Antimicrobial and Herbicidal Secondary Metabolites from Insect-Associated Fungus Leptosphaeria sp. FZN28 in Mecopoda elongata

The global food security faces significant threats from phytopathogenic microbes and weeds. In this study, seven secondary metabolites (1–7) were isolated from the insect-associated fungus Leptosphaeria sp. FZN28 in Mecopoda elongata. Their structures were elucidated through a combination of spectroscopic analyses. In bioactive assays, peniciphenalenin E (1) exhibited great antimicrobial activities against Phytophthora capsici and Sclerotinia sclerotiorum, with EC50 values of 8.8 and 10.8 μg/mL, respectively. Scleroderolide (2) demonstrated EC50 values of 20.4 and 14.8 μg/mL against the same strains, respectively. Notably, as seen with in vitro assays, 100 μg/mL of 1 could effectively prevent infection of P. capsici with a protection efficacy of 69.1%, and compounds 1 and 2 at a concentration of 200 μg/mL could greatly inhibit disease development in S. sclerotiorum-infected cole leaves with inhibitory efficacies of 66.9% and 61.0%, respectively. Moreover, the two compounds could also affect the hyphal morphology of S. sclerotiorum and P. capsici via scanning electron microscope and transmission electron microscope. Additionally, compounds 1 and 2 at a concentration of 200 μg/mL could significantly inhibit the radicle growth and germ elongation of monocotyledon weed and dicotyledon weed, Echinochloa crusgalli and Eclipta prostrata. Considering their antimicrobial and herbicidal activities, compounds 1 and 2 showed promise for the development of new bio-pesticides.