The first detection of multiple resistant (MBC and QoI) strains of Cercospora beticola Sacc. in Poland

Abstract

Long-term and intensive use of fungicides may lead to fungal resistance to active ingredients, even with different modes of action. In Poland, Cercospora leaf spot (CLS), the most remarkable disease of sugar beet, is mainly controlled with benzimidazoles (MBC), triazoles (DMI), and strobilurins (QoI). A constant monitoring of the emergence and the development of resistant fungal strains is required by the limited number of active ingredients. On the basis of RFLP analysis application, the aim of the study was to determine and monitor simultaneous appearing of C. beticola strains with E198A and G143A mutations. Mutation E198A in the β-tubulin gene is the main reason for MBC-resistance. Whereas mutation G143A in the cytochrome b is responsible for QoI-resistance. Most of the 414 tested C. beticola isolates (90%) were able to grow (growth inhibition percentage<50%) on the medium amended with 1 μg/ml thiophanate-methyl, and 34% of the isolates on the medium amended with 1 μg/ml azoxystrobin. Based on the PCR-RFLP analysis both mutations were detected in 44% of the tested isolates. The current study is the pioneer detection of multiple resistances to MBC and QoI fungicides in C. beticola in Poland and the European Union. The presence of multiple resistant isolates in the population of pathogens is adverse and this phenomenon requires thorough monitoring and registration of new active ingredients, allowing effective control of CLS.