Biofertilizer and Antifungal Potential of Streptomyces spp. in Greenhouse-Grown Tomato Plants (Solanum lycopersicum Mill.).

Fusarium oxysporum f. sp. lycopersici is one of the most destructive soilborne pathogens affecting tomato production, reducing plant growth and yield and highlighting the need for sustainable management alternatives. Streptomyces spp. are promising microbial candidates due to their ability to combine antifungal activity with plant growth promotion characteristics. The objective of this study was to evaluate the biofertilizer and antifungal potential of Streptomyces spp. in Chonto tomato (Solanum lycopersicum Mill.) under greenhouse conditions. Seventy actinobacterial strains were screened in vitro against F. oxysporum, and eight exhibited significant antagonistic activity. Based on antagonistic activity, enzymatic profile, cytotoxicity, and plant growth-promoting potential, strains 1B260 and 445 were selected for greenhouse assays. Strain 1B260 achieved 43.5% mycelial growth inhibition and showed the highest phosphate-solubilizing capacity (420 µg/mL), while both strains displayed proteolytic and cellulolytic activity, low cytotoxicity in human skin cell lines (HaCaT and HDFa), nitrogen fixation, and ammonia production. In greenhouse assays under non-infected conditions, 1B260 showed the most consistent biofertilizer effect, promoting stem elongation. Under pathogen pressure, strain 445 improved plant performance compared to the infected control. Overall, strains 1B260 and 445 exhibited complementary roles in tomato crop management, highlighting the potential of multifunctional Streptomyces inoculants for sustainable biofertilization and biocontrol strategies.