Mycogone perniciosa is the fungal pathogen causing the wet bubble of white button mushrooms (Agaricus bisporus). The main symptoms of disease are undifferentiated, irregular forms of mushroom tissue, cap spotting and development of amber liquid droplets on the distorted mushrooms. The aim of the research was to assess the pathogenicity of M. perniciosa isolates that were obtained from the infected sporophores. Six isolates from Polish mushroom farms as well reference strain of Hypomyces perniciosus CBS 322.52 were used in this study. The pathogenicity of isolates was assessed on the basis of severity of disease symptoms and crop reduction in the first flush. Mushroom crop was infected with different suspensions containing of M. perniciosa aleuriospores. Significant variability was shown between tested isolates. It was stated that the pathogenicity of isolates and concentration of conidia had a significant influence on the mushroom yield. The isolate of high pathogenicity caused significant yield losses, after inoculation with 1.3 × 104·m−2, whereas the isolate with fairly pathogenicity did not produce symptoms of wet bubble disease or caused slight deformation of single sporophores, even when the casing soil was inoculated with 1.3 × 106·m−2 spores.
