P-112 - Emergence of resistance to succinate dehydrogenase inhibitor fungicides in Zymoseptoria tritici in Estonia

Septoria tritici blotch caused by Zymoseptoria tritici (Zt) is a severe leaf disease on wheat all over the world. A total of 750 isolates from 2020 to 2024 were assessed in vitro for sensitivity of the Zt population towards fungicides targeting fungal succinate dehydrogenase (SDHIs). In parallel, we analyzed the presence of alterations in SdhB and SdhC proteins which have been demonstrated to confer resistance to SDHI fungicides. Combined data from microtiter plate sensitivity assays and DNA sequencing enabled us to investigate the correlation between reductions in SDHI sensitivity and mutations in the target Sdh genes. This investigation shows a clear link between reduced field efficacy by solo SDHIs as a result of increasing problems of sensitivity shifting and the selection of several SdhC mutations (e.g. C-T79N, C-N86S, and C-H152R). Alterations in SdhB have less effect on sensitivity to SDHIs. Pathogens with observed mutations are more likely to survive SDHI treatment, which could impact disease control strategies. Therefore, there is a clear need for integrated disease management, such as improved crop rotations and stubble management, to reduce disease pressure and prolong the effective lifespan of SDHI fungicides.