Exopolysaccharide‐Based Microencapsulation of Plant Growth‐Promoting <i>Bacillus</i> Strains Improves Germination, Growth, and Yield of Chilean Common Bean Cultivars

ABSTRACT Microbial biostimulants offer sustainable alternatives to chemical fertilizers in legume cultivation by enhancing seed germination, nutrient uptake, and stress resilience, while maintaining the yield. However, their practical application is often limited by weak shelf life and reduced viability under environmental conditions. In this study, we develop a composite hydrogel encapsulation system composed of alginate, chitosan, and bacterial exopolysaccharides (EPSs) to improve the viability and functionality of two plant growth‐promoting bacteria (PGPB): Bacillus proteolyticus Cyn1 and Bacillus safensis Cyn2. These strains, originally isolated from Chilean common bean rhizosphere, were characterized for growth dynamics and morphological traits using optical density monitoring and scanning electron microscopy. The encapsulated formulations were tested for cell viability under 30‐day storage time and evaluated for their growth stimulation efficacy on three Chilean cultivars of Phaseolus vulgaris L. (“Zorzal,” “Sapito,” and “Mantequilla”) under in vitro germination, controlled growth condition, and open‐field condition. Results demonstrated composite hydrogel (alginate–chitosan–EPS) matrix significantly enhanced bacterial viability compared to single‐layer capsules. Confocal microscopy with live/dead staining confirmed sustained cell viability (~70% after 30 days). Seed germination assays revealed improvements in total plant height, plumule and radicle length, root number, and germination rate in biostimulant‐treated groups, with the “Mantequilla” cultivar showing the most noticeable response. The biostimulant enhanced early growth and physiological performance of common bean cultivars in a genotype‐dependent manner, increasing plant height, biomass accumulation, leaf number, and chlorophyll a content, with the strongest responses observed in “Zorzal” and “Sapito,” as supported by multivariate analyses. Importantly, these early physiological advantages translated into improved agronomic performance under field conditions with increases in pod and seed number, biomass, and final yield across cultivars. This study highlights the effectiveness of EPS‐based composite encapsulation systems in improving stability and field performance, offering a promising strategy for sustainable enhancement of legume crop performance in a changing world.