Evaluation of Biocontrol Efficacy of Bacillus velezensis HAB-2 Combined with Pseudomonas hunanensis and Enterobacter soli Against Cowpea Fusarium Wilt

Cowpea Fusarium wilt (CFW) is a soilborne fungal disease caused by <i>Fusarium oxysporum</i> f. sp. <i>tracheiphilum</i> (Fot), leading to substantial yield losses globally. This study evaluates the biocontrol potential of <i>Bacillus velezensis</i> HAB-2 and develops a microbial combination for effective disease management. <i>B. velezensis</i> HAB-2 suppressed <i>F. oxysporum</i> f. sp. <i>tracheiphilum</i> AIQBFO93 growth by 69.8% in vitro and exhibited multiple plant growth-promoting traits. Pot experiments demonstrated that HAB-2 alone achieved a 47.62% control rate against CFW. Furthermore, two compatible plant growth-promoting rhizobacteria (PGPR), <i>Pseudomonas hunanensis</i> HD33 and <i>Enterobacter soli</i> HD42, were isolated from the rhizosphere soil of cowpea previously treated with HAB-2. These two strains were combined with HAB-2 at different concentrations in 15 microbial combinations. The combined application of the three strains provided more consistent disease control, with the optimal combination demonstrating a 15.15% higher control rate than HAB-2 alone. Compared to the untreated control, this combination significantly increased cowpea fresh weight, leaf area, and plant height by 10.60%, 8.04%, and 7.81%, respectively, and upregulated the expression of defense-related genes, indicating enhanced resistance. These results confirm that <i>B. velezensis</i> HAB-2 is an effective biocontrol agent against wilt disease, and its synergistic application with functionally complementary PGPR strains provides a viable strategy for sustainable crop disease management.