Abstract: The potential application of strain YNK-FB0022 in the sustainable management of plant diseases was assessed, providing a foundation for its future industrial development. The strain was characterized through both morphological and molecular biological techniques to determine its taxonomic classification. Single-factor and response surface methodology were employed to optimize its fermentation medium and conditions. The biofilm-forming capacity of the strain was evaluated using a 48-well plate assay, while scanning electron microscopy was utilized to examine its colonization on the root surface of tomato seedlings. Pot experiments were performed to assess the impact of the strain on tomato seedling growth, its efficacy in controlling tomato wilt disease, and the activity of defense-related enzymes in the tomato roots.The strain YNK-FB0022 was identified as Bacillus halotolerans. The optimal fermentation medium for YNK-FB0022 was composed of 15.00 g/L sucrose, 6.25 g/L yeast extract, 8.75 g/L MgSO₄·7H₂O, and 10.00 g/L peptone, with fermentation conditions set at 30℃, pH 5.5, 200 rpm, and a liquid volume of 200 mL. Following optimization, the strain exhibited a 173.35% increase in growth, and its antibacterial activity improved by 7.56%. In the 48-well plate assay, each well formed 189 mg of biofilm, and the strain successfully colonized the root surface of tomato seedlings, with a colonization density of 1.20×10⁷ CFU/mm. Pot trials demonst rated that the optimized YNK-FB0022 fermentation broth significantly enhanced several agronomic traits of tomato seedlings, including plant height, stem diameter, root length, root weight, as well as the fresh and dry weight of aerial parts. Moreover, the broth exhibited substantial protective effects against tomato wilt disease and significantly increased the activity of root defense enzymes, such as POD, SOD, PPO, and CAT. These findings provide a theoretical basis for the development of the Bacillus halotolerans YNK-FB0022 as a biocontrol agent and its application in the management of tomato wilt disease.

Key words: Bacillus halotolerans, single-factor experiment, response surface optimization, tomo wilt disease, defense enzym activity