ASSOCIATION OF ISOZYME GENOTYPES WITH AGRONOMIC AND SEED COMPOSITION TRAITS IN SOYBEAN

Two crosses between Glycine max (L.) Merr. and G. soja Sieb. & Zucc. parents were used to study the association between isozyme marker loci and agronomic and seed composition traits in soybean. The parents possessed different alleles at six isozyme loci for Cross 1 (A80-244036 x PI 326581) and at eight isozyme loci for Cross 2 (A81-157007 x PI 342618A). A total of 480 BC2F4.6 lines from the two crosses was evaluated for 13 traits in two environments. Lines were grouped in locus classes from 0 to 5 according to the number of loci homozygous for the G. soja alleles that they possessed. Within each locus class, each isozyme genotype was represented by five random lines. Selection for G. max alleles at the isozyme loci was not effective in recovering the recurrent parent phenotype in either cross. In cross 1, however, BC2F4-derived lines in the 0- or 1- locus class more closely resembled the G. max parent than lines in the 4- or 5- locus classes for most of the agronomic and seed composition traits evaluated. Significant associations were found between particular isozyme genotypes and every trait analyzed. The estimated effect of genes linked to the Pgml locus was a delay in maturity of 6.0 +/- 3.4 days. In cross 1, the Idh2 locus was associated with a significant effect on linolenic acid content. The percentage of variation accounted for by the models of estimation varied according to the heritability of the trait. The R2 was high (up to 78%) for maturity, lodging, and vining, and low (up to 21%) for seed yield. Most of the variation was associated with the BC2F1 family from which the lines were derived. There was little evidence that digenic epistasis was an important source of variation.