Genetic mapping of a putative Agropyron cristatum-derived powdery mildew resistance gene by a combination of bulked segregant analysis and single nucleotide polymorphism array

The wheat relative Agropyron cristatum (L.) Gaertn. (2n = 4x = 28; genomes PPPP) has often been used as a donor of useful genetic variation for wheat improvement, including enhanced disease resistance to powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt). In this report, resistance to powdery mildew was transferred from A. cristatum to common wheat, and the resulting introgression line PB3558 exhibited all-stage resistance. To identify the resistance gene, genetic analysis was conducted using F2, F2: 3 and recombinant inbreed line populations derived from the cross of PB3558 and the susceptible cultivar Jing 4841. Segregation ratios from inoculation with Bgt isolate E09 indicated that the resistance was conferred by a single dominant gene, temporarily designated PmPB3558. Bulked segregant analysis (BSA) was applied to screen for molecular markers linked to PmPB3558, and five published markers were found. In order to increase the density of the genetic map, we developed ten novel single sequence repeat markers based on the single nucleotide polymorphism (SNP) loci with polymorphisms produced from a combination wheat 90 k SNP array and BSA. PmPB3558 was located on wheat chromosome arm 5DS and flanked by markers Xcfd81 and Xbwm25. Because there are other powdery mildew resistance genes located on 5DS, 21 Bgt isolates were used to compare the reaction differences. PmPB3558 showed unique reactions, suggesting that it was most likely a novel allele. This is the first documentation on transferring an alien powdery mildew resistance gene from A. cristatum, and the germplasm acquired in this study will be useful for broadening the genetic basis for wheat breeding.