Mapping of a resistance gene to loose smut (Ustilago tritici) from the Canadian wheat breeding line BW278

Loose smut is a common disease of wheat caused by the fungus Ustilago tritici (Pers.) Rostr. Production of resistant cultivars is an effective strategy for managing this disease. Relatively few loose smut resistance genes have been identified in bread and durum wheat. The genetic basis of resistance to U. tritici in the Canadian wheat breeding line BW278 was studied in a recombinant inbred line (RIL) population of 94 individuals developed from the bread wheat cross BW278/‘AC Foremost’. BW278 showed complete resistance to U. tritici race T9, whereas ‘AC Foremost’ was susceptible. Phenotypic assessment of the RILs indicated that a single gene, temporarily designated as UtBW278, segregated for loose smut resistance. Markers linked to UtBW278 were identified by bulked segregant analysis. Linkage analysis revealed that UtBW278 was located on the short arm of chromosome 5B and identified four single-nucleotide polymorphism (SNP) loci that co-segregated with UtBW278. Interestingly, UtBW278 mapped closely to a sequence characterized amplified region marker that was previously linked to the loose smut resistance gene Utd1 from durum wheat. Haplotype analysis of a panel of wheat lines was conducted to identify wheat lines that could carry UtBW278. SNP markers were identified for marker-assisted selection of UtBW278.