A gram-positive bacterium was isolated from the spent substrate of Agaricus bisporus that showed a marked antagonistic activity against Pseudomonas agarici. It was identified as Bacillus safensis HC42 based on its cultural, biochemical, and physiological characteristics, and 16S rRNA sequence. B. safensis HC42 was saprophytic, but not parasitic or pathogenic, in cultivated mushrooms and showed strong inhibition of P. agarici in vitro. Moreover, it showed a control efficacy of 66 % against browning disease caused by P. agarici in Agaricus bisporus. Therefore, B. safensis HC42 may be useful in the future for the development of a biocontrol system.

The button mushroom, Agaricus bisporus, is one of the major economical crops cultivated in Korea. This mushroom showed the 5th production to 10,996 M/T in 2012. Several bacteria are known as the causal agents of diseases of the cultivated button mushroom (Agaricus bisporus) and oyster mushroom (Pleurotus ostreatus). Pseudomonas agarici is the causal agent of browning disease of commercial mushrooms. Colonization of mushroom caps by the bacterium results in development of browning lesions on pileus. These lesions are superficial brown spots and can be round or spreading. But P. agarici never caused sunken lesions and rotting of the mushroom tissues. A Gram-positive bacterium was isolated from mushroom media that markedly showed the antagonistic activity against Pseudomonas agarici, the most destructive pathogen of cultivated mushrooms. The HC42 strain was selected as antagonistic bacterium by inhibition zone method and it was identified as Bacillus safensis. by the cultural, morphological and physiological characteristics, and analysis of the 16S rDNA.. The isolated bacterium is saprophytic but not parasitic nor pathogenic to cultivation mushroom. The isolated bacterium for P. agarici cell, was sufficient for inhibition in vitro. Inoculation of the isolated bacterium prevents the development of bacterial disease in Agaricus bisporus. Control efficacy of browning disease of strain HC42 treatment was 66% on Agaricus bisporus. The optimal culture medium for the antagonistic bacteria growth was determined as follows: 1.5% D-galactose, 1.5% yest extract, 1% NH4Cl, 1.5% KCl, and 1.0% L-asparagin at pH 6.0 at 25℃. The suppressive bacterium may be useful in future for the development of biocontrol system and the construction of genetically modified edible fungi resistant to the disease caused by P. agarici.

Mushroom is cultivated as one of the major economical crops in many areas in Korea. The total production has steadily increased from approximately 186,400 M/T in 2007 to 190,111 M/T in 2011. The button mushroom, Agaricus bisporus, showed the 5th production to 13,052 M/T in 2011. Several bacteria are known as the causal agents of diseases of the cultivated button mushroom (Agaricus bisporus) and oyster mushroom (Pleurotus ostreatus). Pseudomonas agarici is the causal agent of browning disease of commercial mushrooms. Colonization of mushroom caps by the bacterium results in development of browning lesions on pileus. These lesions are superficial brown spots and can be round or spreading. But P. agarici never caused sunken lesions and rotting of the mushroom tissues. Antagonists against P. tolaasii, HC42 were selected and their control efficacy of browning disease was investigated in this study. Antagonists against P. agarici, HC42 were selected and their control efficacy of browning disease was investigated in this study. After proceeding antagonistic test, HC42 was selected as a strong antagonist against P. agarici and the HC42 strain was identified as P. safensis with the cultural, physiological and biochemical properties and analysis of the 16S rRNA. The optimal culture medium for the antagonistic bacteria growth was determined as follows: 1.5% D-galactose, 1.5% yest extract, 1% NH4Cl, 1.5% KCl, and 1.0% L-asparagin at pH 6.0 at 25℃. Control efficacy of browning disease by HC42 treatment was 66% on Agaricus bisporus..