Preparation of slow-release regulated Rs-198 bilayer microcapsules and application of its lyophilized bacterial inoculant on Capsicum annuum L. under salt stress

The survival adaptation of bacteria in saline soil is poor. The bilayer microcapsules were prepared by secondary embedding of monolayer sodium alginate (NaAlg) - bentonite (Bent) - sodium carboxymethylcellulose (CMC) microcapsules wrapped with plant growth promoting rhizobacteria (PGPR) Pseudomonas putida Rs-198 by chitosan solution to promote the synergistic effect of bilayer microencapsulation and PGPR. The characterization of the Rs-198 bilayer microcapsules showed that the amino and carboxyl groups were cross-linked and a thin layer of chitosan was formed on the outside of the microcapsule. The bilayer microcapsule (Ch-d) with a chitosan concentration of 0.8 wt% and pH 6 showed a slow release of bacteria with a maximum release of 6.06 × 109 cfu/g on the 7th day. The viable bacteria of Ch-d increased by 4.42% after 60 days of storage compared with monolayer microcapsules. The 0.9 wt% l-cysteine, 10 wt% glycerinum, 10 wt% trehalose and 12 wt% soluble starch were added as bacterial protective agents during the process of preparing the Ch-d lyophilized bacterial inoculant (Ch-d LBI). Pot experiments showed that Ch-d LBI exhibited better growth promotion of Capsicum annuum L. under salt stress. Therefore, the bilayer microcapsule as slow-release bacterial inoculant is a potential alternative for sustainable agriculture.