For the first time, Cladobotryum mycophilum, a causal agent of cobweb disease of Agaricus bisporus, was discovered on mushroom farms in Ukraine. Growth characteristics and morphology features of five strains of C. mycophilum were studied on standard nutrient media of different composition. Particular attention was paid to determining the sensitivity of these strains to the following fungicides: benzimidazole fungicides (carbendazim and benomyl), fluazinam, metrafenone and prochloraz. In the study, we used concentrations recommended by manufacturers for application on mushroom farms. It was found that all strains were resistant to carbendazim. Only one strain had a high sensitivity to benamyl, two strains had a very low sensitivity, and two strains were resistant. Resistance to benzimidazole fungicides and absence of camphor odor are characteristic of C. mycophilum Type II. Prochloraz, which is the most common alternative to benzimidazole fungicides, inhibited the growth of two strains only. Investigation of the influence of these fungicides on micromorphology of C. mycophilum demonstrated that benzimidazole fungicides and prochlorazes do not inhibit sporulation. Metrofenone, a new highly selective fungicide, inhibited the growth of all strains. Only one strain had a low sensitivity to this fungicide. Metraphenone significantly changed the mycelium micromorphology of C. mycophilum: the average thickness of hyphae was reduced by half, with respect to control in a medium without fungicides; the cytoplasm contained numerous inclusions, while conidia and conidiophores were absent. Fluazinam inhibited the growth of all these strains. Hypertrophy of vegetative cells, enlarged deformed conidiophores and conidiogenous cells were observed on the medium with fluazinam. Numerous cells had large vacuoles that occupy up to 70% of the cells. Fluazinam, like metrafenone, completely blocked sporulation of C. mycophilum.
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