Preparation of microcapsules and evaluation of their biocontrol efficacy

In this study, a combination of Serratia nematophila L2 and Bacillus velezensis W24 was used to biocontrol Sclerotinia sclerotiorum. When the mixed ratio of L2 to W24 was 1:1, the inhibition rate on the growth of S. sclerotiorum was 88.1 %. To gain a large number of bacteria, the culture medium and conditions were optimized. When the medium formula involved molasses (8.890 g/L), soy peptone (6.826 g/L), and NaCl (6.865 g/L), and the culture conditions were 32 °C, inoculum 4%, rotation speed 200 rpm, and pH 7, the maximum amounts of bacterial cells obtained. In order to prepare microcapsules, spray drying conditions were optimized. These conditions included the soluble starch concentration of 30 g/100 mL, the inlet air temperature of 160 °C, and the feed flow rate of 450 mL/h. Under these optimized conditions to prepare microcapsules, the mixed strain (L2 and W24) exhibited a survival rate of 93.9 ± 0.9% and a viable bacterial count of 6.4 × 10¹² cfu/g. In addition, microcapsules (GW24Ms) which contained strains L2 and W24 had good storage stability. In the pot experiment, GW24Ms could effectively reduce the disease of soybean plants and the control effect was 88.4%. Thus, the microbial agent represents a promising biocontrol solution for managing Sclerotinia in soybean.