Naturally Occurring Antidotes against Benzimidazole Fungicides

TLC bioautography using precoated glass thin-layer plates impregnated with benomyl or carbendazim (MBC), and Cladosporium herbarum as a test fungus was evaluated as a facil way to detect plant secondary m etabolites antidoting against benzimidazole fungicides. In ad­ dition to emodin and a-tocopherol from Polygonum sachalinense, three phenolics, 3,5-dihydroxy-4-methylstilbene and 5-methoxy-6,7-methylenedioxyflavone from P. lapathifolium, and 2,6-dimethoxybenzoquinone from P. thunbergii were isolated and characterized as new benzimidazole antidotes. Emodin exhibited the antidoting activity not only against benomyl but also against carbendazim (MBC), thiabendazole (TBZ), thiophanate-methyl and nocodazole. Furtherm ore, emodin showed antidoting activity against MBC in the wild-type Neurospora crassa and against diethofencarb in the m utant of N. crassa resistant to benzimid­ azole fungicides but highly susceptible to diethofencarb.