Inactivation of Rhizoctonia solani toxin by a putative alpha-glucosidase from coconut leaves for control of sheath blight disease in rice

Inactivation of a host-specific toxin, RS-toxin, induced by Rhizoctonia sol ani, the cause of rice sheath blight disease was investigated. A putative a lpha -glucosidase identified based on enzyme assay and Western blot analysi s was purified from coconut (Cocos nucifera; the only known non-host of R. solani) leaves and tested for its efficacy in degrading RS-toxin. SDS-PAGE analysis showed the appearance of a 97 kDa protein, which appeared in prote ins extracted from coconut leaf bits during 48 and 96 h after RS-toxin-trea tment and the protein eventually disappeared. A comparison of the u.v. spec tra read at 150-300 nm revealed conspicuous disturbances in the absorbance at 24 h of incubation of RS-toxin with the coconut leaf protein extracts as compared to that at 12 h, indicating the possible degradation of RS-toxin by coconut leaf alpha -glucosidase during incubation. Incubation of rice le af sheath bits with coconut leaf protein extracts significantly reduced ele ctrolyte leakage due to RS-toxin 30 min after the toxin treatment. Simultan eously, there was a significant reduction in sheath blight symptoms when th e incubation of rice leaf sheaths with the coconut leaf protein extracts wa s extended up to 96 or 120 h. This appears to be the first report of purifi cation and characterization of a putative plant alpha -glucosidase.