Production of myrotoxin B by Myrothecium roridum isolated from Myrothecium leaf spot of mulberry in Japan

Myrothecium roridum Tode: Frides, causing leaf spot of mulberry, produces toxins against mulberry. The fungus produces the toxins not only in lesions on mulberry leaves but also on potato sucrose agar medium. Seven toxins, soluble in ethyl acetate, but not in water, were isolated using high pressure liquid chromatograph. Six of the seven toxins were identified with spectroscopic analysis as trichothecenes, including myrotoxin B and D. The remaining toxin was not a trichothecene. The majority (95.1 %) of the isolated toxins was myrotoxin B, which had the highest toxicity against mulberry in the isolated toxins. When spores of M. roridum except for the toxins were used as inoculum on mulberry leaves, no lesions developed. However, the lesion was induced when the spores of M. roridum were inoculated with myrotoxin B at the concentration of which it was not enough to cause necrosis alone. Therefore, myrotoxin B may be an important role in the pathogenicity of M. roridum.