Characterization of PmHHXM, a New Broad-Spectrum Powdery Mildew Resistance Gene in Chinese Wheat Landrace Honghuaxiaomai

Powdery mildew, caused by fungal pathogen Blumeria graminis f. sp. tritici, is an agronomically important and widespread wheat disease causing severe yield losses. Deployment of broad-spectrum disease resistance genes is the preferred strategy to prevent this pathogen. Chinese wheat landrace Honghuaxiaomai (HHXM) was resistant to all 23 tested B. graminis f. sp. tritici isolates at the seedling stage. The F-1, F-2, and F2: 3 progenies derived from the cross HHXM x Yangmai 158 were used in this study, and genetic analysis revealed that a single dominant gene, designated PmHHXM, conferred resistance to B. graminis f. sp. tritici isolate E09. Bulked segregant analysis and molecular mapping initially located PmHHXM to the distal region of chromosome 4AL. To fine map PmHHXM, we identified two critical recombinants from 592 F-2 plants and delimited PmHHXM to a 0.18-cM Xkasp475200 to Xhnu552 interval covering 1.77 Mb, in which a number of disease resistance-related gene clusters were annotated. Comparative mapping of this interval revealed a perturbed synteny among Triticeae species. This study reports the new powdery mildew resistance gene PmHHXM, which seems different from three known quantitative trait loci/genes identified on chromosome 4AL and has significant values for further genetic improvement. Analysis of the polymorphisms of 13 cosegregating markers between HHXM and 170 modern wheat cultivars indicates that Xhnu227 and Xsts478700 developed here are ideal for marker-assisted introgression of this locus in wheat breeding.