Development of a zeolite-incorporated microencapsulation system for Bacillus halotolerans: legacy impact on radish...

Salt stress is one of the most serious issues in agricultural sector, contributes to global food insecurity and reduced crop productivity. Plant growth promoting rhizobacteria play important roles as phytostimulators and phytoremidiators. Bacillus halotolerans, a halophilic bacterium, is known to alleviate stress, control plant diseases, and promote plant growth under extreme conditions. Bacterial encapsulation is an alternative technology used to improve viability during handling and application. This work investigated the legacy influence of microcapsules of B. halotolerans MSR-H4, either alone or with zeolite (1% or 2.5%), on the growth of radish (Raphanus sativus) and subsequently on celery (Apium graveolens) growing under greenhouse conditions. Compared with the control, the application of modified microcapsules with 1% zeolite as inoculants increased microbial populations, phosphate-solubilizing bacteria 9.2 × 10⁷CFU/mL with radish and 9.5 × 10⁷CFU/mL with celery), and soil enzyme activities, and lowered shoot proline accumulation. Notably, zeolite at two concentrations significantly reduced the antioxidant activity, while the microcapsules of B. halotolerans presented maximum chlorophyll contents in both radish (6.7 mg/gfw) and celery (5.8 mg/gfw)and increased dehydrogenase activity to 60.5 and 85. 7 µg TPF g⁻¹dw soil day⁻¹ in radish and celery soils, respectively. Additionally, the microcapsules alone increased the K⁺/Na⁺ ratio in radish and celery by 2.3 and 2.2 mg/gdw, respectively, followed by B. halotolerans microcapsules with 1% zeolite, which increased the K⁺/Na⁺ ratio by 1.3 mg/gdw in radish and 1.7 mg/gdw in celery. The results revealed that B. halotolerans microcapsules alone or with zeolite constitute a sustainable strategy to improve crop quality and productivity under salinization.