A Study of Quantitative Inheritance and an Evaluation of the Efficiency of Early Generation Testing in Soybeans

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P U R D U E U N IV E R SIT Y

THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION

BY

Imam Mahmud________________________________________

entttt ^d

A Study of Quantitative Inheritance and an Evaluation

of the Efficiency of Early Generation Testing in Soybeans.

COMPLIES WITH THE UNIVERSITY REGULATIONS ON GRADUATION THESES

AND IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS

FOR THE DEGREE OF

D o cto r Of PhÜOSOpby

P

August

r o c e sso r in

C h a r g e o r Th e s is

i9 50

/y

TO THE LIBRARIAN:-----

*9B THIS THESIS IS NOT TO BE REGARDED AS CONFIDENTIAL

PHOFE8SOIÎ PS CHARGE

GRAD. SCHOOL FORM 9—3 -4 9 —1M

A STUDY OF QUANTITATIVE INHERITANCE AND AN EVALUATION OF THE EFFICIENCY OF EARLY GENERATION TESTING IN SOYBEANS

A Thesis Submitted to the Faculty of Purdue University by Imam Mahmud In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy August, 1950

ProQuest Number: 27714188

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ACKNOWLEDGMENTS

The vriter wishes to express his sincere appreciation to Dr* Herbert H, Kramer for encouragement, advice and guid­ ance during the course of these investigations, and for his careful review of the manuscript. He is further deeply indebted to Dr. Albert H. Probst for providing the facilities and materials which were needed for carrying out this research.

i

ABSTRACT MAHMUD, IMAM.

A Study of Quantitative Inheritance and an Evaluation of the Efficiency of Early Generation Testing in Soy­ beans.

Inheritance studies in soybeans pertaining to clearly visible characters were reviewed and presented in a summarized tabular form, listing key references. Using the progeny of a cross between Mandarin (Ottawa) x Lincoln, an attempt was made to investigate the nature of segregation, estimate of the number of genes, and interrelations among nine quantitative char­ acters which included:

date of first pod set, number of branches, num­

ber of pods, number of seeds, number of seeds per pod, unit seed weight, seed yield, plant height and date of maturity.

As the parents were not

widely separated for many of the characters, and because of the lack of any record for the

plants, no conclusive opinion could be made re­

garding the nature of gene action. As for the expression of the quantitative characters, it was ob­ vious that environmental variations were highly operative.

This was

brought out by the fact that the variances of the F% in all characters but date of first pod set and plant height were exceeded by those of one or the other parent.

The number of parental plants in comparison

to the size of the Fg populations, however, was small, which could have accounted in part for their high variabilities. Among environmental influences, date of planting was of particu­ lar importance.

In a later date of planting there was a tendency for

increased variation for some characters, decreased variation for others; mean variances of the parents exceeded the variance of the F^ for all

il

but date of first pod set and plant height* Yield, date of first pod set and height were the only characters for which genetic segregation could be demonstrated.

There were indi­

cations for partial dominance of factors for greater yield and taller plants. Seed yield was found to be highly correlated with seed number, number of pods, number of seeds per pod, date of first pod set, date of maturity and plant height.

Seed size (unit seed weight) was found

to be negatively correlated with the same characters as were positive­ ly correlated with yield.

The relationship between seed size and yield,

however, was not significant. Date of planting influenced both the size and direction of sever­ al of the relationships♦ As an example, the relationship between seed size and date of maturity was reduced at the later date of planting; the same was true of the correlation between the number of branches and date of maturity.

In the relations of number of pods to date of first

pod set, date of first pod set to date of maturity, and date of first pod set to height, the r-values, in each case, were changed from a posi­ tive correlation to a negative correlation.

Most of these divergent

cases were explained on the basis of the influence of date of planting on the nutrition of the plant. The efficiency of early generation testing was examined.

The dem­

onstration of significant differences together with high amounts of va­ riation, as late as

was interpreted to indicate that selection for

yield in early generations is of little value in predicting the yield of subsequent segregates• Further, because of the lack of agreement between the genetic variance among

lines used to evaluate

plants

ill

and adjusted variances of populations evaluating ^

plants, it was

again concluded that selection for yield in early generations could not be recommended*

It would, therefore, appear that testing bulk

and F 5 populations, making selections of

plants, later bulking the

F& rows for further testing, as now widely used by soybean breeders, is an adequate procedure*

With its advantage of economy, the bulk

method also permits effective natural selection, and yet retains suf­ ficient variation to permit a wide range for selection in generations as late as

or F^*

Early generation testing can, however, be safely practiced for height and date of maturity, both of which are equally adaptable to either the bulk or pedigree methods of breeding. The inheritance of flower color and pubescence color were found to be simple in nature * In the inheritance of hilum color, a new type, namely gray hilum, was described for the first time.

This type of hi­

lum apparently results from the presence of a factor of inhibition, which is either different from the completely inhibiting factor I re­ ported by previous workers, or is the same factor which is unable to exert its fullest influence when in combination with EOT*

The rela­

tionships between flower, pubescence and hilum colors were found to be in agreement with the findings of other workers*

TABLE OF CONTENTS

ABSTRACT...........

Page i

INTRODUCTION........

1

LITERATURE B M W .............

3

MATERIALS AND METHODS...................

,22

EXPERIMENTAL RESULTS AND DISCUSSION. ♦ ........ .............. 27 A, QUANTITATIVE STUDIES..............

2?

Segregation of Characters and Estimation of Gene Numbers.27 Date when first podset,.......................... 28 Number of branches........................... 30 Number of pods..................................... .31 ................................. 33 Number of seeds. Number of seeds perpod................ 34 36 Seed size...... Seed yield.............. 37 Plant height. .............. 39 Date of maturity.................................... 41 Association of Characters

.......................... ,44

Early Generation Testing..............

49

Test of Genetic Theory....................

59

B. QUALITATIVE STUDIES.................

61

Inheritance of Flower, Pubescence and Hilum Color..... ..61 SUMMARY AND CONCLUSIONS..................................... 67 LITERATURE CITED..............................

70

APPENDIX................................................... 75 VITA....................................................... 82

LIST OF TABLES Table 1, Inheritance studies in soybeans summarized......

Page 8

2* List of Fo selections from Cross 98 (Mandarin (Ottawa) x Lin­ coln. ...... *25 3* Frequency distributions of the date on which the first pod was set for the entire F^ population and both parents...... 29 4* Frequency distributions of the number of branches per plant for the entire Fg population and both parents. ..... 30 5* Frequency distributions of the number of pods per plant for the entire Fg population and both parents * . . . . . . . . . . . . . . 3 2 6 * Frequency distributions of the number of seeds per plant for the entire F^ population and both parents. .... 33

7* Frequency distributions of the number of seeds per pod for ♦. 35 the entire F^ population and both parents....... 8 . Frequency distributions of seed size (unit seed weight) for the entire F^ population and both parents....... *37

9* Frequency distributions of yield (in gms.) per plant for the selected and unselected F^ populations and both parents. . . . . 3 8 10* Frequency distributions of height (in inches) for selected and unselected F^ populations and both parents ..... #40 11* Frequency distributions of the dates of maturity for the selected and unselected F^ populations......

42

12# Estimates of gene numbers and heritabilities for different quantitative characters studied ....

43

13* Simple correlation coefficients of quantitative characters..48 14* Analysis of variance of height, date of maturity and yield, together with components of variance and estimates of the true or genetic variance. ..... 55 15* Least significant differences for height, date of maturity and yield..............

56

16* Computed mean squares, F—values and standard deviations of various generations of selling............

57

Table Page 1?• Genetic classification of F2 segregates from a cross between Mandarin (Ottawa) x Lincoln for flower color, pubescence color and hilum color* ....********* ...... 62 IB* Summary of genetic classification for flower, pubescence and hilum colors in a cross between Mandarin (Ottawa) x Lincoln .............................. *.......... 66 APPENDIX TABLES l* Means of three replications for height in inches, together with heights of selected F2 plants..................... *76 2* Means of three replications for date of maturity — - days after September 1, together with dates of maturity of selected F2 plants *........... *.......... 7B 3» Means of three replications for yield in grams, together with yields of selected F2 plants....................... *80 LIST OF FIGURES Figure 1. Planting plan of the 1949 test **

................. *..... 26

A STUDY OF QUANTITATIVE INHERITANCE AND AN EVALUATION OF THE EFFICIENCY OF EARLY GENERATION TESTING IN SOYBEANS INTRODUCTION The rise of soybeans into a place of prominence in the agricultur­ al economy of this country has been both rapid and astounding*

Simul­

taneously, investigations regarding the genetics, breeding and improve­ ment have followed swiftly, resulting in an extensive amount of infor­ mation about the soybean*

In order to preserve some form of order, a

chronological review of at least the genetic literature was felt neces­ sary, and has accordingly been prepared in the form of a summarized table, listing key references* One of the reasons that made this rapid advancement of the soybean possible is the considerable attention that has been paid to the improve­ ment of existing varieties.

Today, selection following hybridization is

one of the most common breeding procedures.

Either the pedigree or bulk

methods of handling segregating populations or a combination of the two is used.

Associated with hybridization, the need has been felt for an

early evaluation of the breeding material so as to eliminate inferior germ plasm, and thereby, at the same time enhance the probability of su­ perior segregates appearing in the remaining material*

Early generation

testing, which is not new to c o m breeders, has been extended with con­ siderable success to some of the self—pollinated cereals.

However, with

soybeans, early generation testing, so far, has provided very little in­ formation regarding the potential yield performances of subsequent segre­ gates, although the results with regard to characters like date of ma­ turity, plant height and lodging resistance have been more favorable*

2

Since the efficiency of early generation testing depends on the breeding behaviour of desired characters, this study vas designed to furnish information regarding the inheritance of certain quantitative attributes• These included date of first pod set, number of branches, seeds, pods, seeds per pod, unit seed weight, seed yield, plant height and date of maturity# It was also felt necessary to investigate the effects of selection on genetic variances of subsequent generations, since selection is an important part of the breeding programme.

This information, it is hoped,

would perhaps explain why early generation testing for yield was not adaptable in soybeans. Finally, in the course of these studies, the inheritance of flower color, pubescence color and hilum color was investigated*

3

LITERATURE REVIEW Plants with less than 1$ natural crossing are regarded as natu­ rally self-pollinated crops, as broadly classified by Hayes and Immer (ll)^.

In soybeans, experimental evidence seems to indicate considera­

bly less than i& natural crossing*

Piper and Morse (31) reported 0.5%,

Woodworth (60) found it to be about 0*16%, whereas Garber and Odland (6) obtained 0 .14% natural crossing one year and 0.36% the next year. Takagi (41) reported 0.62% in Korea.

The highest reported were the es­

timates of Cutler (3) who, in proposing an easy method for making natu­ ral hybrids in soybeans by planting breeding nurseries close to honey­ bee colonies, obtained natural crossing ranging from 0.76 to 5*0%.

The

conditions under which the experiment was conducted were, however, ex­ tremely favorable to natural crossing, and Cutler* s results need not necessarily be regarded as typical of soybean populations. It may, therefore, be safely assumed that soybeans are naturally self-pollinat­ ed to the extent of almost 99%. The genetics of the soybean have been fairly well investigated, and the results on the inheritance of the characters studied are pre­ sented in a summarized form in Table 1.

Perhaps the largest contribu­

tion to these studies has been made by Hagai (22) and Woodworth (61,62, 64) • Simple Mendelian inheritance has been found for most of the charac­ ters listed, but in a few, as for instance the color of pubescence, coty­ ledon, seed coat and hilum, the inheritance has been complicated, due largely to the interaction of factors.

The contributions of Terao (45),

Hagai (22), Hagai and Salto (24), Woodworth (64 )> Veatch and Woodworth

^Numbers in parenthesis refer to literature cited.

4

(49) » Owen (25,26,27), Stewart (37), Williams (58), and Probst (33) have proved to be of great value in giving a better understanding of the in­ heritance of the above-mentioned characters.

These will be discussed

briefly. Pubescence color has shown simple inheritance in several, cases, Piper and Morse (32), Woodworth (61), Owen (26), Williams (58), Ting (46).

However, exceptional cases of inheritance were observed.

Owen

(26), for example, in a cross between homozygous tawny parents obtained a 15 tawny ; 1 gray segretation in the

Williams (58), on the other

hand, in a cross between homozygous gray parents, obtained a ratio of 13 gray : 3 tawny.

To explain their results, they both suggested dupli­

cate factors and proposed the symbols T^ and T^, with Tg for gray pubes­ cence eplstatic to

for tawny pubescence.

Probst (33) made a careful

analysis of the apparent 3 : 1 ratios presented by Ting (46), and ob­ served that several families gave a better fit to a 9 : 7 ratio than to a 3 : 1 ratio.

In his own work, he made several crosses between homozy­

gous grays and obtained tawny F^s which segregated 3 tawny : 1 gray in the Fg; other crosses involving gray x tawny parents gave 13 : 3 ratios in the Fg.

Accordingly then, the inheritance of pubescence color could

not be regarded as monofactorial in at least some crosses.

On the basis

of the above results it was proposed by Probst (33) that there were ac­ tually duplicate factors for pubescence color, with T^, and T^ inhibiting

and Tg with Ik> linked

in the presence of rg*

This hypothesis

successfully explained the divergent ratios referred to above. The inheritance of cotyledon color has also proved rather inter­ esting.

Piper and Morse (32) observed the simple dominance of yellow

cotyledon over green.

However, very different results were obtained by

5

Terao (45), who reported a case of maternal inheritance which was sub­ stantiated by Piper and Morse (32) and Owen (26) * Woodworth (64) > how­ ever, interpreted his results in Mendelian terms and suggested the pres­ ence of duplicate factors Dq. and Dg (formerly D and I, respectively) to account for the 15 yellow : 1 green and 3 yellow : 1 green segrega­ tions obtained by him in

progenies.

He postulated that either

or Dg could produce yellow and were each equally as effective as when both factors were present*

They were independent of one another and,

therefore, located on separate chromosomes. The corresponding réces­ sives d^ and dg gave rise to what he termed as genetic green, a type that showed segregation in crosses with yellow, as distinguished from maternal greens which showed no segregation in hybrid progeny.

Later

it was shown by Veatch and Woodworth (49) that maternal greens could carry the genes

and

for yellow, and further, a type carrying d^

and dg has also been isolated, Woodworth (64) • The inheritance of seed coat color has indeed been complicated largely due to the interaction of factors controlling pigments, not only in the seed coat but also in the pubescence and flowers.

In the

absence of any inhibiting factors, seed coats are either black or brown or combinations of these. Black is dominant to brown, as first shown by Piper and Morse (32), who assumed single factor inheritance, but did not assign any genes * However, it has since been shown that more than one pair of genes operate in the production of black pigment.

The com­

plementary genes involved have been designated as C, R by Hagai (22), B,H by Woodworth (61), R^, R^ by Owen (27), Stewart (37), Williams (57), Owen’s nomenclature is now the accepted form.

Rj causes the develop-

6

ment of anthocyanin pigment and is complementary with tense black color; with r^ it gives imperfect black,

to give the in­ r^ is recessive

to R-j_ and in combination with Rg a U g h t brown color is produced, while r^rg results in buff. assumed at the

An allelomorphic series

r^ and r^0 has been

locus hy Stewart (37), and confirmed by Williams (58).

r%o is recessive to either R% or r% and in combination with Rg gives a reddish-brown. According to Williams (58), r^r^° is presumably buff. This accounts for the dominance of black over light brown and red-brown, and of light brown over red-brown.

Nagai (22) originally distinguished

light brown from red-brown as being due to factors 0,o.

A second series

of allelomorphs. I, i \ i*1 and i, control the restriction of the pigment over the entire seed coat, to the hilum, to an eyebrow or saddle pattern, and no restriction, respectively, Owen (27), Woodworth (64-) • The first three are synonomous with the restriction factors H, I and K reported by Nagai (22), who also postulated the récessives of these to be of no effect, but later shown by Owen (27) to be inconsistent. The existence of this multiple allelic series has been verified by Stewart (37) and Williams (57).

The relationship between pubescence color and seed coat

color was first demonstrated by Woodworth (64-), who assumed complete linkage between H (now Rg) and T, whereby black and brown pigments were associated with tawny, and imperfect black and buff were associated with gray pubescence.

The rare occurrence of black beans with gray pubes­

cence (e.g. T69 (FPI64698) and Kingwa) has been reported by Woodworth (64), and he regarded these as crossover types with the genotype R^R^t. The other crossover type of the constitution r^r^T, however, has not yet been reported.

Partly on the basis of this, and further, because

of the appearance of tawny segregates in a cross between a non-black

7

gray bean, T24A and T69, Williams (58) pointed out the incorrectness of assuming RjBgt as the genotype for T69 since it must certainly carry a gene for tawny pubescence, the genotypic identity of the other parent T24A having been conclusively established as r^tV. gested the substitution of T for

He, therefore, sug­

assigning to it the properties of

1*2* Thus black and brown seed coats are differentiated from buff and imperfect black through the presence of T or t*

Distinction between

black and brown, and imperfect black and guff is dependent on the fac­ tor pair R^, r^, but in the latter case, a further differentiation ex­ ists through the effect of v on R^, in which case the seed coat is buff* With inhibition due to the presence of I, i* or i^, the seed coat is either green or yellow.

Green is a simple dominant of yellow, as

shown by 3 s 1 ratios obtained by Nagai (22), Nagai and Saito (24.) , Woodworth (62), Owen (27), Terao (45), and Williams (58).

In addition,

cases of maternal inheritance of green seed coat color are also known as reported by Terao (45) , Nagai and Saito (24), Owen (27), and Woodworth (64) * Hilum color inheritance follows a pattern similar to that of seed coat color.

In the absence of inhibition factors, the hilum is the same

as that of the seed coat; in the presence of inhibition factors, the col­ or is black, imperfect black, brown, buff or colorless.

The same genes

producing pigment in the seed coat affect pigmentation in the hilum. Furthermore, the relationships between seed coat color and color of pu­ bescence and flower color also stand in the case of hilum color.

8 Table !•

Inheritance studies in soybeans summarized.

Character

Basic types

Nature of inheritance, symbols, and key references*

Purple and green

A relationship between hypocotyl and flower color was reported by Woodworth, 1923 (62), Morse and Cartter, 1937 (20), Ting, 1946 (46 ), Probst, 1950 (33) • Purple stems always give rise to purple flowers; green to white. W^,w^ assigned.

Normal and faselated

A condition in which the stem is flat­ tened and enlarged as if by the adhering of two or more ordinary stems, Takagi, 1929 (42); acts as a simple recessive to the normal (F); Woodworth, 1932 (64 )> Domingo, 1945 (4) » Probst, 1950 (33)*

Broad (ovatelanceolate) , narrow and oval

Partial dominance of broad (Na) over narrow (na) giving 1:2:1 segregation in F^, Takahashi and Fukuyama, 1919 (44) > 3 broad : 1 narrow ratios obtained by Woodworth, 1932 (64), Takahashi, 1934 (43), Domingo, 1945 (4) > Probst, 1950 (33). Oval type described by Domingo (4 ), as recessive to normal, but cross­ es of oval x narrow resulted in normal; postulated duplicate genes whereby Na0,-normal (or broad), Na-0 0 oval and nanO- narrow.

Number in compound leaf

Normal - 3 Extra - 4 or 5

Extra leaflet condition (X) partial dominant to normal (x), Takahashi and Fukuyama, 1919 (44) * The condition was reported as recessive by Woodworth, 1932 (64 ), and therefore genetically different*

Abcission

Normal, delayed

Delayed abcission (ab) simple recessive to normal (Ab) ; Probst, 1950 (33) *

Variegation

Normal, variegated

Normal (V^) simple dominant to varie­ gated (vJ7; Woodworth, 1932 (64 ), 1933 (65)* “

Purple, white

Purple (W^) a simple dominant to white (wj), Piper and Morse, 1923 (32), Woodworth, 1923 (62), Morse and Cartter, 1937 (20), Williams, 1938 (53), Probst,

Plant Characters Stem Hypocotyl color

Fasciation

Leaflet Shape

Flower Color

9

Table 1. Character

(Cont»d) Basic types

Flower Color (Cont*d)

Nature of inheritance, symbols and key references*

1950 (33) • A dihybrid ratio of 9 purple : 3 purplish blue : 4 white reported by Takahashi and Fukuyama, 1919 (43) who suggested complementary genes. Sawamura, 1933 (34) suggested gene C responsible for chromogen production in petal and its conversion to purple by W.

Sterility

Normal, sterile

Sterility is exhibited by non-functional ovules and pollen; plants are determinate and are characterized by thickened leaves and stems which serve as storage organs; leaves remain green and firmly attached to stems; considerable amounts of starch in stems at the end of the season. Acts as a simple recessive to the normal con­ dition (St), Owen, 1928 (30).

Pseudo mosaic

Normal, pseudo­ mosaic

Normal condition (Pm) simple dominant, Probst, 1950 (33)• Mosaic type character­ ized by crinkly leaves short in growth and approaches sterility; flowers almost absent and small.

Light, dark

Light-colored condition (L) simple domi­ nant to dark colored condition (3.), Piper and Morse, 1923 (32), Woodworth, 1923 (62), Woodworth and Veatch, 1929 (67).

Bearing habit

Indetermi­ nate, de­ terminate

Sparse and even distribution over stem and branches typify indeterminate types (Dt) ; dense array on the central stem and a blunt apex, with a thin dispersal on lateral branches include determinate types (dt), Etheridge et al. 1929 (5)Former type simple dominant, Woodworth, 1932 (64), Mahmud, 1949 (19).

Dehiscence

Non-shatter­ ing, shatter­ ing

Non-shattering (Shi) simple dominant. Piper and Morse, 1911 (31) * Shattering (Shg) dominant to non-shattering, Nagai, m B (22).

Pubescent, glaborous

Mendelian dominant glaborous (Pi) report­ ed by Nagai and Saito, 1923 (2475 also a recessive glaborous (P^) reported by

Pods Color

Pubescence Presence

Table 1.

(Cont'd)

Character

Basic types

Pubescence Presence (Cont'd)

Nature of inheritance, symbols and key ref­ erences*

Stewart and Wentz, 1926 (39) • Pi x Po re lationship shown by 13 glaborous : 3 pu­ bescent ratio in F2 , Woodworth and Featch, 1929 (67), concluding P^ acts as inhibitor for pubescence giving ‘dominant glaborous — ^1^2> recessive glaborous — PiP2« Plant growth inhibited affecting heightand yield, Nagai and Saito, 1923 (24), Owen, 1927 (26); influences vigor in height, maturity, weight of seed and seed number, Veatch, 1930 (48); lowers resistance to infestation by Bmpoasca fabae, Johnson and Hollowell, 1935 (14) • P2 shows slight lowering in yield, Wentz and Stewart, 1927 (52). ?2 is more completely dominant over p2 than- Pi is over pi. Woodworth, 1932 (647*

Tips

Sharp, blunt

(Bl) reported as simple dominant over blunt (bl). Ting, 1946 (46).

Erectness

Appressed, erect

Appressed pubescence (A), as simple dominant over erect (a), Karasawa, 1936 (16).

Color

Tawny, gray

Simple dominance of tawny (%) over gray (_t), Piper and Morse, 1910 (31) > Woodworth, 1921 (61), Owen, 1927 (26), Williams, 1938 (58), Ting, 1946 (46). Exceptional cases reported 15 tawny 2 1 gray in Fg of a cross between homozygous tawny parents, Owen, 1927 (26); 13 gray : 3 tawny of gray x gray cross, Wil­ liams, 1938 (58 ) who postulated duplicate factors, T^ and Tg in which Tg for gray is epistaticto T% Tor tawny* TJomplete linkage between R2 , one of the complementary factors for black™seed coat and % is known. Woodworth, 1921 (61), Owen, 1928 (27), Stewart, 1930 (38). Both 3 : 1 and 13 : 3 ratios ob­ tained in several crosses by Probst, 1950 (33)• To explain his results and those of other workers, he postulated duplicate fac­ tors Ti and T2 for pubescence color, with R 2 linked-to Tj7”and Tg inhibiting T^ in the presence oT-T2 * Thus possible genotypes for tawny are: R 2 T 1R2 T1T2 T2 , ^ T l ^ T l ^ ^ » ^2*^1

11

Table 1* Character

(Coat'd) Basic types

Nature of inheritance > symbols and key ref­ __________________________ erences.

Tall, stocky

Actually height is a quantitative character, but one case of clear cut segregation of 3 tall, luxuriant and late maturing type (S) to 1 short, stocky and early maturing type (_s) reported by Woodworth, 1923 (62).

Genetic dwarfs

Normal, dwarf

Dwarf (df) plants seldom reach a height of more than 10 inches, are weak and spindly; behave as simple récessives to normal (Df), Stewart, 1927 (37).

Branching

Twining, erect

Long twining habit of wild species partially dominant to erect habit of cultivated spe­ cies, Karasawa, 1936 (16). No symbols as­ signed.

Iron utiliza• tion

Efficient, inefficient

Efficient (Fe) simple dominant to ineffi­ cient (fe), Weiss, 1943 (55)•

Maturity

Early, late

Partial dominance of late indicated fcy Woodworth, 1923 (62). However, earlyness seemed to segregate as Mendelian dominant in case reported by Owen, 1927 (26). Genes E,e, in­ volved. Other cases discussed in text re­ port it largely as a quantitative character.

Chlorophyll deficiency

Normal,

Growth Habit Height

*2 *

^3

y5

y6 y?

yg y9

greenish-yellow, weak in vigor, simple re­ cessive, Nagai, 1926 (22). leaves turn yellow as plant grows; Yo complementary for normal green, Nagai, 1926 (22). yellowish leaves, weak; simple recessive. yellowish-green; simple recessive, y, x ygive normal green, and show considerable vigor. pale green leaves that turn to normal with maturity, simple recessive, leaves, stems and pods turn yellow as plant develops; fairly vigorous ; simple recessive. Inheritance of y , - y* reported by Woodworth and Williams, 1938 (68) . yellowish-green in young plant, becoming normal with maturity; simple recessive, Probst, 1950 (33). yellow at emergence ; greenish-yellow by ma­ turity, simple recessive ; Probst, 1950 (33), Mahmud, 1949 (19).

12

Table 1. Character

(Cont'd) Basic types

Nature of inheritance, symbols and key references.

y10

yellow-green leaves in young plant; new­ er leaves show deficiency less and less; simple recessive, Probst, 1950 (33)»

Yellow, green

Yellow simple dominant to green. Piper and Morse, 1910 (31)• Maternal inherit— ance with no segregation in hybrid prog­ eny, Terao, 1913 (45), Piper and Morse, 1923 (32), Owen, 1917 (25). Duplicate factors D3JD2 postulated on basis of 15 yellow : 1 green, segregation, Woodworth, 1921 (61). Each factor is capable of producing yellow of same intensity as when both are present. Hence, both 1— gene and 2-gene type yellows exist. Woodworth, 1921 (61), 1932 (64), Williams, 1933 (53) * Two types of green — mater­ nal, non-segregating and carrying D^Dg; genetic, segregating carrying d^dg for green, Veatch and Woodworth, 193u (49) , Williams, 1933 (53).

Normal, seeds with two embryos

A single case reported by Owen, 1923 (29 ) in a variety 0 -4 where seed with two embryos occurred with a frequency of 0.44%* Inheritance not determined.

Present, absent

Wild and several cultivated beans charac­ terized by the presence of bloom on the seed coat. Character governed by three genes, Bj, and Bo, which act as domi­ nant to’iîormài, Woodworth, 1933 (65 ), Ting, 1946 (46 ).

Hardness of seedcoat

Hard, soft

Hardness of seedcoat measured by the ease with which water is imbibed by the seed, expressed in the time required for such inhibition. Soft seedcoat showed partial dominance, Woodworth, 1933 (65 )• Ting, 1946 (46), however, found hard coat to be dominant; as­ signed symbols H, h.

Surface

Defective

Defective (dej) simple recessive to nor­ mal (Dei) ; Stewart and Wentz, 1930 (40) . However, its expression may be inhibited by factor I for color pigments in the

Chlorophyll deficiency (cont'd) Seed Characters Cotyledon color

Seeds with two embryos

Coat Bloom on seed coat

13

Table 1. Character

(Cont’d) Basic types

Seedcoat Surface (cont’d)

Color

Nature of inheritance, symbols and key references. seedcoat, giving 15 normal 5 1 defective in Fn. A second type of defective de­ scribed in which seedcoat presents a netlike appearance; due to de^ which behaves as a simple recessive, Wüüâvrorth and Will­ iams, 1938 (67). Possible occurrence of a third gene deg proposed, Liu, 19-49 (17).

Black, buff brown (with various shades), imperfect black, yellow, green and com­ binations of above colors

Black (anthoeyanine) dominant to brown (quercetin) on basis of angle factor in­ heritance, Piper and Morse, 1910 (31); no genes assigned. Complementary genes for black suggested — 0, E by Nagai, 1921 (21), B, H by Woodworth, 1921 (61), % , E# by Owen, 1928 (27), Stewart, 1930 (38); Owen’s nomenclature is now the accepted form. RjEg * black, R^rg = imperfect black, r^Rg » brown, r^rg * buff. Com­ plete linkage between and T reported, hence black and brown associated with tawny, imperfect black and buff with gray pubescence, Woodworth, 1921 (61), Owen, 1928 (27), Stewart, 1930 (38 ), Williams, 1938 (58) and Probst, 1950 (33). In ad­ dition, W for purple flowers is necessary for imperfect black, Owen, 1928 (27), Stewart, 1930 (38 ), Williams, 1938 (58 ). An allelomorphic series R , r, and r,° has been proposed to explain the dominance of black over brown and reddish-brown, and of brown over reddish-brown, Owen, 1928 (27), Stewart, 1930 (38), Williams, 1938 (58). A second multiple allelomor­ phic series I, i*, i^ and i control the restriction of color pigments respective­ ly as complete, to the hilum, to an eye­ brow pattern, and no restriction. Accord­ ingly, self-colored seeds are recessive to either green or yellow. In the pres­ ence of restriction factors, seedcoat is either green or yellow, depending on the presence of (G) or (jg) ; green acts as a simple dominant to yellow, Nagai, 1921 (21), Nagai and Saito, 1923 (24). A ma­ ternal type of inheritance is also pres­ ent. Terao, 1918 (45), Nagai and Saito, 1923 (24), Owen, 1928 (27), Woodworth, 1932 (64), Williams, 1938 (58).

U

Table 1* Character Seedcoat (Cont'd) Flecking

Mottling

Hilum Abcission

Color

(Cont'd) Basic types

Nature of inheritance, symbols and key references.

Flecking, non-flecking

Character described as brown flecks on genetic blacks. Flecking (Fl) simple dominant to self-black (fl), Woodworth, 1930 (64).

Mottled, non-mottled

Mottling (M) simple dominant to non­ mottling (m) , Nagai and Saito, 1923 (24) 9 Woodworth and Cole, 1924 (66 ). Subject to environmental influences as rich soil, wide spacing, disease, poor growth conditions, etc., Owen, 1928 (28).

Normal, abnormal

Hilum abcission abnormal when tissues are torn as seed separates from pod. This condition (n) reported as reces­ sive to the normal (N), Owen, 1928 (28).

Black, brown imperfectblack, buff and colorless. Gray (new type discussed in this study).

Pattern of inheritance similar to that in seedcoat. Colorless hilum due to complete inhibition of genes producing pigments which are the same as those producing pigments in the seedcoat. Designated £, L by Nagai, 1921 (21) ; B, H by Woodworth, 1921 (61), and E1, Eg by Owen, 1928 (27). Complete linkage of Eg and T reported, Woodworth, 1932 (64 ). w for white flowers is epistatic to in the presence of t (gray pubescence), Owen, 1928 (27), Stewart, 1930 (38), Probst, 1950 (33) > and Mahmud, 1949 (19), mak­ ing the presence of W (purple flowers) necessary for the production of imper­ fect black hilum. As is shown in this study, w is epistatic to in the presence of and 1, changing a gray hilum to colorless.

15

The nature of quantitative inheritance in soybeans has been extensively investigated^

One of the earliest demonstrations of

hybrid vigor was reported by Wentz and Stewart (51) who obtained hybrids which exceeded their parents in height and in seed yield* hybrid vigor for plant height was manifested only in the later stages of growth, when it made its most rapid appearance during the last two or three weeks of the season*

In the case of yield increases

over the parental average ranged from 59*53 to 394*37%* Veatch (47) conducted extensive investigations on hybrid vigor in soybeans, and found that although the parents were exceeded in 12 out of 13 characters,

hybrids were superior to the better parent

only with respect to average seed weight, number of seeds per pod, straw-grain ratio, and average internode length*

He concluded that

the best criteria for hybrid vigor in soybeans are yield, number of seeds, pods, plant weight, height, number of nodes, and total stem and branch length. In the case of yield, an average increase of 19*6% over the better parent was obtained.

The Fg populations showed transgressive

segregation for yield and plant height, but none of their means were significantly higher than the higher parent, while those for height were intermediate to the parents*

Apparently then, some heterosis was

being carried over into the F^. In a more extensive study using replicated trials, Weiss et al. (57) obtained average increases in seed yield of 3 2 *2% for Fj_ hybrids for all but one of 17 crosses, over the higher parent, when grown in the green­ house, and 14*5% for all crosses when grown in the field*

Differences

in degree of heterosis between crosses were perceptible, and further,

16

responses to greenhouse and field conditions were differential. Some of the ?2 populations exceeded the parents in yield, but the ^heterosis of F]_ and F2 was not consistent among crosses.

With respect to aver­

age date of maturity, average height, and average degree of lodging resistance, all crosses were consistently intermediate to the parents. All F^s exceeded the mean of the better parent in four crosses in yield in one year, and in two out of four crosses in a field study conducted by Kalton (15)»

in the second year,

Here again differences in

the degree of heterosis was noticeable among crosses.

As for mean

date of maturity and plant height, F^s were intermediate to the parents in some cases, and superior to the better parent in others. In inter-specific crosses involving the cultivated type (Cr. max) and the wild species (Or. ussuriensis) Karasawa (16) noted the dominance of the tall and twining habit of the wild parent, but other characters were intermediate.

Ting (46) observed a similar situation and noted

positive skewness for height and seed size. Weber (53) obtained simi­ lar results for seed size in a similar cross, namely positive skewness in the F2 and F^ and postulated partial dominance for genes governing small seed size.

Data obtained by Williams (59) is also of quite the

same nature, and it is of interest to note that in the reports of all of these three workers, seed size was found to be geometric in inherit­ ance.

From the findings of both Weber (53) and Williams (59), the F^s

were intermediate to the parents with regard to mean date of maturity, indicating lack of dominance; Weber postulated additive gene action, and a low number of genes.

Lack of dominance was also typical for oil con­

tent, but its inheritance was complex, being a mixture of geometric and

17

additive gene action*

Transgressive segregation for this character

was not observed, which suggested that the parents represented the genotypic extremes and the possibility of a large number of genes being involved#

The same workers were in accord with the fact that the high

protein content of Cr# us surlensis exhibited partial dominance in the and transgressive segregation in the Fg; additive gene action was inferr­ ed and also a relatively few number of genes being involved#

Like oil

content, the inheritance of iodine number was shown by Weber, to be complex. A somewhat different approach has been used by several workers to simplify the study of yield, and also to possibly facilitate breeding technics for this character#

Woodworth (63) first suggested the break­

ing down of this complex character into its component parts and found (64) that 26 varieties significantly differed from each other with respect to number of nodes per plant, pods per node, seeds per pod, percentage aborted seed, and average seed weight —

factors which supposedly con­

tribute towards the yield of a single plant. The important contribution of any component to total yield was to be ascertained by the signifi­ cance of the respective correlations with yield#

Only percentage aborted

seed and average seed weight were found to be significantly correlated with yield, the former in a negative direction, the latter in a positive direction#

In general, other components were independent of one another.

However, his correlations were run on only 26 pairs of items, which is a rather small number, and he himself has cautioned that interpretation of his r-values be made with wariness# In hybrid populations, Veatch (4 7 ) found seed yield to be significantly

correlated with seed number,

number of pods, number of nodes, plant weight and total stem and branch

18

length#

Weatherspoon and Wentz (50) reported the significant associ­

ations of number of pods, number of nodes and plant height with yield. In contrast to the results of Woodworth, seed size was in no way corre­ lated with yield.

This was accounted for by the positive correlations

of this character with percent abortive seed and negative correlations with number of pods, number of nodes and plant height, all of which are highly and positively correlated with yield, indicating that a physiological relationship is involved. However, by means of partial regression analysis, he was able to show that plant height, number of pods and seed size gave the only significant correlations.

The associ­

ation of number of nodes with yield was therefore probably accounted for by its association with height.

Accordingly then, number of pods and

plant height were among the most important components for estimating yield, followed by seed size.

Another factor which has not so far

received the consideration of most American workers, is one reported by Nagai (23) who found that inter-varietal differences for yield could be partly accounted for by differences in leaf area; a correlation coefficient of 0 .7 3 2 was obtained. Under the subject of correlations, several other interesting associations have been reported. Woodworth (61) reported

a highly

significant relationship between height and the number of nodes per plant.

This has been confirmed by Weatherspoon and Wentz (50) who, in

addition, reported the significant correlation of height to number of pods, seed size, percent aborted seed and number of pods per node.

High

oil and low protein content have consistently shown negative linear correlation in data cited by Weiss (56).

Weber (53) reported large seed

19

size to be notably correlated with high oil content and low iodine number, and slightly correlated with low protein content.

Lateness

of maturity was not associated with compositional characters. Improvement in soybeans today, is largely dependent on hybridi­ zation.

Either the pedigree or bulk methods of handling segregating

populations following hybridization have been used.

To most breeders

an early and accurate appraisal of breeding material has proved of vital interest. What are the most promising crosses, promising in the sense that they will give rise to the most desirable segregates combining nearly all of the preferred agronomic qualities? How early in a breeding programme can such crosses be differentiated, and what are the bases for such evaluations? These are some of the questions which many of the soybean breeders have attempted to answer.

Early

generation testing, studied extensively in some open-pollinated crops, has suggested the possibility of its application to the self- polli­ nated crops.

In some of the small grains, in barley for instance,

Harlan et al. (7 ) reported that yields of unreplicated bulk crosses were highly indicative of the crosses from which high yielding segre­ gates might be expected.

Heterosis as measured in bulk

and

populations of 6 wheat crosses were shown by Harrington (8) to cont­ re ctly predict the value of the cross in subsequent generations♦ limner (11) showed that a replicated comparison of six bulk crosses of barley, through E^,

and

generations, revealed

some crosses

to be consistently higher yielding, but advance generation tests as compared with spaced

plant measurements

were not consistently

comparable due to the interaction of cross x method of planting. The

20

evaluation of segregates within crosses has been attempted largely on the basis of measurements made on spaced F]_ and Pg plants*

However,

the general opinion seems to be that such tests are of little value with respect to yield*

Harrington (9) found that in wheat crosses,

although individual F2 plant measurements correctly predicted earli­ ness, height, stem rust reaction and seed characters, they were mis­ leading for yield*

From an F2 population of nearly 40,000 plants

only 6 lines of questionable value rigorous pedigree selection*

were obtained after 5 years of

Immer (12 ) drew a similar conclusion

with respect to barley crosses and concluded that yield variations of F^ plants were determined largely by environmental factors*

Atkins

and Murphy (l) tested bulk F7 and Fg of ten bulk crosses, together with fifty segregates from each bulk population, and obtained the information that bulk populations which give the highest yields in replicated tests in the early generations, do not necessarily pro­ duce the largest proportion of high yielding segregates in later generations* In soybeans, Weiss et al* (57) reported that there was little association between the degree of heterosis for yield measured in the F%s of 17 crosses and subsequent segregates in later generations*

Bulk

trials from F^ to F 5 indicated the unreliability of predicting for yield and maturity; however, lodging resistance and height were pre­ dicted with reasonable accuracy*

Kalton (15) presented further evi­

dence substantiating the unreliability of bulk population trials in predicting the yield potentialities of crosses*

However, differences

among crosses, for height, date of maturity and lodging resistance

21

remained fairly consistent in Fg to

generations•

Measurements on spaced Fg plants however have given better estimates of prediction*

Weiss et al* (57 ) found that dates of

maturity readings on spaced Fg plants were consistently correlated with the dates of maturity of their Fj progeny3 similar relations for seed yield

were less consistent, while those for lodging re­

sistance were poor*

F^ measurements, likewise were highly indicat­

ive of the F^ dates of maturity, but the correlations for yield were low*

In several other tests, reviewed by Kalton (15), replicated F^

and F^ performances have been useful in predicting values of subse­ quent segregates. However, the results for yield were rather incon­ sistent * Weiss (56) drew the conclusion that replicated Fj tests were useful only for evaluation of plant height, date of maturity and lodging resistance* Some reasons as to why soybeans Respond differentially to methods of early generation testing, as compared to the cereals were postulated by Kalton (15)*

These include (l) greater susceptibility to environ­

mental influences, especially changes in photoperiod, and (2 ) soybeans are a full season crop, and are more responsive to variations in the length of the growing season* Workers in general, Weiss et al* (57), Kalton (15), and Weiss (56) are of the opinion that early generation testing, using either the bulk or pedigree method of testing provides little information, at least before the F/^ generation, on the potential yielding ability of subsequent segregates.

22

MATERIALS AND METHODS A cross between Mandarin (Ottawa), a very early maturing soybean variety and Lincoln, a mid-season to late variety, was made by Dr. A* H» Probst* in 1945> end resulted in three

plants which were grown

to maturity and individually harvested in 1946.

Seed from two of these

plants was at first considered enough to provide an adequate population for further study of this hybrid material, and accordingly these were space-planted in rows approximately 3 feet wide, with a 1-foot spacing between plants within the row, on June 4th. 1947*

Due to extremely dry

conditions, poor emergence was characteristic of these plots, and accordingly it was decided that the seeds from the third be included in the test*

plant also

These were planted in the same field on June

17th. 1947* At the time of both plantings, seed from both parents were included to furnish comparative data.

Each parent was planted in 4

ten-plant plots so as to sample soil variation within the blocks* In the summer of 1947» the following individual plant notes were recorded:- days after July 1, when first pods set; date of maturity measured as the number of days after September 1, when approximately all the leaves had fallen, and well over 90% of the pods were brown; plant height, color of bloom and pubescence.

When mature, plants were

individually harvested and threshed, at which time the following ad­ ditional data were recorded

number of branches, pods, seeds, seed

yield and hilum color* The ratios, seeds per pod and unit seed weight, were calculated for each plant by dividing the number of seeds by the number of pods, and the total seed yield by the total number of seeds * Associate Agronomist, Division of Forage Crops and Diseases, U.S.D.Â.

23

respectively* f 3 progeny rows were planted in 1948 using 40 seeds from each F2

plant*

One of the parents was interspersed every tenth row.

were in all 606

There

progeny rows arising from the F2 seeds planted on

June 4th* 1947> and these will be referred to as group A—B, while there were 330 progeny rows arising from the June 17th. planting* These will be referred to as group C.

Notes on segregation for flower color, pu­

bescence color, and measurements on

average height and average date of

maturity were recorded on a row basis*

One seed from each of twelve

plants within each row was saved for the analysis of hilum color.

At

the time of harvest, approximately 248 rows were selected as would nor­ mally be done in a breeding program.

Ten plants were selected from each

selected row on the basis of general appearance and individually harvest­ ed and threshed.

The yield of these plants was not recorded.

In 1949 , 64 selections were made from the F^ progeny rows.

Selec­

tion was limited to those lines with at least 3 F^ plants with seed suf­ ficient for at least three replications. A specific attempt was made to include lines deviating widely in plant height and date of maturity* The 3 selections from each

row provided the seed

for the F^ lines*

Equal quantities from each of the remaining plants in the row were com­ posited to produce the seed for a bulk F^ row.

Finally remnant seed of

F2 plants from which the Fg progeny originated, was included to give an Fg line.

Each selection was therefore represented by five entries,

namely 3 F4 lines, 1 bulk

and 1 Fg line.

in a triple lattice design.

Each plot consisted of 5 rows, one row

The 64 selections were grown

being assigned at random to each of the five items.

Rows were 9 feet

24

feet long, later trimmed to 8 feet soon after emergence, thus leaving aisles 4 feet wide between series of plots * Row spacing was 40 inches* A complete list of the selections appears in table 2, while the field plan appears in Figure 1. The overall stand was good*

Average plant height and dates of

maturity were recorded on a row basis* dividual rows was recorded*

After harvest, yield of in­

The data were analysed in accordance with

the methods outlined by Cox et al.(2) and Hayes and Immer (10),

Due

to the fact that precision increases over a randomized complete block design were not considered sufficient to warrant an adjustment of means, the experiment was treated as if it were a randomized complete block design with a split-plot feature* Estimates of gene numbers were made from the measurements made on the ?2 plants and individual plants of the parents*

The mean vari­

ance of the parents was used in estimating the environmental variance* Estimates of heritability were computed on the basis of the ratio of the genetic variance to the total or observed variance of the F2 * As reported by Lush (18), the observed variance is made up of vari­ ation due to genetic segregation, and variation due to environment* The latter can be estimated from the variance of the F^ or the mean variance of the parents * This value, when subtracted from the observed variance of the F2 ; gives rise to a residual which was considered to be a measure of the genetic variance of the F2 * Correlation coefficients were calculated by the methods outlined by Snedecor (36).

Genetic ratios were tested by means of chi-square*

25

Table 2*

Identification Number

List of F3 selections from Cross 93 (Mandarin (Ottawa) x Lincoln) grown in 1949. Identifi­ cation Number

F~ selections

F3 selections

1 2 3 4 5 6 7 8

X—98—2—1y —3, -5 -15-1 , —2, —6 —28—3> -4; -11 —30—1f —2, —3 —46—1, -3, -4 -47-5, —6, —8 -51-1, -3, —4 -66-2, -4, -5

33 34 35 36 37 38 39 40

9 10 11 12 13 14 15 16

-87-5, —7; —8 -IO7 -3 —5, —6 -117-1 —2, -5 -119-1 —5, —8 —123—1 —2, —4 -137-1 -4, -5 —138—5 —7, —8 —142—2 —4, —6

41 42 43 44 45 46 47 48

—364—3 —4, —6 —418—1 —4, —6 -430-1 —2, —4 —432—1 —2, —3 —464—4 -5, -8 —488—4 -8, —9 - 502-3 -5, -6 —526—4 -7, -10

17 18 19 20 21 22 23 24

—143—2 —146—1 -178-1 -180-3 -189-2 -195-1 -198-1 -212-2

—5 —9 -5 —8 —4 -8 -6 -7

49 50 51 52 53 54 55 56

-533-3 -562-1 —567—2 -577-5 — 588—1 -596-1 —636—1 -655-4

—4; -2, —4, —8, -4, —4; —2, —8,

-8 —5 —8 —9 —5 —8 —4 —10

25 26 27 28 29 30 31 32

—216—1 -5, -8 -226-2 -3, -7 -273-1 -4, -5 —280—1 —3, —6 —284—4 —7, —8 -292-2 -4, -5 —296—5 -7, -9 -312-1 —4, —6

57 58 59 60 61 62 63 64

—666—1 —679—4 —680—5 -793-2 —867—9 —876—1 -906-2 -934-4

-3, —8, -3, —4, —1, —2, -4, -5,

-4 —9 —4 -5 —10 —6 -7 -7

—4, —8, -3, —4, —3, —7, —5, -5,

X-98-317-1 -319-2 -337-1 -344-1 —345—3 —346—5 -351-3 —354—2

-5, -5, -7, -5> -4, -6, -5> —6,

-8 -6 -9 -9 -5 -7 -6 —8

PL A N T I N G

PLAN,

FIELD

LAYOUT

R E P L I C AT I ON «1

2 6

30

10

41

47

**54 60

ii 31

*

27

•o

32

“ 44

43

53

161

61 42

45

10* 9

50

70

110 111

®

CM

48

46

5

eo

• 81

58

56

51 . . AlP.

381

63

20

• 90

12 33 0

331

• 91

59

5

100

71

* 25

52

60

so

ONE

55 60

*1

29

62

1949

1017

2 160

^ 9

4

*^^35

1*0 e 160 6 __ttJL 13 370

60

2 8

38

la$ 6 *^3 7

21

**13

16 •6 0

33 1»0

M b

40

*?5

9 aao

600

14 ___ 6 * 6

4*1

4 1

49

40

*1 0

8

*6 0

*6 1

1

53

11 610

160

*1 1

3*0

* %

170

*0 1

361 61 371

600

34

38 0

33

24

16

« •0

460

381

»°èo

57

a^ 2 44

64 sa

**45

36

681

27 *9 0

47

30

14

630

34

11

51 600

s6i 35

•“ t

4 ?10

611 59

**63

3

36

*?«

*'&2

31 —--------

—

47

73 0

7 3 33

60

^56

32 760

791.l

*801

35

53

56 18

13 6 6 80

sV o

22 700

660

630

*%0

6519

701

26

4

4 1

7*$b

31

670 67

640

16

710

680

780

601

1

19

2

**63

814 6

29

8

10 63*5

36 800

1.

*%l 8

66 0

880

%So

e l 1b

660

“ te

8

2

68430

45

9

870

54 67è 7 37 8*0 880 REPLICATIO N THREE

Planting

plan

of

49 89 0

the

19^9

3

* * 9

4 6 91 0 12

34 930

25 940 9*1

980

test

Ms

21 900

901

861

881

Fig.

36

610

780

57

470

•

781

42

46

770

7 *0

'

2

17

661

60 0

?di

14

680

690

66 0

32

650

44

42

681

22

+#4

661

680 681

3801 - -------------

26

54

6*0

15

610 611

6

39

6 *1

56

*4 0

6*1 7

10

670 671

**4B

T WO

6 01

661

55

9

*0 0

REPLICATION

57 *6 0

29

36 0

g

*6 1

7* ^ 3

390

361

61 *5X 19

**25

5

360

s u

7*1

37

4

310

24 ,6è

6 I 960

52 96 0

27

EXPERIMENTAL RESULTS AND DISCUSSION A.

QUANTITATIVE STUDIES

Segregation of Characters and Estimation of Gene Numbers Although the

population consisted of 936 plants, complete

records on quantitative data were available for only 601 plants in group A-B, and 320 plants in group C, making a total of 921 plants.

Records

for 47 plants of the Lincoln parent and 39 plants of the Mandarin-Ottawa parent also were available.

In analyzing the mode of segregation of

these characters, frequency distributions were prepared for each, keeping distributions of the two seeding dates, viz. June 4th and June 17th,1947, separate.

This provided an opportunity for studying the influence of time

of planting on the different quantitative characters which were studied. Due to the absence of data for the F^, it was not possible to ascertain as to whether the nature of gene action was arithmetic or geometric. In the estimation of number ofgenes involved, the formula of Wright (68), was used, where: 8(s2F2 -x/a^Px.s^) when n ■ number of genes, s2F2 — the variance of the F2, s2P^ * the vari­ ance of the

parent, s2P2 = the variance of the P2 parent, while D2 =*

the square of the range or the difference between the largest and the smallest variate in the F2 population. variance of the

Wright mentioned that either the

or the mean variance of the parents could be used in

estimating the genetic variance of the F2. In this case the geometric mean of the variance of the parents has been used.

Estimates of herita­

bility were computed in terms of the ratio of the genetic variance of the

28

F2 to the total or observed variance of the Fg, or symbolically:Heritability -

a2F2 -v/a2Pi.a2P2 82p2

Date when First Pod Set The frequency distribution for the number of days after July 1, when the first pod set for the Fg and the parent plants is shown in table 3*

The mean of the Lincoln parent in both dates of planting is

considerably higher than that of Mandarin (Ottawa); this is to be ex­ pected as Lincoln is a later maturing variety*

The Fg mean, in both

cases was intermediate to the parents; in addition, its range was wide enough to include both parental types*

This would indicate the presence

of relatively few genes affecting this character* This supposition is substantiated by the calculated estimate which was found to be from 3 to 9 genes (table 12)* The influence of date of planting seems to be rather interesting in that with the Fg and the Lincoln parent, later planting had a tendency to reduce the variation between plants as shown by the decrease in the coefficients of variation*

With an early maturing varie­

ty like Mandarin (Ottawa), delayed planting had the effect of increasing the variability by almost 50%* This caused a larger environmental vari­ ance which, in conjunction with the lower Fg variance resulted in a higher estimate of the gene number for group C* By expressing this character in number of days after planting instead of in number of days after July 1, the effect of delayed planting on the means could be brought out more vividly* For example, in the Fg, the mean in group A-B would have been 25*8? + 2? (days after June 4th) * 52*87, while for Group C it would have been 35*89 + 14 (days after June 17th) * 49*89*

29

Table 3*

Frequency distributions of the date on which the first pod was set for the entire F2 population and both parents*

Class*1" Fg 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 % 3 X C* V* (*)

5 30 64 49 35 28 37 32 48 42 30 39 49 35 34 25 12 4 2 1

601 2 0 .5 6 25*87 17.51

fthimbai» of individuals Group A-B Group C Lin­ Man­ Lin­ F2 coln darin coln 1 10 3 3 2 1 1

2 8 1 9 4 3 0 3

30 3.84 32*97 5.90

24 3.56 21*50 8.80

1 0 1 5 10 2 4 2 3 14 25 29 47 36 33 38 26 13 7 11 6 7

320 14*48 35.89 10.60

2 1 4 6 0 3 0 0 0 1 17 4*62 40.00 5.67

Man­ darin

1 1 2 0 0 0 0 5 1 2 1 1 0 1

15 14*52 31.67 12.03

^ Number of days after July 1* For Lincoln, the means would have been 59*97 and 54*00, and for Mandarin, Ottawa, 48*50 and 44*67 respectively, for groups A-B and C*

In

each case it is seen that the delayed planting hastened the date of pod set by about as much as 3 days in the case of the Fg* 6 days in the

30

case of Lincoln, and 4 days in the case of Mandarin, Ottawa.

The effect

is therefore, apparently the greatest in the case of a late maturing variety, like Lincoln.

Heritability estimates were found to be 61.65%

in the case of group A-B, and 42*44% for group C, which is approximately one—half the former value. Number of Branches Table 4*

Frequency distributions of the number of branches per plant for the entire population and both parents.

Class**" F2 1 2 3 k 5 6 7 3 9 10

3 11 53 70 94 132 125 39 19 5

n x s C. V. (%)

601 5.88 3.04 29.76

Number of individuals Group C Group A-B Man­ Lin­ Lin­ F2 darin coln coln

4 8 7 2 8 1 30 6.17 2.28 24-48

2 5 6 4 5 2

24 4*4^ 2.17 32.97

4 17 73 92 89 30 13 2 320 5.24 1.62 24.23

1 3 3 6 4 1

18 5.67 1.76 23-45

Man­ darin 1 1 2 2 5 2 0 1

14 4.71 2.20 31.39

Number of branches. The F^ frequency distribution for number of branches per plant as shown in table 4» ranges from a single branch to as many as 10 branches* In either group the parental ranges are adequately covered.

The means

of the ?2 in both groups are intermediate to the parents but they differ in each case very slightly from the parental means.

Extremely high coef­

ficients of variation of parents in comparison with the F^ suggest the

31

possibility of environmental influences, and this is not at all surpris­ ing*

Weber and Weiss (54), show illustrations of the effect of spacing

on height and branching.

Using the variety Mukden, they observed that

plants seeded at normal rates were taller and had fewer branches. With a spacing of eight inches, the plants were shorter, and had many more branches.

Fertility and soil conditions may be other factors which

might effect the amount of branching.

The effect of delayed planting

is reflected in a reduction not only in the means, but also in the amount of variations between plants within groups.

The reduction in the

Fg of the coefficient of variation is particularly noticeable.

An esti­

mate of 12 genes was obtained for goup A-B, but no estimate was possible for group C, as the variability of the F^ was found to be less than the mean variance of the parents.

Heritability was found to be only 2.69%

which further confirms the high susceptibility of this character to environ­ mental influences. Number of pods Table 5 shows the frequency distribution of the F^ and the parents with respect to the number of pods per plant.

In group A—B there seems

to be transgressive segregation in both directions, but is slightly more in the direction of the larger number of pods per plant.

The mean in

this group exceeds even the mean of the larger parent (Lincoln), but not by enough to be considered significant. intermediate to the parents.

In group 0, however, the mean is

Coefficients of variability are high in

comparison to the other characters studied so far.

A heritability esti­

mate of 43 •73% was obtained which shows a considerable amount of suscepti­ bility to environmental variations.

Perhaps the same factors which affect

32

Table 5*

Frequency distributions of the number of pods per plant for the entire population and both —parents*

Class"** *2

0-19 20 - 39 40-59 60-79 80-99 loo - 119 120 - 139 140 - 159 160 - 179 180 - 199 200 - 219 220 - 239 240 - 259 260 - 279 280 - 299 300 - 319 320 - 339 340 - 359 360 - 379 380 - 399

4 17 30 54 67 76 77 78 63 46 34 18 11 14 6 2 2 0 2

Humber of individuals Grouo A-B Lin­ Man­ darin coln 1 1 2 9 4 16 2 2 5 45 46 3 4 2 6 57 2 46 4 47 5 4 2 19 21 5 1 6 0 5 1

n 601 29 g2 3699*38 2115*25 X 157.67 157.03 C* V. (%) 38.57 29*29 1 Humber of pods per plant

24 1868.02 106.75 40.48

320 2028.06 136*44 33.00

Group C Lin­ coln

Man­ darin

2 4 0 3 2 1 3

1 0 0 3 4 3 1 3 0 3

18 2535.65 156.00 32.28

15 1878.23 105.67 41*01

branching and plant height also affect number of pods borne by the plant, as these characters, as will be shown later, are significantly related to pod number* character*

-An estimate of about 11 genes was found to effect this Ho estimate was obtainable for group C owing to the larger

mean variance of the parents as compared to the variance of the F2* Delayed planting has had little effect, if any on the means of the parents, but with the variation*

it has reduced both the mean and the coefficients of

33

Number of Seeds Table 6*

Frequency distributions of the number of seeds per plant for the entire Fg population and both parents.

Number of individuals

"1 Class F2 0 — 4-9 50-99 100 - 14-9 150 - 199 200 - 249 250 - 299 300 - 349 350 - 399 400 — 449 450 - 499 500 - 549 550 - 599 600 - 649 650 - 699 700 - 749 750 - 799 800 - 8 4 9 850 - 899

1 13 21 46 68 75 79 85 73 53 28 24 12 10 8 2 1 2

601 21,204.11 X 356.37 C. V. (%) 40.85

n s

Group A-B Lin— coin

1 0 4 5 8 2 4 2 2 1 1

30 13,983.80 356.70 33.15

Man— darin 3 3 3 5 4 2 3 1

24 11,307.08 231.79 45.87

F2

Group C Lin­ coln

1 4 22 37 49 49 63 40 34 13 3 5

1 1 0 4 2 3 3 0 1 3

320 10,979.21 294.79 35.54

18 926.97 370.50 25.99

Man­ darin 2 2 3 3 1 3 1

15 8,527.76 223.07 41.99

Number of seeds per plant.

In table 6 is to be found the frequency distributions for the num­ ber of seeds per plant.

As in the case of the number of pods per plant,

it is seen that the mean of the Fg in group A—B is as high as the mean of the higher parent (Lincoln), but is intermediate to the parents in group C.

The coefficients of variation also follow a similar pattern,

and the estimate of heritability, 46.53%, likewise shows a high degree

34

of* environmental influence# for this character#

An estimate of about 9 genes was obtained

The results so far should indicate a high degree

of relationship between number of pods and number of seeds# lation coefficient was found to be 0#955*

The corre­

This high correlation indi­

cates the absence of important differences in the number of seeds per pod and that in this, cross the same genes which govern the number of pods, also largely govern the number of seeds, and further that environ­ mental factors governing number of pods also govern number of seeds*

Number of Seeds per Pod Woodworth (64)* from observations on 26 varieties, stated the opinion that nthere is no question that seed number per pod is a varie­ tal characteristic.”

The majority of pods in most varieties contain 2

or 3 seeds; some may have only one, while others may have as many as four.

Takahashi (43), obtained a good fit to a 3 : 1 ratio for number

of seeds per pod when the

plants were divided into two classes accord­

ing to whether less than 10$ or more than 10$ respectively, of the pods from a given plant were four-seeded.

He assigned the symbols F >tf to the

allelomorphic pair governing this difference.

Domingo (4), classified

varieties into high (if the mean number was more than 3 seeds per pod), intermediate (mean number from 1*6 — 3.0 seeds per pod), end low (1.0 1.6 seeds per pod) , and suggested that a few major and several minor genes were responsible for the inheritance of these differences.

He

assigned the symbols Lo (intermediate) and Ip (low) to one of these allelic pairs of major genes.

On the basis of this broad classification

35

Frequency distributions of the number of seeds per pod for the entire F2 population and both parents ♦

1 F

Table 7*

1 Class

Lin­ coln

F2 1.00 - 1.09 1.10 - 1.19 1.20 - 1.29 1.30 - 1.39 1.40 - 1.49 1.50 - 1.59 1.60 - 1.69 1.70 - 1.79 1.80 - 1.39 1.90 - 1.99 2.00 - 2.09 2.10 - 2.19 2.20 - 2.29 2.30 - 2.39 2.40 - 2.49 2.50 - 2.59 2.60 - 2.69 2.70 - 2.79 2.80 - 2.89 2.90 - 2.99 3.00 - 3.09 3.10 - 3.19 3.20 - 3.29 3.30 - 3.39 3.40 - 3.49 3-50 - 3.59 n s2 X

C. V. (%)

0 2 2 3 4 5 9 16 29 31 53 61 96 93 93 54 25 11 3 1 0 1 1 0 0 1 601 0.0839 2.247 12.86

2 0 2 1 3 3 0 9 5 1 1 1 0 1

29 0.0879 2.272 13.02

Number of individuals Grouo C Lin­ Man­ F2 coln darin

2 0 0 1 1 4 6 4 1 3 1

24 0.1123 2.182 15.35

1 0 1 1 1 1 8 6 20 29 59 52 58 37 27 14 4 1

320 0.0712 2.139 12.43

1 0 0 0 0 0 2 3 4 2 2 3 1

18 0.0770 2.371 11.68

Man­ darin

1 2 1 2 0 1 4 4

u

0.0694. 1.990 13.18

"*■ Number of seeds per pod.

both Mandarin (Ottawa) and Lincoln would be considered as having an inter­ mediate number of seeds per pod.

Their frequency distributions together

with that of the F% is shown in table 7.

The F^ mean in both groups is

36

intermediate to the parents, but in group A—B is closer to the higher parent (Lincoln) ♦ The range is vider than either parent, and there is evidence of transgressive segregation*

Ho estimate of gene number vas

possible, firstly because there vas not a very vide difference between the parents, and secondly, because the variability of the parents ex­ ceeded that of the

Variation is, therefore, largely environmental *

This is brought out by the fact that coefficients of variation of the F2 are smaller than those of the parents.

The effect of delayed plant­

ing is similar to the effects on seed number.

The mean for the Lincoln

parent has increased, but showed a reduction in the case of Mandarin (Ottawa), and the Fg*

An increase in the variability for Lincoln was

also noted, with a corresponding decrease in the variability for Man­ darin (Ottawa) and the F^*

Seed Size The frequency distributions for unit seed weight or seed size, for the

population, together with those of the parents are presented in

table 8*

F^ means are not widely divergent from those of the parents,

except in the case of the Lincoln >parent in group C, where the mean is slightly smaller*

The ?2 range, in both cases, adequately covered both

parental distributions.

The number of genes determining this character

was estimated as 12 for group A - B , which agrees rather closely with the estimate of 13 genes obtained by Weber (53) . No estimate of gene number was possible for group C as the mean variance of the parents exceeded that of the

Delayed planting has had little effect, except

37

in the case of the later—maturing parent, Lincoln, where a shorter developmental period reduced the average unit seed weight*

Heritability

was estimated a,t 39%s the estimate made by Weber was 55%*

Table 8.

Frequency distributions of seed size (unit seed weight) for the entire F^ population and both parents *

Class *100 .110 .120 .130 .l^O — .150 .160 — .170 .180 .190 .200 .210 -

.109 .319 .129 .139 .149 .159 .169 .179 .189 .199 .209 .219

n s^ X C. V. (%)

F2

5 13 65 139 153 114 58 25 15 5 4 601 .000280 .156 10.70

Humber of individuals Group A—B Lin­ Man­ *2 coln darin

5 16 7 1 0 0 0 1 30 .000160 .157 8.03

1 2 4 9 6 0 2

1 3 3 30 64 103 72 31 9 3 1

24 .000178 .156 8.53

320 .000199 .155 9.10

Group C Lin­ coln

Man­ darin

1 1 5 3 1 1 2

1 4 8 2 3

18 .000161 .146 8.70

14 .000263 .152 10.72

Grams

Seed Yield One of the most extensively investigated characters in soybeans is yield, and a review of the work done on this character has been dealt with in considerable detail earlier in this study*

The distributions of

seed yield per plant, in grams, is presented in table 9. are widely and uniformly separated in either group*

Parental means

The F^ mean, how—

38

ever, in the earlier date of planting closely approaches the mean of the Lincoln or higher parent, but is intermediate in the later date of plant­ ing.

This would indicate at least a partial dominance of yield factors*

The number of factors conditioning yield was estimated at 9 genes, which seems surprisingly low, with a heritability of 43*35%*

No comparable

estimates were available from the group C data as here again, the mean Table 9*

Frequency distributions of yields (in grams) per plant for selected and unselected F^ populations and both parents*

Number of individuals GrouD A-B Class'1' Fn f2 (Unse— (Se­ lected) lected) 0.O-9.9 10.0-19*9 20.0-29*9 4 3 who further added that this vigor was not apparent till two to three weeks prior to the end of the growing season*

Veatch (47), reported evidence of vigor

in all but 2 out of 16 crosses, and that where parents differed widely, hybrid vigor was carried into the F^ generation* dominance of factors for height*

He concluded partial

Weiss et al* (57) and Kalton (15),

have also presented evidence confirming hybrid vigor for height* In table 10, is to be found the distributions of plant height measured in inches. the parents* tallness.

Here the F2 means are consistently intermediate to

There is also good indications of partial dominance of

The frequency distributions of the F2 populations are wide

and cover both parental ranges*

This would suggest a relatively few

number of genes; estimates obtained equalled 11—13 genes*

Delayed

planting appears to have reduced the means, but the effect is very

40

slight*

Variabilities are also slightly affected*

Estimates of herit—

ability were worked out and found to be 40*49 and 46*05% respectively for groups A-B and C. Table 10.

Class

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 23 29 30 31 32 33 34 35 36

Frequency distributions of height (in inches) for selected and unselected populations and both parents.

__________________Number of individuals ________________ Group A-B _______ Group C Lin­ Lin­ Man­ Man­ *2 *2 coln (Unse— darin (Se­ darin (Unse­ coln lected) lected) lected)

1 5 4 7 5 10 10 6 1 3 0 0 0 0 2

n s2 X

c.v.(%) Inches

54 8.06 26*98

1 0 1 0 2 7 6 16 9 27 22 62 61 83 55 59 51 45 29 22 19 7 8 3 2 4 601 14.41 24.84 15.3

1 4 1 1 3 1 6 3 2 6 2

30 9.29 27.77 11*0

1 1 2 3 2 6 3 1 1 2 1 1

24 7.88 19.16 14.6

1 1 0 0 0 0 1 0 5 3 9 7 15 17 20 23 32 27 47 37 23 14 16 7 7 5 3

1 1 0 3 2 4 0 1 0 3 1 1 1

320 15.97 26.95 14.8

18 11.76 29.83 11.5

3 I 1 0 2 3 4 1

15 6.31 20.80 12.1

41

Date of Maturity It vas unfortunate that the dates of maturity for the parents were not recorded and as such could not be included with the distribu­ tions of the ]?2 as shown in table 11*

Lack of the necessary information

did not permit any conclusions as to the nature of inheritance, number of genes, heritability, etc* of this character.

However, from the

literature it is learned that F-j_ hybrids are usually intermediate to the parents in most cases, e*g* Weiss et al. (54)> Kalton (15), Singh and Anderson (35), Weber (49) • Exceptions to this have, however, been observed.

Woodworth (59), for example, noted a tendency of lateness to

be dominant*

The reverse was reported by Owen (26) , who observed earli—

ness to be the dominant feature*

Singh and Anderson (35), reported that

transgressive segregation for lateness was apparent in most of their crosses, that the type of gene action was not clearly determinable as there was evidence for either geometric or arithmetic gene action, and further, concluded that a few major genes together with several minor genes were responsible for maturity*

Evidence was obtained by Weber (49),

indicating the possibility of just 1 gene, but this, it must be re­ membered is a minimum estimate.

In this study, the only interesting

feature which is clearly brought out, is the influence of date of plant­ ing.

Although later planting resulted in an actually later date of

maturity, the number of days required for the later set to mature, as calculated from the date of planting, is really less* maturity, has relatively been hastened.

In other words,

Another prominent feature of

the effect of delayed planting is that variability has been considerably reduced.

The set of data in group C is thus more uniform, and this is

42

Table IX*

Class U 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 a 42 43 44 45 46 n s2 X C. V. (%)

Frequency distributions of dates of maturity for the selected and unselected F^ populations.

F? (Selected)

Number of individuals _________ Group A-B_______ Group G f2 f2 (Unselected) (Unselected)

1 5 7 0 1 4 0 1 2 6 5 3 3 5 3 2 0 1 0 1 0 0 1 0 0 0 0 1 52 34.63 27.36

Number of days after September 1*

8 16 37 9 6 16 45 71 9 16 31 14 20 31 34 41 17 33 36 42 22 6 6 10 4 5 4 7 0 2 3

601 44.13 26.10 25.44

2 0 5 7 9 0 5 9 5 4 4 6 16 17 35 22 45 50 19 21 11 10 13 4 0 1

320 23.36 31.73 15.35

43

seen not only in the reduced coefficient of variation, but also in the narrower frequency distribution*

These results agree with the findings

of Singh and Anderson (35)* Table 12*

Estimates of gene numbers and heritabilities for different quantitative characters studied.

Character

Group A-B Group C Number Herit— Number Herit— of genes ability(^) of genes ability(3$)

Number of branches per plant

12.38

2.69

+

4-

Number of pods per plant

10.72

43.75

+

+

9.17

46.53

4*

4*

+

*

4*

8.93

43.35

+

+

Seed size (unit seed weight)

11.49

39.00

4-

+

Height

13.36

40.49

11.49

46.05

2.70

81.65

8.77

42.44

Number of seeds per plant Number of seeds per pod Yield per plant

Date first pod set

+

* Mean variance of parents exceeded that of the

mates were available.

and as such no esti­

44

Association of Characters Simple correlation coefficients of nine quantitative characters, namely; seed yield, seed size (unit seed weight), seed number, number of pods, number of seeds per pod, number of branches, date first pod set, date of maturity and height were calculated for all possible combi­ nations of these characters, and the r-values which were obtained are presented in table 13.

The two groups A—B and C were dealt with sepa­

rately, and the revalues of the former group appear as the upper member of the pairs of the r-values in the body of table 13> the lower members referring to group C. In general, seed yield was found to be significantly correlated with all characters but seed size.

The highest coefficients of correlation

were those associating it with seed number and number of pods, which of course, is naturally expected.

Next in importance is the relationship

with height of plants; r—values of 0.605 and 0.653 were obtained in this case.

Weatherspoon and Wentz (50) indicated that the number of pods per

plant and plant height were among the most important factors determining yield; the relationship with number of seeds per plant was not reported. The results of this study, so far, are not at variance with the findings of the above mentioned workers.

Seed size, it will be of interest to note,

was negatively correlated with number of seeds, number of pods, number of seeds per pod, number of branches and plant height, all of which are posi­ tively correlated with seed yield.

This situation is quite similar to

that reported by Weatherspoon and Wentz (50) and would seem to corroborate their hypothesis of the nutritional relationship between seed size and

45

other vegetative parts being involved*

It is of further interest to

consider the relationship of seed size with date of maturity*

Here

the influence of the length of the growing period is rather strikingly brought out*

While with group A-B an r-value of ,505 was obtained, the

same correlation, although significant, was greatly reduced in group C* Evidently then, this may be attributed to delayed planting, which has lessened the period of development, thereby causing the low relation­ ship between the two variables • Other significant relationships which were observed, include the following*

Seed number was highly correlated with pod number, seeds per

pod, number of branches and plant height; pod number with number of seeds per pod, number of branches, date first pod set and plant height*

The

number of seeds per pod was related to the number of branches, date of first pod set, date of maturity and plant height, while a significant relationship between date of first pod set and date of maturity, plant height and date of maturity, and plant height were also obtained* Although in general, these relationships were similar in both dates of planting, several instances might be noticed when the results were dissimilar, and even in some cases, exact opposites of each other.

For

example, the relationship of seeds per podwith number of pods, while positive in one case, was negative in the other* Similarly the

number

of pods per plant, correlated with date of first pod set, gave contrast­ ing revalues*

As a third example, date of first pod set versus date of

maturity, and date of first pod set x plant height, while both negative in groups A-B, were positive in group C* In other relationships, while both were either positive or negative

46

they were yet considerably different in the magnitude of the correla­ tions*

Examples of these diversities may be pointed out in the cases

of seeds per pod x number of branches, seeds per pod x date of maturity, number of branches x date of maturity and date of maturity x height* Evidently the above mentioned differences are partly attribut­ able to differences in dates of planting*

The early date of planting

coincided with the normal date of planting as adopted in areas around Lafayette and vicinity*

This planting should have afforded the normal

period of development necessary for the soybean plants*

The second date

of planting, however, was approximately two weeks later, a delay which undoubtedly had sufficient influence on the developmental and nutrition­ al relations in the soybean plant*

Under normal conditions, there is

apparently sufficient food reserves to permit pod development and large numbers of seeds per pod*

Reduction in the developmental period, how­

ever seriously affects the balance and pod increases occur at the ex­ pense of the number of seeds per pod* The relationship of date first pod set with date of maturity was of doubtful significance with the earlier date of planting; however the same relationship was greatly accentuated when planting was delayed*

One

other discrepancy which was noted, and could not be accounted for was found in the relationship of date first pod set with plant height*

It

would be logical to assume that the appearance of flowers and setting of pods are signs of a reproductive activity, whereas the determination of height is a part of the vegetative process in the plant, and that an early appearance of the former would curtail the latter*

In other words,

types which set their pods early would be shorter than those which began

47

their reproductive processes later*

In group A-B the results ob­

tained are entirely contrary to expectation, and no reason for this deviation seems apparent*

Mention was made in an earlier section

that delayed planting had affected not only means, but also varia­ bilities*

Evidence obtained from this section, seems to indicate that

some of the relationships are modified also*

48

£ v\ oi O VN xO