Halotolerant PGPR bacteria: Amelioration for salinity stress

Abstract

Salinity is one of the major abiotic stresses and brutal environmental factor that adversely affects the productivity of crop and its quality. Approximately 20% of the total cultivated land and 33% of irrigated agricultural lands are oppressed by salinity (salt stress). Agricultural production under elevated salt concentration of soil is highly decreased due to improper nutrition of plants along with osmotic imbalance and drought stress. Salt stress hampers most of the processes including protein synthesis, photosynthesis, growth, and lipid metabolism. In plants, proline amino acid helps in osmotic adjustment, protects macromolecules during dehydration and serves as a scavenger for hydroxyl radical which helps the plants to alleviate the salinity impacts. Under the stressed condition, the tissues of plant are mainly responsible for stunted growth and chlorosis along with nutrient imbalance. Plants like chickpea (Cicer arietinum L.) exposed to saline condition exhibit increased Na+/K+ ratio and decreased uptake of phosphorus (P) in shoot tissue. It has been reported that halotolerant bacteria with genetic diversity may exhibit unique properties like tolerance to the saline condition by various means including synthesis of compatible solutes and biocontrol potential. They improve plant growth under a variety of salinity stress conditions by producing (and regulating) various phytohormones, including indole-3-acetic acid, gibberellic acid, zeatin, abscisic acid, and ethylene, and enhancing phosphate solubilization. The co-inoculation of halotolerant bacteria like Azospirillum, Agrobacterium, Pseudomonas, and several Gram-positive Bacillus is an environment-friendly and economically suited approach for reclaiming salinity-affected lands and maximizing biomass production. In the book chapter, the author will cover the usefulness of various halotolerant bacteria as bioinoculants to improve the soil/plant health against the abiotic stresses.