Genetic mapping of stem rust resistance to Puccinia graminis f. sp. tritici race TRTTF in the Canadian wheat cultivar ‘Harvest’
Hiebert CW, Rouse MN, 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 107:192-197
Plain language summary
Stem rust is a disease of wheat that is caused by a fungus that causes large yield losses when epidemics occur. There are many different strains or races of the stem rust fungus in different regions of the world that vary in their ability to infect different wheat cultivars. There are a number of different races of stem rust that evolved in Africa that represent a threat to Canadian wheat growers. One such race is called TRTTF and originated in Ethiopia. Some Canadian wheat cultivars, including ‘Harvest’, are resistant to TRTTF. The objective of this study was to determine the genetic basis for this resistance. We found that Harvest carried a single stem rust resistance gene for conferred resistance to TRTTF. This resistance gene appears to a gene called Sr8a. A genetic survey showed that the resistance to TRTTF found in Canadian wheat cultivars can be attributed to Sr8a or a second gene called SrCad. Rarely are these two genes found together in the same cultivar. DNA markers were developed for Sr8a that can be used in wheat breeding programs to select for resistance to TRTTF and also to combine Sr8a and SrCad together to ensure longer-lasting resistance.
Stem rust, caused by Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn.(Pgt), is a destructive disease of wheat that can be controlled by deploying effective stem rust resistance (Sr) genes. Highly virulent races of Pgt in Africa have been detected and characterized. These include race TRTTF and the Ug99 group of races such as TTKSK. Several Canadian and United States 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 United States 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 SNP and 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 co-segregating 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.