Salinity Stress in Crops: Mechanisms and Mitigation Techniques Using PGPR and Silicon

Abstract

Agriculture is pivotal to Pakistan's economy, yet soil salinity poses a significant threat to agricultural productivity, impacting 22.67% of GDP and 36.92% of employment. This review delves into the multifaceted issue of soil salinity, exploring its types, sources, symptoms, and the adverse effects on soil properties, crop yield, and overall agricultural sustainability. Salinity stress arises from both natural processes and human activities, leading to yield losses of up to 80%. The review categorizes saline soils and elucidates the physiological and biochemical mechanisms by which salinity impedes plant growth, including osmotic stress, ion imbalance, and oxidative damage. Innovative solutions to mitigate soil salinity are essential. This review highlights the potential of Plant Growth-Promoting Rhizobacteria (PGPR) and silicon application as sustainable strategies to combat salinity. PGPR enhances plant tolerance to salinity through mechanisms such as nutrient solubilization, phytohormone production, ACC deaminase activity, antioxidant enzyme production, exopolysaccharide production, biofilm formation, and osmolyte accumulation. The review documents numerous bacterial strains, including Bacillus, Pseudomonas, and Rhizobium, demonstrating significant improvements in plant growth and stress resistance. Silicon, although not an essential nutrient, is shown to enhance plant resilience to salinity by improving ion homeostasis, boosting antioxidant defenses, modulating gene expression, and facilitating osmolyte production. Silicon-mediated salinity tolerance mechanisms include Na+ hindrance, antioxidant enzyme activity enhancement, proteomic and transcriptomic responses, and phytohormone regulation. Focusing on onion (Allium cepa L.) as a case study, the review underscores the combined efficacy of PGPR and silicon in enhancing salinity tolerance and improving crop yield. The findings suggest that integrating PGPR and silicon into agricultural practices offers a promising approach to managing soil salinity, thereby securing crop productivity and sustainability in salinity-affected regions. Future research directions and practical recommendations for the application of these biotechnological interventions are also discussed.