Abstract
BackgroundThe genetics of resistance to loose smut of wheat (Triticum aestivum L.) caused by the fungus Ustilago tritici (Pers.) Rostr. is not well understood. This study examines loose smut resistance in Sonop (TD-14), a South African spring wheat variety. A doubled haploid (DH) population of 163 lines derived from the cross Diamont/TD-14 was studied. The parents and progenies were inoculated with U. tritici races T2, T9, and T39 individually in growth facilities at Morden and Swift Current, Canada. Loose smut incidence (LSI) and partial loose smut resistance (PLSR) were assessed.ResultsA whole genome linkage map was developed consisting of 11,519 SNP loci found on 31 linkage groups spanning 2845 cM. A new major resistance gene Ut11 was located to the distal end of chromosome arm 7BS. Ut11 conferred resistance to U. tritici race T2, but not races T9 and T39. Quantitative trait locus (QTL) mapping identified four QTL controlling LSI in the Diamont/TD-14 DH population on chromosomes 3B, 4B, 5B, and 7B (at Ut11) with TD-14 contributing the resistance alleles at three of these loci. The major QTL QUt.mrc-5B was effective against all three races and explained up to 81% of the phenotypic variation. The only QTL identified for PLSR coincided with the LSI QTL QUt.mrc-5B indicating that this locus affected both loose smut incidence and partial smutting of spikes.ConclusionsA race-specific resistance gene Ut11 and a broadly effective resistance QTL QUt.mrc-5B were the main loci controlling loose smut resistance in the differential line TD-14 (cultivar Sonop). This study provides insight into the genetics of loose smut resistance in spring wheat Sonop and the single nucleotide polymorphism (SNP) markers linked to the resistance gene Ut11 and QTL QUt.mrc-5B will be useful for selecting loose smut resistance in breeding programs.
Highlights
The genetics of resistance to loose smut of wheat (Triticum aestivum L.) caused by the fungus Ustilago tritici (Pers.) Rostr. is not well understood
Phenotypic analysis of loose smut resistance The resistant parent TD-14 showed nearly complete resistance to U. tritici races T2, T9 and T39, whereas the susceptible parent Diamont was highly susceptible to all three races (Fig. 2; Table 1)
The frequency distributions of loose smut incidence (%) to races T9 and T39 were continuous and bimodal, whereas the Diamont/TD-14 doubled haploid (DH) population was strongly skewed with a high frequency of lines with resistance when tested with race T2 (Fig. 2a)
Summary
The genetics of resistance to loose smut of wheat (Triticum aestivum L.) caused by the fungus Ustilago tritici (Pers.) Rostr. is not well understood. The genetics of resistance to loose smut of wheat (Triticum aestivum L.) caused by the fungus Ustilago tritici (Pers.) Rostr. Loose smut is a common disease throughout the wheatgrowing regions of the world that is caused by the basidiomycete fungus Ustilago tritici (Pers.) Rostr [1]. This seed-borne disease is commonly present in wheat fields of western Canada at low levels of incidence [2, 3] and is common in the United States [2]. Because new races of U. tritici continue to be identified in commercial wheat fields in Canada, it is important to identify new resistance genes and understand the mechanisms of loose smut resistance in wheat [11, 12]
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