P-628 - Exploring the antagonistic potential of Slafractonia legumincola and its metabolites on soil-borne fungal plant pathogens.

Fungal endophytes are increasingly recognized for their role in enhancing plant health, defense against herbivores, pathogens, and resilience against biotic stress. Slafractonia leguminicola, an endophyte of red clover (Trifolium pratense) and other legumes, produces swainsonine and slaframine alkaloids known for toxicity in livestock and their potential anti-cancer properties. However, its role in plant-fungal interactions and fungal pathogen suppression remains unclear. In this study, we assessed the antagonistic activity of S. leguminicola against four agriculturally important phytopathogens:  Rhizoctonia solani, Fusarium oxysporum, Verticillium sp., and Phytophthora capsici, using several in vitro assays: dual culture, cellophane overlay, culture removal and agar well diffusion methods. In dual culture assays, S. leguminicola inhibited F. oxysporum, P. capsici, and Verticillium sp. but not R. solani, likely due to its faster growth. The cellophane overlay assay and the culture removal method resulted in reduced pathogen growth, suggesting the presence of diffusible metabolites. Notably, in the agar well diffusion assay, culture filtrates produced clear inhibition zones against multiple pathogens. Collectively, these results suggest that S. leguminicola secretes potent, bioactive, diffusible antifungal metabolites that can suppress the growth of plant pathogens. Our findings highlighted the potential of S. leguminicola as a natural biocontrol agent, hence, further investigation into its metabolites and mechanisms of action for sustainable disease management is imperative.