Large-scale study validates that regional fungicide applications are major determinants of resistance evolution in the wheat pathogenZymoseptoria triticiin France

Summary Research rationale: In modern cropping systems, the near-universal use of plant protection products selects for resistance in pest populations. The emergence and evolution of this adaptive trait threaten treatment efficacy. We identified determinants of fungicide resistance evolution and quantified their effects at a large spatiotemporal scale. Methods: We focused on Zymoseptoria tritici , which causes leaf blotch in wheat. Phenotypes of qualitative or quantitative resistance to various fungicides were monitored annually, from 2004 to 2017, at about 70 sites throughout 22 regions of France (territorial units of 25 000km 2 on average). We modelled changes in resistance frequency with regional anti- Septoria fungicide use, yield losses due to the disease and the regional area under organic wheat. Key results: The major driver of resistance dynamics was fungicide use at the regional scale. We estimated its effect on the increase in resistance and relative apparent fitness of each resistance phenotype. The predictions of the model replicated the spatiotemporal patterns of resistance observed in field populations (R 2 from 0.56 to 0.82). Main conclusion: The evolution of fungicide resistance is mainly determined at the regional scale. This study therefore showed that collective management at the regional scale could effectively complete local actions.