A quantitative genetic framework highlights the role of epistatic effects for grain-yield heterosis in bread wheat

Analysis of a large bread-wheat genomic data set through a quantitative genetic framework designed to study the genetic basis of heterosis shows that hybrids outperform midparents in grain yield by 10%. Genome-wide prediction and association mapping indicate that epistasis plays a significant role in heterosis of grain yield in wheat. Increasing wheat yield is a key global challenge to producing sufficient food for a growing human population. Wheat grain yield can be boosted by exploiting heterosis, the superior performance of hybrids compared with midparents. Here we present a tailored quantitative genetic framework to study the genetic basis of midparent heterosis in hybrid populations derived from crosses among diverse parents. We applied this framework to an extensive data set assembled for winter wheat. Grain yield was assessed for 1,604 hybrids and their 135 parental elite breeding lines in 11 environments. The hybrids outperformed the midparents by 10% on average, representing approximately 15 years of breeding progress in wheat, thus further substantiating the remarkable potential of hybrid-wheat breeding. Genome-wide prediction and association mapping implemented through the developed quantitative genetic framework showed that dominance effects played a less prominent role than epistatic effects in grain-yield heterosis in wheat.