Isolation, identification, derivatization and phytotoxic activity of secondary metabolites produced by Cladosporium oxysporum DH14, a locust-associated fungus

Three main phytotoxic compounds including lunatoic acid A (1), 5Z-7-oxozeaenol (2) and zeaenol (3) were isolated from the fermentation broth of Cladosporium oxysporum DH14, a fungus residing in the locust (Oxya chinensis) gut. Two additional derivative compounds, compound 1a and 1b, were synthesized by methylation and chlorination of compound 1, respectively. The structures of such compounds were identified on the basis of spectroscopic analysis and by comparison of the corresponding data to those previously reported in the literature. Compounds 1-3 exhibited significantly phytotoxic activities against the radicle growth of Amaranthus retroflexus L. with the 50% inhibitory concentrations (IC50 values) of 4.51, 4.80 and 8.16 μg mL−1, respectively, which is comparable to that positive control 2,4-dichlorophenoxyacetic acid (IC50=1.95 μg mL−1). Furthermore, the compound 1 showed selective phytotoxic activity with the inhibition rate of less than 22% against the crops of Brassica rapa L., Sorghum durra, Brassica campestris L., Capsicum annucm and Raphanus sativus L. under the concentration of 100 μg mL−1. Both derivatives of compound 1 had moderate phytotoxic activity against the radicle growth of A. retroflexus L. The findings of our present study suggest that these compounds provide new promising candidates for the potential management strategies of weeds.