Divergent ecological strategies of Bacillus velezensis Bac2 and Bacillus subtilis Bac1 Drive biocontrol of cucumber fusarium wilt

• Bacillus strains Bac1 and Bac2 reduced cucumber wilt by 75–87%. • Bac2 showed stronger biocontrol and growth promotion activity. • Bac1 and Bac2 acted via distinct ecological strategies. . Cucumber fusarium wilt, caused by Fusarium oxysporum f. sp. cucumerinum (FOC), is a devastating soil-borne disease that threatens global cucumber production. In this study, we isolated and characterized two highly antagonistic bacilli, Bacillus velezensis Bac2 and Bacillus subtilis Bac1. the strains will be characterized and their mechanisms will be explored A systematic evaluation of their biocontrol traits, plant growth promotion, and effects on the rhizosphere microbiome revealed distinct ecological strategies. Bac2 exhibited superior in vitro antagonism against FOC (58.72% inhibition) compared with Bac1 (48.79%), along with faster growth kinetics, enhanced biofilm formation, and higher production of bio-active metabolites (e.g., surfactin, iturin, and bacillaene). Pot experiments confirmed Bac2′s higher biocontrol efficacy (87.4%) against FOC and its superior ability to restore soil enzymatic functions and promote cucumber growth (plant height, stem diameter, fruit shape index) compared with Bac1 (75.1% efficacy). Rhizosphere microbiome analysis revealed divergent strategies: Bac2 promoted microbiome remodeling by enhancing diversity (e.g., enriching Pseudolabrys and Nitrolancea ), whereas Bac1 induced taxon-specific enrichment of Pseudomonas without significant structural change. These findings suggested distinct ecological mechanisms underlying the biocontrol activity of beneficial bacilli and provided insights for developing more sustainable approaches to support cucumber health management.