Antagonistic Activity and Secondary Metabolite Profiles of Bacillus licheniformis Against Sclerotinia sclerotiorum on Sunflower

Abstract

Bacillus licheniformis is recognized as an important biological control agent due to its ability to produce diverse antimicrobial compounds effective against several phytopathogens. The present study evaluated the antagonistic activity and secondary metabolite profiles of Bacillus licheniformis against Sclerotinia sclerotiorum, the causal agent of stem rot disease in Sunflower. Diseased sunflower samples exhibiting characteristic symptoms of stem and head rot were collected, and the pathogen was isolated and identified based on morphological and cultural characteristics. Antagonistic efficacy of B. licheniformis was assessed under in vitro conditions using dual culture and culture filtrate assays. The bacterial isolate significantly inhibited mycelial growth of S. sclerotiorum, causing hyphal deformation and suppression of sclerotial formation. Secondary metabolites produced by B. licheniformis were extracted and analyzed using chromatographic and spectroscopic techniques, revealing the presence of bioactive compounds such as lipopeptides, peptides, and other antifungal metabolites associated with pathogen inhibition. The metabolites demonstrated strong antifungal activity by disrupting fungal cell integrity and reducing pathogen growth. Greenhouse studies further confirmed the biocontrol potential of B. licheniformis, where treated sunflower plants showed reduced disease severity and improved plant vigor compared to untreated controls. The results indicate that B. licheniformis possesses significant antagonistic properties and produces effective secondary metabolites capable of suppressing S. sclerotiorum. This study highlights the potential application of B. licheniformis as an eco-friendly and sustainable biological control agent for managing stem rot disease in sunflower cultivation and reducing dependence on chemical fungicides.