Stem rust, caused by Puccinia graminis f. Sp. Tritici, is a destructive disease of wheat that can be controlled by deploying effective stem rust resistance (Sr) genes. Highly virulent races of P. graminis f. Sp. Tritici in Africa have been detected and characterized. These include race TRTTF and the Ug99 group of races such as TTKSK. Several Canadian and U.S. Spring wheat cultivars, including the widely grown Canadian cultivar 'Harvest', are resistant to TRTTF. However, the genetic basis of resistance to TRTTF in Canadian and U.S. Spring wheat cultivars is unknown. The objectives of this study were to determine the number of Sr genes involved in TRTTF resistance in Harvest, genetically map the resistance with DNA markers, and use markers to assess the distribution of that resistance in a panel of Canadian cultivars. A doubled haploid (DH) population was produced from the cross LMPG-6S/Harvest. The DH population was tested with race TRTTF at the seedling stage. Of 92 DH progeny evaluated, 46 were resistant and 46 were susceptible which perfectly fit a 1:1 ratio indicating a single Sr gene was responsible for conferring resistance to TRTTF in Harvest. Mapping with single nucleotide polymorphism (SNP) and simple sequence repeat (SSR) markers placed the resistance gene distally on the chromosome 6AS genetic map, which corresponded to the location reported for Sr8. SSR marker gwm459 and 30 cosegregating SNP markers showed the closest linkage, mapping 2.2 cM proximal to the Sr gene. Gene Sr8a confers resistance to TRTTF and may account for the resistance in Harvest. Testing a panel of Canadian wheat cultivars with four SNP markers closely linked to resistance to TRTTF suggested that the resistance present in Harvest is present in many Canadian cultivars. Two of these SNP markers were also predictive of TRTTF resistance in a panel of 241 spring wheat lines from the United States, Canada, and Mexico.
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