Isolation and Characterization of a Phytotoxin from Rhizoctonia solani: The Causal Agent of Rice Sheath Blight

Abstract

To isolate and characterize the bioactive components of the Rs-toxin produced by the rice sheath blight pathogen R. solani, various extraction and purification methods, several chemical reactions, ultraviolet- and visible-wavelength light scanning, gas chromatography/mass spectrometry (GC/ MS) and liquid chromatography-tandem mass spectrometry (LC/MS/MS) analyses, were used. The leaf floating soakage method was established for evaluating the phytotoxicity of Rs-toxin. The results of Molish's reaction, ninhydrin test and Fehling's reaction suggested that the bioactive components of Rs-toxin were carbohydrates other than amino acids or proteins. By using GC/ MS technique, the partially purified Rs-toxin was found to contain six saccharides. By means of peak area normalization, the relative amounts of these six saccharides were calculated. The result of LC/MS/MS indicated that neither phenylacetic acid nor its derivatives was detected in Rs-toxin. Taken together, it was concluded that Rs-toxin consists of six saccharides and has obvious maceration effects on rice leaf tissues.