Active Secondary Metabolites from Root-Associated Endophytic Fungus Aspergillus tubingensis ZMGR14 and Their Activities Against Plant Pathogenic Fungi

This study aimed to separate and characterize compounds from Aspergillus tubingensis ZMGR14. The antifungal activities of monomer compounds and the ethyl acetate (EtOAc) layer from the fermented liquor of A. tubingensis were isolated, purified and structurally identified. The EtOAc layer from the fermented liquor showed significant antifungal activity against Fusarium oxysporum and Alternaria alternata with IC50 values of 273.8 and 330.7 μg·mL−1, respectively. The EtOAc extract was further purified by column chromatography and recrystallization to yield six compounds. Antifungal trials showed that Cyclo-(L-Pro-D-Leu) (5) exhibited the highest inhibition against A. alternata and F. oxysporum, with an IC50 value of 48.1 and 232.7 μM, respectively, and cyclo-(L-Pro-L-Leu) (6) displayed moderate antifungal activity against Alternaria solani, with an IC50 value of 493.4 μM. The results suggest that the EtOAc extract of ZMGR14 and its bioactive compounds hold promise as environmentally friendly microbial fungicides.