Association mapping of hybrid seed set and heterosis in a central European multi-parental wheat population

Heterosis in wheat results from a complex interplay of dominance and epistasis, with epistasis playing a major role, underscoring the genetic complexity and challenges in systematically exploiting hybrid vigor. The systematic exploitation of heterosis has the potential to increase wheat yields by around 10% compared to inbred lines. However, the lack of natural cross-pollination in wheat significantly increases the cost of producing hybrid seeds. Our study aimed to address these issues by identifying indirect traits that enhance pollination efficiency in hybrid seed production and by genetically dissecting heterosis for key agronomic traits in the resulting hybrids. We evaluated the pollen donor capacity of 294 doubled haploid (DH) lines derived from ten biparental populations adapted to Central European conditions. While no universally applicable indirect predictors of pollination ability were identified, we found that population-specific traits correlated with pollinator performance. We evaluated the resulting hybrids and their parental lines in multi-location field trials for grain yield, plant height, heading date, and susceptibility to yellow and leaf rust. Quantitative trait locus (QTL) analysis revealed that heterosis in wheat is governed by a complex interplay of dominance effects and epistatic interactions. The relative contribution of these genetic effects varies significantly across traits and populations. Epistasis notably played a substantial role in heterosis, emphasizing the genetic complexity of wheat and explaining the challenges associated with its systematic exploitation.