Chaetoglobosins from Endophytic Chaetomium sp. UJN-EF006 Show Promising Fungicidal Activity against Botrytis cinerea

Nine unreported (1-9) and 15 known (10-24) chaetoglobosin alkaloids were separated from the endophytic Chaetomium sp. UJN-EF006, with their structures determined by extensive spectroscopic analyses. Their fungicidal activities against two agricultural pathogens, Botrytis cinerea and Sclerotinia sclerotiorum, were evaluated, and alkaloid 19 exhibited a more potent antifungal effect than the commercial fungicides azoxystrobin and carbendazim, with EC₅₀ values of 0.80 and 1.47 μg/mL toward the two pathogens, respectively. Further in vivo assays on tomato fruits and seedlings demonstrated that 19 could effectively control the invasion of B. cinerea. Mechanistically, alkaloid 19 caused severe morphological deformity of the fungal hyphae and destroyed the cellular components by damaging the integrity of the cell membrane and inducing oxidative stress. Phytotoxicity assay revealed that 19 showed little or no effect on the germination and shoots of Arabidopsis thaliana. These findings highlight the great potential of chaetoglobosin alkaloids as new promising fungicidal agents for crop protection.