Secondary metabolites of rice sheath blight pathogen Rhizoctonia solani Kühn and their biological activities

Eight compounds were isolated from the fermentation cultures of rice sheath blight pathogen Rhizoctonia solani Kühn. They were identified as ergosterol (1), 6β-hydroxysitostenone (2), sitostenone (3), m-hydroxyphenylacetic acid (4), methyl m-hydroxyphenylacetate (5), m-hydroxymethylphenyl pentanoate (6), (Z)-3-methylpent-2-en-1,5-dioic acid (7) and 3-methoxyfuran-2-carboxylic acid (8) by means of physicochemical and spectroscopic analysis. Among them, 2, 3, 5–8 were isolated from R. solani for the first time. All the compounds were evaluated for their biological activities. 4–6 and 8 showed their inhibitory activities on the radical and germ elongation of rice seeds. 1, 4 and 7 showed moderate antibacterial activity to some bacteria. 4, 7 and 8 exhibited weak inhibitory activities on spore germination of Magnaporthe oryzae. 8 showed moderate antioxidant activity with the 1,1-diphenyl-2-picryhydrazyl (DPPH) and β-carotene-linoleic acid assays. This is the first time to reveal compounds 5, 6 and 8 from rice sheath blight pathogen R. solani to have in vitro phytotoxic activity.