Fungicide resistance of Microdochium nivale strains and its interconnection with virulence

The aim of the study was to analyze the resistance of 21 Microdochium nivale strains (fungi that cause pink snow mold in winter crops), living within a single area and a single crop (winter rye), to fungicides that differ in chemical nature and mechanisms of action as well as to test the interconnection between levels of virulence and fungicide resistance of strains. The virulence of M. nivale strains was determined on detached leaves of rye (Ogonek variety) plants as well as on whole plants grown under sterile conditions in vitro. The resistance of strains to fungicides (Provisor (a.s. azoxystrobin) and Ferazim (a.s. carbendazim)) was determined by inhibition of mycelium growth. As a result of the experiments, more strains (13) capable of growing in the presence of Provisor were revealed than Ferazim-resistant strains (2); however, Ferazim-resistant strains had a greater level of resistance (5-16% of growth inhibition) than Provisor-resistant strains (63-94 % of growth inhibition). A negative correlation (Spearman's correlation coefficient -0.604 and -0.532) between the level of virulence of M. nivale strains and the level of their susceptibility to Provisor was found. This evidently means that the acquisition of resistance to Provisor by M. nivale strains is accompanied by an increase in their virulence. No correlations were found between the fungicide resistance of M. nivale strains and their attribution to one or another phylogenetic group, to which the strains were assigned based on the nucleotide sequence of the ITS2 (internal transcribed spacer 2) region. The study shows that for choosing the fungicide application strategy, it is necessary to analyze phytopathogen populations for the presence of strains that are simultaneously characterized by high virulence and resistance to various fungicides and also take into account that the adaptation of fungi to certain fungicides can be accompanied by an increase in their virulence, which will negatively affect the phytopathological state of agrocenosis.