The development of Agaricus bisporus wet bubble disease and the nuclear phase of pathogen

Abstract:

[Objective] We studied the dynamic nuclear behavior of Hypomyces perniciosus on axenic culture and its disease progression after infection on different growth stages of Agaricus bisporus. [Methods] Infection process was initiated by inoculating different stages of A. bisporus fruit body, and different depths of compost and casing soil with H. perniciosus. Disease progression was studied by observing symptoms on the fruit body using light microscopy and scanning electron microscopy. The nuclear behavior of H. perniciosus was determined by observation using fluorescence light microscopy after binding of DNA specific fluorochrome dye (DAPI:4, 6-Diamidino-2-phenylindole dihydrochloride) to the nuclei. [Results] Inoculating H. perniciosus on different depths of compost and casing soil resulted in different disease rate as follows:on the surface of casing soil>in the center of casing soil>between the casing soil and the compost>in the center of compost. H. perniciosus can infect any stage of fruit body development, when young primordial (up to 3 mm) was infected, large, irregular and tumorous fungal masses were formed. H. perniciosus directly penetrated A. bisporus without the formation of appressorium-like structures. The germination of the conidia led to a necrotic brown lesion symptom on A. bisporus at the beginning stages of disease development. The mycelium of A. bisporus plasmolysed, hydropically degenerated, cytoplasmolysed, emptied of mycelium cytosol and eventual death as the disease advanced. H. perniciosus produced two types of conidia. Group I conidia had no septa, colorless and smooth containing one nucleus. Group II didymoconidium had septa, containing two nuclei, separated by septa. The first round of mitosis occurred in conidia with no nucleus in the germinal tube. Another kind of asexual spore for thicker cell wall wart convex chlamydospore, chlamydospore had two cells. The upper cell had two nuclear while the basal cell had one or two nuclear, when germinated, it produced one or two germinal tubes. The number of nuclear in the germinal tube was irregular, usually contained 0 to 2 nuclear. [Conclusion] H. perniciosus can infect any part of the A. bisporus fruit body and can cause tremendous cytology changed. If we perform single spore isolation to do genetic analysis, one must isolate conidia with no septa.