2-クロロイソニコチン酸アミド誘導体のイネいもち病防除活性と作用機構

抄録

Plant disease control with non-fungicidal compounds is an attractive idea, because it would not encourage the fungicide resistant strain. In thee course of study for new non-fungicidal anti-blast agent, N-phenylsulfonyl-2-chloroisonicotinamide (NPSI), synthesized for herbicide, was found to have anti-blast activity with application via root without any phytotoxicity. It was also found to be non-fungicidal against blast fungi, Pyricularia oryzae. So this compound was considered to be a lead compound of this study. 2-Chloroisonicotinamide derivatives were synthesized, and their anti-blast activities were determined by granular (submerged) application. Among them N-methyl-2-chloroisonicotinamide, N-cyanomethyl-2-chloroisonicotinamide (NCI) and N-propargyl-2-chloroisonicotinamide showed high activities and NCI was selected as the best one. The efficacy of NCI against rice blast was remarkable when NCI was applied granularly 15 days before inoculation. In field tests 240g and 120g a. i. of NCI/10 a had a good control effect 40 days after application, and also 2.4g and 1.6g a. i. of NCI/nursery tray had a good control effect about 50 days after application. Five-hundred ppm of NCI did not inhibit the spore germination, appressorial formation, appressorial penetration, mycelial growth and melanization of P. oryzae in vitro, indicating that NCI has substantially no antifungal activity. NCI significantly inhibited the mycelial growth of P. oryzae in rice sheath inoculation tests using rice plants treated with granular NCI. As the extracts of NCI treated leaves did not exhibit antifungal activity before P. oryzae inoculation, it is not possible that NCI turns into anti-fungal compound in rice plant. Heat treatment, abscisic acid, 2, 4-dinitrophenol and cycloheximide antagonized the NCI activity. In NCI treated rice plants, enzyme activities, such as lipoxygenase, phenylalanine ammonia lyase and peroxidase, were enhanced, when P. oryzae was inoculated. And the degree of lignification of cell wall was higher in NCI treated rice plant than in non-treated plant. These results indicate that NCI enhances the self-defence mechanism of rice plant against the disease. NCI is considered to be a new class of non-fungicidal anti-blast agent.