Why do hybrid crop varieties perform so much better than parental lines?

Genetic composition of yield heterosis in an elite rice hybrid

Gang Zhou, Ying Chen, Wen Yao, Chengjun Zhang, Weibo Xie, Jinping Hua1, Yongzhong Xing, Jinghua Xiao, and Qifa Zhang2

+ Author Affiliations

National Key Laboratory of Crop Genetic Improvement and National Centre of Plant Gene Research (Wuhan), Huazhong Agricultural University, Wuhan 430070, China

Contributed by Qifa Zhang, August 15, 2012 (sent for review June 23, 2012)

 Heterosis refers to the superior performance of hybrids relative to the parents. Utilization of heterosis has contributed tremendously to the increased productivity in many crops for decades. Although there have been a range of studies on various aspects of heterosis, the key to understanding the biological mechanisms of heterotic performance in crop hybrids is the genetic basis, much of which is still uncharacterized. In this study, we dissected the genetic composition of yield and yield component traits using data of replicated field trials of an “immortalized F2” population derived from an elite rice hybrid. On the basis of an ultrahigh-density SNP bin map constructed with population sequencing, we calculated single-locus and epistatic genetic effects in the whole genome and identified components pertaining to heterosis of the hybrid. The results showed that the relative contributions of the genetic components varied with traits. Overdominance/pseudo-overdominance is the most important contributor to heterosis of yield, number of grains per panicle, and grain weight. Dominance × dominance interaction is important for heterosis of tillers per plant and grain weight and has roles in yield and grain number. Single-locus dominance has relatively small contributions in all of the traits. The results suggest that cumulative effects of these components may adequately explain the genetic basis of heterosis in the hybrid.