Secondary Metabolites from the Marine-Derived Fungus Aspergillus udagawae SFC20170619-M03 Exhibiting Disease Control Activity

In our screening program for novel biocontrol agents, we found that the culture filtrate of the marine-derived fungus Aspergillus udagawae SFC20170619-M03 exhibited disease control activity against several fungal plant diseases, including tomato gray mold, tomato late blight, and pepper anthracnose. Bioassay-guided fractionation of the active extracts led to the isolation of sixteen secondary metabolites, comprising nine xanthones (1–9), three benzoquinones (10–12), three spirocyclic furanone lactams (13–15), and one polyene (16). Among these compounds, the xanthone derivative MS-347a (1), a principal bioactive metabolite of A. udagawae SFC20170619-M03, exhibited promising antifungal and antibacterial activities, with minimum inhibitory concentrations ranging from 3.2 to 100 μg/mL. In planta assays further demonstrated that MS-347a (1) effectively suppressed tomato gray mold, tomato late blight, and pepper anthracnose, with control efficacies from 55% to 94% at a concentration of 62.5 μg/mL. The nonepoxidized xanthone AGI-B4 (7) exhibited potent and selective anti-oomycete activity against Phytophthora infestans, with a control efficacy of 91% against tomato late blight at 500 μg/mL. The benzoquinone derivative fumigatin (10) exhibited relatively weaker but broaderspectrum antimicrobial activity in vitro and provided moderate suppression of tomato gray mold in vivo. Taken together, these findings suggest that A. udagawae SFC20170619-M03 and its bioactive metabolites represent promising resources for the development of environmentally sustainable biocontrol agents for agricultural applications.