Genome-Wide Association Mapping for Stem Rust Resistance in the Wild Barley Diversity Collection (WBDC).

The Wild Barley Diversity Collection (WBDC) is a valuable resource for increasing the genetic diversity of cultivated barley for resistance to various biotic and abiotic stresses. It is composed of 318 accessions from diverse ecogeographic regions across the habitat range of Hordeum vulgare ssp. spontaneum. Stem rust is a serious disease of barley in some regions of the world and can cause significant yield reductions. Although the disease has been kept in check in the Upper Midwest USA for nearly 70 years through the deployment of cultivars with the resistance gene Rpg1, there exist both domestic (QCCJB) and foreign (TTKSK aka isolate Ug99) races with virulence for this important gene. To identify resistance to these Rpg1-virulent races, the WBDC was evaluated at the seedling stage in the greenhouse. Additionally, the WBDC was genotyped by DArT-seq protocol, generating about 17,000 markers. To position loci conferring resistance to these two races, we performed genome-wide association mapping using 1) mixed models that accounts for kinship and population structure and 2) a G model that corrects for background chromosomal marker effects to increase the power of gene detection. Using the mixed models that corrects for kinship and population structure, we detected two quantitative trait loci (QTL) on chromosomes 3H and 5H. The G model detected these same two QTLs, plus 8 others on chromosomes 1H, 2H, 3H, 4H, 5H, 6H, and 7H.  These data will be useful for programs focused on breeding for broad-based stem rust resistance.