Biofertilizers mitigate salinity stress: insights from spring wheat physiology and gene expression

Abstract

Introduction: Salinity stress severely restricts plant growth and yield, reducing global crop productivity. Ensuring food security requires sustainable strategies to mitigate salinity damage. Beneficial microorganisms used as biofertilizers enhance plant tolerance to abiotic stresses. This study examined the response of spring wheat (Triticum aestivum L. cv. Yecora Rojo) to biofertilizers under varying salinity levels to assess their potential in enhancing salt stress tolerance. Methods: Three treatments were applied: untreated control (C), grain treatment (GT), and grain plus root treatment (GRT). Salinity stress was imposed using diluted seawater at 0, 2000, 4000, and 6000 ppm. The biofertilizer formulation included Azotobacter chroococcum, Bacillus megaterium, and Bacillus circulans. Physiological traits (chlorophyll, cell membrane stability, relative water content), biochemical markers (proline, malondialdehyde, hydrogen peroxide), and antioxidant enzyme activities (catalase, peroxidase, superoxide dismutase) were measured. Expression of salinity-responsive genes (TaCAT1, TaPOD-D1, TaSOD2, TaHKT1;4, TaNHX2, TaP5CS, TaFER-5B) was also analyzed. Results: Salinity significantly reduced wheat growth, chlorophyll levels, membrane stability, and water content. Biofertilizer treatments, especially GRT, alleviated these effects by maintaining chlorophyll and water status while reducing oxidative damage. Antioxidant enzyme activities increased, improving scavenging of reactive oxygen species. Biofertilizers also upregulated stress-related genes, enhancing osmotic adjustment, ion balance, and antioxidant defenses. Correlation analysis confirmed strong physiological and biochemical interactions supporting stress tolerance. Discussion & conclusion: Biofertilizers represent an eco-friendly and sustainable strategy to enhance wheat salinity tolerance. By boosting antioxidant defenses, osmolyte accumulation, and ion regulation, they mitigate salt-induced damage. GRT provided the greatest benefit, highlighting the synergistic effect of dual grain and root inoculation.