Antagonistic activities of Bacillus subtilis strains newly isolated from rhizosphere against phytopathogenic fungi responsible for Fusarium wilt of tomato

Tomato wilt caused by Fusarium wilt is a devastating soil-borne disease. It is caused by Fusarium fungi, which can live in the soil for more than ten years in the form of chlamydospores, making the illness difficult to manage. The main goal of this study was to evaluate the antifungal potential of three Bacillus subtilis strains (S2DSP-B2C-BM14) recently isolated from agricultural soils and identified by 16S PCR against the two fungi Fusariumoxysporum and Fusariumsolani isolated from tomato using three different methods in vitro. In both confrontation modes, the three Bacillus subtilis bacteria (S2DSP-B2C-BM14) displayed antagonistic tendencies against the two fungal phytopathogens, with Fusariumoxysporum being the most effective. They significantly reduced the mycelial growth of the two treated fungi, with significant inhibition rates that differed significantly depending on incubation time, with the most significant inhibit ion rates against Fusariumoxysporium being 85.43 +/- 00.62%, 84.42 +/- 00.76% 83.92 +/- 1.60%respectively, after 04 days of incubation in the indirect confrontation. This demonstrates that all three bacteria can generate and emit antifungal volatile compounds. The rates of inhibition of mycelial growth of the two phytopathogenic fungi obtained after treatments based on the acellular supernatants of the cultures of different ages of each antagonist bacterium, which range from 44.45 +/- 6.31% and 70.15 +/- 4,78%, confirmed that the antagonistic activities of the bacteria used in this study, as revealed in the co-culture tests, are primarily derived from diffusible secondary metabolites. Optical microscope analysis has revealed that these treatments, particularly the one involving the S2DSP strain, cause substantial alterations in the cellular morphologies of the two fungi studied, including hyphae cell wall breakdown. The three bacterial strains studied were shown to have strong antagonistic properties, indicating that they could be useful biological control agents for Fusarium wilt of tomato in the field and after harvest.