High resolution genetic and physical mapping of a major powdery mildew resistance locus in barley

Abstract

Barley powdery mildew caused by Blumeria graminis f. sp. hordei (Bgh) is a foliar disease with potentially severe impact on yield and malt quality. The cultivated barley lines and landraces have proven to be valuable sources of powdery mildew resistance. The identification of new powdery mildew resistance genes and / or introducing novel alleles of known genes from barley germplasm resources have significantly contributed to the progress in barley resistance breeding. This study describes the high resolution mapping of a resistance locus, named ‘MlLa-H’ derived from an Ethiopian spring barley accession ‘HOR2573’, conferring resistance to seven modern highly virulent European and Israeli isolates. Using the progeny of three identified residual heterozygous lines (RHLs) from an F2S5 recombinant inbred line (RIL) population and the state-of-the-art high throughput DNA sequencing assays as well as recently developed barley web-based genetic resources, the resistance interval was narrowed down from originally 3.5 Mbp to a 850 kb interval. The result revealed that the MlLa-H interval contains four potential candidate genes belonging to disease resistance gene family according to barley reference genome sequence cv. ‘Morex’. Among these four, a receptor like kinase is considered as the strongest candidate gene for MlLa-H. Interestingly, this interval was co-localizing with a previously mapped QTL from Hordeum laevigatum on the basis of Laevigatum-QTL flanking and co-segregating markers, suggesting these two intervals possibly harbor the same gene with different alleles or otherwise different genes. In this regard, a BAC library carrying the MlLa locus was utilized to reconstruct the physical map of the MlLa-H region based on a resistance haplotype as ‘Morex’ is the reference genome for barley physical map and may be lacking the gene of interest. The identified co-segregating markers in this study should be useful for marker-assisted selection in barley breeding employing crosses between resistant genotypes with a resistance interval on the distal portion of chromosome 2HL, and susceptible genotypes. In addition, the final identification of candidate gene will positively contribute to barley resistance breeding programs.