Biological control of green mould and dry bubble diseases of cultivated mushroom (Agaricus bisporus L.) by Bacillus spp.

Compost green mould and dry bubble are the most devastating diseases of the cultivated white button mushroom. In search of efficient disease control, previously and newly isolated Bacillus spp. strains obtained from mushroom substrates were examined for antagonistic activity against Trichoderma aggressivum f. europaeum T77, Trichoderma horzianum T54 and Lecanicillium fungicola var. fungicola Sa(2)V(6) in vitro. All 33 tested Bacillus spp. strains inhibited the growth of pathogens. The strains with the strongest antagonistic activity were selected for in vivo experiments in which the efficacy of strains in pathogen suppression and their effect on mushroom yield were evaluated, in comparison with a commercial biofungicide based on Bacillus velezensis QST 713 and a fungicide based on prochloraz-manganese. In mushroom growing room trials with T. aggressivum f. europaeurn, the most effective in pathogen suppression were (in decreasing order) prochloraz-Mn, Bacillus amyloliquefaciens B-241, Bacillus velezensis QST 713, Bacillus pumilus B-138 and B. subtilis B-233. The commercial prochloraz-Mn fungicide was the best at suppression of L. fungicola var. fungicola, while B. amyloliquefaciens B-241 was the most successful out of the three tested Bacillus spp. strains. In all in vivo experiments, B. amyloliquefaciens B-241 showed similar results in suppression of pathogens as the commercial biofungicide B. velezensis QST 713. Regarding the impact on mushroom productivity in trials with both pathogens, no statistically significant differences were noted when the treatments were compared with inoculated and uninoculated controls. Strain B. amyloliquefaciens B-241 showed the greatest potential for biocontrol of both compost green mould and dry bubble disease, which makes it a good candidate for further trials at commercial scale.