Mutants of Myrothecium roridum with weak pathogenicity induced by irradiation with ultraviolet rays and toxin production ability

Myrothecium leaf spot of mulberry, caused by Myrothecium roridum was reported in 1994 (TAKAHASHI et al.,1994). M.. roriduyn produces toxins against mulberry(MURAKAMI et al.,1995) and the toxins may be one of the pathogenic factors of the fungus(1VIURAKAMI and SHIRATA, 1998).However, there is no clear evidence of the role of the toxins for the factor in pathogenicity. In this paper, the mutants with a weak pathogenicity were induced by irradiation with ultraviolet rays(UV)to clear the role of toxins in the pathogenicity of M. roriduyn, and discussed the relation between the toxins and pathogenicity. Materials and methods Microorganisms and culture:M. yoriduyn(M9403) was isolated from infected mulberry leaves planted from mulberry field in Kagoshima Prefecture in 1994. M. roridum was incubated on potato sucrose agar medium(PSA:broth made of potato 200g, sucrose 20 g, agar 18 g/1 liter)at 25ーC and abundant spores were formed at 2 weeks after inoculation. The spores were washed with sterilized water 3 times and used.