Study On Culture Characteristic And Chemical Control Of Wet Bubble Disease Of Agaricus Bisporus Caused By Mycogone Perniciosa

Agaricus bisporus is an important cultivated mushroom around the world. Wet bubble disease is one of the important diseases in the mushroom production. It often caused serious economic losses and restricted the development of the mushroom industry.This research focused on identification of pathogen, culture characteristics, the occurrence regulation of wet bubble disease and the chemical control under laboratory and field test.One fungus was isolated from the infected mushroom by conventional tissue isolation. Pathogenicity was tested by inoculating mycelia plugs and conidia suspension onto pileus of healthy mushrooms in vivo respectively. The symptoms of tested mushrooms were observed later. Koch’s postulates were fulfilled by re-isolating the fungus from diseased mushrooms. The colony cultivated on potato dextrose agar (PDA) was white and round initially, then turned brown. The pathogen was identified M. perniciosa based on morphologic and microscopic observation and rDNA-ITS sequence analysis.The research of culture characteristics showed that M. perniciosa grew best on CYM, PSA and PDA medium in9different mediums, the worst was Czapek medium. PDA medium was best for spores production, while CYM medium had the less spores.25℃was the optimal temperature, and it was killed more than31℃. The range of pH was3-11, with the optimal pH5-6. The best carbon and nitrogen source were fructose and KNO3. It could grow better in the carbon concentration of8g/L and C:N of160:1.The pot experiment indicated that spores of M. perniciosa in the casing soil inhibited the mycelial growth of A. bisporus, but it also promoted fruiting3d earlier than the control. In this paper, the severity of wet bubble disease was graded from one to five for symptoms. The wet bubble disease was observed from the first flush to the end with an upward tendency during the mushroom crop cycle in the field trail in Zhangzhou, Fujian province. On the other hand, the second flush and the forth flush were the periods of rapid growth of wet bubble disease, the growth rate of disease incidence were183.40%and125.91%respectively, and the growth rate of disease index were201.74%and160.76%respectively.Eight fungicides used in this study were chosen because they were permitted for use with edible fungi, vegetables or fruits by Chinese legislation. Inhibiting of mycelia growth of M. perniciosa by all tested fungicides was assayed on amended PDA medium in toxicity text. The most effective fungicide was prochloraz-Mn, followed by chlorothalonil, then mancozeb, and EC50value of three fungicides were0.048μg/mL,3.678μg/mL and33.518μg/mL respectively. In the second screening, the mycelia of A. bisporus showed the most sensitive to chlorothalonil, followed by prochloraz-Mn, then mancozeb, and EC50value of three fungicides were10.474μg/mL,24.345μg/mL and118.244μg/mL respectively. A selectivity index for each fungicide was calculated as a ratio of its EC50value for M. perniciosa over the corresponding estimate for A. bisporus. Prochloraz-Mn had the smallest selectivity index value (SD=0.002), then mancozeb (SD=0.283), and the last on was chlorothalonil (SD=0.351).In the first trial, the effectiveness of the three fungicides assayed against wet bubble disease infected artificially with the dose of M. perniciosa (107spores/m2). The three concentration of each tested fungicide were applied by spraying on the surface of casing soil or mixing in the casing soil. The result indicated significant differences between the fungicides treatments as regards effectiveness and disease index. The fungicides treatment with the most effective were50%prochloraz-Mn WP diluted2000times spraying on the surface of casing soil or5000times mixing in the casing soil, while the effectiveness could achieve93.12%-97.35%and the disease index was0.37-1.11, and the period of preserving would go on for45d-55d. The effectiveness and disease index of80%mancozeb WP were73.13%-84.27%and2.59-4.40. The effectiveness and disease index of75%chlorothalonil WP were25.54%-76.93%and3.88-10.79.Three concentration of prochloraz-Mn applied by spraying on the surface of casing soil in the second trail, and no spores of M. perniciosa was inoculated into the casing soil. Prochloraz-Mn diluted2000times showed the most effective than diluted5000times and diluted8000times, while the effectiveness were98.05%,50.55%and34.22%respectively.