Effect of N-Cyanomethy1-2-chloroisonicotinamide for Control of Rice Blast

Abstract

Eight N7'-alkyl-2-chloroisonicotinamides were synthesized and their control activities against rice blast was 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 the activities of compounds with saturated alkyl groups containing three or more carbon atoms were comparatively low. The efficacy of NCI against rice blast was remarkable when NCI was applied granularly 15 days before inoculation. In field tests, 240 g and 120 g a.i. of NCI/10 a had a good control effect even about 40 days after application. Five-hundred ppm of NCI did not inhibit the spore germination, appressorial formation, appressorial penetration, mycelial growth and melanization of Pyricularia 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. On the leaves of rice plants treated with NCI, the ratio of minute brownish lesions to the total number of blast lesions noticeably increased. Further, NCI effectively controlled bacterial leaf blight of rice when applied granulary. These results indicate that NCI is related to the resistant reaction of rice plants to the pathogen and that a partial structure of 2-chloroisonicotinamide is important for this activity. © 1990, Pesticide Science Society of Japan. All rights reserved.