Antagonistic Potential of Streptomyces spp. Isolated from Suppressive Soils Against Rhizoctonia solani and Fusarium spp.

Abstract

Soilborne fungal pathogens such as Rhizoctonia solani and Fusarium spp. are responsible for significant yield losses in diverse crop systems, necessitating sustainable biocontrol alternatives. The present study evaluates the antagonistic potential of Streptomyces spp. isolated from disease-suppressive soils against these pathogens under in vitro and greenhouse conditions. Soil samples were collected from fields with a history of low disease incidence, and actinobacterial isolates were obtained using selective media. The isolates were screened for antifungal activity using dual culture assays, and inhibition zones were measured to assess antagonistic strength. Several Streptomyces isolates exhibited strong mycelial growth inhibition of both pathogens, indicating broad-spectrum antifungal potential. Selected isolates were further evaluated for plant growth–promoting traits, including production of chitinases, cellulases, siderophores, and indole-3-acetic acid. Microscopic observations of pathogen hyphae exposed to Streptomyces culture filtrates revealed structural deformities, hyphal lysis, and cytoplasmic leakage, suggesting enzymatic and antibiotic-mediated antagonism. Greenhouse trials demonstrated reduced disease incidence and improved plant growth parameters in treated plants compared to untreated controls. Disease suppression was more pronounced against R. solani than Fusarium spp., indicating differential sensitivity among pathogens. The study highlights the importance of suppressive soils as reservoirs of beneficial Streptomyces with strong biocontrol potential. Overall, the findings demonstrate that selected Streptomyces spp. can effectively inhibit soilborne fungal pathogens through multiple mechanisms and can be integrated into sustainable disease management strategies. These results support the development of microbial inoculants for environmentally friendly control of R. solani and Fusarium-induced diseases in agricultural systems.