Development of Wettable Powder of Bacillus velezensis D-3A and Its Control Efficacy against Tobacco Bacterial Wilt

Bacillus velezensis D-3A, an elite biocontrol strain, was studied for the purpose of optimizing its formulation into a wettable powder (WP) for better application and utilization. A single-factor experimental design was employed to identify the carrier, adjuvant, and their composite ratio that minimally impacted the activity of B. velezensis D-3A. Field trials were conducted to assess the efficacy of the formulated WP against tobacco bacterial wilt caused by Ralstonia solanacearum. The optimal formulation and proportion of the B. velezensis D-3A WP were determined as follows: 85% kaolin as the carrier, 4.8% Tween 80, 7.2% polyethylene glycol, 2% sodium carboxymethyl cellulose, and 1% sorbitol. The viable count of the preparation was 1.37×10¹⁰ cfu/g, fineness 96%, wetting time 14.49 s, suspension rate 95.48%, drying reduction 2.67%, a pH of 7.52, and impurity rate 0, all of which complied with national standards. The results of continuous storage experiments demonstrated that after 180 days of storage, the spore survival rate reached 85.85% at 4℃ and 79.30% at 25℃. Field trials demonstrated that the B. velezensis D-3A WP achieved disease control efficacies of 50.98% and 53.64% on the 7th and 14th days post-treatment, respectively. The B. velezensis D-3A WP exhibits promising efficacy against tobacco bacterial wilt, indicating its potential for further development and application.