Morphological characteristics of wet bubble disease (Mycogone perniciosa) isolated from button mushroom (Agaricus bisporus) and assessment of factors affecting disease development and spread

Wet bubble disease (Mycogone perniciosa) is a devastating disease in the crop production of mushrooms. In India, it has been reported to cause serious crop losses. It is also a common contaminant, occurring in mushroom houses in the Kashmir valley. The aim of the study was to investigate physiological characteristics of M. perniciosa isolated from button mushroom (Agaricus bisporus). The assessment of the factors affecting the development and spread of wet bubble disease was also done. The isolated fungus produced copious flocculent mycelia and the colour of colonies changed from white to pale brown and finally dark brown after 12-14 days of incubation at 24±1°C. The maximal radial growth (90 mm) was recorded on compost agar medium after 15 days, followed by potato dextrose agar (75.5 mm) and malt extract agar (72.0 mm). Microscopic examination of the pathogen reveals that the mycoparasite was both inter and intra-cellular. The conidiophores were erect, long and verticillately branched. Conidia were oval, single, 2-celled and thin walled. The pathogen was successfully re-isolated when admixed with the compost at 6th, 7th or 8th turnings, that is, on the 22nd, 25th and 29th day of composting with a pile temperature of only (0-30°C). The pathogen was also present in viable form in all the test samples of casing mixture in varied populations. The pathogen was continuously present in samples from spent compost of diseased trays. It was also observed that only the garden soil and the spent compost carried the wet bubble pathogen varying in populations each year. The peat soil, virgin soil, farm yard manure and sand did not yield any M. perniciosa propagules during either year.