The Etiology And Pathogenic Mechanisms Of Mycogone Perniciosa Causing Wet Bubble Disease On Agaricus Bisporus

Agaricus bisporus is a widely cultivated edible fungus. With the demand for A.bisporus increasing, factory-style farming for such mushroom is expanding. Variousdiseases occur along with the expansion. Among them, wet bubble disease of A.bisporus is one of the major diseases in mushroom farming, which has occurred inmany areas. In recent years, there is a trend of more areas being infected by thisdisease, causing more and more serious damages. Etiology, population geneticdiversity, pathogenesis and resistance mechanism of this wet bubble disease werestudied in a system in this paper. The main results are:1. During2012to2013, a comprehensive survey of the occurrence and damageof the wet bubble disease of A. bisporus was conducted in main production areas,including Liaocheng City and Guanxian of Shandong Province, Liaocheng City andShenxian of Shandong Province, Luoyang City of Henan Province, YongchangCounty of Gansu Province, Xichong County of Sichuan Province, Wuhan City ofHubei Province, Long Hai City of Fujian Province and Hengxian of GuangxiProvince. Typical infected mushrooms were collected and38strains of the pathogenwere obtained by tissue isolation. The pathogen was identified as Mycogoneperniciosa Magn with traditional morphology and Koch’s postulates testing method,in combination with rDNA-ITS sequence analysis.2. Different growing factors such as media, carbon and nitrogen sources,temperature, pH, lighting and humidity were used to test the optimal conditions forthe pathogen’s mycelium growth and germination. The results showed that themushroom liquid extract was the best culture media for pathogenic mycelia of fourstrains; the optimum temperature and pH of mycelia were25℃and6.0; the optimalC-source for Strains SD01, GS01and HN01was sugar; for Strain SC01, glucose. Theoptimal N-source for Strains HN01and GS01was peptone; for Strain SD01, cornflour, and for Strain SC01, ammonium nitrate. The optimum temperature and pH ofpathogenic conidial germination were30℃and6.0, and relative humidity was100%.Lighting had little effect on the growth of the mycelia and conidial germination.3. Pathogenicity of the38strains of M. perniciosa from different geographicorigins in China was determined by artificial inoculation. The results showed that the 38strains had significant differentiation in pathogenicity, while there was nosignificant correlation with the geographical origins. The strongest pathogenicity ofstrains were collected from Liaocheng City and Guanxian of Shandong Province,Longhai City of Fujian Province, Wuhan City of Hubei Province, disease index wasbetween45.86and41.22.4. SRAP molecular marker was used to explore genetic diversity of the38strainsof M. perniciosa from different areas in China,9SRAP primers were screened, and132polymorphic DNA bands were obtained. The result of NTSYS cluster analysisshowed that the genetic similarity coefficient of SRAP among the38M. perniciosaisolates was from0.59～0.96and these strains were divided into4genetic groupswhen the similarity coefficient was0.716. The analysis results of SRAP suggestedthat the pathogens of wet bubble disease in China had rich genetic diversity. They didnot have a certain correlation between the clustering groups and their geographicdistribution.5. Parasitic relationship was observed between pathogen hypha and A. bisporusmycelium by electron microscopy. The pathogen hypha and A. bisporus myceliumwrapped around each other in two hyphae junction, A. bisporus mycelium withered,dissolved, a pin-like parasitic way also appeared. With cytohistology technology,infection process of M. perniciosa on the fruiting body of A. bisporus was observed.The results showed that the pathogen infected the cell wall of the host through thesecretion of cell wall degradation enzymes and mechanical pressure from theappressorium.6. Development of the activity of defensive enzymes and correlated biochemicalproducts within the fruiting bodies of A. bioporus were studied after inoculation onfruiting bodies of A. bisporus Strains T258, As2796and W192. The activities ofphenylalanine ammonia-lyase, peroxidase, catalase and polyphenol oxidase fromdifferent strains had different performance. Among them, Strain W192contained thehighest amount of the4enzymes, followed by Strain As2796and T258, showing thatthe4enzymes had certain relations with the resistance on M. perniciosa.