Spatio-temporal distribution of DMI and SDHI fungicide resistance of Zymoseptoria tritici throughout Europe based on frequencies of key target-site alterations

BACKGROUND: Over the past decade, demethylation inhibitors (DMIs) and succinate dehydrogenase inhibitors (SDHIs) fungicides have been extensively used to control to septoria tritici blotch, caused by Zymoseptoria tritici on wheat. This has led to the development and selection of alterations in the target-site enzymes (CYP51 and SDH, respectively).RESULTS: Taking advantage of newly and previously developed qPCR assays, the frequency of key alterations associated with DMI (CYP51-S524T) and SDHI (SDHC-T79N/I, C-N86S and C-H152R) resistance was assessed in Z. tritici infected wheat leaf samples collected from commercial crops (n = 140) across 14 European countries prior to fungicide application in the spring of 2019. This revealed the presence of a West to East gradient in the frequencies of the most common key alterations conferring azole (S524T) and SDHI resistance (T79N and N86S), with the highest frequencies measured in Ireland and Great Britain. These observations were corroborated by sequencing (CYP51 and SDH subunits) and sensitivity phenotyping (prothioconazole-desthio and fluxapyroxad) of Z. tritici isolates collected from a selection of field samples. Additional sampling made at the end of the 2019 season confirmed the continued increase in frequency of the targeted alterations. Investigations on historical leaf DNA samples originating from different European countries revealed that the frequency of all key alterations (except C-T79I) has been gradually increasing over the past decade.CONCLUSION: Whilst these alterations are quickly becoming dominant in Ireland and Great Britain, scope still exists to delay their selection throughout the wider European population, emphasizing the need for the implementation of fungicide anti-resistance measures. This article is protected by copyright. All rights reserved.