An elicitor of the rice sheath blight pathogen Rhizoctonia solani exhibits dual function: Elicitation and suppression of tissue necrotization in rice

An elicitor has been isolated from Rhizoctonia solani, the rice sheath blight pathogen. When rice suspension-cultured cells were treated with the elicitor, increased activities of lipoxygenase and lipid peroxidation were observed within 6 h after treatment. H₂O₂ and superoxide anion were found to be produced in cultured cells within 10 min after elicitor treatment. Peroxidase, catalase, and superoxide dismutase activities also increased due to elicitor treatment. An increase in ascorbic acid content was observed in rice cultured cells within 6 h after elicitor treatment. Ascorbate peroxidase activity also increased. Ascorbic acid suppressed the elicitor-induced lipid peroxidation, lipoxygenase activity, phenolic accumulation and peroxidase-dependent oxidation of phenols. Thus the fungal elicitor not only induced cell and tissue necrotization but also defense-related activities such as activation of antioxidants and scavengers of active oxygen species. The importance of dual function of the elicitor in pathogenesis is discussed.