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Physiology and Biochemistry

Mode of Action of Ferimzone, a Novel Systemic Fungicide for Rice Diseases: Biological Properties Against Pyricularia oryzae in Vitro. Tetsuro Okuno, Senior research scientist, Plant Protection Research Laboratories, Agro Division, Takeda Chemical Industries Ltd., Ichijoji, Sakyoku, Kyoto 606, Japan; Iwao Furusawa(2), Kazuho Matsuura(3), and Jiko Shishiyama(4). (2)(4)Associate professor and professor, Laboratory of Plant Pathology, Faculty of Agriculture, Kyoto University, Kitashirakawa, Sakyoku, Kyoto 606, Japan; (3)Head research scientist, Plant Protection Research Laboratories, Agro Division, Takeda Chemical Industries Ltd., Ichijoji, Sakyoku, Kyoto 606, Japan. Phytopathology 79: 827-832. Accepted for publication 13 February 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-827.

Ferimzone (TF-164), (Z)-o-methylacetophenone 4, 6-dimethyl-2-pyrimidinyl-hydrazone, inhibited the mycelial growth of Pyricularia oryzae by more than 96% at 5 g/ml; the inhibition was observed about 4 hr after addition of ferimzone. Ferimzone at 20 g/ml did not inhibit spore germination, and germ tubes grew to several cells with an apparently normal nucleus in each cell. However, the cytoplasm of the spores and hyphae were granulated and localized. Application of fluorescent probes such as calcofluor white, aniline blue, and FITC-conjugated lectins did not reveal any effect of ferimzone in the cell wall architecture of mycelia. The activity of ferimzone was nullified by incubating the treated spores or mycelia in the toxicant-free medium. This suggests that the action of ferimzone is fungistatic and that the binding of ferimzone to cellular target components are rather loose. Ferimzone did not affect the respiratory activity of the mycelia of P. oryzae. Ferimzone caused the leakage of some electrolytes from mycelia, which decreased the pH of the medium, suggesting that ferimzone disrupted membrane function.

Additional keywords: antifungal activity, membrane function, rice blast.