Analysis of bymovirus resistance genes on proximal barley chromosome 4HL provides the basis for precision breeding for BaMMV/BaYMV resistance.

KEY MESSAGE: Unlocking allelic diversity of the bymovirus resistance gene rym11 located on proximal barley chromosome 4HL and diagnostic markers provides the basis for precision breeding for BaMMV/BaYMV resistance. The recessive resistance gene rym11 on barley chromosome 4HL confers broad-spectrum and complete resistance to all virulent European isolates of Barley mild mosaic virus and Barley yellow mosaic virus (BaMMV/BaYMV). As previously reported, rym11-based resistance is conferred by a series of alleles of naturally occurring deletions in the gene HvPDIL5-1, encoding a protein disulfide isomerase-like protein. Here, a novel resistance-conferring allele of rym11 is reported that, in contrast to previously identified resistance-conferring variants of the gene HvPDIL5-1, carries a single non-synonymous amino acid substitution. Allelism was confirmed by crossing to genotypes carrying previously known rym11 alleles. Crossing rym11 genotypes with a cultivar carrying the recessive resistance gene rym1, which was reported to reside on the same chromosome arm 4HL like rym11, revealed allelism of both loci. This allelic state was confirmed by re-sequencing HvPDIL5-1 in the rym1 genotype, detecting the haplotype of the rym11-d allele. Diagnostic PCR-based markers were established to differentiate all seven resistance-conferring alleles of the rym11 locus providing precise tools for marker-assisted selection (MAS) of rym11 in barley breeding.