Anti‐Fungal Compounds From the Deep‐Sea‐Derived <i>Tritirachium oryzae</i> –Inhibited <i>Phytophthora nicotianae</i> by Blocking TCA Cycle

Four new sesquiterpenes (1-4) and 34 known compounds (5-38) were isolated from the deep-sea-derived fungus Tritirachium oryzae. The structures of the new compounds were established by detailed analyses of the nuclear magnetic resonance (NMR), mass spectrometry (MS), optical rotatory dispersion (ORD), and electronic circular dichroism (ECD) data. An in vitro antifungal experiment was conducted against Phytophthora nicotianae, and compound 7 exhibited prominent inhibitory activity with an EC₅₀ value (5 days) of 18.189 µg/mL, surpassing the commercially available fungicide pyrimethanil. Further mechanism studies showed that compound 7 treatment disrupted hyphal morphology and increased membrane permeability in P. nicotianae, resulting in wrinkled and twisted mycelium, increased conductivity, and elevated malondialdehyde (MDA) content. With the increasing concentration of compound 7, succinate dehydrogenase (SDH) and NAD-malate dehydrogenase (NAD-MDH) enzyme activities gradually decreased, ultimately leading to the blockage of the tricarboxylic acid (TCA) cycle. In addition, compound 7 affected the activities of antioxidant enzymes in a concentration- and time-dependent manner, generally leading to a decrease in superoxide dismutase (SOD) and catalase (CAT) activities and fluctuations in peroxidase (POD) and phenylalanine ammonia lyase (PAL) activity. In conclusion, the present study revealed that naturally occurring terpenoids from marine T. oryzae could be used as novel anti-P. nicotianae molecules by blocking the TCA cycle, indicating the potential to develop agrochemical fungicides for tobacco protection.