Co-application of Silicon and Beneficial Microbes Enhances Antioxidant Defense and Physiological Traits in Wheat

Wheat (Triticum aestivum L.), a global staple crop, contributes ~18% of dietary calories and 19% of protein intake. However, excessive use of chemical fertilizers, soil degradation, and salinity stress are threatening its productivity and sustainability. The present study evaluated the effect of silicon (Si), silicate-solubilizing bacteria (SSB), and phosphate-solubilizing bacteria (PSB) on two wheat varieties, Golden Sharbati 306 and HD 2967, under pot culture conditions. Five treatments, including basal NPK and combinations of Si, SSB, and PSB, were applied, and their effects on physiological, photosynthetic pigments, and antioxidant parameters were assessed. Significant improvements were observed under combined applications (DMRT, p < 0.05). In Golden Sharbati 306, leaf relative water content (RWC) increased by up to 15.8% (T2), and root RWC by 9.1% (T3). In HD 2967, the maximum increases were 10.6% (leaves, T3) and 9.0% (roots, T4). Electrolyte leakage was reduced by 41% in Golden Sharbati 306 (T3) and 43% in HD 2967 (T3), indicating improved membrane stability. Photosynthetic pigments also showed significant enhancement: chlorophyll a increased by 41% in HD 2967 (T3), while chlorophyll b reached 0.178 mg/g FW in Golden Sharbati 306. Carotenoid content rose by 35.7% in HD 2967 (T3), and the chlorophyll stability index (CSI) remained 41% higher in combined Si + SSB + PSB treatments compared with P-deficient ones. Antioxidant enzymes were markedly enhanced, with catalase (CAT) activity increasing by 97% and peroxidase (POX) activity by 288% in HD 2967 roots under T3. Overall, the results demonstrate that Si, SSB, sand PSB act synergistically to improve water relations, pigment stability, and antioxidant defense, thereby enhancing stress tolerance in wheat. This integrated nutrient management approach represents an eco-friendly and sustainable strategy to strengthen wheat resilience and productivity under stress-prone environments.