Genetics and mapping of seedling resistance to Ug99 stem rust in winter wheat cultivar Triumph 64 and differentiation of SrTmp, SrCad, and Sr42
Hiebert, C.W., Kassa, M.T., McCartney, C.A., You, F.M., Rouse, M.N., Fobert, P., Fetch, T.G. (2016). Genetics and mapping of seedling resistance to Ug99 stem rust in winter wheat cultivar Triumph 64 and differentiation of SrTmp, SrCad, and Sr42. Theoretical and Applied Genetics (TAG), [online] 129(11), 2171-2177. http://dx.doi.org/10.1007/s00122-016-2765-4
Plain language summary
Stem rust is a destructive disease of wheat worldwide that is caused by a fungus that evolve new strains called races. Stem rust can be controlled by deploying wheat cultivars that carry effective stem rust resistance (Sr) genes. The Ug99 race of stem rust was reported to be virulent to approximately 90 % of the world’s contemporary wheat cultivars and most Canadian wheat cultivars. The emergence of the Ug99 race group stimulated the search for new Sr genes in order to improve resistance to stem rust. Triumph 64 is an American winter wheat cultivar that carries gene SrTmp which is resistant to Ug99. In this study, we genetically mapped SrTmp to a region of chromosome arm 6DS that is similar to the map locations of two other Sr genes, SrCad and Sr42. We also tested SrTmp, SrCad, and Sr42 for functional differences using several different stem rust races and we showed that all three Sr genes are unique as they condition resistance to some races in common while also conditioning resistance to races that differentiate each gene. The markers used to map SrTmp will be helpful for breeding more resistant cultivars against stem rust. In the future we plan to determine if these genes are actually different alleles or forms of the same gene or if they are very closely linked on the chromosome. Determining this detailed relationship will allow breeders to make an informed strategy for utilizing these stem rust resistance genes.
Key Message: Resistance to Ug99 stem rust in Triumph 64 was conferred bySrTmpon chromosome arm 6DS and was mapped to the same position asSrCadandSr42, however, the three genes show functional differences. Abstract: Stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is an important disease of wheat that can be controlled by effective stem rust resistance (Sr) genes. The emergence of virulent Pgt races in Africa, namely Ug99 and its variants, has stimulated the search for new Sr genes and genetic characterization of known sources of resistance. Triumph 64 is a winter wheat cultivar that carries gene SrTmp, which confers resistance to Ug99. The goals of this study were to genetically map SrTmp and examine its relationship with other Sr genes occupying a similar chromosome location. A doubled haploid (DH) population from the cross LMPG-6S/Triumph 64 was inoculated with Ug99 at the seedling stage. A single gene conditioning resistance to Ug99 segregated in the population. Genetic mapping with SSR markers placed SrTmp on chromosome arm 6DS in a region similar to SrCad and Sr42. SNP markers developed for SrCad were used to further map SrTmp and were also added to a genetic map of Sr42 using a DH population (LMPG-6S/Norin 40). Three SNP markers that co-segregated with SrTmp also co-segregated with SrCad and Sr42. The SNP markers showed no difference in the map locations of SrTmp, SrCad, and Sr42. Multi-race testing with DH lines from the Triumph 64 and Norin 40 populations and a recombinant inbred-line population from the cross LMPG-6S/AC Cadillac showed that SrTmp, SrCad, and Sr42 confer different spectra of resistance. Markers closely linked to SrTmp are suitable for marker-assisted breeding and germplasm development.