Antagonistic Activity of Bacillus velezensis Strains Against Fusarium oxysporum and Sclerotinia sclerotiorum In Vitro and In Vivo

Abstract

Soil-borne fungal pathogens such as Fusarium oxysporum and Sclerotinia sclerotiorum cause severe economic losses in numerous agricultural crops worldwide. The increasing concerns regarding environmental contamination and pathogen resistance associated with chemical fungicides have intensified interest in biological control alternatives. The present study evaluated the antagonistic activity of different Bacillus velezensis strains against F. oxysporum and S. sclerotiorum under both in vitro and in vivo conditions. Bacterial isolates were screened for antifungal potential using dual culture assays, inhibition zone measurements, and evaluation of mycelial growth suppression. Significant variation in antagonistic efficacy was observed among the tested strains, with certain isolates exhibiting strong inhibitory effects against both fungal pathogens. Microscopic observations revealed abnormalities in fungal hyphae, including deformation, shrinkage, and disruption of mycelial growth in the presence of bacterial metabolites. Greenhouse and pot experiments further demonstrated that selected B. velezensis strains effectively reduced disease incidence and severity in inoculated plants while enhancing plant growth and vigor. The antagonistic mechanisms were associated with the production of antifungal compounds, competition for nutrients and space, and possible induction of host defense responses. In vivo treatments showed improved plant survival and reduced pathogen colonization compared to untreated controls. The integration of laboratory and greenhouse evaluations confirmed the biocontrol potential of B. velezensis strains against destructive soil-borne pathogens. The findings highlight the applicability of these bacterial strains as eco-friendly biological control agents for sustainable disease management and reduced dependence on synthetic fungicides in agricultural production systems.