Four azoles’ profile in the control of Septoria, yellow rust and brown rust in wheat across Europe

Spatiotemporal dynamics of fungicide resistance in the wheat pathogen Zymoseptoria tritici in France

“…The observed dynamics are consistent with the general gradual erosion of azole efficacy observed in several European countries . Results from a European trial network demonstrated major variations in azole performance across Europe correlated with a clear eastward pattern of decrease in the frequency of all cyp51 mutations, with the exception of the I381V and A379G variants (TriMR genetic background). Spatial heterogeneity in azole efficacy, correlated with population structure for the frequency of resistant genotypes, was also observed in our data set at the scale of France.…”

“…This hypothesis should be explored by performing fitness tests and analysing cyp51 diversity between strains from northern and southern populations. In more recent French populations from the north and south, contrasting azole efficacies were also observed, with reduced epoxiconazole, prothioconazole, metconazole and tebuconazole efficacy positively associated with higher frequencies of the CYP51 V/C136A and D134G changes, largely present in TriHR genotypes, in the north, compared with the south, in 2016 …”

“…They are associated with qualitative resistance (a disruptive shift or single‐step resistance), resulting in a bimodal distribution of phenotypes (individuals either sensitive or resistant), with the resistant phenotype rapidly invading the population . By contrast, DMIs have been used intensively for STB control since the late 1970s; the first resistant strains were selected in the 1980s, and field efficacy has since gradually declined, but this decline has differed between molecules and between sites . A continuum of decreased sensitivity phenotypes (triazole‐resistant phenotypes: TriR) has arisen through progressive accumulation of mutations in the cyp51 target gene, with an overexpression of cyp51 due to insertions in its promoter region, with or without enhanced efflux correlated with three possible insertions in the promoter region of the transporter MFS1 .…”

“…Several phenotypic or molecular methods for detecting and quantifying fungicide resistance in Z. tritici have been reported and can be used to investigate resistance dynamics. Several studies have described the variation over space and/or time of the mean EC 50 (half‐maximal effective concentration, the dose at which 50% of the maximal growth inhibition is observed) and its derivatives (‘resistance intensity‐based approaches’), whereas other studies have described variations in the prevalence of several mutations or phenotypes (‘resistance frequency‐based approaches’). Resistance intensity‐based approaches characterize resistance phenotypes clearly, but require strain isolation, which is labour‐intensive and time‐consuming.…”

“…Far fewer studies have focused on resistance emergence, but the first detection of resistance is now predicted reasonably well. Finally, these models focused on the temporal dimension and rarely take spatial heterogeneity into account, even though such heterogeneity of resistance is frequently observed in Z. tritici populations, especially at the scale of regional/national surveys . This may result from regional heterogeneity in the crop environment, and also in pesticide use.…”