Biological amelioration of water stress in rapeseed (Brassica napus L.) by exopolysaccharides-producing Pseudomonas protegens ML15.

Rapeseed (Brassica napus L.) is a globally significant oilseed crop with high economic value. However, water deficit significantly limits its growth and productivity. Exopolysaccharides (EPS)-producing bacteria offer a promising strategy to counteract drought stress, leveraging their high water retention capabilities and plant growth-promoting (PGP) properties. This study was conducted to characterize the PGP traits of selected EPS-producing bacteria strains and evaluate its efficacy in enhancing rapeseed resilience under drought conditions. Among five EPS-producing bacteria evaluated, Pseudomonas protegens ML15 was selected for its best performance. This strain demonstrated a range of plant growth-promoting traits, such as the solubilization of phosphate, potassium, and zinc, alongside the production of ammonia, siderophores, and proline. It also exhibited antioxidant activity and the ability to form biofilms, even under water-stressed conditions. Inoculation of rapeseed with strain ML15 increased germination percentages and seedling length. Notably, whether rapeseed plants were subjected to drought-induced stress or maintained under normal conditions, treatment with P. protegens ML15 inoculation consistently improved plant length and overall biomass. Under drought-stressed conditions, inoculated plants exhibited reduced malondialdehyde levels and increased vegetation indices, chlorophyll, protein, proline, and phenolic content. They also showed enhanced activity of antioxidant enzymes, such as catalase and peroxidase, compared to uninoculated rapeseed plants. These findings underscore the potential of EPS-producing bacteria like P. protegens ML15 to mitigate water stress in plants, providing ecological and economic benefits that support agricultural sustainability.