Characterization and Association Mapping of Powdery Mildew Resistance in a Wild Barley Collection

Powdery mildew (Blumeria graminis f. sp. hordei, Bgh) is a worldwide disease problem on barley (Hordeum vulgare) with severe impact on yield.  Many alleles for resistance have been described in the genus Hordeum; however, additional diversification is needed to counter changes in the pathogen population.  Wild barley (Hordeum vulgare ssp. spontaneum) is a rich source of novel alleles for a variety of traits including fungal disease resistance.  Our goals in this study were to examine the Wild Barley Diversity Collection (WBDC), composed of over 300 accessions, for powdery mildew resistance and to use association mapping to position resistance loci in the genome. The WBDC was genotyped with 3,072 SNPs and phenotyped for reaction to 40 Bgh pathotypes. Our results show that there are no strong environmental correlations (such as rainfall, or minimum or maximum temperature) with resistance to particular pathotypes(either as individuals, or collectively). However, we did observe geographical hotspots of resistance for specific pathotypes individually and across all pathotypes. In addition to the phenotypic analysis, we combined the genotype and phenotype data and conducted association mapping.  Eleven SNP markers were found significantly associated with powdery mildew resistance on all chromosomes but 6H, with 7H containing the most markers.