Virulence complexity of Australian Blumeria graminis f. sp. tritici and implications for resistance breeding

Abstract

The obligate biotrophic fungus Blumeria graminis f. sp. tritici (Bgt), the causal agent of wheat powdery mildew, has become increasingly prevalent in Australia. Recent reports of fungicide-resistant Bgt isolates further highlight the need for effective management strategies. However, only a few studies have investigated the Australian Bgt population, limiting the effective deployment of resistant cultivars for disease management. To evaluate the virulence complexity of the Australian Bgt population and to identify lines with currently effective wheat powdery mildew resistance genes. To investigate virulence diversity, 30 Australian Bgt isolates from various geographical locations and hosts were collected between 2020 and 2024 and screened against a panel of 24 wheat lines carrying defined major resistance genes. Virulence complexity did not differ between eastern and western Bgt populations (P = 0.695), although Pm3a, Pm16, Pm17, and Pm4b were effective only in the western region, whereas Pm3d was effective only in the eastern region. Khapli (Pm4a) and Tabasco (Pm2), both carrying additional unknown resistance gene(s), were highly resistant to all isolates. Similarly, European cultivars Alchemy, Cordiale, and Einstein remained resistant to representative Australian Bgt isolates. Virulence profiling showed substantial diversity within the Australian Bgt population. However, wheat varieties carrying defined resistance genes and their combinations are available and remain effective against contemporary Australian Bgt isolates. This preliminary study highlights the potential diversity within the Australian Bgt population and emphasises the importance of continuous monitoring to support the effective deployment of resistance resources, ultimately reducing reliance on fungicides.