Genetic and germplasm studies with several isoenzyme loci in soybean (Glycine max [L.] Merr)


The genetics of several electrophoretically detected isoenzyme variants in soybean (Glycine max L. Merr.) were investigated. Four loci conditioning aconitase (aconitate hydratase) mobility variants, as detected on starch gels, were defined. The four loci and their codominant alleles are: Aco1 (a, b), Aco2 (a, b), Aco3 (a, b), and Aco4 (a, b, c). The Enp locus, which conditions endopeptidase mobility variants, was described, and has two codominant alleles, a and b, as detected on starch gels. The Sod2 locus, with codominant alleles a and b, conditions superoxide dismutase mobility variants detected on polyacrylamide gels. All six of these loci are ideal markers for use in soybean genetics and breeding research;The six new loci were used in linkage studies, along with several other isoenzyme and morphological loci, to expand the genetic map of soybean. Both the Sp1 locus, which conditions (beta)-amylase variants, and the Aco3 locus, were assigned to linkage group 1. Sp1 is linked to the T locus (pubescence color) with a recombination frequency of 30.8 (+OR-) 1.6%, and to Y12 (chlorophyll deficient) with a frequency of 19.4 (+OR-) 1.8%. Aco3 is linked to both Sp1 and T, but the frequency of recombination varied widely with the parentage of the cross;The alleles present at 13 loci conditioning isoenzyme variants were determined in 1339 accessions in the USDA cultivated soybean (G. max) and wild soybean (G. soja Sieb. et Zucc.) germplasm collections. Several loci showed definite geographical trends in their distribution. There were differences in allozyme frequency between G. max and G. soja, as well, particularly for the loci Ap, Idh1, and Sod2. Based on gene frequencies and occurrence of multiple-locus genotypes, G. max and G. soja seem to represent different gene pools. Cluster analysis of the isozyme database defined groups of similar accessions across geographic origins. This information will make it possible to select parental materials of diverse origin for genetic and breeding research

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