The effect of Hypomyces perniciosus on the mycelia and basidiomes of Agaricus bisporus.

Hypomyces perniciosus has been reported as a destructive pathogen of Agaricus bisporus. Previous research suggested that the pathogenesis may not only be perpetuated by H. perniciosus, but also by bacteria. Clarification of the interaction between A. bisporus and H. perniciosus is a prerequisite for the development of effective control measures against wet bubble disease. Here, the effects of H. perniciosus on A. bisporus mycelia are examined in dual culture on agar media and in open-ended test tubes. During disease development, the putative causal agents and cytology of wet bubble-diseased mushrooms were followed microscopically. The interaction between H. perniciosus and the basidiome of A. bisporus was also studied using dual-cultured H. perniciosus and basidiome tissues. Dual-cultured mycelia from both fungi showed that growth continued even after contact was made, without any observable antagonistic lines or cytoplasmic changes of A. bisporus mycelia. Hypomyces perniciosus could be isolated from diseased basidiomes any time after inoculation, but bacteria were only recovered after the basidiomes of A. bisporus had been killed by H. perniciosus. Dual culture of the basidiome tissue of A. bisporus and H. perniciosus on agar media established that H. perniciosus can independently and rapidly degrade the basidiomes of A. bisporus. We conclude that H. perniciosus has no pathogenic activity on the mycelial stage of A. bisporus, but it can destroy A. bisporus basidiomes in the absence of bacteria. Wet bubble disease is evidently not caused by bacteria, but by the fungus, although bacteria likely participate in the disease after invasion by the fungus.