The Rrs1 Resistance Locus Against Scald in Barley

Rhynchosporium commune is the causal agent of scald, which is one of the most destructive barley diseases. The first resistance locus described in barley was the Rrs1 locus near the centromeric region of chromosome 3HL. Rrs1 represents a highly complex locus with either many tightly linked genes or multiple alleles at a single locus. 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. QTL mapping after genotyping with the 1,536-SNP Illumina Golden Gate Oligonucleotid Pool assay (BOPA1) and further fine mapping confirmed the Rrs1 locus as the main effect for scald resistance. The genome zipper identified several candidate genes in the region of Rrs1. An enrichment of candidate sequences 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 15,000 F₂ from the cross SBCC145 x Beatrix has been constructed. To physically map the Rrs1 locus, which was not described in any sequenced barley up to date, the whole genome of the resistance donor SBCC145 was sequenced by NGS. The sequence analysis is in progress. The effective Rrs1 allele found and the closely linked markers developed are already useful tools for molecular breeding programs.