Herbicidal and Antifungal Xanthone Derivatives from the Alga-Derived Fungus Aspergillus versicolor D5.

Fungi have been proved as promising and prolific sources of functional secondary metabolites with potent agricultural applications. In this study, 14 xanthone derivatives (1-14), including six new ones, versicones I-N (1-4, 7, 11), and a biogenetically related derivative (15), were isolated from the alga-derived fungus Aspergillus versicolor D5. Their structures were elucidated by comprehensive spectroscopic methods. Versicone L (4) exhibited a broad antifungal spectrum and prominent inhibitory effects on Botrytis cinerea at a minimum inhibitory concentration (MIC) of 152 µM, 7-fold stronger than that of the positive control, carbendazim (MIC = 1.05 × 103 µM). Dihydrosterigmatocystin (13) showed strong antifungal activity toward B. cinerea at MIC = 38.3 µM, almost 30-fold stronger than that of carbendazim. Meanwhile, 13 exhibited potent herbicidal activity toward Amaranthus retroflexus L. with an MIC of 24.5 µM, approximately 4-fold stronger than that of the positive control, glyphosate (MIC = 94.7 µM). Additionally, 13 also displayed remarkable activity against other weeds belonging to Amaranth sp. Analysis of the structure-herbicidal activity relationship indicated that the bifuranic ring played an important role in xanthone phytotoxicity and the presence of a double bond in the furan ring could decrease phytotoxicity. This study indicated that xanthones can be served as promising candidates for lead compounds of agrochemicals.

Phytotoxicity and anti-phytopathogenic activities of marine-derived fungi and their secondary metabolites.

To find new pesticides for agricultural use, 133 fungal strains were isolated from coastal marine habitats, from which 37 independent isolates were identified, belonging to 20 genera in nine orders, and the diversity of the isolated fungi were discussed. The phytotoxicity and anti-phytopathogenic fungal and bacterial activities of these 37 extracts, and two previously isolated fungal extracts were evaluated, displaying different levels of bioactivity. Based on the bioactive and chemical screening, an Alternaria sp. (P8) strain, which showed prominent bioactivity and contained abundant secondary metabolites was selected for further chemical investigation; one new compound, a benzopyranone (1), and seven known compounds (2-8) were obtained. Their structures were determined by analysing extensive NMR spectroscopic data and ECD comparisons. Compounds 1, 2, and 6-8 showed obvious phytotoxicity, especially against amaranth, and compound 1 also showed potent antifungal activity toward Alternaria brassicicola. To the best of our knowledge, this is the first report of the phytotoxicity of marine-derived fungi and their secondary metabolites. These studies should provide the foundation for future research into the use of such fungal extracts to combat weeds and diseases in agriculture.