Genetic mapping of stem rust resistance to Puccinia graminis f. Sp. Tritici race TRTTF in the Canadian wheat cultivar harvest


Hiebert, C.W., Rouse, M.N., Nirmala, J., Fetch, T. (2017). Genetic mapping of stem rust resistance to Puccinia graminis f. Sp. Tritici race TRTTF in the Canadian wheat cultivar harvest. Phytopathology, [online] 107(2), 192-197.

Plain language summary

Stem rust is a highly damaging disease of wheat that can be well controlled by incorporating effective stem rust resistance genes into wheat varieties. The stem rust fungus is classified into races or strains based on which resistance genes that race can overcome and still infect the plant and which resistance genes provide resistance against that race. As the fungus evolves, resistance genes need to be identified that provide the plant resistance to new races of stem rust. A group of stem rust races called TRTTF-type races, evolved in Africa and are more virulent to Canadian wheat varieties than domestic races. Some Canadian wheat varieties are resistant to TRTTF stem rust. This genetic study focused on the wheat cultivar 'Harvest' and determined that the gene Sr8a was responsible for the resistance. It was also determined that this gene is present in several Canadian wheat varieties which makes it easy to incorporate into new varieties. The study also showed that two genes, Sr8a and SrCad, were responsible for all of the TRTTF resistance found in Canadian wheat varieties.


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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