Rapid Identification of Grain-Size Related Genes through Mutational Genomics in Hexaploid Wheat

Yield is an important and highly polygenic trait in wheat. We propose that by breaking down yield into its individual components we can simplify the genetic study of this trait. Our work focuses on grain morphometric parameters (grain length and width) and we have used chemical mutagenesis to generate novel induced variation in hexaploid wheat. We have generated a population of 1,727 hexaploid wheat lines (cv Cadenza) which have a mutation density of >40 mutations per Mb. We conducted a forward genetic screen for grain morphometric mutants on this population over two consecutive field seasons. We identified a set of lines with consistent increases in grain length and width characteristics, many leading to increases in grain weight. To identify the underlying mutation, we have crossed a subset of these lines back to the original parent to create F₂ populations which only segregate for the EMS-induced mutations present in the grain size mutant. Four of these populations were analysed for grain size, including populations in which significant increases in grain weight are observed but where no compensation is observed in other yield components such as spikelet or grain number. We have prepared bulks of extreme lines from either end of the distribution to determine segregation of mutants using exome-capture and next-generation sequencing. We expect to see an association between the phenotype and the mutation frequency within the bulks. This approach is new to wheat research and could lead to the rapid identification of genes related to grain size, or additional traits.