Epistasis for grain yield in two F2 populations of maize

The importance of epistasis in breeding populations of maize (Zea mays L,) is not well understood. The objectives of the study were to: (i) test for epistatic effects of genes controlling grain yield, on the basis of testcross data, in the single crosses A679 x Wx6005 and A679 x FR902 and (ii) to investigate the relationship between identified epistasis and testcross yield of the F-3, backcrosses of F-2 plants to the parental lines, and the cross between the parental Lines. A modification of triple test-cross design was used. Each of 52 F-2 plants was selfed and simultaneously crossed to the parental lines and the F-1 of the cross between the lines. The four F-2-derived generations were testcrossed to inbred lines LH85 and LH163. Yield trials of testcrosses were grown at two Minnesota locations for 2 yr in a randomized complete block design with two replications and a split plot restriction on randomizations. Based on testcross means of families derived from individual F-2 plants, there was evidence of epistasis for grain yield in both populations. Each tester revealed epistasis in a unique group of F-2 individuals and epistasis was nondirectional, Analyses of testcross genotypic variances revealed evidence of epistasis in both populations, but there was no evidence of epistasis based on overall testcross generation means. There was no association between epistasis and testcross yields of F-3 and the backcrosses. Our results suggest the presence of nonallelic interaction as well as linkage disequilibrium in both populations.