Development of 3 billion CFU/g Bacillus wettable powder and its control efficacy on potato Verticillium wilt and scab

Soilborne diseases such as potato Verticillium wilt and potato scab seriously affected the yield and quality of potato and no effective chemical is available to control the diseases. In this study, Bacillus subtilis HMB26553 and B. amyloliquefaciens PHODG36 were used as active ingredients to develop wettable powder (WP). After evaluating the doses of the wetting agent, dispersant, and UV protective agent, the optimal formulation of 3 billion CFU/g Bacillus WP was established as follows: 10% HMB26553 technical concentrate (TK), 10% PHODG36 TK, 1% wetting agent LT-569, 2% dispersant MF, 1% UV protective agent ascorbic acid, talc powder 76%. The spore content of the WP was up to 3.76 billion CFU/g; the rate of mixed bacteria was 2.8%; the pH value was 7.8; the fineness was 98.2%; the drying loss was 1.6%; the wetting time was 95.7 s; and the suspension rate was 80.7%. Pot experiment showed that seed-dressing with 15 to 45 kg/hm² of the WP was safe on potato seedling emergence, and had no adverse effects on potato growth. The control effect on potato Verticillium wilt ranged from 45.1% to 47.4%. Field plot experiments demonstrated that treatments with 15 to 45 kg/hm² of WP could significantly reduce the occurrence of potato scab, the control efficacy was 72.0% and the yield increase rate was 15.5% of treatment with 30 kg/hm² WP. Field trial demonstrations in different regions showed that the control efficacy of potato Verticillium wilt and potato scab was 50.8% to 62.1%, and 63.9% to 65.7%, respectively, with the treatment of 30 kg/hm² WP. Meanwhile, potato yields increased from 14.3% to 29.4%. The results indicated that 3 billion CFU/g Bacillus WP could effectively control potato soil-borne diseases, and significantly increase potato yield, providing a basis for the extensive application of WP in potato production.