Embedding Bacillus velezensis NH-1 in Microcapsules for Biocontrol of Cucumber <i>Fusarium</i> Wilt

Abstract

Cucumber <i>Fusarium</i> wilt, caused by <i>Fusarium oxysporum</i>, is a devastating disease of cucumber and leads to enormous economic losses worldwide. The antagonistic bacterium <i>Bacillus velezensis</i> NH-1 suppresses <i>F. oxysporum</i> For a higher biological control effect, control-released microcapsules of NH-1 were prepared using cell immobilization technology. NH-1 cells were embedded in combinations of the biodegradable wall materials sodium alginate, chitosan, and cassava-modified starch to prepare control-released microbiological microcapsules. For the preparation of alginate single-layer microcapsules, the highest embedding rate of 72.60% was obtained by applying 3% sodium alginate and 2% calcium chloride. After the application of monolayer alginate microcapsules in soil, the number of bacterial cells corresponded to a sustained release curve, and the survival rate of NH-1 was higher than the control in which soil was directly irrigated with NH-1 broth. The use of 0.8% chitosan (pH 3.0) and 0.5% cassava-modified starch in the preparation of double-layer and triple-layer microcapsules changed the performance of the microcapsules and increased the embedding rate. After dry storage for 65 days, the number of NH-1 cells was at the highest level in the monolayer microcapsules. In the field experiment, the control efficiency of alginate-coated monolayer microcapsules on <i>Fusarium</i> wilt was 100%, which was significantly higher than for the NH-1 culture and double-layer and triple-layer microcapsules. Collectively, sodium alginate is an ideal wall material for preparing slow-release bacterial microcapsules to control cucumber <i>Fusarium</i> wilt. Monolayer alginate microcapsules retard the release of <i>B. velezensis</i> NH-1 in soils and significantly improve its biocontrol efficiency on cucumber <i>Fusarium</i> wilt.<b>IMPORTANCE</b><i>Bacillus</i> species are often used for the biocontrol of various plant pathogens, but the control efficiency of <i>Bacillus</i> is usually unstable in field experiments. To improve the control efficiency of <i>Bacillus</i>, in this study, microcapsules of <i>Bacillus velezensis</i> strain NH-1 were prepared using different wall materials (sodium alginate, chitosan, and cassava-modified starch). It was found that the control efficiency of alginate-coated monolayer microcapsules on <i>Fusarium</i> wilt was 100% in field experiments, which was higher than for NH-1 culture and double-layer and triple-layer microcapsules. This study provides a new approach for preparing a biocontrol agent against <i>Fusarium</i> wilt with high biocontrol efficiency.