Towards Positional Isolation of a Barley Gene Conferring Susceptibility to the Spot Blotch Pathogen Bipolaris sorokiniana

Three pathotypes (0, 1, and 2) of the spot blotch pathogen Bipolaris sorokiniana have been identified based on their virulence patterns on three barley differentials (Bowman, ND5883 and NDB112). Barley cv. Bowman is extremely susceptible to pathotype 2 isolates, while it is resistant to the other two pathotypes (0 and 1). Previous research indicated that a single gene (designated Rcs6) on chromosome 5(1H) conferred resistance to pathotype 2 in the double haploid (DH) population derived from the Bowman-BC/Calicuchima-sib cross. Rcs6 was effective at both the seedling and adult plant stages and was contributed by the resistant parent Calicuchima-sib. In the present study, we performed fine mapping of the susceptibility gene allele (SVHv1) in Bowman using the same DH population. A total of 115 DH lines were evaluated by inoculation with the pathotype 2 isolate ND90Pr at the seedling stage and infiltration with intracellular fluids (IF) extracted from pathotype 2-infected Bowman leaves. Results showed that susceptibility to the fungus and sensitivity to IF in Bowman was controlled by the same allele (SVHv1) on chromosome 5(1H). Using a genome-wide putative linear gene index of barley (Genome Zipper), we developed 10 single nucleotide polymorphic (SNP) markers around the SVHv1 region. One marker co-segregated with SVHv1, and the two most closely-linked flanking markers span a genomic region harboring 32 called genes according to the Genome Zipper. A large F₂ population from the Bowman/ND 5883 cross is being phenotyped and genotyped with more SNP markers with the ultimate goal of isolating the target gene.