In the search for antifungal agents from marine resources, we recently found that the culture filtrate of Trichoderma longibrachiatum SFC100166 effectively suppressed the development of tomato gray mold, rice blast, and tomato late blight. The culture filtrate was then successively extracted with ethyl acetate and n-butanol to identify the fungicidal metabolites. Consequently, a new compound, spirosorbicillinol D (1), and a new natural compound, 2′,3′-dihydro-epoxysorbicillinol (2), together with 11 known compounds (3–13), were obtained from the solvent extracts. The chemical structures were determined by spectroscopic analyses and comparison with literature values. The results of the in vitro antifungal assay showed that of the tested fungal pathogens, Phytophthora infestans was the fungus most sensitive to the isolated compounds, with MIC values ranging from 6.3 to 400 µg/mL, except for trichotetronine (9) and trichodimerol (10). When tomato plants were treated with the representative compounds (4, 6, 7, and 11), bisvertinolone (6) strongly reduced the development of tomato late blight disease compared to the untreated control. Taken together, our results revealed that the culture filtrate of T. longibrachiatum SFC100166 and its metabolites could be useful sources for the development of new natural agents to control late blight caused by P. infestans.

Microbial metabolites have been recognized as an important source for the discovery of new antifungal agents because of their diverse chemical structures with novel modes of action. In the course of our screening for new antifungal agents from microbes, we found that culture filtrates of two fungal species Aspergillus candidus SFC20200425-M11 and Aspergillus montenegroi SFC20200425-M27 have the potentials to reduce the development of fungal plant diseases such as tomato late blight and wheat leaf rust. From these two Aspergillus spp., we isolated a total of seven active compounds, including two new compounds (4 and 6), and identified their chemical structures based on the NMR spectral analyses: sphaeropsidin A (1), (R)-formosusin A (2), (R)-variotin (3), candidusin (4), asperlin (5), montenegrol (6), and protulactone A (7). Based on the results of the in vitro bioassays of 11 plant pathogenic fungi and bacteria, sphaeropsidin A (1), (R)-formosusin A (2), (R)-variotin (3), and asperlin (5) exhibited a wide range of antimicrobial activity. Furthermore, when plants were treated with sphaeropsidin A (1) and (R)-formosusin A (2) at a concentration of 500 μg/ml, sphaeropsidin A (1) exhibited an efficacy disease control value of 96 and 90% compared to non-treated control against tomato late blight and wheat leaf rust, and (R)-formosusin A (2) strongly reduced the development of tomato gray mold by 82%. Asperlin (5) at a concentration of 500 μg/ml effectively controlled the development of tomato late blight and wheat leaf rust with a disease control value of 95%. Given that culture filtrates and active compounds derived from two Aspergillus spp. exhibited disease control efficacies, our results suggest that the Aspergillus-produced antifungal compounds could be useful for the development of new natural fungicides.

BACKGROUND In the search for new natural resources showing antifungal activity, we found that the methanol extract of Pterocarya tonkinensis (Fr.) Dode suppressed the disease development caused by fungi. The objectives of this article were (i) to isolate and identify the antifungal substances from the Pterocarya tonkinensis extract based on a bioassay‐guided fractionation and (ii) to investigate their potential as a biocontrol agent with their antifungal activities in vitro and in vivo. RESULTS Eighteen compounds were identified from the methanol extract of Pterocarya tonkinensis, including two new natural products 1 and 2: 1, pterocaryalactone; 2, pterocaryafuranone; 3, (1S, 6R)‐9‐hydroxymegastigm‐7‐en‐3‐one; 4, (S)‐dimethyl malate; 5, α‐linolenic acid; 6–8, α‐tetralones; 9, (R)‐methyl‐2‐hydroxyl‐3‐phenyl‐propanoate; 10, (E)‐4‐hydroxycinnamic acid methyl ester; 11–14, diarylheptanoids, and 15–18, pentacyclic triterpenoids. Based on the results of the in vitro antifungal assay, Magnaporthe oryzae and Phytophthora infestans were the most sensitive to the isolated compounds among the tested phytopathogenic fungi. When ten active compounds were applied onto plants at a concentration of 100 or 500 μg mL−1, compounds 1 and 8 effectively suppressed rice blast disease, and compounds 15 and 16 not only strongly reduced the development of blast on rice but also effectively controlled the development of late blight on tomatoes. CONCLUSION This is the first report to evaluate the in vitro and in vivo antifungal activities of the isolated compounds from a methanol extract of Pterocarya tonkinensis against phytopathogenic fungi, and our results suggest that Pterocarya tonkinensis and its substances can be used as a source to develop natural fungicides. © 2020 Society of Chemical Industry