Identification of stem rust resistance genes in monogenic lines derived from wheat cultivar Waldron

The wheat (Triticum aestivum L.) cultivar Waldron carries at least six genes for resistance to stem rust caused by Puccinia graminis Pers.:Pers. f.sp. tritici Eriks. and Henn. (Pgt). The identity and map location of some of these genes are known, but there is limited knowledge of SrWld1, an important gene that conditions resistance to all North American Pgt races. Our objective was to identify and map additional stem rust resistance genes in Waldron through aneuploid analysis, allelism tests, and linkage with molecular markers. Four lines, WDR-A1, WDR-C2, WDR-D1, and WDR-E4, each carrying a single stem rust resistance gene from Waldron, were crossed to appropriate genetic stocks. Telosomic analysis failed to confirm the previously reported location of SrWDR-C2 to chromosome 7A. Monosomic analysis, allelism tests, and multi-pathotype seedling tests indicated that the genes in WDR-A1 and WDR-D1 were Sr18 and Sr9g, respectively. Telosomic analysis, allelism tests, and marker analysis of WDR-E4 indicated that SrWld1 should be reassigned from chromosome 2A to 2BL. When families were tested with races LBBLB, TMLKC, and TPPKC, co-segregation of resistance was not observed. This suggests that inheritance of the SrWld1 phenotype was quantitative and that additional studies are needed on the inheritance of SrWld1. When results from this study were combined with previous studies, the stem rust resistance genes in Waldron are identified as Sr9g, Sr11, Sr18, Sr41, SrWld1, and SrWld2.