S4-4: Azole fungicides sensitivity screening of Irish Pyrenopeziza brassicae populations and investigation of molecular mechanisms of insensitivity within CYP51 gene

Abstract: Light leaf spot, caused by Pyrenopeziza brassicae, is an economically important
disease of oilseed rape, and disease control currently relies upon the use of fungicides. The
sensitivity status of Irish P. brassicae populations to azole fungicides was assessed in vitro and in planta for tebuconazole and prothioconazole-desthio, using three collections of P. brassicae isolates. The mechanisms of insensitivity present within these populations were also investigated, and results showed that a shift towards decreased sensitivity to tebuconazole was present, while the Irish P. brassicae isolates were still sensitive to prothioconazole-desthio. Two non-synonymous mutations and regulatory inserts of different sizes were identified within the P. brassicae PbCYP51 gene targeted by this class of fungicides, and the presence of these alterations affected sensitivity to azoles. Although the glasshouse experiments showed that the fungicides are still effective in controlling light leaf spot disease in planta, the mechanisms of insensitivity were predominant in the Irish populations and continued monitoring is, therefore, essential.