Date of Award

Fall 1983

Project Type

Dissertation

Program or Major

Genetics

Degree Name

Doctor of Philosophy

Abstract

Over 400 soybean (Glycine max (L.) Merr.) cultivars and plant introductions and more than 100 wild soybean (Glycine soja Sieb & Zucc.) plant introductions from a wide geographic distribution were examined by polyacrylamide, slab electrophoresis for genetic variation in 15 enzymes. Allozymes for 25 loci were found. All but three of these loci were confirmed by experimental crosses. Approximately 20 non-variable loci were also hypothesized. Models presented explaining the genetic control for each of the observed enzyme zymograms, were based on inheritance studies, on patterns of distribution of isozymes in various tissues or developmental stages, zymograms in related species, information from the literature, and the subcellular distribution of isozymes. Both G. max and G. soja were highly homogeneous within cultivars or plant introductions. However, G. soja was found to have a nine times greater observed heterozygosity (1.0% vs. 0.11%), a higher expected heterozygosity (12.1% vs. 10.3%), a significantly higher level of polymorphism (47% vs. 33%, at the 99% polymorphism level), and a significantly higher number of alleles/locus (1.8 vs. 1.5). Nearly 50% of the shared alleles had significant differences in frequencies. While the overall correlation between allele frequencies was high (R = .84, for variable loci), this correlation was reduced (R = .23) when frequencies were compared within geographic areas of seed origin. Alleles were more widely dispersed in G. max, while several alleles also appeared to have distinct distribution patterns. Northeast China had slightly higher levels of diversity for G. max, while Korea had significantly higher levels for G. soja. These observations suggest that domestication has reduced genetic diversity, changed the distribution of alleles, and in many cases allele frequencies. While sampling effects can't be totally eliminated from consideration, the change in selection pressures and migrational influences brought about by domestication were probably responsible for the differences observed among these isozyme loci. While wild soybeans clearly had higher genetic diversity, the soybean germplasm appeared to have average diversity relative to other self-pollinating plants. Data were also included for using these isozyme loci in cultivar fingerprinting, linkage mapping and considering the possible polyploidy of the Glycine genus.

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