Abstract
Drylands are stressful environment for plants growth and production. Plant growth-promoting rhizobacteria (PGPR) acts as a rampart against the adverse impacts of drought stress in drylands and enhances plant growth and is helpful in agricultural sustainability. PGPR improves drought tolerance by implicating physio-chemical modifications called rhizobacterial-induced drought endurance and resilience (RIDER). The RIDER response includes; alterations of phytohormonal levels, metabolic adjustments, production of bacterial exopolysaccharides (EPS), biofilm formation, and antioxidant resistance, including the accumulation of many suitable organic solutes such as carbohydrates, amino acids, and polyamines. Modulation of moisture status by these PGPRs is one of the primary mechanisms regulating plant growth, but studies on their effect on plant survival are scarce in sandy/desert soil. It was found that inoculated plants showed high tolerance to water-deficient conditions by delaying dehydration and maintaining the plant’s water status at an optimal level. PGPR inoculated plants had a high recovery rate after rewatering interms of similar biomass at flowering compared to non-stressed plants. These rhizobacteria enhance plant tolerance and also elicit induced systemic resistance of plants to water scarcity. PGPR also improves the root growth and root architecture, thereby improving nutrient and water uptake. PGPR promoted accumulation of stress-responsive plant metabolites such as amino acids, sugars, and sugar alcohols. These metabolites play a substantial role in regulating plant growth and development and strengthen the plant’s defensive system against various biotic and abiotic stresses, in particular drought stress.
Highlights
Desertification, drought, and land degradation are major challenges to sustainable crop production throughout the world especially in developed countries
This review identifies the challenges of drought stress and involvement of Plant growth-promoting rhizobacteria (PGPR) in the mitigation of drought stress in plants for sustainable production
Many plant-associated bacteria are well known for their ability to promote plant growth and improve water-use efficiency and tolerance to various abiotic stresses
Summary
Desertification, drought, and land degradation are major challenges to sustainable crop production throughout the world especially in developed countries. Drought stress enhances formation of free radicals that damage plant defence system resulting in an increase in reactive oxygen species (ROS), such as superoxide radicals, hydroxyl radicals, and hydrogen peroxide induces oxidative stress. Water stress is responsible for high economic losses in arid and semi-arid regions It disturbs plant–water relations at cellular and whole plant levels, resulting in specific and non-specific responses [14]. Inoculation of plants with growth-promoting microorganisms can improve water retention strategies and drought tolerance of plants grown in arid or semi-arid regions [20]. These useful microbes inhabit the rhizosphere/endogenous rhizosphere of the plant through various direct-indirect mechanisms and promote plant growth (Figure 1).
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