Evidence of a distinct Blumeria graminis f. sp. tritici pathotype structure in Australian wheat powdery mildew: implications for resistance breeding.

The obligate biotrophic fungus Blumeria graminis f. sp. tritici (Bgt) is the causal agent of wheat powdery mildew. To investigate virulence diversity, 30 Australian Bgt isolates collected between 2020 and 2024 were screened against a panel of 24 wheat lines carrying defined resistance (R) genes. Pathotyping analysis indicated that the Australian Bgt population is diverse in its virulence profile. Non-metric multidimensional scaling analysis of disease phenotyping revealed evidence of six distinct Bgt pathotype groups. In addition, we identified wheat varieties carrying defined R genes and their combinations that remain effective against the contemporary Australian Bgt. Notably, wheat cvs Khapli and Tabasco, possessing Pm4a and Pm2, respectively, in addition to unknown R gene(s), were highly resistant to all the isolates tested. Furthermore, elite European varieties that possess durable resistance, such as Alchemy and Cordiale, display complete to moderate resistance against all selected isolates representing the Australian pathotype groups.