Use of Biopolymer-Coated Rhizobacteria to Enhance Drought Resistance in Oenothera Macrocarpa Seeds

Overview

Climate-change induced drought stress has intensified the need for sustainable and resilient agricultural practices. Among various techniques, biopriming with plant growth–promoting rhizobacteria (PGPR) enhances seed germination through multiple biochemical mechanisms: secretion of phytohormones, extracellular enzymes, and lipopeptides. These compounds improve nutrient uptake, strengthen plant immunity, and increase tolerance to abiotic stresses. Rhizobacterial suspensions are impractical due to poor bacterial survival and inconsistent colonization of plant roots. The objective was to evaluate biopolymer-based seed coatings as a delivery method to enhance the effectiveness of Bacillus subtilis bioinoculants on Oenothera macrocarpa seeds. Biopolymer coatings xanthan gum, chitosan, and sodium alginate were used to encapsulate PGPR during seed priming. Germination and early seedling growth were evaluated under drought simulation using polyethylene glycol 8000 (PEG) to create a water deficit.Moderate drought stress (10% PEG) demonstrated not effective enough, while 30% PEG created conditions so extreme coated seeds struggled to survive. Drought simulation was most pronounced at 20% PEG, testing seed tolerance under extreme water deficit. The results at optimal drought levels (20% PEG): chitosan and sodium alginate demonstrated a slight benefit, and xanthan gum resulted in the highest increase in germination (+71.43%) compared to the PGPR-only treatment (p < 0.05). Despite natural biological variation, statistical analysis indicates the observed patterns are unlikely due to chance alone. These findings suggest biopolymer encapsulation provides a protective microenvironment that enhances bacterial viability. In conclusion, biopolymer coatings could offer a simple low-cost approach to enhance crop productivity in water-limited regions.