Fine Mapping of a Gene for Resistance to a New Pathotype of Bipolaris sorokiniana in Barley

Spot blotch, caused by Bipolaris sorokiniana, is an economically important disease of barley in many production areas and is best controlled through the deployment of resistant cultivars. In the Upper Midwest region of America, the spot blotch resistance derived from the barley line NDB112 has been effective for over 50 years. However, a new pathotype of the fungus has been identified in North Dakota and Canada, which can overcome the NDB112 resistance. To identify novel sources of resistance to this new pathotype, a total of 2,062 barley accessions from the USDA small grain collection were inoculated at the seedling stage and only 44 (2.1%) were rated as resistant. To study the genetics of spot blotch resistance, a cross was made between a resistant parent (PI235186) and a susceptible parent (PI356741). The results showed that all F₁ plants were resistant and the 212 F₂ individuals segregated into a 3 (resistant) to 1 (susceptible) ratio, suggesting dominant resistance with monogenic inheritance. Bulk segregant analysis was conducted on the F₂ population using 192 SSR markers, localizing the resistance gene to the short arm of chromosome 6H. To fine map this gene, 20 single nucleotide polymorphism (SNP) markers in this region were selected to genotype the F₂ population. Additional markers flanking the resistance gene are also being developed with the barley genome sequences released by International Barley Sequencing Consortium (IBSC) in 2012. The fine mapping results will be presented in the meeting.