Encapsulation of Bacillus velezensis and its biocontrol efficiency against Plasmodiophora brassicae in Chinese cabbage

Biological control agents are beneficial microorganisms that protect plants from disease. However, the effectiveness and viability of microorganisms are often influenced by severe environmental conditions. Encapsulation of microbial cells can protect them from biotic and abiotic stresses. The objectives of this work were to encapsulate Bacillus velezensis ZF481 (ZF481) with chitosan and carrageenan to prepare macrospheres and evaluate their control effect on clubroot disease. Macrospheres with different ratios of chitosan (2 % w/w)/carrageenan (0.3 % w/v) were synthesized by an ionic gelation method, and the bacterial cells of ZF481 were loaded into macrospheres. The maximum swelling ratio (634 %) and maximum survival rate (64.72 ± 2.65 %) were obtained from macrospheres with chitosan: carrageenan ratio of 1: 1. The number of bacteria released from macrospheres into sterile phosphate buffer solution (pH 7.4) reached a release balance after 48 h. The bacteria could be slowly released from macrospheres into the soil. The survival rate of the encapsulated bacteria respectively was 73.33 % and 67.31 % when stored at 4 °C and 25 °C for 80 days, respectively. The control efficiency of ZF481 macrospheres (chitosan: carrageenan, 1: 1) on clubroot disease in pak choi under greenhouse conditions and Chinese cabbage under field conditions was significantly higher than that of ZF481 culture. Moreover, the ZF481 macrospheres also enhanced the plant growth. Collectively, chitosan and carrageenan are ideal wall materials for preparing slow-release bacterial macrospheres to control clubroot. The macrospheres retard the release of B.velezensis ZF481 in soils and significantly improve its biocontrol efficiency on clubroot in pak choi and Chinese cabbage. Thus, this study paves the way for forming formulations against the clubroot disease.