Azole resistance in Blumeria

Blumeria graminis f.sp. tritici (wheat powdery mildew) isolates from the USA and UK were compared for sensitivity to the lanosterol demethylation inhibitor (DMI) azole fungicides tebuconazole and prothioconazole and assayed for Cyp51 sequences, copy number and expression. Median effective doses (ED50) of tebuconazole spanned a wider range than prothioconazole and US isolates had much greater mean sensitivity than UK isolates. Four genetic models involving multiple resistance mechanisms were identified, including increased copy number and expression of Cyp51. Molecular field diagnostics should survey the full range of genetic mechanisms involved in azole resistance.