Impact of DMI and SDHI fungicides on disease control and CYP51 mutations in populations of Zymoseptoria tritici from Northern Europe
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Zymoseptoria tritici is a dominant pathogen in wheat causing Septoria leaf blotch (SLB), and sterol 14α-demethylation inhibitors fungicides (DMI) are commonly used for control in Northern Europe. In 14 winter wheat trials carried out in Denmark, Lithuania, and Sweden in the years 2011 to 2013, fungicides containing DMIs were investigated for their efficacy and impact on CYP51 mutations in Z. tritici populations. All fungicide treatments were applied twice – each time using 50 % of the standard rate, applied at GS 37 & 55. The single-agent DMIs, epoxiconazole and prothioconazole and a mixture of difenoconazole + propiconazole gave similar control and crop yields. The best solution varied among localities. Adding prochloraz to prothioconazole as well as using co-formulations of DMIs + SDHIs generally improved control compared with using DMIs alone. Yield responses were significant from all treatments, but co-formulations of DMIs plus SDHIs increased yield the most. Specific CYP51 mutations in Z. tritici were analysed by pyrosequencing and qPCR. Their frequency varied across sites and countries. The amount of I381V was high in all trials whereas the amount of A379G was moderate. Levels of D134G, V136C, and S524T were low to moderate across all sites. DMIs and mixtures of DMIs + SDHI selected differently for CYP51 mutations. Prochloraz increased selection for D134G and V136A and decreased selection for A379G and I381V. The lowest selection pressure towards D134G and V136A/C was recorded in the presence of the mixture difenoconazole and propioconazole. Mixtures of DMIs and SDHI tended to lower the frequency of V136A/C compared to DMIs used alone but had no measurable impact on the frequency of I381V and A379G. No responses were seen in relation to S524T, which only occurred at a very low level.
KeywordsSterol 14α-demethylation inhibitor Fungicide resistance Mycosphaerella graminicola Septoria leaf blotch Succinate dehydrogenase inhibitor
The authors would like to acknowledge the technicians at Aarhus University, Flakkebjerg (DK), Hushållningssällskapet, Malmöhus (SWE) and Institute for Agriculture, Dotnuva (LT) for carrying out the practical part of the field trials. We also like to thank BASF SE, Bayer CropScience, and Syngenta Crop Protection for financial support of the trials and for their involvement in CYP51 characterisation.
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