Mapping of the novel powdery mildew resistance gene Pm2Mb from Aegilops biuncialis based on ph1b-induced homoeologous recombination.

A novel powdery mildew resistance gene Pm2Mb from Aegilops biuncialis was transferred into common wheat and mapped to chromosome 2ML bin FL 0.49-0.66 by molecular cytogenetic analysis of 2M recombinants. Aegilops biuncialis, a wild relative of common wheat, is highly resistant to powdery mildew. Previous studies identified that chromosome 2M in Chinese Spring (CS)-Ae. biuncialis 2M disomic addition line TA7733 conferred high resistance to powdery mildew, and the resistance gene was temporarily designated as Pm2Mb. In this study, a total of 65 CS-Ae. biuncialis 2M recombinants were developed by ph1b-induced homoeologous recombination and they were grouped into 12 different types based on the presence of different markers of 2M-specificity. Segment sizes and breakpoints of each 2M recombinant type were further characterized using in situ hybridization and molecular marker analyses. Powdery mildew responses of each type were assessed by inoculation of each 2M recombinant-derived F progenies using the isolate E05. Combined analyses of in situ hybridization, molecular markers and powdery mildew resistance data of the 2M recombinants, the gene Pm2Mb was cytologically located to an interval of FL 0.49-0.66 in the long arm of 2M, where 19 2M-specific markers were located. Among the 65 2M recombinants, T-11 (T2DS.2DL-2ML) and T-12 (Ti2DS.2DL-2ML-2DL) contained a small 2ML segment harboring Pm2Mb. Besides, a physical map of chromosome 2M was constructed with 70 2M-specific markers in 10 chromosomal bins and the map showed that submetacentric chromosome 2M of Ae. biuncialis was rearranged by a terminal intrachromosomal translocation. The newly developed 2M recombinants with powdery mildew resistance, the 2M-specific molecular markers and the physical map of chromosome 2M will benefit wheat disease breeding as well as fine mapping and cloning of Pm2Mb.