Salt-Tolerant Plant Growth-Promoting Bacteria (ST-PGPB): An Effective Strategy for Sustainable Food Production

Soil is the backbone of the agricultural economy of any country. Soil salinity refers to the higher concentration of soluble salts in the soil. Soil salinity is a ruinous abiotic stress that has emerged as a threatening issue for food security. High salt concentration causes an ionic imbalance that hampers water uptake, affecting photosynthesis and other metabolic processes, ultimately resulting in inferior seed germination and stunted plant growth. A wide range of strategies have been adopted to mitigate the harmful effects of salinity such as efficient irrigation techniques, soil reclamation, habitat restoration, flushing, leaching or using salt-tolerant crops, but all the methods have one or more limitations. An alternative and effective strategy is the exploitation of salt-tolerant plant growth-promoting bacteria (ST-PGPB) to mitigate salt stress and improve crop productivity. ST-PGPB can survive in salinity-tainted environments and perform their inherent plant growth-promoting and biocontrol functions effectively. Additionally, ST-PGPB can rescue plants via stress-responsive mechanisms including production of growth regulators, maintenance of osmotic balance, aminocyclopropane-1-carboxylate (ACC) deaminase activity, exopolysaccharides (EPS) activity, improvement in photosynthesis activity, synthesis of compatible solutes, antioxidant activity and regulation of salt overly sensitive (SOS) signaling pathway. Several well-known ST-PGPB, specifically Azospirillum, Bacillus, Burkholderia, Enterobacter, Pseudomonas and Pantoea, are used as bioinoculants to improve the growth of different crops. The application of ST-PGPB allows plants to cope with salt stress by boosting their defense mechanisms. This review highlights the impact of salinity stress on plant growth and the potential of ST-PGPB as a biofertilizer to improve crop productivity under salt stress.