Effective Applications of <i>Bacillus subtilis</i> and <i>B. amyloliquefaciens</i> as Biocontrol Agents of Damping-Off Disease and Biostimulation of Tomato Plants

Using <i>Bacillus</i> species as bioagents for environmentally sustainable and economically viable plant disease management is a viable strategy. Thus, it is important to promote their use in agriculture. In this study, two <i>Bacillus</i> species were isolated from the rhizosphere of tomato plants, while three fungal species were isolated from samples of tomato plants that were infected with damping-off disease. The <i>Bacillus</i> strains were tested in vitro for their antagonistic activity against fungal species using a dual culture technique. In a greenhouse experiment, the effectiveness of applying antagonistic bacteria with soilborne fungal disease on induced damping-off of tomato (cv. Super Strain B) plants, their physiological attributes, antioxidant enzymes, mineral content, and yield under greenhouse conditions during the 2022 and 2023 seasons were determined. The fungal isolates were identified as <i>Fusarium oxysporum</i> KT224063, <i>Pythium debaryanum</i> OP823136, and <i>Rhizoctonia solani</i> OP823124, while the <i>Bacillus</i> isolates were identified as <i>B. subtilis</i> OP823140 and <i>B. amyloliquefaciens</i> OP823147 on the basis of the rRNA gene sequences. The dual culture test revealed that <i>B. subtilis</i> outperformed <i>B. amyloliquefaciens</i> in resistance to <i>R. solani</i> and F. <i>oxysporum</i>, which were recorded as 28.33 and 33.00 mm, respectivley. In contrast, <i>B. amyloliquefaciens</i> caused the highest antagonistic effect against tested <i>P. debaryanum</i> fungus. Additionally, in a greenhouse experiment, tomato plants treated with each of these antagonistic <i>Bacillus</i> strains significantly suppressed fungal disease, displayed improved plant growth parameters, had an increased content of photosynthetic pigments, antioxidants enzymes, and total phenols, and an increased macronutrient content and yield during the two growing seasons. In conclusion, effective applications of <i>B. subtilis</i> and <i>B. amyloliquefaciens</i> had the potential to mitigate damping-off disease, which is caused by <i>F. oxysporum</i>, <i>P. debaryanum</i>, and <i>R. solani</i> in tomato plants, while simultaneously promoting growth dynamics.