Prevalence of key resistance alleles associated with DMI and SDHI fungicide resistance in European Zymoseptoria tritici populations in 2022

In Northern Europe, the application of fungicides to winter wheat crops is primarily for the control of septoria tritici blotch (STB) caused by the fungal pathogen Zymoseptoria tritici . Unfortunately, intensive use of the demethylation inhibitors (DMI) and succinate dehydrogenase (SDHI) fungicides has led to the development of resistance in the European Z. tritici population. Levels of disease control achieved by both modes of action are partly dependent on the presence and frequencies of specific alleles, including CYP51-S524T, SDHC-T79N, C-N86S and C-H152R, in the population. To determine how frequent these are across the major wheat producing regions of Europe, a survey of Z. tritici was conducted in 2022, using specific qPCR assays to detect the frequencies of each allele. A west–east gradient of resistant allele frequencies was observed, with higher levels observed in the west. Comparing frequencies detected to a previous survey conducted in 2019 confirms the continued evolution of fungicide resistance in the European Z. tritici population. To ensure the continued effectiveness of these fungicides, it is essential ensure they are applied as part of an integrated disease control strategy that aims to reduce the overall need for their application.