Sensitivity evolution in Venturia inaequalis towards SDHIs in comparison to other modes of action

Abstract

Abstract Succinate dehydrogenase inhibitors (SDHIs) are an important group of fungicides (FRAC Group 7) for the control of Venturia inaequalis. Mechanisms which lead to reduced SDHI sensitivity in fungi are based on mutations in the SDH-subunits B, C, or D of the target gene. Monitoring studies have shown that most of the European population is still sensitive to SDHIs. Single cases of SDHI resistance have been detected shortly after market introduction although mainly at trial sites. The underlying resistance mechanisms have been identified as target site mutations (B-T258I, C-N85S and C-H151R). However, these were single findings which did not increase in frequency or even disappeared when the same field was analyzed one or more seasons later. This is in contrast to findings on other resistance cases which are stable over several seasons even without selection pressure, such as QoI and benzimidazole resistance. High frequencies of target site mutations for QoIs and benzimidazoles (G143A and E198A, respectively) have been detected in a 2022 survey, whereas no SDHI target site mutation exceeded the detection limit of our molecular detection assay in any sample.