Enhancement of drought stress tolerance in crops by plant growth promoting rhizobacteria

Abstract

Drought is one of the major constraints on agricultural productivity worldwide and is likely to further increase. Several adaptations and mitigation strategies are required to cope with drought stress. Plant growth promoting rhizobacteria (PGPR) could play a significant role in alleviation of drought stress in plants. These beneficial microorganisms colonize the rhizosphere/endo-rhizosphere of plants and impart drought tolerance by producing exopolysaccharides (EPS), phytohormones, 1-aminocyclopropane- 1-carboxylate (ACC) deaminase, volatile compounds, inducing accumulation of osmolytes, antioxidants, upregulation or down regulation of stress responsive genes and alteration in root morphology in acquisition of drought tolerance. The term Induced Systemic Tolerance (IST) was coined for physical and chemical changes induced by microorganisms in plants which results in enhanced tolerance to drought stresses. In the present review we elaborate on the role of PGPR in helping plants to cope with drought stress.

l-tryptophan-assisted PGPR-mediated induction of drought tolerance in maize (Zea maysL.)

“…Hence, it was observed that inoculation with PGPR strains alleviated the plant drought stress, increasing plant growth and yield, and different strains performed differently (Sarma et al 2012;Vurukonda et al 2016). It was also evident from the result that IAA production was stimulated by 5-6× in plants as compared to rhizosphere soil when inoculated with Bacillus pumilus and Bacillus cereus, in the presence of L-tryptophan under induced drought stress.…”

“…These findings are in accordance with those of Armada et al (2014) and Gusain et al (2015), who reported an increased accumulation of compatible solutes like proline, which is an important adaptation mechanism for metabolic adjustment of plants grown under drought stress. Moreover, PGPR inoculation have been reported to increase plant biomass and photosynthetic pigments (Chl a, b and carotenoids) under drought stress as compared to uninoculated control (Vurukonda et al 2016).…”

Effects of exogenously applied plant growth regulators in combination with PGPR on the physiology and root growth of chickpea (Cicer arietinum) and their role in drought tolerance

“…PGPR are the main components of soil biodiversity and play a key role in enhancing soil nutrients and moisture content as they colonize the rhizosphere of plants and produce various substances including exopolysaccharides, phytohormones, aminocyclopropane-1-carboxylate deaminase, induce accumulation of osmolytes, antioxidant enzymes and adopt root morphology to drought stress (Vurukonda et al 2016). PGPR appear to act synergistically to augment the chlorophyll content of the leaves and the sensitive variety was more responsive to PGR and PGPR.…”

Rhizosphere engineering: Enhancing sustainable plant ecosystem productivity

“…The rhizosphere and associated microbiota play critical roles in controlling the ability of plants and plant ecosystems to cope with drought. PGPRs colonize the rhizosphere/endo-rhizosphere of plants and confer drought tolerance by: (i) producing exopolysaccharides (EPS), 1-aminocyclopropane-1-carboxylate (ACC) deaminase, VOCs, phytohormones like abscisic acid (ABA), gibberellic acid, cytokinins, and indole-3-acetic acid (IAA); (ii) inducing accumulation of osmolytes and antioxidants; and (iii) regulation of stress-responsive genes and alteration in root morphology (Vurukonda et al, 2016a). For example, IAA-producing Azospirillum spp.…”