Accessing Genetic Diversity in the USDA National Small Grains Collection through a Multi-Parent Barley Nested Association Mapping Population

Germplasm collections hold allelic diversity that can be used for crop improvement and to understand the genetic architecture of complex traits. To gain access to the genetic diversity within the USDA National Small Grain Collection, we developed a 6-row spring barley nested association mapping (NAM) population with 88 landrace accessions crossed to a common parent (Rasmusson). The 88 parents were randomly selected from a core subset of the National Small Grains Collection that represents the genetic diversity of landrace and breeding accessions. In total, 6658 recombinant inbred lines were generated with a range of 51-112 lines per family. For each family both F1 and BC1 inbred lines were derived providing the opportunity to explore genetic architecture of traits with lines containing different amounts of recurrent parent background. Genotypes for the parents and progeny were obtained from genotyping-by-sequencing (GBS) technology. We examined the number of unique loci and the number of allelic variants that contribute to two quantitative traits, flowering time and plant height. Though these are highly correlated traits, we detected distinct QTL influencing each trait. For a major flowering time QTL detected by joint population analysis, we observed both positive and negative allele effects relative to Rasmusson in all 35 families segregating for the SNP marker, suggesting the presence of an allelic series. The use of multiple parents of diverse origins in this population allowed us to estimate allele effects and diversity across families as a bridge to better understand and utilize phenotypic variation in this germplasm resource.