Fine mapping of a dominant gene conferring resistance to spot blotch caused by a new pathotype of Bipolaris sorokiniana in barley.

KEY MESSAGE: We fine-mapped and physically anchored a dominant gene (Rbs7) conferring resistance to spot blotch caused by a new pathotype of Bipolaris sorokiniana in a genomic interval of 304 kb on barley chromosome 6H. Spot blotch, caused by Bipolaris sorokiniana, is an economically important disease on barley in the Upper Midwest region of the USA and Prairie Provinces of Canada. A new pathotype (pathotype 7, represented by isolate ND4008) of B. sorokiniana has been identified, which is highly virulent on barley cultivars with resistance to other pathotypes of the fungus. In this study, we fine-mapped a dominant gene conferring resistance to pathotype 7 in the barley line PI 235186. Genetic analysis of the F1 and F2 plants from a cross between PI 356741 (highly susceptible to ND4008) and PI 235186 (highly resistant to ND4008) indicated that a single dominant gene (Rbs7) controls the resistance in PI 235186. This result was confirmed by genetic analysis of the F2:3 families and a recombinant inbred line (RIL) population derived from the same cross. Bulked segregant analysis using simple sequence repeat markers localized Rbs7 on the short arm of chromosome 6H. Additional DNA markers were developed from the 6H pseudomolecule sequence of barley cv. Morex and mapped to the genomic region carrying Rbs7 using the RIL population and F2 recombinants derived from the PI 356741 × PI 235186 cross. Rbs7 was fine-mapped between two markers (M13.06 and M13.37), which spans a physical distance of 304 kb on Morex chromosome 6H. These results provide a foundation for future cloning of the resistance gene and development of user-friendly molecular markers that can be used for development of spot-blotch-resistant cultivars in barley breeding programs.