Plant growth-promoting bacteria mitigate drought stress in a new forage oat variety (Avena sativa AV25T)

Abstract Background and Aims Climate change is posing a major threat to global agricultural productivity. Plant growth-promoting bacteria (PGPB) have emerged as sustainable tools to enhance crop tolerance to abiotic stress through different mechanisms. This study aimed to evaluate the physiological, biochemical, and transcriptomic responses of the Altoandina oat variety ( Avena sativa AV25T) under water deficit and to determine the effectiveness of PGPB inoculation. Methods Six PGPB strains were evaluated: Azospirillum brasilense D7, Pseudomonas fluorescens N7, Herbaspirillum sp. AP21, Bacillus subtilis XT13, Priestia megaterium XT14, and B. amyloliquefaciens XT17. Altoandina oat seedlings were inoculated with individual or dual suspensions and drought stress was induced by suspending irrigation. Physiological and biochemical parameters, including stomatal conductance, chlorophyll content, biomass, proline, soluble sugars, and antioxidant enzyme activities, were measured. Transcriptomic profiling was performed on plants subjected to mild water deficit to identify gene expression changes associated with drought response and PGPB inoculation. Results Water deficit significantly affected oat physiology, reducing stomatal conductance and chlorophyll content while inducing the accumulation of osmoprotectants and activation of antioxidant enzymes. N7 and XT17 inoculation mitigated these effects, improving water retention, photosynthetic efficiency, enhanced proline and sugar accumulation compared to non-inoculated controls. Transcriptomic analysis revealed a coordinated activation of genes involved in developmental, signaling, and photosynthetic pathways under mild stress. Conclusions This study demonstrates that selected PGPB strains can enhance drought recovery in the Altoandina oat variety through physiological and biochemical adjustments. Further multi-omics studies are needed to elucidate the molecular mechanisms underlying these beneficial interactions.