Optimization of Bacillus amyloliquefaciens Lx-11 suspoemulsion by response surface methodology to control rice bacterial blight

Bacillus amyloliquefaciens Lx-11 can effectively control rice bacterial blight. This study developed a new formulation of B. amyloliquefaciens to further improve its field utilization. This formulation was derived from a raw fermentation broth of B. amyloliquefaciens Lx-11, adsorbed by nano-level fume silica, and emulsified to prepare an oil-in-water B. amyloliquefaciens suspoemulsion (SE). Inert ingredients, including soybean oil, emulsifier ST (a mixture of Span 80 and Tween 80), ethylene glycol, AEC-9NA, and SY-6535 showed good biocompatibility with B. amyloliquefaciens strain Lx-11. A Plackett–Burman experiment demonstrated that sodium alginate, AEC-9NA, and glycol were significant factors affecting the count of viable B. amyloliquefaciens . In addition, results of the steepest ascent experiment showed that concentrations of the three significant factors influencing viability were 1.00 g l −1 for sodium alginate, 15.00 ml l −1 for AEC-9NA, and 20.00 ml l −1 for glycol. A Box-Behnken design was applied to describe the nature of the response surface in the experimental region, and the optimal formulation was determined as follows: 10% silica, 40% soybean oil, 8% ST, 1.51% AEC-9NA, 2.36% glycol, 0.08% sodium alginate, and 2% SY-6535. Under optimized conditions, the viable count of B. amyloliquefaciens Lx-11 SE was up to 9.3×10 8 colony forming units (cfu) per ml. The results showed that the regression equation model had satisfactory accuracy in predicting the viable count of B. amyloliquefaciens Lx-11 SE. Pot experiments indicated that spraying 200 ml 667 m −2 B. amyloliquefaciens Lx-11 SE effectively controlled rice bacterial blight with a control effect of 64.8–66.0%, equivalent to 20% Thiosen copper.