Genetic mapping of SrCad and SNP marker development for marker-assisted selection of Ug99 stem rust resistance in wheat


Kassa, M.T., You, F.M., Fetch, T.G., Fobert, P., Sharpe, A., Pozniak, C.J., Menzies, J.G., Jordan, M.C., Humphreys, G., Zhu, T., Luo, M.C., McCartney, C.A., Hiebert, C.W. (2016). Genetic mapping of SrCad and SNP marker development for marker-assisted selection of Ug99 stem rust resistance in wheat. Theoretical and Applied Genetics (TAG), [online] 129(7), 1373-1382.

Plain language summary

Wheat stem rust is a devastating disease that can completely destroy the crop. A new strain of stem rust in Africa known as Ug99 can attack nearly all Canadian wheat varieties and threaten our wheat production. The best and most economical way to control stem rust disease is by using host resistance genes. A gene known as SrCad was previously identified in the Canadian cultivar AC Cadillac that provides excellent resistance to Ug99, but should be incorporated along with other genes to prolong its effectiveness. In order to combine SrCad with other genes, molecular markers can assist plant breeders in selecting lines with both SrCad and other stem rust resistance genes. Our work developed new molecular markers (SNPs) that are very tightly linked to the SrCad gene, and also could tell the difference between SrCad and two other genes (Sr42 and SrTmp) that are near the same chromosome location. Use of the new SNP molecular markers will enable the plant breeders to ensure that SrCad is in new wheat varieties to provide protection to Ug99 stem rust.


Key message: New SNP markers that can be used for marker-assisted selection and map-based cloning saturate the chromosome region carryingSrCad, a wheat gene that confers resistance to Ug99 stem rust. Abstract: Wheat stem rust, caused by Puccinia graminis f. sp. tritici, is a devastating disease of wheat worldwide. Development of cultivars with effective resistance has been the primary means to control this disease, but the appearance of new virulent strains such as Ug99 has rendered most wheat varieties vulnerable. The stem rust resistance gene SrCad located on chromosome arm 6DS has provided excellent resistance to various strains of Ug99 in field nurseries conducted in Njoro, Kenya since 2005. Three genetic populations were used to identify SNP markers closely linked to the SrCad locus. Of 220 SNP markers evaluated, 27 were found to be located within a 2 cM region surrounding SrCad. The diagnostic potential of these SNPs was evaluated in a diverse set of 50 wheat lines that were primarily of Canadian origin with known presence or absence of SrCad. Three SNP markers tightly linked proximally to SrCad and one SNP that co-segregated with SrCad were completely predictive of the presence or absence of SrCad. These markers also differentiated SrCad from Sr42 and SrTmp which are also located in the same region of chromosome arm 6DS. These markers should be useful in marker-assisted breeding to develop new wheat varieties containing SrCad-based resistance to Ug99 stem rust.