The Rrs1 resistance locus against scald in barley

Abstract

Scald, caused by Rhynchosporium commune, is one of the most prevalent barley diseases worldwide. To date, four major scald resistance genes have been mapped in cultivated barley (Hordeum vulgare ssp. vulgare), and another four in wild barley (Hv. Spontaneum) or Hv. bulbosum. The most abundant and effective one is the Rrs1 resistance locus, which was mapped to the centromeric region of chromosome 3H. However, it is still not clear whether Rrs1 formerly known as Rh-Rh3Rh4 locus is a collection of several R-genes close to each other or several alleles of the same gene. A search for new resistance sources revealed that Spanish landrace-derived lines SBCC145 and SBCC154 showed outstanding resistance to scald. To analyze the genetic basis in more detail two large DH mapping populations were developed crossing each donor line with cv. Beatrix. A large QTL in the centromeric region of chromosome 3H was found in both populations, therefore, suggesting this locus as the only resistance locus in both populations. To confirm and enclose this locus, the “Rrs1 region” has been saturated with all available SSR and SNP-markers and a consensus map was constructed. New markers for this region are developed based on the lllumina iSelect custom 9K barley chip and candidate genes derived from the barley genome zipper. Because of a low gene/cM density, an enrichment of candidate sequences in the region of Rrs1 is done by a BSTA (bulked segregant transcriptome analysis) with four normalized cDNA libraries and Illumina HiSeq in combination with a high resolution mapping program. For fine mapping and haplotyping a mapping population comprising >10,000 F2 from the cross SBCC145 x Beatrix has been constructed. F2 screening of about 11,000 lines to select recombinant lines between two flanking markers has identified around 442 verified recombinant plants. The effective Rrs1 allele found and the closely linked markers developed are already useful tools for molecular breeding programs.