Induction of resistance against rice blast disease by a novel class of plant activator, pyrazolecarboxylic acid derivatives

Synthesis and characterization of anti-rice blast activity of pyrazole derivatives was described. Structure-activity relationship study indicated that a carboxyl group at 5-position of 1-methyl-1H-pyrazole played an important role in the activity and that a halogen atom such as a chlorine or bromine at 3-position enhanced the activity. Among the derivatives, 3-chloro-1-methyl-1H-pyrazole-5-carboxylic acid (CMPA) exhibited the highest anti-rice blast activity with the ED80 (80% effective dose, the concentration needed for 80% inhibition of disease development) of 0.05 mg/pot. CMPA did not have any significant effects on the hyphal growth, spore germination, and appressorium formation of Pyricularia oryzae, suggesting that CMPA induces systemic acquired resistance in rice plants.