Application of fungal phytotoxins is one of the possible solutions to reduce the use of chemical products in agricultural fields. Phytotoxic compounds isolated from phytopathogenic fungi provide a promising source of environmentally friendly herbicides. This paper focuses on the phytotoxic fungus Coniolariella gamsii Iran 2506C as a fungal pathogen against Iranian knapweed (Centaurea depressa) in the western Iran and investigate its phytotoxic constituents. The fungal pathogen was identified on the basis of morphological characteristics and confirmed by sequencing of the internal transcribed spacer (ITS) region and partial LSU rDNA gene. Pathogenicity tests were conducted on the weed seedlings and C. gamsii Iran 2506C isolate with high disease severity was selected for phytotoxin studies. Phytotoxic activity of the isolate was checked by screening the production of phytotoxins, which interestingly inhibited seed germination and seedling growth of Iranian knapweed as compared to wheat in the bioassays. The active metabolites were extracted from cell-free culture filtrate (CFCF) by ethyl acetate and separated by thin layer chromatography (TLC). The results indicated that two out of four spots had phytotoxicity with Rf values of 0.43 and 0.82 on the weed, whereas wheat was not sensitive in the bioassays. Using Gas Chromatography-Mass spectrometry (GC-MS), 3-Carene and Oleic acid were identified as the main constituents and quantified by a gas chromatographic method with 12.7 ± 0.03 and 2.9 ± 0.01 μg ml−1 respectively. This is the first finding presented on the phytotoxic effects of the active metabolites of C. gamsii Iran 2506C and highlights its herbicidal potential which can be used as a biocontrol agent of C. depressa.
