Wheat straw biochar enhances rhizosphere colonization of Bacillus amyloliquefaciens B1408 for biocontrol of cucumber Fusarium wilt.

Abstract

Background: Plant growth-promoting rhizobacteria (PGPR) offer a sustainable alternative for managing soilborne diseases, yet their field efficacy is often compromised by poor rhizosphere persistence. Here, we tracked the spatiotemporal colonization dynamics of a GFP-labeled Bacillus amyloliquefaciens B1408 strain and developed a wheat straw biochar-based formulation to overcome this bottleneck.

Results: At 120 days post-inoculation, the biochar formulation increased B1408 populations from 7.49 × 10³ to 4.96 × 10⁴ CFU g^-1 in the rhizosphere soil and from 1.41 × 10⁴ to 7.58 × 10⁴ CFU g^-1 on the rhizoplane, corresponding to 6.62- and 5.36-fold increases, respectively. In pot trials, the formulation reduced the cucumber Fusarium wilt disease index from 73.33% to 20%. The WSBA treatment was associated with enhanced soil nutrient-cycling enzyme and plant antioxidant enzyme activities, altered rhizosphere microbial community structure, reduced the connectivity of FOC-associated microbial co-occurrence networks, and enriched several indigenous bacterial genera, including Allorhizobium and Sphingomonas. In validation assays, Allorhizobium sp. 813 and Ensifer sp. 4724 isolated from the WSBA-treated rhizosphere significantly increased cucumber plant height and fresh weight.

Conclusion: These findings demonstrate that wheat straw biochar enhances the rhizosphere persistence and biocontrol efficacy of B1408 and is associated with changes in rhizosphere microbial composition and network connectivity. This formulation provides a promising strategy for improving the stability and performance of B. amyloliquefaciens-based biocontrol agents. © 2026 Society of Chemical Industry.