Role of a Host-specific Toxin Produced by Rhizoctonia solani in Suppression of Defense Mechanisms in Rice

The effect of a host-specific toxin produced by Rhizoctonia solani, the rice sheath blight pathogen on the elicitor-induced accumulation of phenolics and activities of phenylalanine ammonia-lyase, chitinase and ß-1,3-glucanase in rice was studied. Treatment of rice leaf sheaths with elicitor isolated from the mycelial walls of R. solani induced the accumulation of phenolics and activities of phenylalanine ammonialyase, chitinase and ß-1,3-glucanase. Maximum increase was observed 48 h after treatment. The phenolic content and phenylalanine ammonia-lyase, chitinase and ß-1,3-glucanase activities were significantly reduced when rice leaf sheaths were treated with R. solani toxin. Pretreatment of rice leaf sheaths with toxin suppressed the elicitor-induced accumulation of phenols and activities of phenylalanine ammonia-lyase, chitinase and ß-1,3-glucanase.