i n i n b r e e d i n g t a x a . I n Avena s a t i v a , r e s p o n s e has been o b s e r v e d t o s e l e c t i o n f o r i n c r e a s e d p a n i c l e w e i g h t (15% i n 2 c y c l e s ) (Chandhanamutta and F r e y , 1 9 7 3 ) , r e d u c e d p l a n t h e i g h t ( 2 i n c h e s i n 4 c y c l e s ) (Romero and F r e y , 1 9 6 6 ) , and t o one c y c l e o f d i v e r g e n t s e l e c t i o n f o r h e a d i n g d a t e ( + 2 2 % ) , p l a n t h e i g h t (+5%, - 4 % ) , g r a i n y i e l d ( + 9 % ) , w i d t h ; o f seed (+5%, - 3 % ) , seed w e i g h t (+5%, - 3 % ) , and number o f s p i k e l e t s p e r p a n i c l e (+5%, -1%) (Geadelmann and F r e y , 1 9 7 5 ) . I n Avena f a t u a s u c c e s s f u l d i v e r g e n t s e l e c t i o n has p r o d u c e d changes i n growth h a b i t ( +13%, - 3 1 % ) , f l o w e r i n g t i m e ( +13%, - 2 8 % ) , and h e i g h t t + 1 0 % , - 1 5 % ) i n - 20 one c y c l e (Imam and A l l a r d , 19_65) . As n o t e d e a r l i e r , b o t h A. f a t u a and i t s more h i g h l y se 1 f e d r e l a t l v e ' A, B.arbata have been s e l e c t e d f o r i n c r e a s e d and d e c r e a s e d seed s i z e and h e a d i n g d a t e ( J a i n and M a r s h a l l , 19 7 0 ) . G l y c i n e max has been s e l e c t e d f o r extremes o f s e e d s i z e (+10%, -4% i n 3 c y c l e s ) and s p e c i f i c g r a v i t y o f seeds ( F e h r and Weber, 1968). D i v e r g e n t s e l e c t i o n f o r 10 c y c l e s i n Sorghum b i c o l o r has changed t h e mean seed w e i g h t (+34%, - 1 8 % ) , p l a n t h e i g h t (+31%, - 2 6 % ) , and f l o w e r i n g t i m e (+10%, -2%) ( F o s t e r e t a l . , 1980). F o u r c y c l e s o f mass s e l e c t i o n f o r i n c r e a s e d g r e e n w e i g h t o f l e a v e s i n N j c o t i a n a tabacum r e s u l t e d i n an i n c r e a s e o f 18% ( M a t z i n g e r and Wernsman; 1968). A l l a r d e t a l . (1968) i n t h e i r r e v i e w o f the g e n e t i c s o f i n b r e e d i n g s p e c i e s r e p o r t s u c c e s s f u l s e l e c t i o n f o r i n t e n s i t y o f c o a t c o l o u r i n seeds o f P h a s e o l u s l u n a t u s , and extremes o f seed s i z e i n P. l u n a t u s (+ 7.5% i n 4 c y c l e s ) , P. v u l g a r i s (+4.5% i n 4 c y c l e s ) and b a r l e y . I n E l e u s i n e , H i l u and deWet (1980) were a b l e t o i n c r e a s e g e r m i n a t i o n r a t e s by 20-100% i n 4 c y c l e s of s e l e c t i o n i n t h r e e s p e c i e s , E. i n d i c a , B. c o r a c a n a , and E. t r i s t a c h y a . As has been t h e case w i t h s e l e c t i o n e x p e r i m e n t s i n n e a r l y e v e r y o r g a n i s m , p l a n t o r a n i m a l , and f o r n e a r l y e v e r y c h a r a c t e r s t u d i e d , enough g e n e t i c v a r i a b i l i t y i s p r e s e n t i n b o t h b r e e d i n g s y s t e m groups f o r a r e s p o n s e t o s e l e c t i o n t o o c c u r . One p o t e n t i a l p r o b l e m w h i c h s h o u l d be m entioned i s t h a t n e g a t i v e r e s u l t s ( i n t h i s c a s e , l a c k of r e s p o n s e t o a r t i f i c i a l s e l e c t i o n ) may n o t be r e p o r t e d i n - th e l i t e r a t u r e . . G i v e n t h e i n v e s t m e n t i n t i m e and e f f o r t i n v o l v e d i n most c a r e f u l s e l e c t i o n e x p e r i m e n t s , t h i s i s p r o b a b l y n o t i n f a c t a p r o b l e m , and i t appears f r o m t h e e v i d e n c e examined h e r e t h a t b o t h o u t c r o s s e d and s e l f e d t a x a show c o n s i d e r a b l e r e s p o n s e t o s e l e c t i o n f o r a number o f c h a r a c t e r s . I t i s o n l y f r o m s t u d i e s s u c h as t h a t w i t h Avena f a t u a and A. b a r b a t a , w h i c h comes c l o s e t o m e e t i n g t h e i d e a l c o n d i t i o n s o f r e l a t i v e - l y n a t u r a l l e v e l s o f g e n e t i c v a r i a b i l i t y , n a t u r a l b r e e d i n g s y s t e m s , and - 21 mass s e l e c t i o n , t h a t the most u s e f u l c o m p a r i s o n s may be drawn. B r e e d i n g s y s t e m , g e n e t i c v a r i a b i l i t y , and t h e r e s p o n s e t o s e l e c t i o n i n P l e c t r i t i s The o b j e c t i v e o f t h i s s t u d y was t o examine t h e r e s p o n s e s t o d i v e r g e n t a r t i f i c i a l s e l e c t i o n o f two n a t u r a l p o p u l a t i o n s o f p l a n t s w h i c h d i f f e r m a i n l y i n t h e i r b r e e d i n g s y s t e m . I f d i f f e r e n c e s i n s e l e c t i o n r e s p o n s e were o b s e r v e d , t h i s c o u l d r e f l e c t d i f f e r e n c e s i n t h e amount and / o r o r g a n i z a t i o n o f t h e u n d e r l y i n g g e n e t i c v a r i a b i l i t y . The p l a n t s chosen f o r t h i s s t u d y were t h e two s p e c i e s of P l e c t r i t i s , P. c o n g e s t a and P. b r a c h y s t e m o n . There a r e a number of f e a t u r e s o f t h e t w o ' s p e c i e s w h i c h make them i d e a l f o r t h i s p u r p o s e . The two s p e c i e s a r e v e r y c l o s e l y r e l a t e d . Morey ( 1 9 6 2 ) , i n t h e most r e c e n t t r e a t m e n t o f t h e genus, c o n s i d e r e d them s u b s p e c i e s of P_̂  c o n g e s t a . H i t c h c o c k and o t h e r s have n o t even g i v e n them t h a t r a n k , c o n s i d e r i n g them one s p e c i e s ( H i t c h c o c k and C r o n q u i ^ t , 19 7 3 ) . The s p e c i e s a r e v e r y d i f f i c u l t t o d i s t i n g u i s h b e f o r e t h e y have f l o w e r e d , s i n c e t h e y have n e a r l y i d e n t i c a l v e g e t a t i v e h a b i t . P o p u l a t i o n s o f t h e two grow s y m p a t r i c a l l y i n a number o f v l o c a t i o n s , and even when a l l o p a t r i c t h e y occupy t h e same t y p e o f h a b i t a t s , t h a t i s , t h i n , e d a p h i c a l l y d r y s u b s t r a t e s on r o c k y c o a s t a l b l u f f s and h e a d l a n d s , and open s l o p e s and c l e a r i n g s i n l a n d , w i t h t h e same community o f a s s o c i a t e d a n n u a l and p e r e n n i a l h e r b s . I t i s s a f e t o assume t h a t t h e l a r g e s c a l e s e l e c t i v e p r e s s u r e s t h a t t h e y have e n c o u n t e r e d i n terms of h a b i t a t have n o t d i f f e r e d s i g n i f i c a n t l y between t h e two s p e c i e s f o r many g e n e r a t i o n s . N e v e r t h e l e s s , the p o p u l a t i o n s of t h e two s p e c i e s w h i c h o c c u r i n B r i t i s h C o l u m b i a are q u i t e d i s t i n c t , d i f f e r i n g i n a' number o f f l o r a l m o r p h o l o g i c a l c h a r a c t e r s ( f l o w e r c o l o u r and s i z e , degree o f " p t o t a n d r y , n e c t a r - 22 p r o d u c t i o n ) w h i c h a l s o r e f l e c t t h e i r b a s i c b r e e d i n g s y s t e m d i f f e r e n c e . P l e c t r i t i s c o n g e s t a i s l a r g e l y c r u t c r o s s e d , w i t h a mean o u t c r o s s i n g r a t e measured i n a number o f p o p u l a t i o n s and o v e r a number of seasons o f 70%; P. br a c h y s t e m o n i s h i g h l y s e l f e d , w i t h a mean o u t c r o s s i n g r a t e o f l e s s t h a n 2% ( C a r e y and Ganders, 1980; Ganders e t a l . , 1977a., 1977b.; L a y t o n , 1 9 8 0 ) . I n a d d i t i o n , t h e two s p e c i e s have p r o v e d t o be i n t e r s t e r i l e i n l a b o r a t o r y c r o s s e s , and no i n t e r m e d i a t e forms have been o b s e r v e d i n a number o f l o c a t i o n s where the two grow s y m p a t r i c a l l y . I n e f f e c t , t he o n l y major b i o l o g i c a l d i f f e r e n c e between t h e two s p e c i e s appears t o be t h e i r b r e e d i n g s y s t e m . B o t h s p e c i e s a r e s m a l l , r e l a t i v e l y e a s y t o grow i n crowded c o n d i t i o n s i n greenhouses o r c o n t r o l l e d e n v i r o n m e n t chambers, and complete t h e i r l i f e c y c l e , s e e d t o s e e d , w i t h i n 5 months under s u i t a b l e c o n d i t i o n s . I n a d d i t i o n , i n d e p e n d e n t e s t i m a t e s o f g e n e t i c v a r i a b i l i t y a r e a v a i l a b l e f o r t h e two s p e c i e s f r o m two s t u d i e s . Isozyme d a t a has been a n a l y s e d t o d e t e r m i n e l e v e l s o f w i t h i n ; and between p o p u l a t i o n d i v e r s i t y i n a number o f p o p u l a t i o n s o f b o t h s p e c i e s ( L a y t o n , 1980) i M o r p h o m e t r i c c h a r a c t e r s o f the f r u i t s have a l s o been examined i n p o p u l a t i o n s o f e a c h s p e c i e s (Ganders and M a z e , . u n p u b l i s h e d ) . - 23 M a t e r i a l s and Methods Source p o p u l a t i o n s The s e e d f o r t h e base p o p u l a t i o n s o f the two s p e c i e s came from two p o p u l a t i o n s Cone o f each s p e c i e s ) g r o w i n g s y m p a t r i c a l l y i n M i l l H i l l P a r k n e a r V i c t o r i a on s o u t h e r n V a n c o u v e r I s l a n d , B r i t i s h C o l u m b i a , Canada. B o t h l o c a l p o p u l a t i o n s a r e p a r t o f more e x t e n s i v e p o p u l a t i o n s c o v e r i n g t h e open h i l l s i d e s i n t h e p a r k , more o r l e s s c o n t i n u o u s l y i n t h e case o f P. c o n g e s t a , b u t i n i s o l a t e d p o c k e t s i n t h e case o f P. b r a c h y s t e m o n . The h a b i t a t i s t y p i c a l f o r t h e s p e c i e s : open, r o c k y h i l l s i d e s w i t h p a t c h e s o f s h a l l o w s o i l , wet i n w i n t e r and e d a p h i c a l l y d r y by e a r l y summer, w i t h a community o f g r a s s e s , b r y o p h y t e s , and h e r b a c e o u s w i n t e r a n n u a l s and p e r e n - n i a l s under s c a t t e r e d ' Quercus g a r r y a n a , ' A r b u t u s , and C y t i s u s . N i n e hundred s i x t y t h r e e p l a n t s o f P. c o n g e s t a and 590 p l a n t s of P_ b r a c h y s t e m o n were c o l l e c t e d i n l a t e f r u i t i n June 1977. These numbers p r o b a b l y r e p r e s e n t 50 - 75% o f the t o t a l numbers i n the l o c a l p o p u l a t i o n . The e x t e n t o f t h e two l o c a l p o p u l a t i o n s c o l l e c t e d and t h e i r o v e r l a p i s diagrammed i n F i g u r e 1. The numbers o f f r u i t s p e r p l a n t i n the p o p u l a t i o n s v a r i e d from 1 o r 2 t o many; a l l f r u i t s were c o l l e c t e d f r o m each p l a n t . I made no e f f o r t t o c o l l e c t e q u a l numbers o f f r u i t s f r o m e a c h p l a n t , and f r u i t s f r o m each s p e c i e s were lumped i n b u l k samples. F r e q u e n c i e s o f w i n g ed and. w i n g l e s s f r u i t e d p l a n t s were r e c o r d e d , i n ^ P. c o n g e s t a f o r use i n a progeny t e s t t o d e t e r m i n e o u t c r o s s i n g r a t e . The winged and w i n g l e s s f r u i t s were b u l k e d s e p a r a t e l y . A l l p l a n t s o f P.. b r a c h y s t e m o n a t t h i s l o c a l i t y a r e w i n g l e s s f r u i t e d .  - 25 Growing c o n d i t i o n s A l l p l a n t s i n the e x p e r i m e n t were grown i n s t a n d a r d 25 x 50 cm p l a s t i c f l a t s . F r u i t s were p l a n t e d 1 cm deep i n a p p r o x i m a t e l y 4 cm o f steam t r e a t e d s o i l . The f r u i t s were p l a n t e d 200 t o a f l a t i n a g r i d o f 10 rows and 20 columns s p a c e d 2.5 cm a p a r t . F e r t i l i z e r ( H i - S o l 20-20-20).. was added t o t h e s o i l p r i o r t o p l a n t i n g , t o remove some p o s s i b l e s o u r c e s o f h e t e r o g e n e i t y w i t h i n and between f l a t s i n n u t r i e n t l e v e l s . The amount of f e r t i l i z e r added v a r i e d f r o m g e n e r a t i o n t o g e n e r a t i o n , as h i g h e r l e v e l s i n t h e e a r l y g e n e r a t i o n s caused e x c e s s i v e g r o w t h , w h i c h made t h e p l a n t s d i f f i c u l t t o h a n d l e ( T a b l e I ) . A l l e x p e r i m e n t a l p o p u l a t i o n s were grown i n a s i n g l e C o n v i r o n w a l k - i n c o n t r o l l e d e n v i r o n m e n t chamber. The c o n d i t i o n s o f l i g h t and t e m p e r a t u r e were s e t as much as p o s s i b l e t o s i m u l a t e n a t u r a l c o n d i t i o n s ; the p l a n t s were g e r m i n a t e d i n a c o l d chamber, and t h e n l i g h t and t e m p e r a t u r e were i n c r e a s e d as t h e p l a n t s matured. The l i g h t and t e m p e r a t u r e c o n d i t i o n s v a r i e d s l i g h t l y f r o m g e n e r a t i o n t o g e n e r a t i o n as I a t t e m p t e d t o f i n d t h e b e s t compromise between a s h o r t g e n e r a t i o n t i m e and a p l a n t h a b i t b e s t s u i t e d f o r m a n i p u l a t i o n ( s h o r t , s t o c k y p l a n t s w i t h a s t r o n g r o o t system) ( T a b l e I ) . P o s i t i o n s o f t h e f l a t s i n t h e growth chamber were a s s i g n e d a t random and the f l a t s were s h u f f l e d s e v e r a l t i m e s d u r i n g each g e n e r a t i o n t o remove p o s i t i o n e f f e c t s . A l l f l a t s were w a t e r e d t o s a t u r a t i o n d a i l y w i t h t a p w a t e r u n t i l f r u i t s e t was c o m p l e t e , and t h e p l a n t s were t h e n a l l o w e d t o d i e as t h e s o i l d r i e d . Measurements A l l p l a n t s i n e a c h t r e a t m e n t p o p u l a t i o n and e v e r y g e n e r a t i o n were T a b l e I . Growing c o n d i t i o n s G e n e r a t i o n F e r t i l i z e r Temperature ( g m / f l a t ) ( C n i g h t / C day) G 8 7/12 - 39 days 0 10/15 - b a l a n c e 8 7/12 - 39 days 10/15 - b a l a n c e 4 7/12 42 days 10/15 - b a l a n c e 4 7/12 33 days 10/15 - 38 days 12/20 - 64 days 12/23 b a l a n c e 2 7/12 _ 28 days 10/15 — 12 days 10/18 18 days 11/20 b a l a n c e 2 7/12 28 days 10/15 —* 8 days 11/20 b a l a n c e L i g h t N o t e s ( h r d a r k / h r l i g h t ) 8/16 -growth chamber out o f o p e r a t i o n day 82 day 89, p l a n t s a t room t e m p e r a t u r e - s p r a y e d f o r a p h i d s ( I s o t o x ) day 103 8/16 8/16 - s p r a y e d f o r m i l d e w (Benomyl) day 39 8/16 8/16 - i n t e n s i t y o f l i g h t d u r i n g day i n c r e a s e d day 79 8/16 - 27 measured f o r t h e f o l l o w i n g c h a r a c t e r s ; 1 , Days t o emergence The number o f days- between p l a n t i n g and t h e complete emergence o f t h e c o t y l e d o n s above t h e s o i l s u r f a c e was r e c o r d e d . 2, Days t o a n t h e s i s ( f l o w e r i n g t i m e ) The number of days between p l a n t i n g and t h e o p e n i n g o f t h e f i r s t f l o w e r on e a c h p l a n t was r e c o r d e d . 3, H e i g h t a t a n t h e s i s The h e i g h t o f the p l a n t i n mm, from t h e s o i l s u r f a c e t o t h e top o f the main i n f l o r e s c e n c e ( F i g u r e 2) was r e c o r d e d on t h e f i r s t day o f a n t h e s i s . 4, Number o f nodes a t a n t h e s i s The number o f nodes between the s o i l s u r f a c e and t h e base o f t h e main i n f l o r e s c e n c e ( i n c l u s i v e ) was r e c o r d e d f o r each p l a n t on t h e f i r s t day o f a n t h e s i s . I n P. b r a c h y s t e i i t o n , i n w h i c h t h e upper nodes a r e s t i l l h i g h l y compressed a t a n t h e s i s , the nodes were counted by i d e n t i f y i n g p a i r s o f l e a v e s a t each node. 5, Number o f p r i m a r y b r a n c h e s a t a n t h e s i s The number o f b r a n c h e s o r b r a n c h buds v i s i b l e i n t h e a x i l s o f l e a v e s on t h e main a x i s on the f i r s t day o f a n t h e s i s was r e c o r d e d . T h i s i s an u n d e r e s t i m a t e o f t h e t o t a l amount o f b r a n c h i n g , as t h e r e a r e some p r i m a r y b r a n c h e s , as w e l l as s e c o n d a r y , t e r t i a r y , and h i g h e r o r d e r b r a n c h e s , w h i c h do n o t b e g i n t o d e v e l o p u n t i l l a t e r i n t h e f l o w e r i n g p e r i o d ( F i g u r e 2 ) . 6, F r u i t p r o d u c t i o n The r i p e f r u i t s were c o l l e c t e d from t h e main i n f l o r e s c e n c e o f e a c h p l a n t and c o u n t e d . T h i s f i g u r e i s s u b j e c t t o a l a r g e amount of e x p e r i m e n t a l e r r o r ; f r u i t s , when r i p e , a r e e a s i l y d i s l o d g e d from t h e p l a n t and l o s t , and P. c o n g e s t a r e q u i r e s a r t i f i c i a l p o l l i n a t i o n t o p r o d u c e f r u i t w e l l i n t h e l a b o r a t o r y , so u n a v o i d a b l e v a r i a t i o n i n p o l l i n a t i o n l e v e l s w i l l have F i g u r e 2. M o r p h o l o g y of P l e c t r i t i s , - 29 a f f e c t e d f r u i t s e t i n t h i s - species:, 7. F r u i t p h e n o t y p i c c h a r a c t e r s The f r u i t f r o m e a c h p l a n t was s c o r e d f o r a number o f p h e n o t y p i c c h a r a c t e r s . F r u i t s o f P. b r a c h y s t e m o n were a l l monomorphic ( i n t h i s case) f o r t h e s e c h a r a c t e r s . I n P. c o n g e s t a , f r u i t s c o u l d be s c o r e d f o r w i n g phenotype (winged o r w i n g l e s s , see F i g u r e 3 ) , pubescence p a t t e r n ( F i g u r e 4 ) , f r u i t c o l o u r (body and wings s c o r e d s e p a r a t e l y on t h e b a s i s o f an a r b i t r a r y c o l o u r c l a s s i f i c a t i o n u s i n g 4 c o l o u r c l a s s e s ) , and the p r e s e n c e i n w i n g ed f r u i t s o f a c h a r a c t e r i s t i c i n d e n t a t i o n i n t h e m a r g i n o f t h e f r u i t ' w i n g . I a t t e m p t e d t o r e c o r d the shape o f t h e f r u i t w i n g , w h i c h v a r i e d c o n s i d e r a b l y between p l a n t s and r e l a t i v e l y l i t t l e w i t h i n p l a n t s . The v a r i a t i o n , however, was t o o c o n t i n u o u s and complex t o a l l o w f o r an adequate s c o r i n g s y s t e m and n o t amenable t o any s i m p l e -measurement. I n a d d i t i o n t o t h e s e c h a r a c t e r s , I r e c o r d e d v a r i o u s o t h e r s p o r a d i c and anomalous c h a r a c t e r s i n c l u d i n g : a b e r r a t i o n s i n t h e number of c o t y l e d o n s , p r e s e n c e o f more or l e s s f u s e d c o t y l e d o n s , c h l o r o t i c s e e d l i n g s , e x c e s s i v e l y d a r k l y pigmented s e e d l i n g s , abnormal b r a n c h i n g p a t t e r n s and o t h e r a b n o r m a l i t i e s i n t h e a d u l t growth h a b i t , and a b n o r m a l i t i e s i n f l o w e r i n g c h a r a c t e r i s t i c s , most commonly a b o r t e d a n t h e r s and l a c k of good p o l l e n , as w e l l as f l o w e r s w i t h abnormal numbers of p a r t s ( f o r example, more t h a n 5 c o r o l l a l o b e s , more t h a n t h r e e stamens, e t c . ) . B r e e d i n g p r o c e d u r e Three groups o f p o p u l a t i o n s were i n v o l v e d i n t h e e x p e r i m e n t , b a s e d on a c o m b i n a t i o n o f s p e c i e s and b r e e d i n g p r o c e d u r e . P l e c t r i t i s c o n g e s t a r e q u i r e d manual p o l l i n a t i o n because i t i s p r o t a n d r o u s and does n o t F i g u r e 3. P l e c t r i t i s - f r u i t w i n g p h e n o t y p e s . W i n g l e s s ventral view- d o r s a l view - 32 a u t o m a t i c a l l y self-poll£nate s u c c e s s f u l l y i n t h e growth chamber, I to o k advantage o f t h i s t o s e t up two groups o f P^.-"congesta p o p u l a t i o n s , one o u t c r o s s e d and one s e l f e d . The p l a n t s i n each p o p u l a t i o n were e i t h e r s e l f - p o l l i n a t e d o r c r o s s e d t o r e l a t i v e l y u n r e l a t e d p l a n t s ( n o t s i b l i n g s ) . The p o l l i n a t i o n was done by removing n e w l y opened a n t h e r s w i t h f i n e f o r c e p s f r o m t h e p o l l e n p a r e n t , and u s i n g them t o p o l l i n a t e a p p r o p r i a t e s t i g m a s . The s u c c e s s o f t h i s b r e e d i n g p r o c e d u r e was e v a l u a t e d by e x a m i n i n g p a r t i c u l a r p r o g e n i e s i n subsequent g e n e r a t i o n s . P l e c t r i t i s b r a c h y s t e m o n i s not p r o t a n d r o u s , s e l f - p o l l i n a t e s a u t o m a t i c a l l y , and s e t s f r u i t v e r y s u c c e s s f u l l y i n t h e growth chamber; i t i s n o t e a s y t o o u t c r o s s , because o f t h e s m a l l s i z e o f the f l o w e r s . F o r t h e s e r e a s o n s o n l y s e l f e d p o p u l a t i o n s o f P_. br a c h y s t e m o n were i n v o l v e d i n t h e e x p e r i m e n t . S e l e c t i o n p r o c e d u r e The s e l e c t i o n method was s i m p l e i n d i v i d u a l o r mass s e l e c t i o n , i n w h i c h c e r t a i n i n d i v i d u a l s o f one g e n e r a t i o n were s e l e c t e d on t h e b a s i s o f t h e i r phenotype t o produce s e e d f o r t h e n e x t g e n e r a t i o n . The s e l e c t i o n p r e s s u r e was a p p r o x i m a t e l y 90%, t h a t i s 20 p l a n t s were s e l e c t e d f r o m t h e 200 i n a p a r t i c u l a r p o p u l a t i o n t o form t h e n e x t g e n e r a t i o n . L i n e s were s e l e c t e d s e p a r a t e l y f o r s h o r t h e i g h t a t a n t h e s i s , t a l l h e i g h t a t a n t h e s i s , e a r l y a n t h e s i s , and l a t e a n t h e s i s . An u n s e l e c t e d c o n t r o l l i n e was a l s o m a i n t a i n e d f o r e ach s p e c i e s group. One f l a t was p l a n t e d w i t h the l a s t g e n e r a t i o n , c o n t a i n i n g 100 i n d i v i d u a l s o f each s p e c i e s from t h e s o u r c e p o p u l a t i o n s ; t h i s s e r v e d as an e x t e r n a l c o n t r o l t o changes w h i c h might have a f f e c t e d t h e i n t e r n a l , u n s e l e c t e d c o n t r o l l i n e s . These p o p u l a t i o n s a r e d e s i g n a t e d P. c o n g e s t a G,. s o u r c e and P. br a c h y s t e m o n G,. s o u r c e . - 33 Base p o p u l a t i o n The f i r s t g e n e r a t i o n , base p o p u l a t i o n s (G Q) c o n s i s t e d o f 9. p o p u l a t i o n s o f 200 i n d i v i d u a l s , 3 e a c h f o r t h e 3 s p e c i e s g roups: P. c o n g e s t a o u t c r o s s e d (PCO) , -P, c o n g e s t a s e l f e d ( P C S ) , and P. bra c h y s t e m o n s e l f e d ( P B S ) . F o r e a c h group t h e r e was a c o n t r o l p o p u l a t i o n , an a n t h e s i s p o p u l a t i o n , and a h e i g h t p o p u l a t i o n . The f r u i t s f rom w h i c h t h e base p o p u l a t i o n s were grown were s e l e c t e d a t random f r o m t h e b u l k sample f r o m t h e s o u r c e p o p u l a t i o n s . Winged and w i n g l e s s f r u i t s i n t h e PCO and PCS p o p u l a t i o n s were p l a n t e d i n f r e q u e n c i e s e q u a l t o t h e i r f r e q u e n c i e s i n t h e s o u r c e p o p u l a t i o n (12.5% w i n g l e s s , 87.5% w i n g e d ) . F i r s t c y c l e o f s e l e c t i o n Prom t h e base p o p u l a t i o n s , 20 p l a n t s were s e l e c t e d as p a r e n t s f o r the n e x t g e n e r a t i o n , G^. Ten f r u i t s f r o m each were t a k e n t o f o r m a p o p u l a t i o n of 200. S e l e c t i o n l i n e s f o r e a r l y and l a t e a n t h e s i s were begun by t a k i n g t h e 20 e a r l i e s t and l a t e s t f l o w e r i n g p l a n t s i n t h e G^ a n t h e s i s p o p u l a t i o n as- p a r e n t s . S i m i l a r l y , s h o r t and t a l l l i n e s were s e l e c t e d f r o m t h e GQ h e i g h t p o p u l a t i o n . Twenty p l a n t s were s e l e c t e d a t random f r o m t h e GQ c o n t r o l p o p u l a t i o n t o f o r m t h e G^ c o n t r o l p o p u l a t i o n . Thus t h e r e were 15 t r e a t m e n t p o p u l a t i o n s i n G^ and subsequent g e n e r a t i o n s as i n d i c a t e d i n F i g u r e 5. Subsequent c y c l e s o f s e l e c t i o n I n e a c h g e n e r a t i o n from G^ on, t h e 20 e a r l i e s t , l a t e s t , s h o r t e s t , and . /- • t a l l e s t p l a n t s were s e l e c t e d i n t h e r e s p e c t i v e p o p u l a t i o n s as p a r e n t s f o r - 34 Figure 5. Experimental populations-maintained through 5 generations of s e l e c t i o n , G.. to G . P. congesta P. brachystemon PCO PCS PBS Control NF=200 N=200 N==200 Early anthesis N=200 N=200 N=200 Late anthesis N=200 N=200 N=200 Short height N-200 N=200 N-200 T a l l height N=200 N=200 N=200 the s u bsequent g e n e r a t i o n . ' A g a i n , t h e c o n t r o l l i n e s were c o n t i n u e d by- s e l e c t i n g p l a n t s a t random f r o m t h e c o n t r o l p o p u l a t i o n s , i n a l l s e l e c t i o n s i n PCO t h e p o l l i n a t i o n s were made, as f a r as p o s s i b l e , between s e l e c t e d i n d i v i d u a l s o f d i f f e r e n t f a m i l i e s . The r e q u i r e m e n t t h a t 10 f r u i t s be p r o d u c e d b e f o r e a p l a n t q u a l i f i e d as a p a r e n t f o r s e l e c t i o n meant t h a t some i n d i v i d u a l s w h i c h w o u l d o t h e r w i s e have been s e l e c t e d on t h e b a s i s o f t h e i r f l o w e r i n g t i m e o r h e i g h t were d i s q u a l i f i e d . I n e f f e c t , t h e r e was s e l e c t i o n f o r a minimum l e v e l o f f e c u n d i t y i n a d d i t i o n t o s e l e c t i o n f o r h e i g h t and f l o w e r i n g t i m e . I n G^ t h e PCS and PBS p o p u l a t i o n s s e l e c t e d f o r s h o r t h e i g h t p r o d u c e d t o o few f r u i t s p e r i n d i v i d u a l t o even r e a c h t h e minimum f e c u n d i t y l e v e l , so I had ,to r e d u c e t h e f a m i l y s i z e of 10 i n t h i s c a s e . T h i r t y - s e v e n i n d i v i d u a l s f r o m PCS s h o r t and 35 f r o m PBS s h o r t were s e l e c t e d t o c o n t r i b u t e f a m i l i e s o f v a r y i n g s i z e (1 - 10 progeny) t o the n e x t g e n e r a t i o n G^. Progeny t e s t and o u t c r o s s i n g r a t e i n P. c o n g e s t a The w i n g ed and w i n g l e s s phenotype f r e q u e n c i e s i n t h e s o u r c e p o p u l a t i o n , t o g e t h e r w i t h the o b s e r v e d f r e q u e n c i e s o f winged and w i n g l e s s morphs i n t h e i r p r o g e n i e s (GQ) a l l o w e d a progeny t e s t w h i c h gave an e s t i m a t e of t h e o u t c r o s s i n g r a t e , t , i n the s o u r c e p o p u l a t i o n (Ganders e t a l . , 1977a.). D a t a t r e a t m e n t and a n a l y s e s A l l measured o r s c o r e d c h a r a c t e r s i n e v e r y l i n e and g e n e r a t i o n were punched on computer c a r d s and s t o r e d i n f i l e s i n t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a computer s y s t e m f o r a n a l y s i s . Most s t a t i s t i c a l a n a l y s e s were p e r f o r m e d u s i n g t h e MIDAS s t a t i s t i c a l package (Fox and G u i r e , 1 9 7 6 ) . M e t r i c a l c h a r a c t e r s I u s e d t h e s i x m e t r i c a l c h a r a c t e r s - days t o emergence, days t o a n t h e s i s , h e i g h t a t a n t h e s i s , number o f nodes a t a n t h e s i s , number o f p r i m a r y b r a n c h e s a t a n t h e s i s , and f r u i t p r o d u c t i o n - t o compute a f u r t h e r s e t o f s i x t r a n s f o r m e d c h a r a c t e r s as f o l l o w s . The grand mean and s t a n d a r d d e v i a t i o n of e a c h were computed f o r a l l s i x P. cOrigesta p o p u l a t i o n s t o g e t h e r , and f o r a l l t h r e e P., b r a c h y s t e m o n G ^ p o p u l a t i o n s t o g e t h e r . I n d a t a f o r s u bsequent g e n e r a t i o n s , a l l p o p u l a t i o n s w i t h i n a p a r t i c u l a r s p e c i e s group were t r a n s f o r m e d by a m u l t i p l i c a t i v e and an a d d i t i v e f a c t o r , so t h a t t h e d i s t r i b u t i o n o f t h e t r a n s f o r m e d c h a r a c t e r i n t h e c o n t r o l ( u n s e l e c t e d ) p o p u l a t i o n had t h e same mean and s t a n d a r d d e v i a t i o n as t h e GQ s t a n d a r d . An example i s g i v e n i n F i g u r e 6. T h i s t r a n s f o r m a t i o n e f f e c t i v e l y removes th e f o l l o w i n g two s o u r c e s o f v a r i a t i o n from t h e d a t a , w h i c h w o u l d o t h e r w i s e i n t e r f e r e w i t h t h e i n t e r p r e t a t i o n o f t h e e x p e r i m e n t a l r e s u l t s : 1. the common e f f e c t s o f g e n e r a t i o n t o g e n e r a t i o n f l u c t u a t i o n s i n g r o w i n g c o n d i t i o n s and o t h e r e n v i r o n m e n t a l f a c t o r s , and 2. t h e e f f e c t s o f any u n c o n t r o l l e d s e l e c t i o n p r e s s u r e s ( f o r example, s e l e c t i o n f o r growth under growth chamber c o n d i t i o n s ) and t o some e x t e n t t h e e f f e c t s o f i n b r e e d i n g w h i c h c o u l d be presumed t o be a c t i n g e q u a l l y on s e l e c t e d and u n s e l e c t e d l i n e s . D e s c r i p t i v e s t a t i s t i c s The d i s t r i b u t i o n s of t h e m e t r i c a l c h a r a c t e r s , raw. and t r a n s f o r m e d , were d e s c r i b e d i n a l l p o p u l a t i o n s i n terms o f number of i n d i v i d u a l s measured, maximum and minimum v a l u e s o b s e r v e d , p o p u l a t i o n mean, s t a n d a r d F i g u r e 6. An example o f d a t a t r a n s f o r m a t i o n p r o c e d u r e used on m e t r i c a l c h a r a c t e r s Days t o emergence PCO c o n t r o l PCO e a r l y PCO l a t e PCO s h o r t PCO t a l l raw d a t a x s ,d. 20.77 5,55 21.03 4.47 21.81 5.17 19.43 4.08 21.22 5.53 c o r r e c t i o n X. x 0.7522 + 2.776 t r a n s f o r m e d x' s.d! 18.4 4.17 18.6 3.36 19.2 3.89 17.4 3.07 18.7. 4.16 "0 s t a n d a r d s. d 18.4 4.1 x - 38 deviation, c o e f f i c i e n t of v a r i a t i o n , skewness, and k u r t o s i s . In addition, frequency histograms of a l l distributions- were generated to depict them gra p h i c a l l y . Comparisons between d i s t r i b u t i o n s For every m e t r i c a l character the d i s t r i b u t i o n s of the selected populations were compared to those of the control i n the same generation (for example, PCO ea r l y G^vs.. PCO control G^) by means of Kr u s k a l l - W a l l i s tests (non-parametric analysis of variance). The transformed data were also compared between generations within l i n e s by means of Kr u s k a l l - W a l l i s tests ( f o r example, PCS short G ^ vs. PCS short G,_) . Correlations Correlations between a l l pairs of m e t r i c a l characters within each population were calculated by Spearman's rank c o r r e l a t i o n procedure. H e r i t a b i l i t y estimates 2 Estimates of narrow sense h e r i t a b i l i t y (h , the proportion of the t o t a l phenotypic variance i n a population which i s a t t r i b u t a b l e to additive genetic e f f e c t s ) were calculated i n the experimental populations f o r the selected characters, flowering time and height at anthesis, by two methods. Realized h e r i t a b i l i t y was calculated a f t e r the method of H i l l (1972 ). This estimate i s based on the r a t i o s of s e l e c t i o n d i f f e r e n t i a l ( s e l e c t i o n pressure) to. response i n l i n e s under divergent s e l e c t i o n . H e r i t a b i l i t i e s were a l s o c a l c u l a t e d f o r a l l m e t r i c a l c h a r a c t e r s - by t h e -method of p a r e n t - o f f s p r i n g r e g r e s s i o n s - i n the' c o n t r o l l i n e s ( F a l c o n e r , I 9 6 0 ) , V a r i a n c e w i t h i n p o p u l a t i o n s The components o f v a r i a n c e w i t h i n p o p u l a t i o n s were a n a l y z e d by u n i v a r i a t e ANOVA f o r t h e m e t r i c a l c h a r a c t e r s . The v a r i a n c e was p a r t i t i o n e d i n t o components between f a m i l i e s and w i t h i n f a m i l i e s . O t her c h a r a c t e r s F r e q u e n c i e s o f f r u i t w i n g p h e n o t y p e s , pubescence p a t t e r n s , f r u i t w i n g and body c o l o u r s , p r e s e n c e o f w i n g i n d e n t a t i o n , and a b e r r a n t c h a r a c t e r s were t a b u l a t e d f o r e v e r y p o p u l a t i o n . R e s u l t s B r e e d i n g s ystems i n P l e c t r i t i s - c o n g e s t a • and P__ Brachystemon O u t c r o s s i n g r a t e s i n t h e s o u r c e p o p u l a t i o n s ( M i l l H i l l Pk., 1977) The o u t c r o s s i n g r a t e i n t h e P. c o n g e s t a s our ce p o p u l a t i o n i n 1977 was e s t i m a t e d by t h e progeny t e s t method (Ganders e t a l . , 1977a.) t o be 61.6%. T h i s i s b a s e d on a t o t a l sample o f 1175 i n d i v i d u a l s grown f r o m s e e d . T h i s e s t i m a t e compares w e l l w i t h o t h e r e s t i m a t e s o f o u t c r o s s i n g r a t e s i n p o p u l a t i o n s o f t h e s p e c i e s , w h i c h have averaged around 70% (Ganders e t a l . , 1977a*, Carey and Ganders, 1980; L a y t o n j 1980). S i n c e the s o u r c e p o p u l a t i o n o f P^ brachystemon was monomorphic f o r a l l o f the m o r p h o l o g i c a l markers w h i c h might have been used i n a progeny t e s t , no e s t i m a t e o f t h e o u t c r o s s i n g r a t e i s y e t a v a i l a b l e f o r i t . T here i s no r e a s o n t o e x p e c t t h i s p o p u l a t i o n t o d i f f e r s u b s t a n t i a l l y f r o m o t h e r s measured t h r o u g h o u t t h e range of t h e s p e c i e s i n B r i t i s h C o l u mbia. Ganders e t a l . (1977b,) and L a y t o n ( 1 9 8 0 ) , u s i n g t h e f r u i t w i n g p o l y m o r p h i s m and a l l o z y m e polymorphisms r e s p e c t i v e l y , e s t i m a t e t h a t t h e average o u t c r o s s i n g r a t e i n P^ b r a c h y s t e m o n i s 2%, and no p o p u l a t i o n s were found e x c e e d i n g 5%. O u t c r o s s i n g r a t e s i n t h e e x p e r i m e n t a l p o p u l a t i o n s The e f f e c t of t h e e x p e r i m e n t a l b r e e d i n g s y s t e m as p r a c t i s e d can be r o u g h l y , e s t i m a t e d i n P. c o n g e s t a by e x a m i n i n g p a r t i c u l a r p r o g e n i e s as f o l l o w s . I n t h e s e l f e d g r o u p , PCS, the p r o g e n i e s o f w i n g l e s s f r u i t e d p l a n t s (homozygous r e c e s s i v e s ) can be s c o r e d t o o b t a i n t h e f r e q u e n c y of w i n g ed - 41 f r u i t e d p r o g e n y , w h i c h a r e n e c e s s a r i l y t h e r e s u l t o f o u t c r o s s i n g e v e n t s . T h i s f r e q u e n c y w i l l u n d e r e s t i m a t e t h e a c t u a l r a t e of o u t c r o s s i n g , as a ( s m a l l ) p r o p o r t i o n o f the w i n g l e s s f r u i t e d progeny a r e l i k e l y a l s o t o be the r e s u l t o f o u t c r o s s e s t o o t h e r homozygous r e c e s s i v e o r h e t e r o z y g o u s p l a n t s . I n t h e o u t c r o s s e d group, PCO, p r o g e n i e s o f w i n g l e s s f r u i t e d p l a n t s w h i c h have been c r o s s e d t o homozygous dominant winged f r u i t e d p l a n t s can be s c o r e d t o o b t a i n t h e f r e q u e n c y , x , o f w i n g l e s s f r u i t e d o f f s p r i n g . I f t h e s e were a l l t h e r e s u l t o f a c c i d e n t a l s e l f i n g , t h e o u t c r o s s i n g r a t e w o u l d B e . l - :x. I n p r a c t i c e t h i s e s t i m a t e i s a g a i n an u n d e r e s t i m a t e o f t h e a c t u a l o u t c r o s s i n g r a t e , as some o f t h e w i n g l e s s f r u i t e d progeny a r e a g a i n l i k e l y , t o be the r e s u l t of a c c i d e n t a l o u t c r o s s e s , i n t h i s case t o some p l a n t o t h e r t h a n t h e p o l l e n p a r e n t o f r e c o r d . The e r r o r i n t h e s e e s t i m a t e s i s l i k e l y t o be l a r g e , and m o s t l y depends on t h e a l l e l e f r e q u e n c i e s i n t h e p o p u l a t i o n s C t h e h i g h e r t h e f r e q u e n c y of t h e r e c e s s i v e a l l e l e , t h e l a r g e r w i l l be t h e e r r o r ) ; n e y e r t h e l e s s , the e s t i m a t e s are of i n t e r e s t , , a n d a r e g i v e n i n T a b l e I I . C h a r a c t e r i s t i c s of the base p o p u l a t i o n s D e s c r i p t i v e s t a t i s t i c s o f t h e m e t r i c a l ( q u a n t i t a t i v e ) c h a r a c t e r s The i n i t i a l d i s t r i b u t i o n s o f t h e v a r i o u s measured c h a r a c t e r s i n t h e b ase p o p u l a t i o n s , Gg,,of t h e two s p e c i e s a r e g i v e n i n T a b l e I I I . Under the e x p e r i m e n t a l c o n d i t i o n s i n the growth chamber, P. b r a c h y s t e m o n emerges l a t e r , grows t a l l e r , p r o d u c e s more nodes and more p r i m a r y b r a n c h e s , f l o w e r s l a t e r , and p r o d u c e s more f r u i t t h a n P. c o n g e s t a . E x a m i n i n g t h e c o e f f i c i e n t s o f v a r i a t i o n , w h i c h a r e s c a l e f r e e e s t i m a t e s o f t h e p h e n o t y p i c v a r i a b i l i t y , - 42 T a b l e I I . E s t i m a t e s o f o u t c r o s s i n g r a t e s i n t h e - e x p e r i m e n t a l p o p u l a t i o n s . P. c o n g e s t a s e l f e d P o p u l a t i o n Number of p r o g e n i e s E s t i m a t e d o u t c r o s s i n g r a t e PCS c o n t r o l G o 3 0.25 PCS l a t e G o 3 0.19 PCS s h o r t G o 5 0.35 PCS t a l l G o 3 0.08 PCS c o n t r o l G l 4 0.18 PCS e a r l y G l 1 0.00 PCS l a t e G l 6 0.10 PCS s h o r t G l 5 0.12 PCS t a l l G l 4 0.04 PCS c o n t r o l G 2 4 0.05 PCS l a t e G 2 6 0.22 PCS s h o r t G 2 6 0.06 PCS t a l l G 2 6 0.04 PCS c o n t r o l G 3 4 0.28 PCS l a t e G 3 7 0.22 PCS s h o r t G 3 17 0.15 PCS t a l l G 3 8 mean 0.14 0.15 P. c o n g e s t a o u t c r o s s e d PCO e a r l y G o 1 0.80 PCO l a t e G o 1 0.60 PCO l a t e ' . G l 3 0.59 PCO e a r l y G 2 2 0.68 PCO l a t e G 2 1 0.29 PCO s h o r t G 2 2 0.94 PCO l a t e G 3 1 0.67 PCO t a l l G 3 1 mean 0.63 0.65 T a b l e I I I . Measured c h a r a c t e r s : , b a s e p o p u l a t i o n s . N "Mean S t a n d a r d C o e f f i c i e n t o f d e v i a t i o n v a r i a t i o n P_. c o n g e s t a Days t o emergence 9Q5 18.40 4.177 22.70 **a Chumber] H e i g h t a t a n t h e s i s 855 223,87 45.121 20.15 ** (mm) Nodes a t a n t h e s i s 855 8.91 1.108 12.43 ** (number) • P r i m a r y b r a n c h e s 855 2.71 3.417 126.09 ** (number) Days t o a n t h e s i s 855 95.02 7.379 7.76 * (number) F r u i t p r o d u c t i o n 861 25.10 18.820 74.99 (number) P. b r a c h y s t e m o n Days t o emergence 304 21.08 5.729 27.17 (number) H e i g h t a t a n t h e s i s 293 302.91 72.618 23.97 (mm) Nodes a t a n t h e s i s 293 11.80 1.656 14.03 (number) P r i m a r y b r a n c h e s 293 6.43 6.841 106.40 (number) Days t o a n t h e s i s 292 116.76 8.088 6.93 (number) F r u i t p r o d u c t i o n 291 61.26 28.48 68.80 A s t e r i s k s i n d i c a t e c o e f f i c i e n t s o f v a r i a t i o n s i g n i f i c a n t l y d i f f e r e n t f rom t h o s e i n P b r a c h y s t e m o n ; ** a t t h e 1% l e v e l , * a t the 5% l e v e l , a c c o r d i n g t o m o d i f i e d F - t e s t s ( L e w o n t i n ; 1966). i t appears t h a t P. b r a c h y s t e m o n i s more v a r i a b l e than P. c o n g e s t a f o r days t o emergence, h e i g h t , and number o f nodes a t a n t h e s i s , and l e s s v a r i a b l e f o r number o f p r i m a r y b r a n c h e s a t a n t h e s i s and f l o w e r i n g t i m e . There was no s i g n i f i c a n t d i f f e r e n c e i n t h e c o e f f i c i e n t o f v a r i a t i o n f o r f r u i t p r o d u c t i o n . F r e q u e n c i e s o f q u a l i t a t i v e c h a r a c t e r s P l e c t r i t i s b r a c h y s t e m o n i s monomorphic f o r a l l t h e f r u i t c h a r a c t e r s s c o r e d ; t h e s c o r e s f o r t h e base p o p u l a t i o n s o f P. c o n g e s t a f o r pubescence p a t t e r n a r e p r e s e n t e d i n F i g u r e s 7 t o 10, and w i l l be d i s c u s s e d l a t e r . The phenotype f r e q u e n c i e s o f winged and w i n g l e s s f r u i t s p l a n t e d i n GQ were th e same as i n t h e s o u r c e p o p u l a t i o n (12.5% w i n g l e s s , 87.5% w i n g e d ) ; t h e phenotype f r e q u e n c i e s o f t h e a d u l t p l a n t s i n GQ a r e p r e s e n t e d i n F i g u r e 11 Response to s e l e c t i o n o f t h e s e l e c t e d c h a r a c t e r s H e i g h t a t a n t h e s i s Means ' The mean h e i g h t s of p l a n t s i n t h e p o p u l a t i o n s s e l e c t e d f o r h e i g h t a t a n t h e s i s d e p a r t e d s i g n i f i c a n t l y f rom t h e c o n t r o l ( u n s e l e c t e d ) p o p u l a t i o n i n most g e n e r a t i o n s , the e x c e p t i o n s b e i n g PCO s h o r t G ^ , PCO t a l l G ^ and G ^ PCS" s h o r t G ^ PCS t a l l G 2 , and PBS s h o r t & 2 ( F i g u r e 1 2 ) . I n t h e case of the P. .congesta p o p u l a t i o n s , t h e means i n t h e s e l e c t e d l i n e s d i v e r g e d o v e r the, c o u r s e of the e x p e r i m e n t w i t h , i n most c a s e s , t h e t a l l l i n e s b e i n g - 45 Figure 7. Frequency' of v a r i o u s pubescence types (see Figure 4) I n the experimental p o p u l a t i o n s , a. Pubescence type 0 i n PCO populations b. Pubescence t y p e l i n PCO populations c. Pubescence type 2 i n PCO populations F i g u r e 7. a. PCO t y p e 0 .06 .04 .02 A / \ / v / \ / / \ v b. PCO t y p e 1 o e 0 ) fi cr-cu M «w fi M 0 ) 4-> 4-1 cd cu a) o fi a) o to a) •8 P4. .06 .04 .02 \ \ j _ a t e \ ' \ t a l l \ C o n t r o l H e i g h t A n t h e s i s >4 l a t e c. PCO t y p e 2 e a r l y s h o r t G e n e r a t i o n s o f s e l e c t i o n < - 4 7 F i g u r e 8. F r e q u e n c y o f v a r i o u s pubes-cence t y p e s Csee F i g u r e 4) i n the e x p e r i m e n t a l p o p u l a t i o n s - . a. Pubescence t y p e 3 b. . Pubescence t y p e 4 c. Pubescence t y p e 5 i n PCO p o p u l a t i o n s i n PCO p o p u l a t i o n s i n PCO p o p u l a t i o n s F i g u r e 8. a. PCO t y p e 3 . 6 h ^ s h o r t e a r l y b. PCO t y p e 4 o cu cr a) u <4-l 0 cu a) o C cu o C D co ,3 r .2 r s h o r t e a r l y •\ t a l l ^ l a t e 4 C o n t r o l H e i g h t A n t h e s i s c. PCO t y p e 5 e a r l y t a l l G e n e r a t i o n s of s e l e c t i o n - 49 F i g u r e 9. F r e q u e n c y of v a r i o u s ...pubescence t y p e s , ( s e e F i g u r e 4) i n t h e e x p e r i m e n t a l p o p u l a t i o n s . a. Pubescence t y p e 0 b. Pubescence t y p e 1 c. Pubescence t y p e 2 i n PCS p o p u l a t i o n s i n PCS p o p u l a t i o n s i n PCS p o p u l a t i o n s gure 9. PCS type. 0 PCS t y p e 1 PCS t y p e 2 .04 r G e n e r a t i o n s of s e l e c t i o n - 51 F i g u r e 10... F r e q u e n c y o f v a r i o u s pubescence .types (see F i g u r e 4) i n £he. e x p e r i m e n t a l p o p u l a t i o n s . a. -Pubescence t y p e b. Pubescence t y p e c. Pubescence t y p e 3 i n PCS p o p u l a t i o n s 4 i n PCS p o p u l a t i o n s 5 i n PCS p o p u l a t i o n s F i g u r e 10. - 52 a. PCS t y p e 3 s h o r t 0 1 2 3 4 G e n e r a t i o n s of s e l e c t i o n F i g u r e U.., Frequency,.of? w i n g l e s s ; f r u i t e d . p l a n t s i n t h e e x p e r i m e n t a l . p o p u l a t i o n s : a. . PCO p o p u l a t i o n s b. PCS p o p u l a t i o n s / C o n t r o l — H e i g h t — • — A n t h e s i s - 55 F i g u r e 12. Mean he i g h t , . a t a n t h e s i , s w i n , , . p o p u l a t j o n s s e l e c t e d f o r . > h e i g h t , . a t .anthesis.- 'Means: a r e - e x p r e s s e d as a p e r c e n t a g e o f t h e ...means, i n t h e c o n t r o l l i n e s . . : . P o p u l a t i o n s - w h i c h . . i n t e r s e c t t h e , v e r t i c a l l i n e s .did .not d i f f e r s i g n i f i c a n t l y f r o m t h e c o n t r o l ... - p o p u l a t i o n i n . the. same g e n e r a t i o n ( t h e v e r t i c a l l i n e s do n o t r e p r e s e n t s t a n d a r d d e v i a t i o n s ) . The f o l l o w i n g p a i r s o f c o n s e c u t i v e p o p u l a t i o n s w i t h i n l i n e s d i d n o t d i f f e r s i g n i f i c a n t l y : PCO s h o r t GQ and G ^ G ^ and G ^ PCO t a l l GQ and G 1 PCS t a l l G 2 and G 3 PCS s h o r t G . and G C 4 5 PBS t a l l G . and G C 4 5  t a l l e r t h a n .the c o n t r o l , and the:,sh.ort-: l i n e s s h o r t e r t h a t . the. c o n t r o l . I n PCO t h e d i v e r g e n c e , h y , ' t h e . : : f i f t h i " c y c l e of. s e l e c t i o n " amounted t o 66% of the c o n t r o l h e i g h t (+41%, -25%) o r 148 mm (+92 mm, -56mm). I n PCS, t h e d i v e r g e n c e b y .G amounted .to .78% of t h e c o n t r o l h e i g h t . (+27%,.-51%) o r 175 mm (+61 mm, -114 mm).. The means, i n . t h e .,P. . b r a c h y s t e m o n s e l e c t e d l i n e s d e p a r t e d s i g n i f i c a n t l y from t h e c o n t r o l l i n e s , b u t d i d n o t d i v e r g e , r a t h e r f l u c t u a t i n g e r r a t i c a l l y w i t h b o t h l i n e s b e i n g s h o r t e r t h a n t h e c o n t r o l i n G ^ , and G , ., and t a l l e r t h a n t h e c o n t r o l i n G ^ . I n a d d i t i o n , t h e t a l l l i n e ;was s h o r t e r t h a n t h e s h o r t l i n e i n G.. and G , . 1 4 The mean h e i g h t s i n t h e v a r i o u s s e l e c t e d l i n e s were a l s o compared g e n e r a t i o n t o g e n e r a t i o n . a n d p r o v e d t o be s i g n i f i c a n t l y d i f f e r e n t i n most c a s e s , t h e f o l l o w i n g b e i n g t h e e x c e p t i o n s : PCO s h o r t G ^ v s . G Q , G ^ V S . G „ , PCO t a l l G ~ v s . G N , PCS s h o r t . G C v s . G . , PCS t a l l G „ v s . G _ , and PBS 3 I 0 5 4 3 2 t a l l G C v s . G . . 5 4 E s t i m a t e s o f v a r i a b i l i t y • Variances The v a r i a n c e s f o r b o t h t h e raw and t r a n s f o r m e d v a l u e s o f h e i g h t were compared among a l l p o p u l a t i o n s . The v a r i a n c e s i n t h i s c a s e a r e p h e n o t y p i c , a l t h o u g h some.of t h e e n v i r o n m e n t a l component has h o p e f u l l y been e l i m i n a t e d w i t h i n g e n e r a t i o n s by t h e use o f a common e n v i r o n m e n t , and between g e n e r a t i o n s by c o r r e c t i n g t h e s e l e c t e d p o p u l a t i o n v a l u e s a g a i n s t . a n . . u n s e l e c t e d c o n t r o l . S i n c e . t h e v a r i a n c e o f a c h a r a c t e r i s dependent on t h e mean ( i n a p o p u l a t i o n , w i t h a l a r g e r mean, t h e v a r i a n c e w i l l . a l s o t e n d t o be l a r g e r ) , t h e ...selected l i n e s , were compared, by means o f t h e c o e f f i c i e n t s o f - v a r i a t i o n ( t h a t is„..,the . s t a n d a r d w d e v i a t i o n .of.:;the, mean, .as . a ..percentage o f t h e mean) i n a m o d i f i e d F - t e s t ( L e w o n t i n ; 1966) ( F i g u r e 1 3 ) . The v - 58 Figure 1 3 . G p e f fi.ci.ents,,.o.f .'-yari.a.t'ion.^0,): height ,at anthesis;~ifi .populations . , .selected for,. height.-at.;anthesls.-.. Coefficients of, v a r i a t i o n are expressed as a percentage of :.the coefficients:.in. the control . l i n e s . Populations which i n t e r s e c t the v e r t i c a l l i n e s did not .di f f e r s i g n i f i c a n t l y from the ..control population i n the same .. -generation (the v e r t i c a l l i n e s do not represent standard de v i a t i o n s ) .  c o e f f i c i e n t s o f . . v a r i a t i o n . ±n..tbe-. s e l e c t e d . ..populations .-were s i g n i f i c a n t l y . . d i f f e r e n t from t h e c o n t r o l i n 14 o u t : o f 30 c a s e s , namely PCO s h o r t G^, G^, and G. ,._PCO t a l l -G-. ,..G„ , G' , andr Gcy., PCS' s h o r t G " and ,G. , PCS t a l l G-,., PB&; 4 1 2 4 5 3 4 1 s h o r t G^» and.. PBS. t a l l . Ĝ ., G^, and .Ĝ ..... Of.. t h e s e , s i x p o p u l a t i o n s showed. an i n c r e a s e i n v a r i a t i o n (PCS and PBS l i n e s ) and e i g h t showed a d e c r e a s e i n v a r i a t i o n (PCO l i n e s , PCS t a l l ) . H e r i t a b i l i t i e s The n a r r o w sense h e r i t a b i l i t y f o r . h e i g h t a t a n t h e s i s w a s . e s t i m a t e d two 2 ways. N a r r o w . s e n s e ~ h e r i t a b i l i t y . ( h ) i s t h e p o r t i o n of t h e t o t a l p h e n o t y p i c v a r i a b i l i t y i n a p o p u l a t i o n w h i c h can be a t t r i b u t e d t o . a d d i t i v e g e n e t i c e f f e c t s , ( t h a t i s , g e n e t i c . e f f e c t s e x c l u d i n g dominance, e p i s t a s i s , and o t h e r i n t e r a c t i v e e f f e c t s ) . . - R e a l i s e d 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 . . a f t e r t h e method .of. H i l l (1972) ( T a b l e IV) . I n t h e P. ..congesta : l i n e s . t h e h e r i t a b i l i t y o f h e i g h t i s s i g n i f i c a n t and a p p r o x i m a t e l y e q u a l between t h e 2 PCS (b o r h = 0.58) and PCO (b .= 0 . 5 3 ) . l i n e s . P l e c t r i t i s b rachystemon c c * has e s s e n t i a l l y no h e r i t a b i l i t y f o r h e i g h t .under t h e c o n d i t i o n s o f t h i s e x p e r i m e n t . The e s t i m a t e s f o r PBS i n T a b l e IV a r e b r a c k e t e d because t h e method i s n o t meant t o be a p p l i e d . i n c a s e s where t h e s e l e c t e d l i n e s d i v e r g e i n t h e d i r e c t i o n o p p o s i t e t o t h e d i r e c t i o n of s e l e c t i o n , as i s t h e c a s e h e r e (see F i g u r e . 12., PBS - l i n e s . . ih.G^.. and G^) . . The e s t i m a t e d s t a n d a r d d e v i a t i o n s f o r t h e h e r i t a b i l i t y e s t i m a t e s .are q u i t e l a r g e . The e s t i m a t e d , . h e r i t a b i l i t i e s , : f r o m . . . p a r e n t - o f f s p r i n g - r e g r e s s i o n s . ( T a b l e . V) a r e i n reasonable,,agreement w i t h t h e - r e a l i s e d h e r i t a b i l i t y e s t i m a t e s . 2 The P. c o n g e s t a . l i n e s , have a f a i r l y l a r g e h and t h e r e i s l i t t l e d i f f e r e n c e 2 2 ' between t h e PCS (h = 0.44) and PCO ( h = 0.45) l i n e s . P l e c t r i t i s Table IV. Realised h e r i t a b i l i t y , calculated using the method of H i l l (1972). P. congesta PCO PCS Selection f o r early b 0.77 0.75 c or l a t e anthesis s d u 0.12 0.14 b c Selection for short b 0.53 0.58 c or t a l l height sd. 0.61 0.64 D C P. brachystemon PBS 0.49 0.22 (0.06) (0.34) Table V. H e r i t a b i l i t y , from p a r e n t - o f f s p r i n g r e g r e s s i o n s * P. congesta PCO PCS 2 Days to anthesis h 0.60 0.72 r 2 0.53 0.55 2 Height at anthesis h 0.45 0.44 r 2 0.36 0.30 * Means of four generations of c o n t r o l populations. PBS 0.42 0.48 -0.06 0.23 i ON - 63 b r achystemon .agaitu.has e s s e n t i a l l y a h e r i t a b i l i t y of zero f o r t h i s 2 character. The r . .valuesaljstech estimate .the. proportion, of,.the..total variance explained .by the regression, ori.in other words the goodness of 2 f i t of the •regression l i n e to the parents-offspring points. The r values for height are f a i r l y low, and quite a b i t lower than those for flowering time. •Components of variance An analysis of variance-was performed for a l l populations between and Gj., .partitioning the observed (phenotypic). variance i n t o components within and between fam i l i e s i n each.population. I t i s only i n p a r t i c u l a r cases, such as i n progenies i n pure breeding l i n e s or i n the F^ of a cross between pure breeding lines,.. that the variances , so p a r t i t i o n e d can be considered precise .estimates of. environmental or additive genetic components. (Falconer., I960).. . The within .family variance -in a-.pure-breeding': -line i s a-precise estimate of the environmental variance, as there i s no genetic variance present. The populations i n t h i s experiment do not represent pure breeding l i n e s , although P. brachystemon i s c e r t a i n to be highly inbred. The information that can be obtained.from.an ANOVA.comes, therefore more from any changes which might be observed.over the course of the experiment i n the p a r t i t i o n i n g of the phenotypic variance between and within f a m i l i e s . In theory ..inbreeding...will tend, .to .reduce, the.genetic .component of the within, family variance .and.-increase.-the .genetic .component of the. between .family variance. Selection, and random-drift..will, tend to decrease . the genetic components i n both within and.between family estimates. In the present - 64 s i t u a t i o n y;, .where... the., genet ic, Mstrucfcu re „of ..thei,populations.,, of,.;the two..: . . species -is unknown:,,:..,there, i s .̂ ,no';':S'$mple-̂ •p̂ .e4,i:e.ti.on'..of.̂  the ..results- of ..the ANOVA; i n . . f a c t . , the.. r e s u l t s showed v e r y . . l i t t l e . ..For. height: -at anthesis a l l three species groups had a s i g n i f i c a n t between f a m i l y component of v a r i a n c e i n most populations (Appendix 1 ). There were, no obvious trends which might have been expected,...particularly the decrease..in between f a m i l y variance which might have been expected i n response to s e l e c t i o n . Other changes i n d i s t r i b u t i o n There was no evidence from the frequency histograms of height at anthesis i n the.various.populations to suggest that there had Beenchanges i n the d i s t r i b u t i o n .other :than ..the .changes i n .mean and v a r i a n c e . That i s , there was no evidence of changes i n skewness -or k u r t o s i s , or development of b i m o d a l i t y i n the d i s t r i b u t i o n s . Days to an t h e s i s ( f l o w e r i n g time) Means As-with h e i g h t . a t a n t h e s i s , the.mean f l o w e r i n g times f o r the s e l e c t e d populations d i f f e r e d s i g n i f i c a n t l y from.the.controls In most cases, the s o l e exception i n t h i s case.being PCS e a r l y G^ (Figure 14'). High and.low s e l e c t i o n l i n e s i n a l l three, species..groups- sdiverged,.,with-.:the^early. l i n e s f l o w e r i n g e a r l i e r , than the c o n t r o l s , and the l a t e l i n e s f l o w e r i n g l a t e r . The divergence by the . f i f t h , c y c l e ..of ̂ selection.was,,, .in -the ...case .of .PCO.,.. 33.5%. of.the murnber . . of days -to. .anthesis,;.in.„the,..control.\.(«fc20%,,̂ 13.. 5%.)... or .31..8 .. days (+19..days, -12.8 days). . In PCS the .divergence was 28.7% of the c o n t r o l (+16.3%, -12.4) - 65 F i g u r e 14 Mean .number o f . days t o anthesis... ( f l o w e r i n g t i m e ) i n p o p u l a t i o n s - s e l e c t e d .for f l o w e r i n g t i m e . . Cleans a r e e x p r e s s e d as a p e r c e n t a g e o f t h e means i n t h e c o n t r o l l i n e s . . P o p u l a t i o n s w h i c h . i n t e r s e c t t h e v e r t i c a l l i n e s d i d n o t d i f f e r s i g n i f i c a n t l y f r om t h e c o n t r o l . p o p u l a t i o n i n t h e same g e n e r a t i o n ( t h e v e r t i c a l l i n e s do n o t r e p r e s e n t s t a n d a r d d e v i a t i o n s ) . The f o l l o w i n g p a i r s o f c o n s e c u t i v e p o p u l a t i o n s w i t h i n l i n e s d i d n o t d i f f e r s i g n i f i c a n t l y : PCO e a r l y • G 3 and PCO l a t e G., and G„; G. and G. 1 2 3 4 PCS e a r l y G Q,and G^ PCS l a t e G 1 and G 2; .G2 and G 3 PBS l a t e G 1 and G 2; G 2 and G 3; G^ and F i g u r e 14. PBS - 67 or 27.3 days (+15.5 .days, -11"•.8.. days J . In PBS the divergence was 18.5% of the co n t r o l (+12.2%, -6.3%) or 21.5 days.(+14.2 days, -7.3 days). The mean.flowering.times'were also compared generation to generation within the..selected, lines,, with the following populations proving nofr'to be s i g n i f i c a n t l y d i f f e r e n t : PCS early G ^ vs. G Q , PCS l a t e G ^ vs. G ^ , G ^ vs. G ^ , PCO l a t e G 2 vs. G 1 , and PBS l a t e G 2 vs. G ^ G 3 vs. G 2 . Estimates of v a r i a b i l i t y Variances The variances i n the populations were converted to c o e f f i c i e n t s of v a r i a t i o n to remove scale e f f e c t s . The c o e f f i c i e n t s of v a r i a t i o n are presented g r a p h i c a l l y i n Figure 15. The selected l i n e s were compared to the controls by means of the modified F - t e s t . f o r c o e f f i c i e n t s of v a r i a t i o n , . and were found to be s i g n i f i c a n t l y d i f f e r e n t i n 16 of the 30 populations, namely PCO ea r l y G 2 through G^, PCO l a t e G ^ and G 5 > PCS early G 2 through G 5 , PCS l a t e G 2 , G ^ , and G 5 > PBS early G 3 and G ^ , and PBS l a t e G 5 > Of these, i n a l l cases except PCS l a t e G 2 and PBS l a t e G, . the v a r i a t i o n was l e s s i n the selected l i n e s than i n the controls. The general trend i n a l l s i x selected l i n e s was towards a decrease i n the c o e f f i c i e n t of v a r i a t i o n . H e r i t a b i l i t i e s The r e a l i s e d h e r i t a b i l i t i e s . ( T a b l e IV) again reveal the basic agreement ? between the.PCO. (b .or h =0.77) and PCS (b =0.75) l i n e s . P l e c t r i t i s c c brachystemon also has a reasonably large h e r i t a b i l i t y . f o r flowering time (b = 0.49). In a l l .cases the standard deviation for the estimates i s - 68 F i g u r e 1 5 . . . C o e f f i c i e n t s , o f - v a r i a t i o n - f o r . :days t o a n t h e s i s ; i n , p o p u l a t i o n s s e l e c t e d f o r f l o w e r i n g ..time. . . C o e f f i c i e n t s o f . / v a r i a t i o n a r e e x p r e s s e d as a p e r c e n t a g e o f t h e c o e f f i c i e n t s i n t h e c o n t r o l l i n e s . . P o p u l a t i o n s w h i c h i n t e r s e c t t h e v e r t i c a l l i n e s d i d n o t . d i f f e r s i g n i f i c a n t l y f r o m t h e c o n t r o l p o p u l a t i o n i n t h e same g e n e r a t i o n , ( t h e v e r t i c a l l i n e s do n o t r e p r e s e n t s t a n d a r d d e v i a t i o n s ) . PBS — - 70 c o n s i d e r a b l y •; s m a l l e r t h a n i n t h e h e r i t a b i l i t y . e s t i m a t e s f o r h e i g h t a t a n t h e s i s . The e s t i m a t e d , h e r i t a b i l i t i e s f r o m p a r e n t - o f f s p r i n g r e g r e s s i o n s f o r f l o w e r i n g t i m e ( T a b l e y ) . a r e . c o m p a r a b l e t o t h e r e a l i s e d h e r i t a b i l i t y 2 e s t i m a t e s , w i t h t h e two P. c o n g e s t a c o n t r o l l i n e s s i m i l a r (PCO h = 0.60, 2 2 PCS h = 0.72) and t h e P. b rachystemon l i n e s l i g h t l y l e s s (h = 0.42), b u t s t i l l a p p r e c i a b l e . A g a i n , t h e r e l i a b i l i t y o f t h e e s t i m a t e s i s i n d i c a t e d 2 by t h e goodness o f f i t of t h e r e g r e s s i o n l i n e s t o t h e d a t a ( r ) , w h i c h 2 i n t h i s c a s e shows a more r e l i a b l e e s t i m a t e o f h t h a n d i d t h e r e g r e s s i o n f o r h e i g h t a t a n t h e s i s . Components o f v a r i a n c e As w i t h h e i g h t a t a n t h e s i s i n l i n e s s e l e c t e d f o r h e i g h t , a l l t h e l i n e s s e l e c t e d f o r f l o w e r i n g t i m e showed a s i g n i f i c a n t between f a m i l y component of v a r i a n c e f o r f l o w e r i n g t i m e i n most p o p u l a t i o n s . Once a g a i n , t h e r e was no s i g n i f i c a n t t r e n d i n t h e s e p a r a m e t e r s o v e r t h e c o u r s e o f t h e e x p e r i m e n t (Appendix 1 ) . O ther changes i n d i s t r i b u t i o n There was no e v i d e n c e f r o m . t h e f r e q u e n c y h i s t o g r a m s of f l o w e r i n g time i n t h e p o p u l a t i o n s s e l e c t e d f o r f l o w e r i n g t i m e t o s u g g e s t t h a t t h e r e had been changes i n t h e d i s t r i b u t i o n .other t h a n changes i n mean and v a r i a n c e . That i s , t h e r e was no e v i d e n c e of changes i n skewness o r k u r t o s i s , o r development o f b i m o d a l i t y i n t h e d i s t r i b u t i o n s . Changes i n the unselected characters -during the experiment - 71 The characters not under s e l e c t i o n - days to emergence, height at anthesis in. the l i n e s selected for flowering time, number of nodes at anthesis, number of-primary branches at anthesis, flowering time i n l i n e s selected for height at anthesis, and f r u i t production - were analysed i n the same manner as the selected characters. Means Days to emergence A number of populations departed s i g n i f i c a n t l y from the controls i n terms of the me.an- number of days to emergence: PCO early , PCO t a l l G^, PCS early G 2 > G 3 > PCS l a t e G.̂ , G^ PBS early G^ PBS t a l l G^ and PBS short G^ (Figure 16). In a l l groups selected for either height.or flowering time, the G,. means f o r days to emergence i n the plus selected l i n e s were greater than the means i n the minus selected l i n e s , with the exception of PCS selected for flowering time. However, a number of l i n e s experienced r e v e r s a l s , with the plus selected l i n e f a l l i n g , below, the minus ..selected l i n e : PCS anthesis and PCO height G^.PCS height G^, and PBS height G^. There appears to be no regular trend i n the changes i n emergence date. Height at anthesis ( i n l i n e s selected for flowering time) In the l i n e s selected f o r .flowering time, the .mean heights d i f f e r e d s i g n i f i c a n t l y from the controls i n PCO e a r l y G_, G , PCO l a t e -G. , G,, PCS - 7 2 F i g u r e 16. Mean .number ...of. d a y a ^ t o emergence . i n v a r i o u s ..populations. Means a r e . expressed-..as a . p e r e e n t a g e c o f - t h e / m e a n s i n t h e c o n t r o l l i n e s . P o p u l a t i o n s which, i n t e r s e c t .the v e r t i c a l , l i n e s d i d . n o t d i f f e r s i g n i f i c a n t l y f rom t h e c o n t r o l p o p u l a t i o n i n t h e same g e n e r a t i o n , (.the v e r t i c a l l i n e s do h o t r e p r e s e n t s t a n d a r d d e v i a t i o n s ) . a. Mean number of days t o ..emergence i n p o p u l a t i o n s s e l e c t e d f o r f l o w e r i n g t i m e . b. Mean number o f days t o emergence i n p o p u l a t i o n s s e l e c t e d f o r h e i g h t a t a n t h e s i s . PBS - 74 e a r l y -Ĝ . .PCS late. G^, •,PBS,.early » G 3 » a n d PBS l a t e G 3 (Figure 17). The plus selected lines^vere..allvtalle.r ,,than.;.the:minus selected l i n e s by G,., b u t . a l l l i n e s were shorter.than the control with the exception,of PBS l a t e . Both P. congesta, l i n e s ..experienced,^reversals i n G^. . Again, there appear to be no long, term trends.in changes i n height at anthesis i n the l i n e s selected for flowering time. Nodes at anthesis The mean number of nodes at anthesis departed s i g n i f i c a n t l y f.rom the controls i n a l l populations except PCO l a t e G^, PCO short G^jG^, PCO-tall. •G^, PCS short G^, PCS t a l l G^, and.PBS t a l l G^ (Figure 18). There was a strong trend toward divergence i n l i n e s selected for both height and flowering time, with a l l plus populations except PBS t a l l G^ above the control and a l l minus populations except PBS short G^ below i t . The strong trend toward divergence i s undoubtedly due i n part to the same factors which l e a d to a strong c o r r e l a t i o n between the number of nodes at anthesis and flowering time (see Correlations below) as the divergence i s more marked i n l i n e s selected for flowering time. Primary branches at anthesis The number of primary branches at anthesis i n the selected l i n e s showed large and somewhat e r r a t i c departures from the controls, the means being s i g n i f i c a n t l y . d i f f e r e n t i n a l l cases except PCO e a r l y G^> PCO l a t e G^, G 3, PCO short G 2, PCO t a l l . Ĝ ., G^, PCS early G 2„ PCS l a t e G^,, G 2, G3,. PCS short G , PCS t a l l G , PBS early G , PBS l a t e G,, PBS short G , .and PBS t a l l - 75 Figure 17. a. Mean height at anthesis i n populations selected f o r flowering time. Means are expressed as a percentage of the means i n the con t r o l l i n e s . Populations which i n t e r s e c t the v e r t i c a l l i n e s did not d i f f e r s i g n i f i c a n t l y from the con t r o l population i n the same generation ( the v e r t i c a l l i n e s do not represent standard deviations). b. Mean number of days to anthesis i n populations selected f o r height at anthesis. Means are expressed as a percentage of the means i n the con t r o l l i n e s . Populations which i n t e r s e c t the v e r t i c a l l i n e s did not d i f f e r s i g n i f i c a n t l y from the control population i n the same generation (the v e r t i c a l l i n e s do not represent standard deviations). F i g u r e 17. - .76 o u CO 4-1 •H G CO o cu a 4 J CH C O 4-1 60 rt rt 4-1 4-1 C cu 60 o •H H cu a) ^ ! ft C cn rt rt a) v—' 140 100 60 r 20. r b . CO •1-1 CO a) .—* 4-1 O rt M 4 J O c 4-1 o u CO >•> CH rt o T 3 cu 4-1 60 O rt 4 J H « a) CU ,g o u cu ci ft C CO rt rt cu s 110 h 100 90 t a l l s h o r t s h o r t s h o r t G e n e r a t i o n s o f s e l e c t i o n PCO PCS PBS - 77 Figure 18. Mean number of nodes at anthesis i n various populations. Means are expressed as a percentage of the means i n the control l i n e s . Populations which i n t e r s e c t the v e r t i c a l l i n e s did not d i f f e r s i g n i f i c a n t l y from the control population i n the same generation (the v e r t i c a l l i n e s do not represent standard deviations). a. Mean number of nodes at anthesis i n populations selected f o r flowering time. b. Mean number of nodes at anthesis i n populations selected f o r height at anthesis. PBS — - 79 G^ (Figure 19). In most cases there was divergence, with the plus selected l i n e s having more primary branches than the minus l i n e s . A number of reversals were observed i n the l i n e s selected f o r height at anthesis (PBS G^ and G^, PCO G^) and most l i n e s f luctuated e r r a t i c a l l y , often above and below the controls i n d i f f e r e n t generations. There may have been some e f f e c t of s e l e c t i o n i n the l i n e s selected f o r flowering time, but otherwise there were no trends i n the changes of the means. The f a c t that the selected l i n e s seem to cycle up and down r e l a t i v e to the controls from generation to generation r e f l e c t s changes i n the controls rather than i n the selected l i n e s , and indicates the s e n s i t i v i t y of t h i s character to changes i n the environment from generation to generation. Flowering time ( i n l i n e s selected f o r height at anthesis) Selection f o r height at anthesis appears to have had some e f f e c t on flowering time. A l l the selected l i n e s have diverged somewhat, with a l l being s i g n i f i c a n t l y d i f f e r e n t from the controls except PCO short G^, G^, PCO t a l l G l 9 PCS short G^ PBS short G 2 > and PBS t a l l Gl (Figure 17). The strong c o r r e l a t i o n between flowering time and number of nodes at anthesis can be seen i n the s i m i l a r i t y between the changes i n the means for the two i n l i n e s selected f o r height at anthesis (compare Figure 17 b with Figure 18 b). F r u i t production F r u i t production was a character whose measurement was subject to a great deal of error. As can be seen i n Figure 20, the means i n the selected l i n e s departed s i g n i f i c a n t l y from the controls i n many cases, the exceptions - 80 Figure 19. Mean number of primary branches at anthesis i n various populations. Means are expressed as a percentage of the means i n the control l i n e s . Populations which i n t e r s e c t the v e r t i c a l l i n e s did not d i f f e r s i g n i f i c a n t l y from the con t r o l population i n the same generation (the v e r t i c a l l i n e s do not represent standard deviations). a. Mean number of primary branches at anthesis i n populations selected f o r flowering time. b. Mean number of primary branches at anthesis i n populations selected f o r height at anthesis.  - 82 Figure 20.. Mean f r u i t production i n various populations. Means are expressed as a percentage of the means i n the control l i n e s . a. Mean f r u i t production i n populations selected f o r flowering time. The following populations did not d i f f e r from the control i n the same generation: PCO early G^, PCO l a t e G^, PCS early G 2 > G 3 > G^, PCS l a t e G ^ G 3 > PBS early G^, G 3 > and PBS l a t e G ^ Gy G^. b. Mean f r u i t production i n populations selected f o r height at anthesis. The following populations did'not d i f f e r from the cont r o l i n the same generation: PCO short G^, PCO t a l l G^, G PCS short G^, G 3 > PCS t a l l G ^ G 2 > G 3 > G^, PBS short G , and PBS t a l l G,, G.. 1 4 PBS being PCO early G^, PCO short G^, PCO t a l l G^, PCS e a r l y G 2, G 3, PCS late.Gj^,. G , PCS short G^ G^, PCS t a l l G^, G^, G 3 > PBS early G^ PBS l a t e G^, G , PBS short G^, and PBS t a l l G^. I t can also be seen that p a i r s of l i n e s , plus and minus, wander e r r a t i c a l l y but together, suggesting that most of the movement i s due to chance or error, and strongly,influenced by the f r u i t production i n the control l i n e s . Estimates of v a r i a b i l i t y Variances The variances i n the unselected characters, expressed as c o e f f i c i e n t s of v a r i a t i o n , are presented i n Appendix 2, and g r a p h i c a l l y f o r days to emergence and number , of nodes at anthesis i n Figures 21 and 22. V a r i a t i o n i n days to emergence shows a general increase, with wide f l u c t u a t i o n s , as does v a r i a t i o n i n the number of primary branches at anthesis. Height at anthesis i n l i n e s selected f o r flowering time i s les s v a r i a b l e i n PCO and PCS early by Ĝ _, and s l i g h t l y more v a r i a b l e i n PCS l a t e and PBS. V a r i a t i o n i n the number of nodes at anthesis tended to decrease, p a r t i c u l a r l y i n those l i n e s selected f o r flowering; time. V a r i a t i o n i n flowering time i n l i n e s selected f o r height at anthesis decreased i n the P^ congesta l i n e s , but fluctuated above and below the con t r o l i n the P. brachystemon l i n e s . V a r i a t i o n i n f r u i t production also changed very e r r a t i c a l l y , r e f l e c t i n g the error inherent i n the measurements. H e r i t a b i l i t i e s - 85 F i g u r e 21'. C o e f f i c i e n t s o f v a r i a t i o n f o r number o f days t o emergence i n t h e e x p e r i m e n t a l p o p u l a t i o n s . C o e f f i c i e n t s o f v a r i a t i o n a r e e x p r e s s e d as a p e r c e n t a g e o f t h e c o e f f i c i e n t s o f v a r i a t i o n i n t h e c o n t r o l l i n e s . a. C o e f f i c i e n t s o f v a r i a t i o n f o r number of days t o emergence i n PCO p o p u l a t i o n s . b. C o e f f i c i e n t s o f v a r i a t i o n f o r number of days t o emergence i n PCS p o p u l a t i o n s . c. C o e f f i c i e n t s o f v a r i a t i o n f o r number o f days t o emergence i n PBS p o p u l a t i o n s .  - 87 F i g u r e 22.. C o e f f i c i e n t s o f v a r i a t i o n f o r number o f nodes a t a n t h e s i s i n t h e e x p e r i m e n t a l p o p u l a t i o n s . C o e f f i c i e n t s o f v a r i a t i o n a r e e x p r e s s e d as a p e r c e n t a g e o f t h e c o e f f i c i e n t s o f v a r i a t i o n i n t h e c o n t r o l l i n e s . a. C o e f f i c i e n t s o f v a r i a t i o n f o r number o f nodes a t a n t h e s i s i n PCO p o p u l a t i o n s . b. C o e f f i c i e n t s o f v a r i a t i o n f o r number o f nodes a t a n t h e s i s i n PCS p o p u l a t i o n s . c. C o e f f i c i e n t s o f v a r i a t i o n f o r number o f nodes a t a n t h e s i s i n PBS p o p u l a t i o n s .  - 89 There was only one estimate of h e r i t a b i l i t y f o r the unselected characters from the experiment, as the r e a l i s e d h e r i t a b i l i t y procedure i s not a p p l i c a b l e . The h e r i t a b i l i t y estimates from parent-offspring regressions i n the c o n t r o l l i n e s f o r these characters are presented i n Table VI. 2 As i n d i c a t e d by the c o e f f i c i e n t s of determination, r , the f i t of the 2 regression l i n e i s quite poor i n most cases. I f the cases where r i s greater than 0.2 are considered alone, the following h e r i t a b i l i t i e s may be 2 estimated. For days to emergence, h =0.49 i n PCO. For nodes at anthesis, 2 h = 0.55 i n PCO, 0.57 i n PCS, and 0.28 i n PBS.; these values are comparable and somewhat intermediate to the estimated h e r i t a b i l i t i e s f o r the selected characters. Only PBS has reasonably precise estimates f o r the number of 2 . primary branches, h =0.29, and none of the l i n e s provided a r e l i a b l e estimate f o r the h e r i t a b i l i t y of f r u i t production. Components of variance There were s i g n i f i c a n t between family components of variance i n a l l the unselected characters i n a l l three species groups and most populations (Appendix 1). As with the selected characters, there were no consistent trends over the course of the experiment, and nothing to suggest changes due to s e l e c t i o n i n the p a r t i t i o n i n g of the t o t a l variance between and within f a m i l i e s . Other changes i n d i s t r i b u t i o n As with the selected characters, there was no evidence from the frequency histograms of the unselected characters to suggest any changes i n d i s t r i b u t i o n s other than the changes i n mean and v a r i a n c e / T a b l e V I . H e r i t a b i l i t i e s f rom p a r e n t - o f f s p r i n g r e g r e s s i o n s , u n s e l e c t e d c h a r a c t e r s . PCO c o n t r o l PCS c o n t r o l PBS c o n t r o l Days t o emergence .68 .09 .31 .0007- .65 .0058 .20 .0000. .43 ,18 ,12 ,28 .14 .03 .018 .082 .16 ,21 ,32 ,14 .026 .056 .14 .10 .49 Nodes a t a n t h e s i s .71 .48 .46 .17 .48 .48 .39 .059 .43 .73 .49 .65 .20 .53 .46 .80 .066 .13 .28 .13 .0084 .052 .25 .087 x .55 .57 .'28 P r i m a r y b r a n c h e s a t a n t h e s i s .05 .27 .076 .12 .0043 .092 .02 .035- .081 .34 .24 .38 .02 .22 .22 .18 .22 .29 ,20 .13 .069 .14 .18 .053 .29 Table VI, continued. PCO c o n t r o l PCS c o n t r o l PBS c o n t r o l u 2 2 .,2 2 ,2 ' 2 h r h r ' h r F r u i t p r o d u c t i o n G .05 .0052 -.015 .0009 .15 .14 G 3 -.10 ' .055 .11 . .07 -.034 .0045 G. .15 .099 .11 .023 -.083 .011 4 G 5 .079 , .02 -.11. .055 -.033 .0059 - 92 The e f f e c t s of s e l e c t i o n on c o r r e l a t i o n s among the measured characters The c o r r e l a t i o n between height at anthesis and flowering time, the characters under s e l e c t i o n . The correlation.between the selected characters, height at 1,anthesis and flowering time, was i n i t i a l l y s i g n i f i c a n t and p o s i t i v e i n a l l three species groups (Figure 23). I t decreased more or l e s s s t e a d i l y towards no c o r r e l a t i o n i n the PBS l i n e s , even becoming s i g n i f i c a n t l y negative i n two cases (PBS t a l l and PBS short G^). There was some decrease evident i n the P_ congesta-. l i n e s , p a r t i c u l a r l y i n the t h i r d cycle, G^, when several of the populations showed a s i g n i f i c a n t negative c o r r e l a t i o n , but by G^ the c o r r e l a t i o n s were mostly p o s i t i v e again, and i t i s d i f f i c u l t to discern any trend from the f i r s t f i v e generations of s e l e c t i o n . Other c o r r e l a t i o n s The other c o r r e l a t i o n s can be divided into three broad groups. In some cases, the c o r r e l a t i o n s d i f f e r e d between the P. congesta l i n e s and the P. brachystemon l i n e s . In the c o r r e l a t i o n s between height at anthesis and number of primary branches (Figure 24), number of nodes and number of primary branches (Figure 25), and height at anthesis and f r u i t production (Figure 26) the c o r r e l a t i o n s i n the PBS l i n e s were strong and p o s i t i v e , while the c o r r e l a t i o n s i n the PCO and PCS l i n e s were mostly not s i g n i f i c a n t and not con s i s t e n t l y p o s i t i v e or negative. In some cases the c o r r e l a t i o n s were e s s e n t i a l l y s i m i l a r in. a l l three species groups and mostly not s i g n i f i c a n t , or when s i g n i f i c a n t not - 93 Figure 23. Correlations between height at anthesis and flowering time. 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 i s graphed f o r every population. C o r r e l a t i o n c o e f f i c i e n t s which are s i g n i f i c a n t at the 5% l e v e l are joined by a continuous l i n e ; l i n e s are broken at those generations i n which the c o r r e l a t i o n was not s i g n i f i c a n t at the 5% l e v e l . a. Correlations i n PCO populations. b. Correlations i n PCS populations. c. Correlations i n PBS populations. early X v ? : l a t e S.\. t a l l V s h o r t N e a r l y l a t e e arly ^ t a l l short Generations of s e l e c t i o n Control Height Anthesis - 95 Figure 24. Correlations between height at anthesis and number of primary branches at anthesis. 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 i s graphed f o r every population. C o r r e l a t i o n c o e f f i c i e n t s which are s i g n i f i c a n t at the 5% l e v e l are joined by a continuous l i n e ; l i n e s are broken at those generations i n which the c o r r e l a t i o n was not s i g n i f i c a n t at the 5% l e v e l . a. Correlations i n PCO populations. b. Correlations i n PCS populations. c. Correlations i n PBS populations. Figure 24. .5 a. PCO b. PCS c. PBS CO •H CO C U Xi 4-1 0 c0_ 4J n) co cu Xi a fl cd H >. H Cfl •S M ft CO > CO •rH. CO cu 4-1 c cc) 4-> n) 4-1 Xi 6 0 •H CU Xi 4-1 a cu •H O •H 4-1 m cu o o a o •H cu H M O I l a t e 5 e a r l \ short - t a l l -.5 .5 r t a l l _ l a t e short e a r l y -.5 1- l a t e short — t a l l e a r ly - . S i - Generations of s e l e c t i o n Control Height . Anthesis - 97 Figure 25. C o r r e l a t i o n s between number of nodes at anthesis and number of primary branches at a n t h e s i s . 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 i s graphed f o r every p o p u l a 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 which are s i g n i f i c a n t at the 5% l e v e l are j o i n e d by a continuous l i n e ; l i n e s are broken at those generations i n which the c o r r e l a t i o n was not s i g n i f i c a n t at the 5% l e v e l . a. C o r r e l a t i o n s i n PCO populations. b. C o r r e l a t i o n s i n PCS p o p u l a t i o n s . c. C o r r e l a t i o n s i n PBS populations. Figure 25. - 98 a. PCO CO •w CO cu Xi •U Ci cd .5 CO cu Xi a % -.5 XI >. u cd I a. b. PCS CO > CO •H CO <u Xi CO Q) O d .5 -.5 I- c. PBS cu •H a <4-( <-H (U O O c O •H J-l cd r H (U rJ o O I short .5 r early -.5 Generations of s e l e c t i o n ..A Control Height Anthesis - 99 Figure 26. Correlations between height at anthesis and f r u i t production. 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 i s graphed f o r every population. C o r r e l a t i o n c o e f f i c i e n t s which are s i g n i f i c a n t at the 5% l e v e l are joined by a continuous l i n e ; l i n e s are broken at those generations i n which the correlation: was not s i g n i f i c a n t at the 5% l e v e l . a. Correlations i n PCO populations. b. Correlations i n PCS populations. c. Correlations i n PBS populations. Figure 26. a. PCO .5 - 100 short l a t e e arly t a l l b. PCS o • r l 4-> a T) O u PH 4 J • H 3 H 4-1 to > CO • H CO cu XI 4-1 a CO - .5 I- .5 early V" «short x l a t e - ' t a l l xi 6 0 • r l 0 ) Xi - .5 c. PBS cs d) • r l CJ • r l •4H m CU o o c o • r l 4 J n) rH cu M rl o CJ .5 -.51- 0 - early y •==^^»-^_. late' short t a l l Generations of s e l e c t i o n Control Height Anthesis - 101 co n s i s t e n t l y p o s i t i v e or negative within a species group. For example, co r r e l a t i o n s between days to emergence and height at anthesis (Figure 27), days to emergence and number of nodes at anthesis (Figure 28), number of nodes at anthesis and f r u i t production (Figure 29), and primary branches and flowering time (Figure 30) f l u c t u a t e between being s i g n i f i c a n t and p o s i t i v e , n o n - s i g n i f i c a n t , and s i g n i f i c a n t and negative, often within the same l i n e (for example, primary branches vs. flowering time i n PBS short shows t h i s kind of pattern), F i n a l l y , some of the c o r r e l a t i o n s were for the most part s i g n i f i c a n t i n a l l three species groups, and remained so throughout the experiment. This i s the case with negative c o r r e l a t i o n s between days to emergence and number of primary branches (Figure 31), days to emergence and f r u i t production (Figure 32), and flowering time and f r u i t production (Figure 33). S i g n i f i c a n t p o s i t i v e c o r r e l a t i o n s were observed c o n s i s t e n t l y between days to emergence and flowering time, with the exception of and G,. i n the PBS l i n e s , i n which the c o r r e l a t i o n disappeared (Figure 34), between number of nodes and flowering time (Figure 35), number of primary branches and f r u i t production (Figure 36), and height at anthesis and number of nodes, with the exception of some of the populations i n G^, i n which the c o r r e l a t i o n dropped (Figure 37). I t must be remembered that these are phenotypic, rather than genotypic, c o r r e l a t i o n s , and as such are subject to environmental e f f e c t s . Nevertheless, there does not appear to have been any change i n any of the c o r r e l a t i o n s between the various characters which could be a t t r i b u t e d to the e f f e c t s of s e l e c t i o n , except perhaps i n the case of the c o r r e l a t i o n s between the selected characters. - 1 0 2 Figure 27. Correlations between number of days to emergence and height at anthesis. 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 i s graphed f o r every population. C o r r e l a t i o n c o e f f i c i e n t s which are s i g n i f i c a n t at the 5% l e v e l are joined by a continuous l i n e ; l i n e s are broken at those generations i n which the c o r r e l a t i o n was not s i g n i f i c a n t at the 5% l e v e l . a. Correlations i n PCO populations. b. Correlations i n PCS populations. c. Correlations i n PBS populations. F i g u r e 27. - 103 a. PCO b. PCS c. PBS cn •H cn cu xi •U c cO ^ 3 6 0 •r4 CU X ! CO > cu CJ C cu 6 0 H CU a cu cn > CO . T3 4-1 a cu •H a •H 4-1 <4-l CU O CJ C o •H 4-1 cd r H CU H H O O e a r l y t a l l h o r t a t e G e n e r a t i o n s o f s e l e c t i o n C o n t r o l H e i g h t A n t h e s i s - 1 0 4 Figure 28. Correlations between number of days to emergence and number of nodes at anthesis. 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 i s graphed f o r every population. C o r r e l a t i o n c o e f f i c i e n t s which are s i g n i f i c a n t at the 5% l e v e l are joined by a continuous l i n e ; l i n e s are broken at those generations i n which the c o r r e l a t i c was not s i g n i f i c a n t at the 5% l e v e l . a. Correlations i n PCO populations. b. Correlations i n PCS populations. c. Correlations i n PBS populations. Figure 28. .5 - 105 Generations of selection Control Height Anthesis - 106 Figure 29. Correlations between number of nodes at anthesis and f r u i t production. 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 i s graphed f o r every population. C o r r e l a t i o n c o e f f i c i e n t s which are. s i g n i f i c a n t at the 5% l e v e l are joined by a continuous l i n e ; l i n e s are broken at those generations i n which the c o r r e l a t i o n was not s i g n i f i c a n t at the 5% l e v e l . a. Correlations i n PCO populations. b. Correlations i n PCS populations. c. Correlations i n PBS populations. Figure 29. . 5 a. PCO " l a t e ' a^, . early :short t a l l b. PCS a o • r l 4 J O 0 'U o u o. 4-> • r l P u 4-1 CO > CO • r l CO QJ X I 4-1 c cd -4-1 cd CO a) o a - . 5 I l a t e — : early -~ t a l l short c. PBS 4-> C CU • r l a • r l m <4H o CJ o • r l (U i - l O CJ 3 . 5 early ' l a t e - . 5 r Generations of s e l e c t i o n Control Height Anthesis - 108 Figure 30. Correlations between number of primary branches at anthesis and flowering time. 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 i s graphed f o r every population. C o r r e l a t i o n c o e f f i c i e n t s which are s i g n i f i c a n t at the 5% l e v e l are joined by a continuous l i n e ; l i n e s are broken at those generations i n which the c o r r e l a t i o n was not s i g n i f i c a n t at the 5% l e v e l . a. Correlations i n PCO populations. b. Correlations i n PCS populations. c. Correlations i n PBS populations. F i g u r e 30. - 109 .5i a. PCO b. PCS S •r l 60 •r l u CD O CO > CO CD x; o "S u >. M ec) & ! - l -.51 0 s h o r t c. PBS a CD •r l o •r l m a) o o cl o •r l CD u o CJ Pi s h o r t f -. e a r l y '" t a l l l a t e G e n e r a t i o n s o f s e l e c t i o n C o n t r o l H e i g h t A n t h e s i s - 110 Figure 31. Correlations between number of days to emergence and number of primary branches at anthesis. 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 i s graphed for every population. C o r r e l a t i o n c o e f f i c i e n t s which are s i g n i f i c a n t at the 5% l e v e l are joined by a continuous l i n e ; l i n e s are broken at those generations i n which the c o r r e l a t i o n was not s i g n i f i c a n t at the 5% l e v e l . a. Correlations i n PCO populations. b. Correlations i n PCS populations. c. Correlations i n PBS populations. F i g u r e 31. .5 a. PCO co QJ o a rt H rQ > , H rt s • r l H ft -.5 t a l l 44 b. PCS CO > a) o C cu 60 H a) a cu _ o 4J CO rt _____ x - ^ c r — \ — i : e a r l y JxC l a t e -.5 — s h o r t t a l l e QJ •A U •H 4-1 4H CU O CJ (3 O •H .5 c. PBS cu u u o o u Pi -.5 + e a r l y t a l l s h o r t G e n e r a t i o n s o f s e l e c t i o n C o n t r o l H e i g h t A n t h e s i s - 112 Figure 32. Correlations between number of days to emergence and f r u i t production. 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 i s graphed f o r every population. C o r r e l a t i o n c o e f f i c i e n t s which are s i g n i f i c a n t at the 5% l e v e l are joined by a continuous l i n e ; l i n e s are broken at those generations i n which the c o r r e l a t i o n was not s i g n i f i c a n t at the 5% l e v e l . a. Correlations i n PCO populations. b. Correlations i n PCS populations. c. Correlations i n PBS populations Figure 32. - 113 a. PCO a o •H 4- 1 O 3 T) O 5- I PH 4 J •H 3 U 4-1 -.5 • l a t e - t a l l short early b. PCS > cu a 0) 60 cu § 4-1 CO >^ a) T3. -.5 short — -=~"= l a t e e arly t a l l 4-1 Cl CU •H CJ •H <4-l m cu o a CJ o •H c. PBS (U ! - l U O a Pi early :•• - r :• short t a l l — - l a t e -.5 Generations of s e l e c t i o n Control Height Anthesis - 114 Figure 33. Correlations between flowering time and f r u i t production. 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 i s graphed f o r every population. C o r r e l a t i o n c o e f f i c i e n t s which are s i g n i f i c a n t at the 5% l e v e l are joined by. a continuous l i n e ; l i n e s are broken at those generations i n which the c o r r e l a t i o n was not s i g n i f i c a n t at the 5% l e v e l . a. Correlations i n PCO populations. b. Correlations i n PCS populations. c. Correlations i n PBS populations. Figure 33. a. PCO o •H •U CJ s 13 O M ft U •H 3 H m -.5 l a t e »—^ early *' short t a l l CO > b. PCS c M H QJ_ & O 4H S CD •H O •rl 4-1 HH <u o o (3 O •H .5 I- 0 .5 i- c. PBS cu u u o o Ai u Pi -.5 I- short ~ 1 e a r l y — t a l l l a t e Generations of s e l e c t i o n Control Height — Anthesis — - 116 Figure 34. Correlations between number of days to emergence and flowering time. 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 i s graphed f o r every population. C o r r e l a t i o n c o e f f i c i e n t s which are s i g n i f i c a n t at the 5% l e v e l are joined by a continuous l i n e ; l i n e s are broken at those generations i n which the c o r r e l a t i o n was not s i g n i f i c a n t at the 5% l e v e l . a. Correlations i n PCO populations. b. Correlations i n PCS populations. c. Correlations i n PBS populations. Figure 34-. a. PCO .5 h t a l l e a r l y short l a t e Generations of s e l e c t i o n Control Height Anthesis - 118 Figure 35. Correlations between number of nodes at anthesis and flowering time. 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 i s graphed f o r every population. C o r r e l a t i o n c o e f f i c i e n t s which are s i g n i f i c a n t at the 5% l e v e l are joined by a continuous l i n e ; l i n e s are broken at those generations i n which the c o r r e l a t i o n was not s i g n i f i c a n t at the 5% l e v e l . a. Correlations i n PCO populations. b. Correlations i n PCS populations. c. Correlations i n PBS populations. F i g u r e 35-. C o n t r o l H e i g h t A n t h e s i s - 120 Figure 36. Correlations between number of primary branches at anthesis and f r u i t production. 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 i s graphed f o r every population. C o r r e l a t i o n c o e f f i c i e n t s which are s i g n i f i c a n t at the 5% l e v e l are joined by a continuous l i n e ; l i n e s are broken at those generations i n which the c o r r e l a t i o n was not s i g n i f i c a n t at the 5% l e v e l . a. Correlations i n PCO populations. b. Correlations i n PCS populations. c. Correlations i n PBS populations. F i g u r e 36. G e n e r a t i o n s o f s e l e c t i o n C o n t r o l — H e i g h t A n t h e s i s - 122 Figure 37. Correlations between height at anthesis and number of nodes at anthesis. 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 i s graphed f o r every population. Correlation c o e f f i c i e n t s which are s i g n i f i c a n t at the 5% l e v e l are joined by a continuous l i n e ; l i n e s are broken at those generations i n which the c o r r e l a t i o n was not s i g n i f i c a n t at the 5% l e v e l . a. Correlations i n PCO populations. b. Correlations i n PCS populations. c. Correlations i n PBS populations. Figure 37. - 1 a. PCO CO • r l CO cu xi 9 .5 -.5 b. PCS CO cu T 3 o CO > CO • r l CO cu Xi 4-1 a cd Xi oo • r l CU l a t e t a l l e a r ly short c. PBS a cu • r l o • H 14-1 cu o o s o • H CU M U o o Ai Pi .5 l a t e short t a l l x early -.5 Generations of s e l e c t i o n Control Height , Anthesis - 124 Changes i n q u a l i t a t i v e characters A number of q u a l i t a t i v e f r u i t characters were recorded i n the P^ congesta l i n e s , namely numbers and frequencies of winged and wingless f r u i t e d plants from generation to generation, numbers and frequencies of the various pubescence patterns, and numbers and frequencies of various f r u i t colours. The winged and wingless frequncies i n the experimental populations are presented i n Figure 11, and the frequencies of the pubescence patterns i n Figures 7 to 10. I decided that the f r u i t colour scoring was too a r b i t r a r y and l i k e l y to have been subject to systematic change over the s i x generation period, and so have not attempted to include an analysis of t h i s character. . There are d e f i n i t e l y d i f f e r e n t colour morphs i n t h i s species which, l i k e the wing shape character are fairly constant within plants and v a r i a b l e between, but a more r e l i a b l e and objective scoring procedure needs to be devised to work with them. Winged and wingless plant frequencies There i s no evidence of anything other than random d r i f t a f f e c t i n g the phenotype frequencies at the f r u i t wing locus. There i s no consistent divergence or other r e l a t i o n s h i p between the plus and minus selected l i n e s , whether selected f o r flowering time of height at anthesis. The increase i n variance i n the observed frequencies among the l i n e s (from 0 to 0.020 i n the PCO l i n e s and from 0 to 0.043 i n the PCS l i n e s ) i s 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 dispersion expected to r e s u l t from random d r i f t (from 0 to 0.022 i n 4 generations) (Falconer, 1960). - 125 Pubescence patterns The s i t u a t i o n with the pubescence patterns i s s i m i l a r to that with the f r u i t wing phenotypes. There i s no apparent pattern or trend i n the frequencies which might be explained by or a t t r i b u t e d to the s e l e c t i o n procedure. In t h i s case the increase i n variance among the PCO l i n e s appears to be s l i g h t l y larger than among the PCS l i n e s , p a r t i c u l a r l y i n pubescence types 2, 3, and 4, but as the genetic mechanism c o n t r o l l i n g the character i s unknown, the change i n dispersion cannot be compared to any t h e o r e t i c a l p r e d i c t i o n , as i t could i n the case of the f r u i t wing locus. As may be expected i n such r e l a t i v e l y small, inbred populations, the rarer phenotypes 0 and 1 have been l o s t i n many of the l i n e s . Aberrant characters The frequencies of the various i n d i v i d u a l s or characters observed are presented i n Table VII. The o v e r a l l trend was towards an increase i n frequency compared to the frequencies observed i n the base populations. The PCO l a t e and PCS short l i n e s had p a r t i c u l a r l y high frequencies of abnormal types, and the P. congesta populations produced s i g n i f i c a n t l y 2 more abnormals than the P. brachystemon populations (x^£^_= 67.95, p < 0.0001). The G,_ source populations had low frequencies of aberrant types, s i m i l a r to the frequencies observed i n the G^ base populations, to which they are 2 comparable (X(_£_1= 0.85, p = 0.4). Comparisons between the i n t e r n a l c o n t r o l populations and the G^ source population. T a b l e V I I . . F r e q u e n c i e s of a b e r r a n t i n d i v i d u a l s . C o t y l e d o n s Three Fused S e e d l i n g s C h l o r o t i c Dark Pigment PCO PCS PBS PCO PCS PBS . PCO PCS PBS PCO PCS PBS 2 3 3 3 4 7 3 1 3 4 9 2 1 5 2 1 2 1 2 6 1 5 5 9 2 2 5 7 4 3 26 12 12 2 14 ' 5 15 1 1 3 6 2 1 2 H a b i t O t h e r s PCO •PCS PBS PCO PCS PBS 1 2 !0 •6 15 8 1 2 11 9 12 8 11 1 3 10 PCO 452 680 •806 837 919 932 G,. s o u r c e PCS 453 588 785 799 858 909 75 PBS 304 796 765 872 974 915 93 T o t a l 1209 2004 2356 2508 2751 2756 168 PCO .020 .028 .038 .017 .034 .033 Frequency PCS PBS .007 .029 .046 .024 .024 .053 .013 .003 .008 .021 .003 .006 .019 0 T o t a l .011 .020 .035 .014 .021 .034 .006 - 127 The two source populations, one of P. congesta and one of P. brachystemon, were grown i n order to investigate whether uncontrolled s e l e c t i o n pressures, random d r i f t , or other processes had affected the i n t e r n a l c o n t r o l l i n e s . Quantitative characters The s t a t i s t i c s f o r the measured characters i n the PC source G^ and PB source G,. populations are presented i n Table VIII, along with the s t a t i s t i c s f o r the G^ controls, f o r comparison. P l e c t r i t i s congesta The P. congesta co n t r o l l i n e s d i d not change s i g n i f i c a n t l y i n mean height at anthesis, number of nodes at anthesis, or number of primary branches at anthesis over the course of the experiment. There was a s i g n i f i c a n t decrease i n mean number of days to emergence and i n days to anthesis, which may w e l l be the r e s u l t of some s e l e c t i v e pressure f o r a shortened l i f e cycle under the crowded conditions i n the experimental populations. The phenotypic variance as estimated by the c o e f f i c i e n t of variance was unchanged i n a l l characters except the number of primary branches at anthesis, for which both co n t r o l l i n e s became s i g n i f i c a n t l y more v a r i a b l e , and flowering time, f o r which the PCS control l i n e became s i g n i f i c a n t l y more v a r i a b l e . P l e c t r i t i s brachystemon The P_̂  brachystemon con t r o l populations developed s i g n i f i c a n t Table VIII. Measured characters: G 5 source populations compared with control populations. N Mean Standard C o e f f i c i e n deviation v a r i a t i o n Days to emergence PCO con t r o l G 5 195 15.344 2.4198 15.77 PCS con t r o l G 5 192 15.620 2.6101 16.71 PC source G,_ 74 18.554* 2.9477 15.89 PBS con t r o l G 5 187 15.829 2.7519 17.39 PB source G,. 93 17.946* 2.8028 15.62 Height at anthesis (mm) PCO con t r o l G 5 157 331.19 68.334 20.63 PCS control G 5 165 339.05 61.979 18.28 PC source G,- 73 315.92 53.351 16.89 PBS con t r o l G 5 153 524.42 84.939 16.20 PB source G<- 89 444.07* 55.570 12.51** Number of nodes at anthesis PCO control G 5 159 7.9686 0.9963 12.50 PCS con t r o l G 5 164 8.1829 1.4197 17.35 PC source G^ 73 7,8219 1.1942 15.27 PBS con t r o l G 5 153 10.209 1.0108 9.90 PB source G,. 89 9.618* 0.9944 10.34 Number of primary branches PCO con t r o l G 5 158 5.5506 3.7204 67.03 PCS con t r o l G,. 165 5.5212 3.8407 69.56 PC source G^ 73 6.6301 3.5099 52.94** PBS con t r o l G 5 153 10.993 5.0945 46.34 PB source G,. 89 11.775 7.3450 62.37** T a b l e V I I I , c o n t i n u e d . N Mean S t a n d a r d C o e f f i c i e n t o f d e v i a t i o n v a r i a t i o n Days t o a n t h e s i s PCO c o n t r o l G 5 163 73.736 5.1169 6.94 PCS c o n t r o l G 5 174 75.167 6.4217 8.54 PC s o u r c e G c 73 75.616* 4.4648 5.90** ( v s . PCS) PBS c o n t r o l G 5 160 93.331 4.6415 4.97 PB s o u r c e G 5 91 88.835* 5.0514 5.69 * Mean v a l u e s i n t h e s o u r c e p o p u l a t i o n s i n d i c a t e d a r e s i g n i f i c a n t l y d i f f e r e n t f r o m t h e c o n t r o l p o p u l a t i o n s a t t h e 5% l e v e l . ** C o e f f i c i e n t s o f v a r i a t i o n i n t h e s o u r c e p o p u l a t i o n s i n d i c a t e d a r e s i g n i f i c a n t l y d i f f e r e n t f r o m t h e c o n t r o l p o p u l a t i o n s a t t h e 1% l e v e l . - 130 differences from the source population over the course of the experiment for a l l the characters except number of primary branches. The mean number of days to emergence decreased s i g n i f i c a n t l y i n the con t r o l line;, and the mean height at anthesis, number of nodes at. anthesis, and days to anthesis a l l increased s i g n i f i c a n t l y with respect to the source population. The variance of the PBS con t r o l was s i g n i f i c a n t l y increased i n height at anthesis, and s i g n i f i c a n t l y decreased i n number of primary branches at anthesis; variances f o r the other characters were unchanged* Correlations There were no s i g n i f i c a n t c o r r e l a t i o n s i n the G,. source populations which suggested that there had been any change i n the con t r o l l i n e over the course of the experiment (Table IX). Table IX. Correlations i n the G,. source populations. P. congesta Height at anthesis -.2163 Nodes at anthesis -.2769* 0.1698 Primary branches -.3123* 0.2056* 0.3121* Days to anthesis 0.3443* 0.0174 0.6226* Days to Height at Nodes at emergence anthesis anthesis P. brachystemon Height at anthesis Nodes at anthesis Primary branches Days to anthesis -.4984* -.2756* -.2936* 0.1290 Days to emergence 0.2987* 0.3381* -.0137 Height at anthesis 0.3864* 0.4910* Nodes at anthesis * C o r r e l a t i o n c o e f f i c i e n t s s i g n i f i c a n t at the 5% l e v e l . -.0234 Primary branches 0.0558 Primary branches - 132 Summary of r e s u l t s Breeding system i n P l e c t r i t i s Source populations P l e c t r i t i s congesta had an estimated outcrossing rate of 61.6%. In P l e c t r i t i s brachystemon the outcrossing rate was not estimated, but assumed to be less than 5%. Experimental populations The P. congesta outcrossed populations (PCO) had an estimated outcrossing rate of 65%. The P. congesta s e l f e d populations (PCS) had an estimated outcrossing rate of 15%. The P. brachystemon populations ;(PBS) had an assumed outcrossing rate of less than 5%. C h a r a c t e r i s t i c s of the base populations The mean values for days to emergence, height at anthesis, number of nodes at anthesis, number of primary branches at anthesis, days to emergence, and flowering time were greater i n the P. brachystemon populations than i n the P. congesta populations. P. brachystemon was more v a r i a b l e f o r days to emergence, height at anthesis and nodes at anthesis, less v a r i a b l e f o r primary branches and flowering time. Response to s e l e c t i o n Selected characters Height at anthesis Means The PCO l i n e s diverged 66% or 148 mm compared to the control (+ 41%, 92mm; - 25%, 56mm); the PCS l i n e s diverged 78% or 175 mm (+ 27%, 61 mm; - 51%, 114 mm); the PBS l i n e s showed no divergence, but e r r a t i c f l u c t u a t i o n s r e l a t i v e to the c o n t r o l . - 133 Variances There were no trends i n the changes i n variance as estimated by c o e f f i c i e n t s of v a r i a t i o n ; some populations showed s i g n i f i c a n t increases, some s i g n i f i c a n t decreases r e l a t i v e to the c o n t r o l . H e r i t a b i l i t i e s In PCO the r e a l i s e d h e r i t a b i l i t y (b c) was estimated as 2 0.53; h e r i t a b i l i t y from parent-offspring regressions (h ) 2 was estimated as 0.45. In PCS b = 0.58, h =0.44. In c PBS neither estimate was s i g n i f i c a n t l y d i f f e r e n t from zero. Components of variance S i g n i f i c a n t between family variance components were observed i n most populations. There were no trends i n changes i n the p a r t i t i o n i n g of between / within family components over the course of the experiment. to anthesis (flowering time) Means The PCO l i n e s diverged 33.5% or 31.8 days compared to the control (+ 20%, 19 days; - 13.5%, 12.8 days); the PCS l i n e s diverged 28.7% or 27.3 days (+ 16.3%, 15.5 days; - 12.4%, 11.8 days); and the PBS l i n e s diverged 18.5% or 21.5 days (+ 12.2%, 14.2 days; - 6.3%, 7.3 days). Variances The trend i n a l l s i x selected l i n e s was towards a decrease i n the variance of flowering time as estimated by the c o e f f i c i e n t of v a r i a t i o n . H e r i t a b i l i t i e s In PCO b = 0.77, h 2 = 0.60; i n PCS b =0.75, h 2 = 0.72; c c - 134 2 and i n PBS b =0.49, h = 0.42. c Components of variance S i g n i f i c a n t between family variance components were observed i n most populations. There were no trends i n changes i n the p a r t i t i o n i n g of between / within family components over the course of the experiment. Unselected characters Days to emergence There were no strong trends i n changes i n means or variances. 2 H e r i t a b i l i t y (h ) was estimated at 0.49 i n PCO con t r o l l i n e ; Height at anthesis ( i n l i n e s selected f o r flowering time) There was some divergence i n the means i n the P___ congesta plus and minus l i n e s , but no trend i n the means i n the PBS l i n e s . There were no trends i n the changes i n variances. Number of nodes at anthesis There was marked divergence i n the means for a l l l i n e s except PBS selected f o r height at anthesis. Some trend toward a decrease i n variance was observed, p a r t i c u l a r l y i n l i n e s 2 selected f o r flowering time. H e r i t a b i l i t y (h ) was estimated as 0.55 i n PCO, 0.57 i n PCS and 0.28 i n PBS. Number of primary branches at anthesis There was some divergence i n the means except f o r PBS selected for height at anthesis. There were e r r a t i c , changes i n the means from generation to generation r e l a t i v e to the controls. There were no trends i n changes i n the variances. H e r i t a b i l i t y 2 (h ) was estimated as 0.29 i n PBS co n t r o l . Days to anthesis ( i n l i n e s selected f o r height at anthesis) - 135 There was marked divergence i n means and a decrease i n variances i n the P.. congesta l i n e s ; there were no trends i n changes i n means, or variances i n the PBS l i n e s . Fruit.production There were no trends i n changes i n means or variances i n any of the l i n e s . Correlations There were many s i g n i f i c a n t c o r r e l a t i o n s , both p o s i t i v e and negative, among the measured characters. The only s i g n i f i c a n t change i n co r r e l a t i o n s over the course of the experiment was the disappearance of the strong p o s i t i v e c o r r e l a t i o n between the two selected characters, height at anthesis and flowering time. Q u a l i t a t i v e characters There was no evidence of anything other than random d r i f t a f f e c t i n g the frequencies of the f r u i t wing phenotypes and f r u i t pubescence pattern phenotypes over the course of the experiment. There was some evidence of an increase of aberrant types, p a r t i c u l a r l y i n the P. congesta populations, which might be at t r i b u t e d to inbreeding. - 136 D i s c u s s i o n The q u e s t i o n s t o w h i c h t h i s s t u d y was a d d r e s s e d a r e : 1. I s a p o p u l a t i o n o f i n b r e e d i n g p l a n t s more o r l e s s v a r i a b l e g e n e t i c a l l y t h a n a p o p u l a t i o n o f o t h e r w i s e i d e n t i c a l o u t b r e e d i n g p l a n t s w i t h r e s p e c t t o q u a n t i t a t i v e l y i n h e r i t e d c h a r a c t e r s ; 2. Does th e r e s p o n s e to s e l e c t i o n f o r s u c h c h a r a c t e r s i n the two p o p u l a t i o n s r e f l e c t t h e d i f f e r e n c e ; and 3. How does t h e g e n e t i c v a r i a b i l i t y as e s t i m a t e d by t h e r e s p o n s e t o s e l e c t i o n compare t o o t h e r e s t i m a t e s o f g e n e t i c v a r i a b i l i t y i n t h e two p o p u l a t i o n s ? The e x p e r i m e n t a l s p e c i e s P l e c t r i t i s c o n g e s t a and P_j_ b r a c h y s t e m o n a r e as n e a r l y i d e n t i c a l as two s e x u a l l y r e p r o d u c i n g s p e c i e s w i t h r e s p e c t i v e l y o u t c r o s s i n g and s e l f i n g b r e e d i n g systems a r e l i k e l y t o be. I n b o t h v e g e t a t i v e h a b i t and h a b i t a t t h e y a r e n e a r l y i m p o s s i b l e t o d i s t i n g u i s h . They b o t h have chromosome numbers r e p o r t e d o f n = 16 (Morey, .1963; T a y l o r and Brockman, 1966). The M i l l H i l l p o p u l a t i o n s have t h e r e q u i r e d b r e e d i n g s y s t e m d i f f e r e n c e s , w i t h an o u t c r o s s i n g r a t e of 61.6% i n t h e P. c o n g e s t a p o p u l a t i o n , and a r a t e o f l e s s t h a n 5% i n t h e P^ b r a c h y s t e m o n p o p u l a t i o n . G e n e t i c v a r i a b i l i t y and t h e r e s p o n s e t o s e l e c t i o n D i r e c t r e s p o n s e s P l e c t r i t i s c o n g e s t a o u t c r o s s e d v e r s u s P_j_ c o n g e s t a s e l f e d There i s no e v i d e n c e o f any d i f f e r e n c e between t h e two s.ets o f c o n g e s t a - 137 populations i n t h e i r d i r e c t response to s e l e c t i o n f o r e i t h e r height at anthesis or flowering.time,, despite an estimated difference i n outcrossing r a t e under the experimental conditions of about 50% (PCO t = 0.65, PCS t = 0.15). There was approximately equal change i n the means, that i s , a divergence of 66% i n PCO,.78% i n PCS plus and minus l i n e s selected f o r height at anthesis, and of.33.5% i n PCO 28.7% i n PCS plus and minus l i n e s selected f o r flowering time. There was no differ e n c e between the outcrossed and se l f e d P. congesta groups i n the trends i n the c o e f f i c i e n t s of v a r i a t i o n , with e r r a t i c changes i n both f o r the v a r i a b i l i t y of height at anthesis, and a general decrease i n both f o r the v a r i a b i l i t y of flowering time. And, f i n a l l y , the estimates of h e r i t a b i l i t y were e s s e n t i a l l y the same for height at anthesis ( b c : PCO = 0.53, PCS.= 0.58; h 2 : PCO =0.45, PCS-= 0.44) and for flowering time ( b c : PCO = 0.77, PCS = 0.75; h 2 : PCO = 0.60, PCS = 0.72). It i s l i k e l y that the small population s i z e s i n the experiment (N = 200) combined with the i n t e n s i t y of the s e l e c t i o n (90%) to produce a rate of inbreeding which swamped any differences i n inbreeding a t t r i b u t a b l e to differences i n the outcrossing rates. In comparisons with the P. brachystemon populations, therefore, I w i l l t r e a t the P. congesta l i n e s e s s e n t i a l l y as duplicates, and r e f e r to them together. P l e c t r i t i s congesta versus P^ brachystemon Height at anthesis There was s i g n i f i c a n t d i f f e r e n c e between P_. congesta and P___ brachystemon i n response to s e l e c t i o n f o r height at anthesis. The plus and minus l i n e s diverged 66% i n PCO and 78% i n PCS, but no consistent divergence resulted i n - 138 the PBS l i n e s , which fluctuated e r r a t i c a l l y . There i s no difference between P. congesta and P. brachystemon i n the changes i n the phenotypic variance, which were e r r a t i c i n a i l three species groups. The r e a l i s e d h e r i t a b i l i t y estimates, however, r e f l e c t e d the s i g n i f i c a n t response i n P. congesta, which resulted i n a r e a l i s e d h e r i t a b i l i t y of 55% compared to an estimated h e r i t a b i l i t y of zero for P. brachystemon, which showed no response. In e f f e c t there appeared to be no genetic variance i n height at anthesis a v a i l a b l e for s e l e c t i o n i n the P. brachystemon population, but enough genetic variance present i n the P_̂_ congesta populations to r e s u l t i n a s i g n i f i c a n t response. I t i s i n t e r e s t i n g .that•• while-the-estimated genetic variance for height at anthesis i s greater i n P. congesta, the phenotypic variance measured in.the base populations was s i g n i f i c a n t l y larger i n P. brachystemon.. This anomaly could be explained by an increased phenotypic v a r i a b i l i t y or p l a s t i c i t y i n the g e n e t i c a l l y l e s s v a r i a b l e P. brachystemon. There i s a body of evidence to suggest that highly homozygous organisms may be phenotypically more v a r i a b l e as a r e s u l t of t h e i r homozygosity, or conversely that heterozygosity has a b u f f e r i n g e f f e c t on phenotypic v a r i a b i l i t y ( A l l a r d and Bradshaw, 1964; Baker, 1974; Bradshaw, 1965*, Dobzhansky and Wallace, 1953,* Falconer; 1960; Lerner, 1954; Lewontin, 1957). In a study of P. congesta, s i x m e t r i c a l characters - height, dry weight, degree of branching, number of primary branches, number of secondary branches, and number of nodes - were a l l more v a r i a b l e i n plants homozygous for e i t h e r the dominant or recessive a l l e l e at the f r u i t wing locus, than i n plants heterozygous at the same locus. Whether the plants were grown i n a warm, dry environment, or i n a co o l , \<ret environment, t h i s b u f f e r i n g e f f e c t of heterozygosis was apparent (Carey and Ganders, 1980; Carey, unpublished). In Limrianthes, Brown and J a i n (1979) found that the se l f e d f loccosa - 139 showed more phenotypic p l a s t i c i t y than the outcrossed L. alba. Harding et a l . (1974) found s i m i l a r r e s u l t s working with the Lupinus nanus group of subspecies, i n which the more highly s e l f e d subspecies were more va r i a b l e phenotypically than the outcrossed subspecies. F i n a l l y , Avena barbata, a more highly s e l f e d species than i t s r e l a t i v e , A. fatua, i s also* more v a r i a b l e phenotypically, but maintains le s s genetic v a r i a b i l i t y and responds l e s s w ell to s e l e c t i o n (Jain and Marshallj 1967, 1970). Flowering time The d i r e c t response to s e l e c t i o n f or flowering time also d i f f e r e d between the two species, but.the differences were not marked, and only appeared i n the f i f t h cycle of s e l e c t i o n . Through the fourth cycle of s e l e c t i o n there was no appreciable d i f f e r e n c e , with PCO, PCS, and PBS l i n e s responding equally well to s e l e c t i o n and diverging about 20% compared to the c o n t r o l (Figure 14). In the f i f t h c y c l e , the P. congesta l i n e s continued to diverge, with a f i n a l divergence of. 33.5% (PCO) and 28.7% ( P C S ) , but the P. brachystemon populations ceased to diverge, with the f i n a l divergence being only 18.5% of the control value. The phenotypic variances (Figure 15) followed a s i m i l a r pattern, with a r e l a t i v e l y steady decrease over the f i r s t four cycles for a l l three species groups. The decrease continued i n the f i f t h cycle i n the case of the P-. congesta, but not i n the case of P. brachystemon, i n which the phenotypic variance increased again. F i n a l l y , the r e a l i s e d h e r i t a b i l i t y estimates for flowering time showed approximately equal h e r i t a b i l i t y i n the PCO and PCS .lines (0.77 and 0.75) and s l i g h t l y l e s s , but s t i l l appreciable h e r i t a b i l i t y i n the PBS l i n e s (0.49). A l l of the evidence indicates that there i s s u b s t a n t i a l genetic variance for - 140 flowering time i n both P l e c t r i t i s species, with somewhat more i n P. congesta than i n P. brachystemon. The fact that.the .response of P. brachystemon was s i m i l a r to that of P. congesta for the.early generations, and then changed abruptly i n the f i f t h generation, may i n d i c a t e that the genetic variance i s organized d i f f e r e n t l y i n the se l f e d species. This i s not unexpebted; since there i s so l i t t l e outcrossing i n P. brachystemon populations, the genetic variance i n these populations could be expected to derive l a r g e l y from differences between f a m i l i e s , that i s , between one or a number of r e l a t i v e l y highly homozygous l i n e s . The s e l e c t i o n response would then represent s e l e c t i o n of f a m i l i e s rather than i n d i v i d u a l s , and the depletion of the variance and t a i l i n g o f f of the response would occur r a p i d l y , p a r t i c u l a r l y i n small populations such as those maintained i n t h i s experiment. In contrast, P. congesta could continue to maintain genetic variance between and within f a m i l i e s , i n spite of the s e l e c t i o n pressure, by means of the recombination coming d i r e c t l y from outcrossing, and from segregation i n subsequent generations. Confounding phenomena 1 There are a number of phenomena which could p o t e n t i a l l y confound the e f f e c t s of d i r e c t s e l e c t i o n on flowering time and height at anthesis. The f i r s t i s sampling error (genetic d r i f t ) , which could operate against the d i r e c t i o n of s e l e c t i o n i n very small populations. The s e l e c t i v e pressures used i n t h i s experiment were large enough to reduce.to i n s i g n i f i c a n c e the p o s s i b i l i t i e s that d r i f t could a f f e c t the characters under d i r e c t s e l e c t i o n . There i s , however, evidence.that random processes may have affected some of the unselected characters. The f r u i t wing phenotype and f r u i t pubescence - 141 pattern frequencies increased i n variance among the various P___ congesta l i n e s over the course of the experiment, and the increase i n dispersion was not inconsistent with that expected to r e s u l t from random genetic d r i f t ; c e r t a i n l y there seemed to be no connection between the changes i n p a r t i c u l a r l i n e s and the s e l e c t i o n pressure. A second f a c t o r which might have affected the response to s e l e c t i o n i s the e f f e c t of s e l e c t i v e forces accompanying the response to the intended a r t i f i c i a l s e l e c t i o n , which act to counter or reduce that response. These could include, f o r example, reduced v i a b i l i t y or reduced fecundity i n the selected i n d i v i d u a l s or t h e i r progeny i n proportion to the degree to which they depart from the control mean. There was some evidence of a decrease i n v i a b i l i t y and fecundity i n some of the extreme i n d i v i d u a l s , e s p e c i a l l y those i n d i v i d u a l s which were very short and those which flowered very l a t e i n a l l three species groups. Since the c r i t e r i a f o r s e l e c t i o n included s u r v i v a l to produce at l e a s t ten apparently v i a b l e f r u i t s (except i n those cases noted, that i s , PCS short G 3 and PBS short G 3) the e f f e c t of t h i s counter s e l e c t i o n was reduced somewhat. There was no obvious reduction i n the t o t a l population rates of germination, s u r v i v a l , f i t n e s s , or f r u i t production i n the l a t e r generations, and no notable diffe r e n c e between P. congesta and P. brachystemon i n the deleterious e f f e c t s of s e l e c t i o n . A t h i r d f a c t o r which might have affected the d i r e c t response to s e l e c t i o n i s inbreeding depression. In p a r t i c u l a r , t h i s might be expected to have aff e c t e d the outcrossed P. congesta. Inbreeding i n the experimental populations, which was unavoidable with such small populations and heavy s e l e c t i o n , might r e s u l t i n an increase i n homozygosity which could produce r e l a t i v e l y u n f i t homozygous recessive genotypes. In a s e l f i n g species l i k e P. brachystemon these u n f i t genotypes would presumably have been selected - 142 against and eliminated from natural populations. I f the u n f i t homozygotes were involved i n the characters being selected, t h e i r deleterious e f f e c t would be equivalent to the counter s e l e c t i o n mentioned above, except that the same inbreeding depression would be expected to a f f e c t the c o n t r o l (unselected) l i n e s more or l e s s equally with the selected l i n e s . There was some evidence of inbreeding e f f e c t s i n the increase i n frequency of aberrant i n d i v i d u a l s over the course of the experiment. Plants with abnormal numbers of cotyledons or fused cotyledons, c h l o r o t i c seedlings, excessively pigmented seedlings, and plants with other abnormalities i n t h e i r habit a l l increased i n frequency, p a r t i c u l a r l y i n the P. congesta populations. There was no evidence that aberrant types increased i n frequency i n the treatment populations any more than i n the control populations, though some l i n e s had p a r t i c u l a r l y high frequencies i n most generations (PCO l a t e and PCS short). The higher frequencies noted i n P. congesta as compared to P. brachystemon were to be expected, since the s e l f e d species would be l e s s l i k e l y to r e t a i n deleterious recessive a l l e l e s i n the population. The source populations had low frequencies of aberrant types, comparable to the frequencies i n the GQ populations. I n d i r e c t responses to s e l e c t i o n Unselected characters There was considerable change i n the unselected characters, some of which could be a t t r i b u t e d to s e l e c t i o n . As mentioned above, the f r u i t phenotypic frequencies i n the P. congesta. l i n e s seemed to change more i n response to random d r i f t than i n response to s e l e c t i o n pressure. In most - 143 of the m e t r i c a l characters, however, there were changes i n the means that could be r e l a t e d to the s e l e c t i o n pressure. This could be seen most often as a divergence between the plus and minus l i n e s , with a l l three plus l i n e s (PCO, PCS, and PBS) having higher mean values than the corresponding minus l i n e s . In many cases, the divergence between the plus and minus l i n e s was not accompanied by a divergence of both away from the control l i n e , that i s , e i t h e r the plus or the minus l i n e i n these cases was 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 c o n t r o l , though both were 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 selected l i n e . Thus, days to emergence measured i n each of the plus l i n e s was greater than i n the minus l i n e s by the f i f t h cycle of s e l e c t i o n , except i n the PBS l i n e s selected f o r height at anthesis; height at anthesis i n the l i n e s selected f o r flowering time was greater i n the plus l i n e s than i n the minus l i n e s except i n the PBS l i n e s ; i n a l l cases the number of nodes at anthesis was greater i n the plus l i n e s than i n the minus l i n e s ; number of primary branches at anthesis was greater i n plus l i n e s than i n minus l i n e s except i n the PBS l i n e s selected f o r height at anthesis; and flowering time i n those l i n e s selected f o r height at anthesis was greater i n the plus l i n e s than i n the minus l i n e s . The measurement of f r u i t production was subject to a large error, and I found no consistent trends which could be a t t r i b u t e d to s e l e c t i o n . The f a c t that i n general the unselected characters tended to track the selected characters i s r e f l e c t e d i n the r e l a t i v e l y strong c o r r e l a t i o n s among the characters. Thus, flowering time and number of nodes at anthesis were strongly correlated, and the coincident changes i n mean values r e f l e c t t h i s . Height at anthesis and flowering time were strongly correlated i n the f i r s t three generations, which probably explains the i n i t i a l divergence i n flowering time observed i n the plus and minus l i n e s selected f o r height at - 144 anthesis. Days to emergence and flowering time were strongly correlated, as were height at anthesis and number of nodes at anthesis. I f the c o r r e l a t i o n s do i n d i c a t e some degree of underlying genetic linkage, then the response of the unselected characters may have been due i n part e i t h e r to a d i r e c t l i n k with the selected characters which were themselves responding to s e l e c t i o n (nodes at anthesis, height at anthesis, and days to emergence correlated with flowering time i n l i n e s selected f o r the l a t t e r ; flowering time and number of nodes at anthesis correlated with height at anthesis i n l i n e s selected f o r the l a t t e r ) . A l t e r n a t i v e l y an i n d i r e c t l i n k through one of the unselected characters could conceivably have produced the response (days to emergence correlated with flowering time i n l i n e s selected f o r height at anthesis). Other s e l e c t i o n studies The r e s u l t s I observed i n t h i s experiment are comparable to the r e s u l t s i n such other s e l e c t i o n experiments as were designed s i m i l a r l y , that i s , with mass s e l e c t i o n i n a population that has not been r a d i c a l l y a l t e r e d i n i t s genetic c h a r a c t e r i s t i c s by inbreeding ( i n outcrossed taxa) or by outcrossing ( i n s e l f e d taxa), and where generations are produced by a more or le s s n atural breeding programme. There are few reports i n the l i t e r a t u r e of a lack of response to s e l e c t i o n , l a r g e l y , I suppose, because s e l e c t i o n i s successful to some degree i n most cases. In the studies mentioned i n the introduction (pp. 17 - 20),.the 21 cases i n outcrossed taxa f o r which a per cycle response was recorded had an average change i n the mean value of the selected character of 14.8% per cycle of s e l e c t i o n . In the s e l f i n g taxa, the 15 cases where a - 145 per cycle response, was. recorded-.had .an. average,, change i n the mean of 8.3% per cyc l e . I f the two . . P l e c t r i t i s species are treated i n the same way, the average per cycle change in.the -mean value of the two.selected characters was approximately 5% iri P. congesta and approximately 1% i n P. brachystemon. Some of the s e l e c t i o n studies reported i n the l i t e r a t u r e used the same characters as I.did, that, i s , height and flowering time, although height was not always measured at the same stage of the l i f e cycle. In Limnanthes alba, an outcrosser, s e l e c t i o n . f o r height resulted i n a 6% change per cycle of s e l e c t i o n ( J a i n , 1979) . Three.studies.involved s e l e c t i o n for height i n se l f e d taxa, with responses res p e c t i v e l y of 4.5% per cycle i n Avena.sativa (Geadelmann and Frey, 1975), 12.5% per cycle i n A. fatua (Imam and A l l a r d , 1965), and 2.8%.per cycle in' Sorghum.bicolor (Foster et a l . , 1980); the mean response i n se l f e d taxa was 6.6% per cycle. Both breeding system groups had a response to s e l e c t i o n for t h i s character s i m i l a r i n degree to the response of 7.2% per cycle (+ 66% i n PCO, + 78% i n PCS a f t e r 5 cycles) noted i n P___ congesta. Sele c t i o n f o r flowering time has been.reported i n a number of species. Among s e l f i n g taxa, i n Avena s a t i v a Geadelmann and Frey (1975) found a response to s e l e c t i o n of 22% per cycle;.Imam and A l l a r d (1965) noted a ; response of 20.5% per cycle i n A. fatua; and i n Sorghum b i c o l o r Foster et a l . (1980) found a response of 0.6% per cycle. In Brassica campestris var. brown sarson Murty et a l . (1972) observed a response of 1.7% per c y c l e . The mean response i n these taxa i s about 12%.per cycle, which i s considerably higher than ei t h e r the 3% per cycle response i n P. congesta or the 2% per cycle response i n P. brachystemon. The longer.the s e l e c t i o n continues, the lower w i l l be the per cycle response, as the t o t a l response w i l l decrease with the depletion of genetic variance. The two experiments with Avena, i n which the - 146 per c y c l e response was.relatively,high, involved only.one cycle of s e l e c t i o n , whereas the experiments with Sorghum and B f a s s i c a involved 10 and 3 cycles r e s p e c t i v e l y . Allowing f o r these differences between experiments, the response to s e l e c t i o n f o r the two characters, height and flowering time, i n both P l e c t r i t i s species would seem to f a l l w e l l within the range of observed responses i n other plant species. To answer the f i r s t two questions posed.at the beginning of the discussion, the P l e c t r i t i s brachystemon population, which i s highly inbred, has s i g n i f i c a n t l y l e s s genetic v a r i a b i l i t y f o r one q u a n t i t a t i v e l y i n h e r i t e d character, height at anthesis, than the P. congesta population, which i s highly outbred but otherwise nearly i d e n t i c a l ; the d i f f e r e n c e between the two species i n l e v e l s of genetic v a r i a b i l i t y i s r e f l e c t e d i n the response to s e l e c t i o n for height. In contrast, however, there i s considerable genetic v a r i a b i l i t y for the second q u a n t i t a t i v e l y i n h e r i t e d character, flowering time, i n both populations, and t h i s , too, i s r e f l e c t e d i n the response to s e l e c t i o n for t h i s character. The l e v e l s of genetic v a r i a b i l i t y and s e l e c t i o n response for both characters i n P l e c t r i t i s are s i m i l a r to those found i n other plant species. The t h i r d question was how independent estimates of genetic v a r i a b i l i t y compare to the estimates derived from the response to s e l e c t i o n for the two quantitative characters. Independent estimates of genetic v a r i a b i l i t y i n P l e c t r i t i s There i s ample evidence (based mainly on isozyme data) to i n d i c a t e - 147 that outcrossed taxa are more diverse, that i s , more highly heterozygous and more polymorphic on average, .than are selfed..taxa. The evidence from the studies of Layton (1980) i n P. congesta and P. brachystemon i s i n agreement with t h i s . He calculated Nei's index of gene d i v e r s i t y within populations f o r the two species to be 0.22 for P. congesta and.0.06 for P. brachystemon. Ganders and Maze (unpublished)'studied f r u i t wing characters measured i n two populations of "P^ congesta and one of P_;_ brachystemon and concluded that the v a r i a b i l i t y i n the outcrossed species was s i g n i f i c a n t l y greater than that i n the se l f e d species. The two p a r t i c u l a r populations chosen as sources f o r t h i s experiment d i f f e r i n the amount of phenotypic v a r i a b i l i t y shown i n c e r t a i n characters. The P^ congesta population at M i l l H i l l i s polymorphic for a number of f r u i t characters: presence or absence of f r u i t wings, pubescence pattern, wing shape, and f r u i t colour. The P. brachystemon.population, i n contrast, i s monomorphic: a l l plants produce medium brown wingless f r u i t s with the same pubescence pattern. The base populations, G Q , which are presumed to be.a random or unselected sample of genotypes i n the source populations, also provide some evidence of differences i n v a r i a b i l i t y . For the measured characters the c o e f f i c i e n t s of v a r i a t i o n were s i g n i f i c a n t l y d i f f e r e n t between the two species i n 5 of 6 cases, with the c o e f f i c i e n t being larger i n P. congesta for the number of primary branches at anthesis and flowering time, and larger i n P. brachystemon for number of days to emergence, height at anthesis, and number of nodes at anthesis. These c o e f f i c i e n t s are based on variances which are e s s e n t i a l l y phenotypic, although the environmental component has been reduced by the use of a common co n t r o l l e d environment. I t i s possible that the greater v a r i a b i l i t y shown by P^ brachystemon for three characters i s due - 148 to phenotypic p l a s t i c i t y , about which I w i l l say more l a t e r . The f i n a l evidence, independent of the selection.experiment, f o r differences between the two species i n . v a r i a b i l i t y comes from the estimates of h e r i t a b i l i t y from the parent-offspring regressions i n the three c o n t r o l l i n e s . For the two selected characters . (Table V) P . brachystemon has considerably l e s s genetic variance as estimated by h e r i t a b i l i t y f o r height at anthesis ( e s s e n t i a l l y none as compared to 45% for P___ congesta), and only s l i g h t l y l e s s genetic variance f o r flowering time (42% as compared to 60-70% for P . congesta). For the.unselected characters (Table VI) there are too few good estimates of h e r i t a b i l i t y to make a comparison between P . congesta and P . brachystemon p o s s i b l e , except i n the case of the number of nodes at* anthesis. In t h i s case the h e r i t a b i l i t i e s are comparable to those estimated 2 for flowering time, with P . brachystemon showing les s genetic variance (h = 2 0.28) than P . congesta (h = 0.55), but both species having low to intermed- i a t e h e r i t a b i l i t i e s f o r the character. The s i m i l a r i t i e s i n the h e r i t a b i l i t i e s for these two characters, flowering time and number of nodes at anthesis, i s not s u r p r i s i n g considering the strong and consistent p o s i t i v e c o r r e l a t i o n between them, which was evident i n a l l experimental populations (Figure-35). It i s i n t e r e s t i n g that the c o e f f i c i e n t of v a r i a t i o n f or number of nodes at anthesis was greater i n P . brachystemon G ^ t h a n in-the two P . congesta GQ populations, while the h e r i t a b i l i t y estimates indicate that genetic-variance' i s greater i n P . congesta. There are s i m i l a r anomalies which were noted when comparing the r e s u l t s of the s e l e c t i o n experiment with the GQ c o e f f i c i e n t s of v a r i a t i o n , and they w i l l be discussed i n the following sections. The answer to the t h i r d question posed at the beginning of the discussion, then, i s that the independent evidence of genetic v a r i a b i l i t y i n the two - 149 species i s equivocal. 'Most of., the.characters are more v a r i a b l e i n the outcrossed P. congesta than in.-the se l f e d P...brachystemon. . These include the isozyme and f r u i t . phenotype-. polymorphisms, and the phenotypic variances i n number of primary branches'and flowering time i n the base populations grown i n c o n t r o l l e d , a n d . i d e n t i c a l environments. These characters agree with the l e v e l s of v a r i a b i l i t y i n height at anthesis as observed i n the response to s e l e c t i o n . The phenotypic variances of days to emergence, height at anthesis, and number of nodes at anthesis i n the GQ populations are higher i n the P. brachystemon populations than i n the P. congesta populations. I f we assume that the environmental components are constant i n both species (perhaps a tenuous assumption) then t h i s evidence would i n d i c a t e that there was more genetic v a r i a b i l i t y i n the s e l f e r than i n the outcrosser. None of the independent evidence agrees c l o s e l y with the observed l e v e l s of approximately e q u a l g e n e t i c variance in..both species i n response to s e l e c t i o n f o r flowering time. The e f f e c t s of breeding system on the population genetic structure of P l e c t r i t i s The two species of P l e c t r i t i s are very s i m i l a r i n habit and habitat, but are w e l l distinguished by t h e i r breeding biology and population genetic structure. Isozyme studies show that the genetic d i v e r s i t y i s much greater i n t o t a l and within populations i n P. congesta than i n P^ brachystemon; most of the genetic d i v e r s i t y i n P. brachystemon i s between populations (Laytori, 1980).. S i m i l a r l y , the genetic d i v e r s i t y i n the f r u i t phenotypic characters - presence of f r u i t wings (for which the genetics are known), pubescence pattern, wing shape, and f r u i t colour (for which the genetics are - 150 not known) - i s greater i n P. congesta populations than i n P. brachystemon populations. With respect to the f r u i t phenotype characters, the M i l l H i l l populations of P l e c t r i t i s are t y p i c a l , that i s , P. congesta i s r e l a t i v e l y highly polymorphic and P. brachystemon i s monomorphic. The isozyme patterns i n these p a r t i c u l a r populations have not yet been studied. A l a r g e l y winged-fruited population of P__ brachystemon was le s s v a r i a b l e f o r f r u i t wing characters than two comparable winged populations of P. congesta; t h i s comparison dealt with the phenotypic v a r i a b i l i t y of the characters that were measured, but the p a r t i c u l a r characters are c e r t a i n to have a small or n e g l i g i b l e environmental component (Ganders and Maze, unpublished). The phenotypic v a r i a b i l i t y of the two M i l l H i l l populations as estimated by the variances i n the G^ populations was greater f o r P. brachystemon i n some cases and f o r P. congesta i n others. In the cases where the genotypic component of t h i s variance could be estimated, e i t h e r by parent-offspring regressions or by the response to s e l e c t i o n , P___ congesta was the more va r i a b l e taxon g e n e t i c a l l y , although s i g n i f i c a n t genetic variance was indicated f o r P. brachystemon i n number of nodes at anthesis and flowering time. In two cases, height at anthesis and number of nodes at anthesis, P. brachystemon was more v a r i a b l e phenotypically but le s s v a r i a b l e g e n e t i c a l l y than P. congesta, a r e s u l t which can only be explained by postulating a r e l a t i v e l y higher element of phenotypic p l a s t i c i t y i n P___ brachystemon, at l e a s t under the experimental conditions. P l e c t r i t i s brachystemon P l e c t r i t i s brachystemon, a highly s e l f e d species, appears to have l o s t - 151 genetic d i v e r s i t y as a consequence of having evolved a s e l f i n g breeding system. I t has not l o s t a l l of i t s genetic v a r i a b i l i t y f o r some characters, however, and there presumably has been some s e l e c t i o n pressure to maintain genetic variance i n flowering time and number of nodes at anthesis, while genetic variance f o r height at anthesis has been l o s t . The difference between the low genetic d i v e r s i t y as estimated from isozymes and f r u i t characters, and the presence of s i g n i f i c a n t genetic variance i n other characters can be explained i n a number of ways. Occasional outcrossing events which occur i n h a b i t u a l l y s e l f i n g populations w i l l continue to segregate heterozygous i n d i v i d u a l s f o r a number, of generations, subject to the forces of random d r i f t , inbreeding, and s e l e c t i o n . In t h i s case the low genetic d i v e r s i t y i n the isozymes and low genetic variance i n height at ( anthesis could be the r e s u l t of s e l e c t i o n acting on these characters, reducing t h e i r v a r i a b i l i t y . Conversely, the high genetic variance i n flowering time and number of nodes could represent the l e v e l of v a r i a b i l i t y maintained by occasional outcrossing and segregation. This explanation requires that the genetic determinants of flowering time and number of nodes be nearly n e u t r a l , and that the outcrossing rate be high enough and population sizes large enough to permit accumulation of these heterozygous types. None of these assumptions i s reasonable f o r P. brachystemon populations. A l t e r n a t i v e l y , the low genetic d i v e r s i t y i n isozymes and low genetic variance i n height at anthesis could be mainly the r e s u l t of the high l e v e l s of inbreeding, small population s i z e , and random loss of a l l e l e s . The r e l a t i v e l y high genetic variance i n flowering time and number of nodes could be the r e s u l t of s e l e c t i o n f o r v a r i a b i l i t y . The balance of s e l e c t i v e and random forces acting on isozymes i s s t i l l a subject of much debate, but there - 152 i s probably s e l e c t i o n acting on at l e a s t some of the l o c i , and there i s l i k e l y to be s e l e c t i o n a f f e c t i n g height at anthesis to some degree i n na t u r a l populations. I t i s l i k e l y that the actual s i t u a t i o n i n P. brachystemon populations i s somewhere between the two extremes. There i s probably some se l e c t i o n acting on isozymes and height, but the low l e v e l s of genetic ; v a r i a b i l i t y i n these t r a i t s r e l a t i v e to P. congesta r e f l e c t l a r g e l y the e f f e c t s of breeding system and random loss of v a r i a b i l i t y . The r e l a t i v e l y high genetic variance i n flowering time and nodes at anthesis i s probably maintained by s e l e c t i o n . S e l e c t i v e forces which maintain v a r i a b i l i t y involve a number of mechan- isms. , Those which involve mutation, migration, or d i s a s s o r t a t i v e mating as sources of new v a r i a b i l i t y are not l i k e l y to be the major forces involved i n the short term i n P. brachystemon populations. A form of s e l e c t i o n which i s more p l a u s i b l e i n t h i s l i g h t i s heterozygote advantage. Heterozygote advantage can be used i n a narrow sense, r e f e r r i n g to an absolute f i t n e s s advantage of a heterozygote over homozygotes under a l l conditions, or i n a broad sense, where the net f i t n e s s advantage of the heterozygote only appears as the f i t n e s s values of the various.genotypes change i n time or space. Heterozygote advantage has been demonstrated to operate i n P. congesta under some conditions at the f r u i t wing locus (Carey and Ganders, 1980) and may be a f a c t o r i n preserving some of the polymorphism i n that species. In P. brachystemon, however, there are probably too few heterozygotes produced i n n a t u r a l populations to permit heterozygote advantage to be a f a c t o r i n the maintenance of genetic variance. The frequency of heterozygotes at the f r u i t wing locus i n one population was estimated to be less than 3% (Ganders et a l . , 1977$; the frequency of heterozygotes observed at polymorphic isozyme l o c i i n P___ brachystemon - 153 populations averaged 0.45% (Layton, 1980). There i s some evidence that heterozygote advantage may be operating i n some s e l f i n g species to maintain variance ( A l l a r d , J a i n and Workman, 1968; J a i n and A l l a r d , 1960). A l l of t h i s evidence comes from characters i n which the genotypes can be observed (monogenic or simply i n h e r i t e d characters). Maintenance of genetic variance i n q u a n t i t a t i v e l y i n h e r i t e d characters by heterozygote advantage i n a s e l f i n g species requires even higher rates of production of the hetero- zygotes than those required to maintain monogenic polymorphisms. The most l i k e l y form of s e l e c t i o n to maintain genetic v a r i a b i l i t y i n P_j_ brachystemon populations i s some type of patterning of the s e l e c t i v e pressures e i t h e r i n time or i n space. I f microhabitats and t h e i r associated s e l e c t i o n pressures occur, p a t c h i l y or form a mosaic, then the segregating l i n e s which r e s u l t from the rare outcrossing events i n P^ brachystemon populations could be maintained, highly homozygous within each microhabitat but with d i f f e r e n t genotypes i n d i f f e r e n t microhabitats. That genetic variance i s divided among a number of homozygous l i n e s i n jP^ brachystemon i s also suggested by the observed form of the response to s e l e c t i o n f o r flowering time. A r e l a t i v e l y large response i n the early generations, followed by a rapid t a i l i n g o f f i n the l a s t generation, could occur as the selected l i n e s were reduced i n number and variance between the l i n e s was no longer a v a i l a b l e f o r s e l e c t i o n . I t i s possible that an examination of a number of the isozyme l o c i simultaneously i n i n d i v i d u a l s from P. brachystemon populations would reveal a number of l i n e s of d i f f e r e n t multilocus homozygotes; the l e v e l s of isozyme polymorphism discovered to date i n populations would allow for a maximum of 11 d i f f e r e n t homozygous l i n e s per population at 13 isozyme l o c i (Layton, 1980). The isozyme data i n P l e c t r i t i s have not :been analysed i n t h i s way to determine multilocus genotypes, but there i s evidence from other - 154 predominantly s e l f i n g species f o r a population structure composed of l i n e s of homozygous genotypes. In Avena barbata a number of studies have indicated that i n some populations a few multilocus genotypes are present i n excess over the expected frequency, and appear to be adapted to d i f f e r e n t microhabitats within the habitat ( A l l a r d et a l . , 1972; Clegg and A l l a r d , 1972)* Multilocus organization i n A__ fatua and Festuca microstachys populations has also been studied and a s i m i l a r s i t u a t i o n noted ( A l l a r d , 1975). The question that follows l o g i c a l l y from the observation of genetic v a r i a b i l i t y i n P___ brachystemon i s why there might be such r e l a t i v e l y strong s e l e c t i o n to maintain v a r i a b i l i t y i n flowering time and number of nodes at anthesis i n the species, to the point that i t i s nearly as v a r i a b l e as P. congesta. Since P. brachystemon i s highly s e l f - p o l l i n a t e d , there i s not l i k e l y to be a connection with p o l l i n a t o r behaviour as might be the case i n the outcrossed species. In P. congesta, v a r i a b i l i t y i n flowering time (and number of nodes, which are correlated) could serve to extend the flowering period i n the population, thus decreasing the chance of poor f r u i t set due to lack of synchrony with the a c t i v i t y of p a r t i c u l a r p o l l i n a t o r s . This i s p a r t i c u l a r l y l i k e l y i n a species l i k e P.,congesta which does not appear to r e l y on one major p o l l i n a t o r , but rather a number of p o l l i n a t o r s . One possible explanation f o r the advantage to be gained from v a r i a b i l i t y i n flowering time i n P___ brachystemon i s that i t r e f l e c t s v a r i a b i l i t y i n some p h y s i o l o g i c a l or developmental character which i s subject to multiniche s e l e c t i o n . A l t e r n a t i v e l y , flowering time may be d i r e c t l y subject to such d i s r u p t i v e s e l e c t i o n . For example, i t i s possible that i n microsites which dry early i n the season, early flowering i s s e l e c t i v e l y advantageous, while i n wetter microsites, delaying flowering may maximize fecundity. - 155 In contrast to the genetic v a r i a b i l i t y present i n flowering time are the r e l a t i v e l y higher l e v e l s of phenotypic v a r i a b i l i t y f o r height at anthesis observed i n J?^ brachystemon, compared to those i n P_̂  congesta. This p l a s t i c i t y may be advantageous i n populations exposed to a mosaic of s e l e c t i v e forces, or i t may merely be a non-adaptive side e f f e c t of the increased homozygosity which has accompanied the evolution of a highly s e l f e d breeding system. If homozygous genotypes are by nature more p l a s t i c , there may have been no way f o r brachystemon to avoid the increased p l a s t i c i t y were i t to have proved disadvantageous. Phenotypic p l a s t i c i t y could be adaptive i n a number of ways. I t could make phenotypically uniform a population of plants which are g e n e t i c a l l y diverse, maintaining genetic v a r i a b i l i t y i n the face of s t a b i l i z i n g s e l e c t i o n . Bradshaw (1965) has likened t h i s to the e f f e c t s of dominance and gives examples i n which i t may be operating, namely i n Plantago maritima (Gregor,1956) and a number of species examined by Turesson (1922, 1925). A l t e r n a t i v e l y , phenotypic p l a s t i c i t y could allow phenotypic v a r i a b i l i t y i n a population of plants which are genotypically r e l a t i v e l y uniform. This i s the p o t e n t i a l which has been a t t r i b u t e d to some hypothetical weedy or col o n i z i n g species, which would be composed of one or more general-purpose genotypes, at once highly homozygous and highly p l a s t i c (Baker, 1974). There are weedy species which do e x h i b i t more phenotypic v a r i a b i l i t y i n some characters than t h e i r non-weedy r e l a t i v e s . Examples are Sonchus oleraceus (weedy) versus S. arvensis (Lewin, 1948) and Chenopodium album (weedy) versus C. rubrum (Cumming, 1959). S i m i l a r l y there are other species p a i r s i n which the more g e n e t i c a l l y v a r i a b l e species i s l e s s phenotypically v a r i a b l e (species of Limnanthes, Lupinus, and Avena mentioned on pages 138 and 139). I t i s unfortunate that there are no measurements of phenotypic variance yet - 156 av a i l a b l e f o r natural populations of P___ congesta and P. brachystemon, so i t i s not possible to compare l e v e l s of v a r i a b i l i t y under natural and uniform (growth chamber) conditions, nor to estimate the extent of phenotypic p l a s t i c i t y i n nature. The r e l a t i v e l y large d i f f e r e n t i a t i o n between populations of P. brachystemon i n isozyme patterns (Layton, 1980), the presence of s i g n i f i c a n t genetic variance i n some characters, and the f a c t that neither P. congesta nor P. brachystemon i s p a r t i c u l a r l y aggressive or weedy, suggest that the notion of a species composed of general-purpose, highly homozygous, highly p l a s t i c genotypes which has been suggested f o r some s e l f i n g species i s not an adequate d e s c r i p t i o n of the s i t u a t i o n i n P. brachystemon. Occasional outcrossing and multiniche s e l e c t i o n among the segregating l i n e s f o r the genetic determinants of flowering time are' likely„to have been important,adaptive processes - i n P. brachystemon. I t i s not possible at the moment to say whether the increased phenotypic v a r i a b i l i t y i n height at anthesis i n P. brachystemon i s or i s not adaptive, or whether low genetic v a r i a b i l i t y and high phenotypic v a r i a b i l i t y f o r height i n P___ brachystemon and high genetic v a r i a b i l i t y and low phenotypic v a r i a b i l i t y f o r height i n P. congesta are -different solutions to the same evolutionary problem. P l e c t r i t i s congesta The presence of genetic v a r i a b i l i t y i n flowering time, height at : anthesis, and number of nodes at anthesis i n P. congesta i s easy to account fo r as a consequence of the processes of recombination and segregation accompanying the habi t u a l outcrossing i n the species. I t i s impossible to say whether the l e v e l s of v a r i a b i l i t y so maintained are more or less than - 157 expected. Since the habitats are s i m i l a r , presumably the same type of multiniche s e l e c t i v e pressures postulated to be operating i n P. brachystemon would also a f f e c t P. congesta. Populations of the l a t t e r , however, would not be able to develop g e n e t i c a l l y d i f f e r e n t i a t e d l o c a l subdividions as e a s i l y , because of the mixing e f f e c t of outcrossing. In a d d i t i o n , unlike P. brachystemon, P. congesta has a p o l l i n a t i o n biology which could t h e o r e t i c a l l y support s e l e c t i o n f o r greater v a r i a b i l i t y i n flowering time i n response to p o l l i n a t o r behaviour, to increase the r e l i a b i l i t y of f r u i t set; the o r i g i n and maintenance of genetic v a r i a b i l i t y i n flowering time i s e a s i l y explained i n 7^ congesta. Heterozygote advantage has been shown to operate to maintain at l e a s t one of the polymorphisms i n P. congesta populations, and inbreeding depression was more marked i n the experimental P̂ _ congesta populations than i n the P. brachystemon populations. Given no evidence to the contrary; one may conclude that the higher l e v e l s of genetic v a r i a b i l i t y and the outcrossed breeding system which generates them are both s e l e c t i v e l y advantageous fo r P. congesta. Further study i n P l e c t r i t i s The differences between the two P l e c t r i t i s species i n breeding system have d e f i n i t e l y a f f e c t e d the genetic structure of t h e i r populations, inbreeding i n P^ brachystemon having decreased the genetic d i v e r s i t y of isozyme and f r u i t morph characters and the genetic variance i n height. Yet i t i s obvious from the genetic variance i n flowering time and the phenotypic variance i n height and number of nodes that brachystemon has not s a c r i f i c e d a l l of i t s sources of v a r i a b i l i t y to i t s breeding system. - 158 More study of both species i s warranted, to c l a r i f y the differences and to answer what may be the fundamental evolutionary and systematic question, namely, how and why P. brachystemon evolved a s e l f i n g breeding system at some point i n the past, and how and why both species are equally successful i n sympatry at present. Experiments with P. brachystemon could be designed to determine whether this taxon does i n f a c t have a population genetic structure a f f e c t e d by a number of d i f f e r e n t microhabitats and multiniche s e l e c t i o n . F i r s t , multilocus isozyme genotypes could e a s i l y be determined f o r a population. Since 13 isozyme l o c i have already been studied, and expansion of the number of l o c i a v a i l a b l e f o r c h a r a c t e r i z a t i o n i s quite f e a s i b l e (Layton, personal communication), one should be able to d i f f e r e n t i a t e a number of multilocus genotypes, i f present, even within a r e l a t i v e l y i n v a r i a b l e P. brachystemon population. If microhabitat patterning i s a f a c t o r i n a population, i t might be possible to detect at l e a s t some of i t s dimensions with s u i t a b l e measurements of p h y s i c a l factors ( s o i l , moisture, micro- topography) and b i o t i c f a c t o rs (correlated plant species), and r e l a t e the multilocus isozyme patterns to p a r t i c u l a r microhabitats, as has been done with other species ( A l l a r d et a l . , 1972; A l l a r d , 1975). Since comparisons with sympatric P. congesta populations are p o s s i b l e , one could do the same thing with that species, to v e r i f y whether the e f f e c t of oucrossing has been to produce the expected larger number of isozyme genotypes, but without any subdivided pattern based on microhabitat differences. One of the most i n t e r e s t i n g experiments would involve measurements of the phenotypic variance i n n a t u r a l populations of both species for the characters used i n t h i s experiment, i n order to estimate the n a t u r a l l y occurring l e v e l s of phenotypic p l a s t i c i t y . For example, under experimental - 159 conditions V\_ congesta was g e n e t i c a l l y more v a r i a b l e f o r height than was P. brachystemon, but phenotypically l e s s v a r i a b l e . One could measure the phenotypic variance f o r height i n natural populations to see i f the d i f f e r e n t l e v e l s of genetic v a r i a b i l i t y t r a n s l a t e / i n t o s i m i l a r or d i s s i m i l a r l e v e l s of phenotypic v a r i a b i l i t y under n a t u r a l conditions. As a f i n a l example, one could extend the studies to other species i n the genus, which because of t h e i r f l o r a l morphology are presumed to be more high l y s e l f e d than P^ congesta, and to other sections of the ranges of P. congesta and P_j_ brachystemon. There are reports of populations of the two species in;the more southerly parts of t h e i r ranges which are more s i m i l a r to each other than are any that have been studied i n B r i t i s h Columbia (Morey, 1962). This appears to be the case i n some populations observed recently i n C a l i f o r n i a , and i t would be i n t e r e s t i n g to see how extensive the apparent intermediacy i s , i n terms of breeding system and population genetics and biology. J a i n ,et a l . (1970) have pointed out the danger i n extending arguments from studies of a population i n one area to other species or other populations i n the same species; populations of P. congesta i n the southern part of the range appear to be f a r l e s s polymorphic within populations f o r some f r u i t characters than are those i n B r i t i s h Columbia. Implications f o r other studies The estimation and comparison of l e v e l s and organization of genetic v a r i a b i l i t y i n r e l a t i o n to breeding systems i n various organisms i s an acti v e area of study among population g e n e t i c i s t s . In th i s f i e l d i t i s important to d i s t i n g u i s h between p o t e n t i a l or hidden genetic v a r i a b i l i t y - 160 (genetic d i v e r s i t y ) and r e a l i s e d or free genetic v a r i a b i l i t y (genetic variance). In the two P l e c t r i t i s species studied here, a reasonably good r e l a t i o n s h i p was observed between the breeding system, the amount of genetic d i v e r s i t y , and the l e v e l of genetic variance present i n a population. In comparison to the outcrossed P. congesta, the s e l f e d P. brachystemon has l e s s genetic d i v e r s i t y and l e s s genetic variance.. There i s , however, s t i l l considerable genetic variance i n the Pv brachystemon f o r at l e a s t one character, flowering time, perhaps more than one would expect from such a highly s e l f e d organism, or on the basis of the lack of d i v e r s i t y i n the isozymes. Moreover, the l e v e l s of phenotypic v a r i a b i l i t y measured i n some of the characters i n d i c a t e more v a r i a b i l i t y i n P. brachystemon than i n P. congesta; t h i s may be misleading, however, as i n at l e a s t one case (height at anthesis) the difference i s caused by high phenotypic p l a s t i c i t y rather than genetic v a r i a b i l i t y . In studies where isozymes are being examined, i t i s important that a lack of genetic d i v e r s i t y i n isozymes not be interpreted to i n d i c a t e a general lack of genetic variance i n a l l characters, without other supporting evidence. Isozymes have so f a r proved to be good i n d i c a t o r s of r e l a t i v e l e v e l s of v a r i a b i l i t y , f o r instance between outcrossers and s e l f e r s i n general; nevertheless, amounts of genetic variance which are s i g n i f i c a n t from an evolutionary point of view can be maintained along with isozyme monomorphism. Isozymes w i l l and should continue to be used to estimate population genetic parameters because they are more nearly estimates of the genotype than are characters which have a large environmental component to t h e i r v a r i a t i o n . A l l e l e frequencies at many i n d i v i d u a l l o c i can be examined, and the sampling i s r e l a t i v e l y f a s t , easy, and precise. Their contribution to the phenotype, other than t h e i r e l e c t r o p h o r e t i c m o b i l i t y , - 161 i s often unknown, and th e i r s e l e c t i v e values are correspondingly d i f f i c u l t to i n t e r p r e t . When studies are direc t e d to v a r i a b i l i t y of quantitative characters i n populations, the roles of genetic variance and phenotypic p l a s t i c i t y or environmental variance should be assessed c a r e f u l l y . Lacking evidence as to the genetic components of variance, i t may be tempting to argue that an outcrossed population which i s phenotypically more v a r i a b l e than a s e l f e d population i s expressing higher l e v e l s of genetic variance. By the same reasoning, a s e l f e d population that i s more v a r i a b l e than an outcrossed one might be regarded as e x h i b i t i n g c h a r a c t e r i s t i c a l l y higher l e v e l s of phenotypic p l a s t i c i t y . Some of the e a r l i e r descriptions of increased phenotypic p l a s t i c i t y i n weedy or s e l f i n g plant species have been based on observations of phenotypic variance i n comparison with r e l a t e d non-weedy or outcrossing species, and are not accompanied by an estimate of the genetic component of the variance (for example Cumming, 1959 and Lewin, 1948). Later studies, such as those with Lupinus (Harding et a l . , 1974), Limnanthes (Brown and J a i n , 1979),and Avena (Jain and Marshall, 1970), have estimated the genetic components; d i f f i c u l t as they may be to obtain, such estimates do a great deal to increase our confidence i n speculations about the contribution of genetic variance vs. phenotypic p l a s t i c i t y i n strategies of populations of various species. Selection experiments may: not be the f a s t e s t way to study the genetic components of v a r i a t i o n i n q u a n t i t a t i v e l y i n h e r i t e d characters. I t may be fa s t e r to do large scale breeding experiments of the type which are common i n crop science and a g r i c u l t u r a l research (various c o n t r o l l e d crossing methods and progeny t e s t i n g methods). Selection experiments have the advantage of smaller space requirements, and consequently better control - 162 of the environmental heterogeneity may be p o s s i b l e . 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Mass s e l e c t i o n i n sweet potato: breeding f o r resistance to insects and diseases and f o r h o r t i c u l t u r a l c h a r a c t e r i s t i c s . J . Amer. Soc. Hort. S c i . 101:. 701 - 704. Josefsson, A. 1963. E f f e c t s of s e l e c t i o n i n fodder beets. In "Recent Plant Breeding Research". E. Akerberg, A. Hagberg, G. Olsson, and 0. Tedin, eds. John Wiley & Sons, New York. Kannenberg, L. W., and R. W. A l l a r d . 1967. Population studies i n predominantly s e l f - p o l l i n a t e d species. VIII. Genetic v a r i a b i l i t y i n the Festuca microstachys complex. Evolution 21: 227 - 240. Lande, R. 1977. The influence of the mating system on the maintenance of genetic v a r i a b i l i t y i n polygenic characters. Genetics 86: 485 - 498. Layton, C. L. 1980. The genetic consequences of contrasting breeding systems i n P l e c t r i t i s . M. Sc. Thesis, U n i v e r s i t y of B r i t i s h Columbia, Vancouver, B.C., Canada. Lerner, I. M. 1954. "Genetic Homeostasis". O l i v e r and Boyd, Edinburgh and London. Levin, D. A. 1975. Genetic consequences of tr a n s l o c a t i o n heterozygosity i n plants. Bioscience 25: 724 - 728. 1978. Genie heterozygosity and pr o t e i n polymorphism among l o c a l populations of Oenothera biennis. Evolution 32(2): 245 - 263. Lewin, R. A. 1948. B i o l o g i c a l f l o r a of the B r i t i s h I s l e s . Sonchus oleraceus L. J . E c o l . 36: 204 - 216. Lewontin, R. C. 1957. The adaptation of populations to varying environments. Cold Spring Harbor Symp. Quant. B i o l . 22: 395 - 408. 1966. On the s t a t i s t i c a l measurement of r e l a t i v e v a r i a b i l i t y . Syst. Zool. 15: 140 - 141. Marshall, D. R., and S. K. J a i n . 1969. Genetic polymorphism i n natural populations of Avena f atua and _A;_ barbata. Nature (London) 221: 276 - 278. Matzinger, D. F., and E. A. Wernsman. 1968. 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M o d i f i c a t i o n of saponin c h a r a c t e r i s t i c s of a l f a l f a by s e l e c t i o n . Crop S c i . 13: 731 - 735. Rick, C. M., and J . F. Fobes. 1975. Allozymes of Galapagos tomatoes: polymorphism, geographic d i s t r i b u t i o n , and a f f i n i t i e s . Evolution 29: 443 - 457. Rick, C. M., J . F. Fobes, and M. Holle. 1977. Genetic v a r i a t i o n i n Lycopersicon p i m p i n e l l j f o l i u m : evidence of evolutionary change i n mating systems. Plant Syst. Evol. 127: 139 - 170. Rogers, S. 1971. Studies on B r i t i s h poppies. 4. Some aspects of v a r i a b i l i t y i n the B r i t i s h species of Papaver and t h e i r r e l a t i o n to breeding mechanisms and ecology. Watsonia 8: 263 - 276. Romero, G. E., and K. J . Frey. 1966. Mass s e l e c t i o n f o r plant height i n oat populations. Crop S c i . 6: 283 - 287. Schaaf, H. M. 1968. Phenotypic s e l e c t i o n i n crested wheatgrass. Crop S c i . 8(6): 643 - 647. S o l b r i g , 0. T. 1972. 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K r a u s e , E. H i l d e b r a n d , and P. J . L o e s c h , Jr.. 1971. E v a l u a t i o n o f 10 g e n e r a t i o n s o f mass s e l e c t i o n f o r c o r n earworm r e s i s t a n c e . Crop S c i . 11: 16 - 18. Between f a m i l y / w i t h i n f a m i l y v a r i a n c e r a t i o s i n e x p e r i m e n t a l p o p u l a t i o n s . a. PCO p o p u l a t i o n s . Treatment G e n e r a t i o n C o n t r o l E a r l y a n t h e s i s L a t e a n t h e s i s S h o r t h e i g h t T a l l h e i g h t rs t o .He i g h t a t Nodes a t P r i m a r y Days t o F r u i t i r g e n c e a n t h e s i s a n t h e s i s b r a n c h e s a n t h e s i s p r o d u c t i o n 1.02* 1.82 2.30 1.31* 2.15 1.40* 3.13 10.82 5.13 4.16 8.52 2.93 3.82 5.71 3.21 1.28* 6.63 1.53* 3.11 9.44 3.91 3.82 6.36 2.39 6.34 3.85 1.93 1.89 2.54 1.54* 2.53 2.99 1.87 1.40* 1.01* 2.43 7.05 3.74 7.44 2.74 2.34 5.82 2.60 4.68 1.63* 1.86 2.22 2.89 6.61 3.71 3.52 3.11 1.79 2.99 6.63 4.49 3.15 2.38 1.40* 4.58 2.23 1.75 2.07 1.24* 1.91 3.43 4.01 1.37* 3.11 1.74 2.35 8.14 2.56 2.73 2.51 1.12* 4.00 3.36 4.76 2.14 3.95 3.45 3.22 5.30 3.75 3.18 3.35 2.66 3.49 2.90 2.56 6.44 7.30 1.98 2.66 3.11 2.31 4.72 2.25 1.03* 2.87 5.31 3.20 4.54 2.37 1.79 4.09 5.22 1.58* 4.41 1.54* 3.61 5.43 4.83 7.84 4.47 4.25 1.06* 2.26 2.75 1.59* 1.04* 3.40 4.72 1.87 2.28 2.97 2.38 6.04 3.33 3.58 0.75* 2.69 1.40* 2.91 4.17 6.14 2.73 5.15 1.57* 2.86 1.80 5.86 3.60 2.95 b. PCS p o p u l a t i o n s . Treatment G e n e r a t i o n Days t o H e i g h t a t Nodes a t P r i m a r y Days t o F r u i t C o n t r o l G 1 G 2 G 3 G 4  G 5 E a r l y G1 a n t h e s i s G G 3 G 5 L a t e Gj^ a n t h e s i s G„ G 3 G 4 S h o r t G h e i g h t G 4 G 5 T a l l G h e i g h t G G 3 G 4  G 5 rgence a n t h e s i s a n t h e s i s b r anches a n t h e s i s p r o d u c t i o n 1.68 * 4.99 2.93 1.73 3.36 0.86 * 2.92 6.03 9.97 3.09 9.76 2.40 6.16 3.07 6.61 1.70 6.96 1.85 3.75 5.99 11.95 6.66 11.53 1.57 * 3.17 5.37 6.92 2.73 6.09 1.77 2.28 2.59 1.95 2.84 1.44 * 2.20 5.07 4.00 6.78 5.34 3.91 9.78 3.71 3.35 3.38 4.64 2.15 1.65 * 1.34 * 3.94 2.73 4.05 1.91 3.02 7.01 6.58 1.94 6.73 1.51 * 4.41 3.39 1.17 * 2.59 1.17* 3.62 5.40 4.50 1.65 * 1.87 2.48 5.27 2.91 5.24 6.99 2.13 1.24 * 2.60 6.96 4.45 2.74 2.51 3.48 2.00 5.14 6.43 4.22 3.66 2.52 1.57 7.50 4.63 6.20 1.23 * 2.04 2.67 6.06 2.74 4.97 4.59 3.96 5.39 8.40 6.44 8.88 2.26 1.60 * 5.83 15.09 4.24 6.59 1.17 * 3.41 3.74 2.48 6.88 3.72 1.17 * 3.06 5.53 2.54 5.40 3.47 2.42 3.83 10.71 2.44 4.80 1.13 * 1.87 7.53 6.24 4.63 4.35 2.06 1.63 * 4.22 4.00 2.12 4.40 c. PBS p o p u l a t i o n s . T reatment G e n e r a t i o n Days t o H e i g h t a t Nodes a t P r i m a r y C o n t r o l Days t o F r u i t E a r l y a n t h e s i s L a t e a n t h e s i s S h o r t h e i g h t T a l l h e i g h t r g e n c e a n t h e s i s a n t h e s i s b r a n c h e s a n t h e s i s p r o d u c t i o n 2.15 4.66 3.23 4.19 4.47 1.36* 2.34 21.49 5.18 10.69 3.57 3.29 3.09 5.13 3.64 4.83 6.53 2.19 2.27 2.81 3.18 4.76 5.60 3.03 1.33* 2.42 1.88 2.59 1.39* 0.71* 1.19 2.81 1.36 * 2.58 0.70* 4.03 5.93 2.98 2.84 6.07 2.85 1.67 2.55 2.15 1.92 2.04 1.94 3.95 13.17 3.08 3.69 3.67 4.86 1.59* 1.95* 1.90* 3.43 1.44* 1.32* 7.91 1.84 8.63 3.19 3.39 1.90 4.41 2.17 1.34* 1.31* 2.06 4.00 3.92 2.12 6.01 3.71 2.08 1.68 2.88 2.60 1.95 3.27 4.46 1.59* 2.09 1.36* 1.71* 4.82 2.60 1.86 5.16 4.63 5.08 2.53 5.33 16.20 4.37 10.36 5.72 4.96 4.57 1.57* 5.06 2.30 3.66 1.12* 2.79 1.39* 1.68 1.02* 1.91 2.47 4.59 4.31 4.72 5.57 3.97 1.78 8.66 2.78 5.04 1.20* 1.92 1.54* 1.47* 4.30 2.16 2.80 1.38* 2.86 5.85 8.57 3.58 10.22 3.02 2.28 3.49 1.63* 2.88 10.57 C o e f f i c i e n t s of v a r i a t i o n , u n s e l e c t e d c h a r a c t e r s . -• . «d PCO PCS PBS § a. E a r l y L a t e Short' T a l l E a r l y L a t e S h o r t T a l l E a r l y L a t e S h o r t T a l l ' to' Days t o emergence G Q ( C o n t r o l ) 22.7 22.7 27.17 G ' 18.09 20.29 17.63 22.18 26.05 21.3 18.58 17.46 37.95 32.32 24.04 19.42 G 2 32.47 42.03 35.36 31.79 , 30.89 30.11 35.78 32.73 17.64. 20.58 37.59 39.42 G 3 18.85 26.09 35.10 25.66 21.62 28.01 27.43 24.90 29.82 28.07 26.31 2 8 . 2 1 ; G. 24.38 27.48 24.86 23.32 24.4 16.98 39.76 22.38 35.73 37.95 39.76 32.36 4 - . . . G 5 ' H e i g h t a t a n t h e s i s GQ ( C o n t r o l ) 20.16 20.16 23.97 - Gl 17.31. 18.13 17.39 18.46 138.76 28.15 G 2 16.53 17.62 .22.23 25.13 21.81 29.62 G 3 14.05 20.54 15.41 20.95 19.5 22.2 G. 17.29 16.53 17.52 21.57 "30.11 19.9 4 • G 5 to A p p e n d i x 2, c o n t i n u e d . - 173 pq co cj O a cfl H M o xi to QJ 4J cfl r H W Cfl W cd H H O XI CO CO r4 H W CO H 4J M O XI cu co to w ro O ro CO cn r H •H cn cu xi • 4-1 ' C ^ cd O H 4J 4-1 cd C o • CO . C_J OJ ' o c .53 C J V O CM in 00 rH • • • a VO rH CM VO r-1 rH rH rH 00 rH VO rH rH o- CM • • a a L O rH <r rH rH rH rH C N CO <r L O CO CM CO >• • • • CM oo r-l rH rH CO oo CO CN L O CO VO • • • • rH o CM C N rH rH rH CO CM CO rH O 00 rH a • • a a-* CO O Y rH rH 00 rH r~- rH C N O CT. CM • • a a CN o •CM r-» rH rH i—1 rH VO 00 CM rH m CM CM VO • • • • a o rH rH 00 »—1 rH rH rH r-» VO 00 VO • * a • rH rH CTN 00 rH <r <o <r O L O L O • • a • CTi CM o rH rH rH r-» CM rH rH L O VO • • a a C N CTi rH rH rH •H rH CM CT. VO • • a * a O o CM rH rH rH rH L O VO CO CO CO O rH L O • • a a m o C N CO rH rH rH rH rH C N CO < O o CM rH 00 00 1-^ ,—1 h~ 00 o CO CO .00 CM rH v O . <r o-> 00 VO o L O o o> VO ' C M rH VO f » rH r o o CO rH o rH a a a a o- CM o 00 L O O o •—< rH c o CO 00 CTi CM rH L O OY <r a a a CTi rH rH ' rH #* rH o 1^ CO rH rH. L O CO CO L O L O ON O VO CO CM O O C N L O rH rH rH rH OO L O o> O r o CO VO CO a a a CM 00 VO o •* c o CM VO O o- rH CM rH VO rH C N rH L O CM L O ' CO 00 rH a a a a VO CM o r - . r o rH L O rH rH rH . CM rH CM L O rH rH L O a a a • CO H o> r—i CO rH CO 00 CM ' rH • rH 00 C O L O ro CO c j cn CM CM •rH rH rH CM rH ' cn a) L O VO XI rH ; c^ o 4J a a a a s VO CO CM 00 cO VO CM o o o L O rH CM 4J a CO VO <t- r o r ~ •—t CM L O m rH a a a 0) L O L O L O Xi C N CO r o CJ rH rH CM a /•—N cd rH L O ON M •o L O r~- O Xi H a a a 4-1 rH CO CM rO a L O rH u . o CM rH H CO cj S - •H U o rH C N CO- P n C J O o •o o C J - 174 Appendix 2, c o n t i n u e d . C O C O C O r H r H C O C M r H in C O vo . 1—1 o C O C O " r H • • • * • • • cd V O in r H m O N H . m C O 4J C O . in O N C N r—1 C N V O 1H O N o in m r H C O O N O • • • • • • • xi • vo C O vo m r H C O r-. r-H co C O m in vo o- O N C O vo C O C O m C O V O C N C O •M • • • • • . cd V O vo o V O r-1 <!- V O C O CO pq U cd W m m O N CO . m O N • • • CN . CO in m vo CO CN CO -o- O N CO CN m r H r H CO m CN ON CN r H • • .. • • • • • CO vo in r H o CO H CO ON 00 4J vo r H r H CN vo v O r H O N in r-H in O N m CO o • • • • • • • • XI VO in CO VO r H as CO VO oS o ON as CO CN m in OS a) r-. O N ON O N •. • . • cd CO CO as CN ON CO as 00 CN >N r H as CO r H ON 00' <r u • • CO O r-- C O , o w VO VO m o a P H as ON m r H . o in CO as CM co r H • • • ' • • • • • CJ vo ; m VO in vO CO CO VO H CO ^> VO vo 4-1 <!• o CN vo r H CO CO U r H r H VO VO ; as r- CO o . . . • • Xi in VO in CN 00 VO CO VO OS CO m r-» as . -CM CM r-. r-. a) CM VO r-- 4J CO Cl • • • CO • r l o r H VO ' -vi- 00 cn •H CO 00 v o VO •  a) 4J X /—s a r»N 4J r H 3 r H ON m m r H a o -d O 00 r H U cd U o u • • • cd ' 4J u 4J . ON CO CN w o Cl a, Cl 00 m in 4J o o 4J O CO v_^ •rl 3 cd o r H CN CO m U - o r H CM CO < o o O . O o o O O C J

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