Abstract

The culture filtrates of Rhizoctonia solani was significantly toxic to rice leaves, being similar to that caused by R. solani. The culture filtrate from R. solani was extracted using ethyl acetate and isolated by silica gel column chromatography, which showed significantly high toxicity. The toxin was thermally stable even after incubation at 121°C for up to 30 min. A pH of 2.0 was helpful for pathogenesis; after 12 h, yellow lesions were found. The solvent system ethyl acetate/methanol (10:1, v/v) was the optimal solvent system used for preparative thin-layer chromatography. Eightfractions were chosen to be collected by silica gel column chromatography, but only three spots were obtained in the thin-layer chromatography analysis. The secondfraction was found to be the one with the highest activity and the toxin appeared to be mainly present in this fraction. The ultraviolet and infrared spectral data indicated that lactone, ketone and benzene groups existed in the culture filtrate. This report is the first describing the preliminary characterisation of phytotoxins from an R. solaniculture filtrate; it briefly presents the isolation, purification and bioassay method for the phytotoxin produced by R. solani.

Key words: Richard's medium, crude extracts, bioassay, thin-layer chromatography, silica gel column chromatography.