Mapping and validation of all-stage resistance to stem rust in four South African winter wheat cultivars

Several South African winter wheat cultivars express all-stage resistance to local races of Puccinia graminis f. sp. tritici (Pgt). To study the inheritance of resistance, cultivars Komati, Koonap, Limpopo and SST 387 were crossed with the stem rust susceptible Line 37-07. Segregation of reaction to Pgt race PTKST in each of the four F-2 populations indicated the presence of a single dominant resistance gene. Allelism tests among the resistant parents indicated that the same gene, alleles of the same gene, or closely linked genes were involved. The resistance gene(s) mapped to the short arm of chromosome 6D and was flanked by SSR markers barc183 and wms4862. The four cultivars tested negative using single nucleotide polymorphism (SNP) markers linked to Sr42, SrTmp and SrCad also located on chromosome arm 6DS. Allelism tests between the resistant cultivars and Norin 40 (Sr42) and CnsSrTmp (SrTmp) also suggested common genes for resistance. Multi-race phenotyping ruled out involvement of Sr42 and SrCad in all tested cultivars. The available evidence suggested the presence of previously uncharacterised gene(s) or alleles of Sr42, SrTmp or SrCad in all four cultivars. SNP marker BS00085937 and SSR markers psp3200 and wms4862 were 90.9-92.7% effective in predicting stem rust resistance among 55 South African genotypes and could be useful for marker-assisted selection.