Bedlogs of shiitake, Lentinula edodes (Berk.) Pegler, are often attacked by Trichoderma spp. such as T. harzianum Rifai and T. polysporum Rifai, which produce antifungal substances and mycolytic enzymes. However, shiitake is more or less able to reject Trichoderma attacks. Shiitake cultures possess at least five straight-chain alcohols with double and triple bonds, which act as antifungal substances. Trichoderma inoculation tests for shiitake cultures showed that the resistance of shiitake in a wood-powder medium correlated positively with that in bedlogs when T. harzianum was used. Screening assays using the wood-powder medium showed some highly resistant and susceptible strains among 164 different wild shiitake strains. Monokaryons derived from basidiospores of a highly resistant strain, TMI-407, had high rejecting abilities compared with those from a susceptible strain, TMI-1161. Crossing between monokaryons from the two strains revealed that resistance was dominant. In general, these resistant mycelia produced much more antifungal substances than did susceptible mycelia. Key words: Lentinula edodes, shiitake, mushroom cultivation, resistance to Trichoderma spp., selection method, antagonism.

The present study was carried out to investigate the applicability and usefulness of the protoplast isolation and regeneration method as a new technique for artificially dedikaryotizing Lentinula edodes dikaryons. When protoplasts derived from dikaryons were incubated in a regeneration agar medium at 25°C, about 11% of them individually started regeneration into hyphae within 3 days and formed visible colonies, varying in size, after 7 days of incubation.By isolating preferentially smaller colonies out of these visible colonies, it was found that neohaplonts could be obtained at the high frequencies of 40-92% in every dikaryon sampled and that the two-component nuclear types appeared. These neohaplonts showed considerable variation of mycelial growth rates.However, robust neohaplonts exhibited no apparent change in biological properties such as colony morphology, and electophoretic zymograms of esterase and malate dehydrogenase, suggesting that they might retain the original genetic traits. From these results, it is concluded that the protoplast regeneration method for dedikaryotizing L. edodes dikaryons is more useful than previous methods such as the physical procedure and chemical treatment.

Lentinus edodes (Berk.) Sing., •gShiitake•h mushroom, is well known as one of the most important edible fungi in Japan. Many reports on the biological natures of

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