Biocontrol of tomato bacterial wilt by a combination of Bacillus subtilis GSJB-1210 and ningnanmycin

Bacillus subtilis GSJB-1210 with strong antagonism against Ralstonia solanacearum was combined with different bactericides to investigate its ability to mitigate tomato bacterial wilt. The control activity of six bactericides and GSJB-1210 against tomato bacterial wilt was determined via the bacteriostasis assay, and the concentration for 50% of maximal effect (EC50) value was calculated. The compatibility of the bactericide and GSJB-1210 was determined by ultraviolet spectrophotometry, and the compound scheme was determined by the Horsfall method. The EC50 of ningnanmycin was 3.66 mg/L and it had good biocompatibility with the GSJB-1210 strain. When ningnanmycin (3.66 mg/L) was combined with GSJB-1210 (1.0 x 108 CFU/mL) at a volume ratio of 4:6, the mitigation effect on tomato bacterial wilt reached 77.02%, which was significantly higher than that of the individual agents. To determine the impact of GSJB-1210 on the tomato rhizosphere microbial communities, the V3-V4 regions of 16S rRNA were amplified. The & alpha;- and & beta;-diversity of tomato rhizosphere bacteria were increased and the relative abundance of potential beneficial bacteria at genus level (Pseudomonas and Burkholderia) was improved. Ningnanmycin can be combined with B. subtilis GSJB-1210 to control bacterial wilt, with a significant synergistic effect. Mixed application can reduce the required amount of chemical pesticides by half. This combination can be used as a novel biocontrol agent to attain sustainability in disease management due to its intense antibacterial activity and ability to transform the microbial community structure toward a healthy state.