Formulation optimization of the wettable powder of Bacillus amyloliquefaciens: a novel marine microbial pesticide for the control of cabbage clubroot

Clubroot is one of the major global diseases of cruciferous crops, but the available pesticide against it is very limited. A marine habitat Bacillus amyloliquefaciens Txc2-1, which was isolated by our research group possessed a significant antagonistic effect on the clubroot of cruciferous cabbage. After the screening of the carrier and adjuvant followed by the optimization with the mixture design, the optimal formulation of the wettable powder of Txc2-1 (Txc2-1 WP) was obtained. Meanwhile, the 3 billion CFU/g Txc2-1 wettable powder was prepared and applied in the investigation of the control efficacy against cabbage clubroot in the green house and field. Results showed that the optimal carrier, wetting agent and suspending agent for Txc2-1 WP were light calcium carbonate (LCA), sodium dodecyl sulfate (SDS), and polyvinyl alcohol (PVA), respectively. All of them possessed high biocompatibility with Txc2-1 and good physical and chemical properties. Subsequently, The optimum ratio of LCA, SDS and PVA was 83 : 9 : 8 obtained by the mixture design. According to the above formulation, the 3 billion CFU/g Txc2-1 WP was obtained using 5 L fermentor and spray drying tower. The control efficacy of Txc2-1WP on the clubroot of cruciferous cabbage was tested in green house (for 40 days) and field experiments (for 60 days), and the control efficacies were 70.53% and 66.8%, respectively. This Txc2-1 WP met the state quality standards and performed good control efficacy against cabbage clubroot. The above results have provided a foundation for developing Txc2-1 WP as the first marine microbial fungicide against cabbage clubroot.