| Summary: | Soil-borne pathogens, including phytopathogenic fungi and root-knot nematodes, could synergistically invade vegetable roots and result in serious economic losses. The genus of <i>Trichoderma</i> has been proven to be a promising reservoir of biocontrol agents in agriculture. In this study, the search for antagonistic metabolites from a marine-derived fungus, <i>Trichoderma longibrachiatum,</i> obtained two structural series of sesquiterpenes <b>1</b>−<b>6</b> and cyclodepsipeptides <b>7</b>−<b>9</b>. Notably, the novel <b>1</b> was a rare norsesquiterpene characterized by an unprecedented tricyclic-6/5/5-[4.3.1.0<sup>1,6</sup>]-decane skeleton. Their structures were elucidated by extensive spectroscopic analyses, while the absolute configuration of novel <b>1</b> was determined by the comparison of experimental and calculated ECD spectra. The novel <b>1</b> and known <b>2</b> and <b>3</b> showed significant antifungal activities against <i>Colletotrichum lagrnarium</i> with MIC values of 8, 16, and 16 μg/mL respectively, even better than those of the commonly used synthetic fungicide carbendazim with 32 μg/mL. They also exhibited antifungal potential against carbendazim-resistant <i>Botrytis cinerea</i>. Cyclodepsipeptides <b>7</b>−<b>9</b> showed moderate nematicidal activities against the southern root-knot nematode (<i>Meloidogyne incognita</i>). This study constitutes the first report on the antagonistic effects of metabolites from <i>T. Longibrachiatum</i> against soil-borne pathogens, also highlighting the integrated antagonistic potential of marine-derived <i>T. Longibrachiatum</i> as a biocontrol agent.
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