Dissection of heterosis for yield and related traits using populations derived from introgression lines in rice

Despite the great success achieved by the exploitation of heterosis in rice, the genetic basis of heterosis is still not well understood. We adopted an advanced-backcross breeding strategy to dissect the genetic basis of heterosis for yield and eight related traits. Four testcross (TC) populations with 228 testcross F1 combinations were developed by crossing 57 introgression lines with four types of widely used male sterile lines using a North Carolina II mating design. Analysis of variance indicated that the effects of testcross F1 combinations and their parents were significant or highly significant for most of the traits in both years, and all interaction effects with year were significant for most of the traits. Positive midparent heterosis (HMP) was observed for most traits in the four TC populations in the two years. The relative HMP levels for most traits varied from highly negative to highly positive. Sixty-two dominant-effect QTL were identified for HMP of the nine traits in the four TC populations in the two years. Of these, 22 QTL were also identified for the performance of testcross F1. Most dominant-effect QTL could individually explain more than 10% of the phenotypic variation. Four QTL clusters were observed including the region surrounding the RM9-RM297 region on chromosome 1, the RM110-RM279-RM8-RM5699-RM452 region on chromosome 2, the RM5463 locus on chromosome 6 and the RM1146-RM147 region on chromosome 10. The identified QTL for heterosis provide valuable information for dissecting the genetic basis of heterosis.