Epistatic expression of quantitative trait loci (QTL) in soybean [Glycine max (L.) Merr.] determined by QTL association with RFLP alleles.

Quantitative trait values for seed oil and protein content or for maturity were measured in recombinant inbred lines (RIL) of soybean derived from a cross between two soybean cultivars: 'Minsoy' PI 27890 and 'Noir 1' PI 290136. Seed oil was found to be inversely correlated to protein content. By analyzing DNA from plants with extreme phenotypes, we were able to identify quantitative trait loci (QTL) for these traits as being linked to several restriction fragment length polymorphism (RFLP) loci, including R183 for oil and protein content and R79 for maturity. Cumulative distributions of trait values were graphed for those RIL with 'Minsoy' alleles and for those with 'Noir 1' alleles. As already suggested by the alleles found associated with extreme phenotypes, the distributions were consistent with an independent and additive expression of the maturity QTL linked to R79. That is, the cumulative distributions for plants with 'Minsoy' alleles and for plants with 'Noir 1' alleles were similar in shape, but the entire 'Noir 1' curve had been shifted to later maturity dates. In contrast, the trait distributions for a locus affecting oil and protein content linked to R183 were not compatible with an additive model. These results suggest that this approach can be used for rapid identification of QTLs with epistatic expression.