Date of Award

Winter 1989

Project Type

Dissertation

Program or Major

Genetics

Degree Name

Doctor of Philosophy

First Advisor

Yun-Tzu Kiang

Abstract

Isozymes and quantitative traits were used to explore the organization of genetic variation within and among seven natural populations of the wild soybean, Glycine soja, from Mishima, Japan. Seed enzymes were separated by horizontal starch and polyacrylamide gel electrophoresis. One-hundred and eleven individuals were scored for their genotypes at 48 gene loci resolved from 20 enzyme systems and one seed protein. Fifteen of the isozyme gene loci were polymorphic. The values for average polymorphism per locus (using the 99% criterion), average number of alleles per locus, and the proportion of heterozygotes observed were 0.140, 1.14 and 0.002, respectively. The average value for G$\sb{\rm ST}$ was 0.627. The average value for Nei's genetic distance was 0.063.

Estimates of phenotypic and life-history variation in populations of wild soybean were obtained by growing seed collected in the field in two "common garden" experiments (one in 1986 and one in 1987). Of the 32 traits examined, 21 were significantly different among populations in 1986 and 18 were significantly different in 1987. In both years, approximately 70% of the total phenotypic variation resided within populations. Canonical discriminant analysis demonstrated that the populations have diverged most significantly for those traits related to flower size, leaf shape, and yield.

The correlation between Nei's genetic distance (D) and Mahalanobis' phenotypic distance (D$\sp2$) was not significant in 1986 (r$\sb{\rm s}$ = 0.61, p = 0.14), but was significant in 1987 (r$\sb{\rm s}$ = 0.85, p = 0.02). This inconsistency was attributed to small sample sizes, experimental error, and phenotypic plasticity.

Variation in six reproductive yield components was examined among the seven populations of G. soja. The three early yield components (number of flower buds, flowers and immature pods per inflorescence) were significantly different among the seven populations; the three late yield components (number of mature pods and seeds per inflorescence and mature seed weight per inflorescence) were not significantly different among the populations. The rates of abortion for wild soybean ranged from 61.4% for immature pods to 3.5% for flower buds. The patterns of abortion were likely associated with resource availability.

Aspects of soybean germplasm conservation and directions for future research were discussed.

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