Genetic variance components and quantitative trait loci mapping for soybean (Glycine max L.) seed size

Seed size is inherited quantitatively with high heritability. Knowledge of the degree of genetic variance and the relative size of its various components is helpful in designing breeding methods and selection procedures for developing extremely small or large-seed soybean cultivars. Griffing\u27s diallel analysis (Method 4 and Model II) applied to 66 matings derived from a half-diallel mating of 12 parents revealed that the general combining ability (GCA) and specific combining ability (SCA) mean squares were highly significant for seed size (g/100 seed) in F$\sb1$ through F$\sb5$ generation, indicating that seed size was controlled by both additive and non-additive gene action. However, the GCA mean squares were several times larger than SCA mean squares, suggesting the predominant role of additive gene effects. The mean seed size in F$\sb1$ generation was less than the midparent value, but the mean of the F$\sb2$ and later generations was similar to the mean of F$\sb1$ generation. Frequency distributions exhibited a positive skewness. A partial dominance of small seed size was observed. The seed size in the F$\sb1$ generation was highly correlated with that in the F$\sb5$ generation, with R square of 0.9501. Therefore, seed size in the F$\sb1$ generation seems to be a reliable indicator of seed size in more inbred generations. Leaf size (width) was correlated (r = 0.76) with seed size with an R square of 0.574 in the F$\sb1$ and was highly correlated (r = 0.91) with seed size with an R square of 0.833 in the F$\sb2$ generation. One-hundred-fifty-six random amplified polymorphic DNA (RAPD) markers were used to identify genetic linkages in a 68-plant F$\sb2$ segregation population from a mating between Mercury (small seed) and PI 467.468 (large seed). A genetic linkage map was constructed with one-hundred-thirteen markers which formed twenty-nine linkage groups. These linkage groups spanned a genetic distance of 1043 cM. The average distance between markers was 9.23 cM. Significant (P $\u3c$ 0.01) associations were found between several RAPD markers and putative QTLs for seed size, seed protein, and seed oil using single-factor ANOVA and the QTL log-likelihood scans of MAPMAKER-QTL