Abstract
The pathogen of bacterial rot of oyster mushroom (Pleurotus ostreatus) was isolated from cultivated oyster mushroom in Niigata Prefecture, and was identified as Pseudomonas tolaasii Paine. The culture filtrate of P. tolaasii caused brown or black lesions on oyster mushroom, “enokitake” (Flammulina velutipes) and potato tuber slices identical to those caused by the bacterium, and also inhibited the growth of microorganisms. Since “enokitake”, potato tuber slices and P. syringae pv. coronafaciens showed high sensitivity to the culture filtrate, they were used as indicators of the toxins during the isolation procedure. In order to improve the production of the toxins, the optimal conditions (medium, strain, temperature, period of incubation) were determined. The simple method for isolation of the toxin was established by using the cartridge of Absorbex RP-18. The eight toxins were purified from the culture filtrate, and the toxins 4 and 6 were identified as tolaasin I and II, respectively. Toxin 4 was the main component of the toxins, and caused brown lesions on oyster mushroom, “enokitake” and potato tuber slices at concentrations of 125, 16, and 4ppm, respectively. The toxin 4 inhibited the growth of phytopathogenic microorganisms, and the sensitivity was varied with the species. The fungi were generally more sensitive than the bacteria, the minimum inhibitory concentration of toxin 4 was 16-500ppm for fungi and 4-16ppm for bacteria.
