Biocontrol efficacy of Trichoderma viride TVa199 against Fusarium wilt and growth promotion in cucumber through direct and indirect mechanisms.

Abstract

Fusarium oxysporum f. sp. cucumerinum is a destructive soilborne pathogen that causes Fusarium wilt in cucumbers. This study evaluated the antagonistic activity of the endophytic fungus Trichoderma viride TVa199 against F. oxysporum f. sp. cucumerinum and the mechanisms underlying its suppression of fungal virulence. TVa199 exhibited strong activity against F. oxysporum f. sp. cucumerinum, achieving 96.03 % inhibition in a dual culture assay. The culture filtrate, ethyl acetate, and methanol extracts of T. viride effectively inhibited mycelial growth, spore germination, and germ tube elongation of F. oxysporum f. sp. cucumerinum. The ethyl acetate extract caused severe damage to the morphology and ultrastructure of the hyphae and conidia of the pathogen, as evidenced by SEM and TEM observations. GC-MS analysis identified various bioactive secondary metabolites. Molecular docking predicted strong interactions between representative metabolites and virulence-associated proteins, including Avr2, M36 metalloprotease, and feruloyl esterase C. In the greenhouse experiments, the incidence of Fusarium wilt was reduced by 89.9 %, with a control efficacy of 87.5 % following the application of T. viride culture filtrate at 80 %. It also enhanced host defense by increasing phenolic content and defense-related enzyme activities while reducing oxidative stress markers. These results demonstrate that T. viride TVa199 suppresses F. oxysporum f. sp. cucumerinum via a multi-target mechanism involving direct microbial antagonism, disruption of fungal cellular integrity, and metabolite-mediated interference with virulence-associated proteins. This study provides mechanistic evidence that fungal secondary metabolites contribute to the suppression of pathogen virulence. These findings expand the current understanding of microbial antagonism beyond conventional growth inhibition and support the development of sustainable biocontrol strategies against Fusarium wilt.