Fixed effect genetic analysis of a diallel cross in dry beans (Phaseolus vulgaris L.)

A full diallel cross among four diverse homozygous strains of dry edible beans (Phaseolus vulgaris L.) was evaluated for yield, protein content, and culinary quality traits in the F2 and F3 generations in two locations. Interpretation of diallel effects [Method 1 Model I] using a fixed-effect genetic model made it possible to combine data from two generations into a single analysis and quantify the relative contributions of additive and dominance genetic effects to general (GCA) and specific (SCA) combining abilities. GCA was found to arise from three potential sources: additive effects, dominance interactions at homozygous loci, and average dominance interactions in hybrids involving the parent in question. SCA was found to be a function solely of dominance. Additive effects were the primary determinant of GCA and were highly significant. Specific dominance interactions were significant for seed yield, cooked bean moisture content, and texture but not for protein content. Texture was the only trait for which the additive-dominance model failed to provide an adequate fit to the data, suggesting that texture is significantly affected by epistatic interaction. One cross ('Brazil-2' × 'Sanilac') was identified that exhibited a large heterotic effect for seed yield although the parents' additive effects were nonsignificant. Such a "nicking" effect was attributed to complementation between the two parents.