Quantitative trait loci mapping and epistatic analysis for grain yield and yield components using molecular markers with an elite maize hybrid

The aim of this investigation was to map quantitative trait loci (QTL) associated with grain yield and yield components in maize and to analyze the role of epistasis in controlling these traits. An F-2:3 population from an elite hybrid (Zong3 x 87-1) was used to evaluate grain yield and yield components in two locations (Wuhan and Xiangfan, China) using a randomized complete-block design. The mapping population included 266 F-2:3 family lines. A genetic linkage map containing 150 simple sequence repeats and 24 restriction fragment length polymorphism markers was constructed, spanning a total of 2531.6 cM with an average interval of 14.5 cM. A logarithm-of-odds threshold of 2.8 was used as the criterion to confirm the presence of one QTL after 1000 permutations. Twenty-nine QTL were detected for four yield traits, with 11 of them detected simultaneously in both locations. Single QTL contribution to phenotypic variations ranged from 3.7% to 16.8%. Additive, partial dominance, dominance, and overdominance effects were all identified for investigated traits. A greater proportion of overdominance effects was always observed for traits that exhibited higher levels of heterosis. At the P <= 0.005 level with 1000 random permutations, 175 and 315 significant digenic interactions were detected in two locations for four yield traits using all possible locus pairs of molecular markers. Twenty-four significant digenic interactions were simultaneously detected for four yield traits at both locations. All three possible digenic interaction types were observed for investigated traits. Each of the interactions accounted for only a small proportion of the phenotypic variation, with an average of 4.0% for single interaction. Most interactions (74.9%) occurred among marker loci, in which significant effects were not detected by single-locus analysis. Some QTL (52.2%) detected by single-locus analysis were involved in epistatic interactions. These results demonstrate that digenic interactions at the two-locus level might play an important role in the genetic basis of maize heterosis.