From Biological Traits to Field Performance: Screening and Application of Tobacco Rhizosphere <i>Bacillus</i> Strains for Fusarium Root Rot Management

Tobacco Fusarium root rot, caused mainly by Fusarium oxysporum and F. solani, poses a major threat to tobacco production by severely impairing root function and reducing yield and quality. In the context of sustainable agriculture, biological control has gained increasing attention as an environmentally friendly and effective alternative to chemical pesticides. This study evaluated four tobacco rhizosphere Bacillus strains to clarify how key biological traits relate to field performance in controlling Fusarium root rot. Strains were assessed for antifungal activity, indole-3-acetic acid (IAA) production, chemotaxis toward root exudates, biofilm formation, and colonization capacity. Significant differences were observed, with G12 and G51 exhibiting the most favorable profiles. Both showed strong antifungal activity (42.42%-57.50%), robust chemotaxis toward root exudates from healthy tobacco plants (RCI up to 35.86), efficient biofilm formation, and successful colonization of tobacco tissues. Greenhouse assays demonstrated that G12 and G51 reduced disease indices to below 10.00 and achieved control efficacy above 90%, approaching that of chemical treatment. Multi-location field trials in 2024-2025 further confirmed their effectiveness, with both strains reducing disease incidence by more than 60% and consistently improving agronomic traits. G51 provided the most stable yield benefits across years and sites, while G12 and G51 also accelerated the decline of chlorophyll and leaf nitrogen content at later stages, suggesting a role in promoting earlier maturation. Overall, this study establishes a link between chemotaxis, biofilm formation, colonization, and field efficacy, underscoring the importance of integrating multiple biological traits when screening biocontrol agents. These findings provide scientific support for the application of tobacco rhizosphere Bacillus strains in the sustainable management of Fusarium root rot.