Induction of resistance against rice bacterial leaf blight by 3-chloro-1-methyl-1H-pyrazole-5-carboxylic acid

A pyrazole derivative, 3-chloro- 1 -methyl- 1H-pyrazole-5 -carboxylic acid (CMPA), exhibited high anti-rice blast activity without any significant antimicrobial activity. To assess the mode of action of CMPA, its effects on rice bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae and the expression of a defenserelated gene were examined. The treatment of CMPA reduced the disease symptoms in a dose-dependent manner, but CMPA did not exhibit any direct antibacterial activity against X. oryzae at concentrations up to I mg/ml. The treatment of CMPA induced the expression of PBZI, a defense-related gene, which is evoked by several plant activators. This ability to induce PBZI expression and enhance disease resistance without antimicrobial activity suggests that CMPA can activate systemic acquired resistance in rice as well as in tobacco. (c) Pesticide Science Society of Japan.