Plant-growth-promoting rhizobacteria: drought stress alleviators to ameliorate crop production in drylands

Abstract

Drylands are known for being a drought stressed environment, which is an alarming constraint to crop productivity. To rescue plant growth in such stressful conditions, plant-growth-promoting rhizobacteria (PGPR) are a bulwark against drought stress and imperilled sustainability of agriculture in drylands. PGPR mitigates the impact of drought stress on plants through a process called rhizobacterial-induced drought endurance and resilience (RIDER), which includes physiological and biochemical changes. Various RIDER mechanisms include modification in phytohormonal levels, antioxidant defense, bacterial exopolysaccharides (EPS), and those associated with metabolic adjustments encompass accumulation of several compatible organic solutes like sugars, amino acids and polyamines. Production of heat-shock proteins (HSPs), dehydrins and volatile organic compounds (VOCs) also plays significant role in the acquisition of drought tolerance. Selection, screening and application of drought-stress-tolerant PGPRs to crops can help to overcome productivity limits in drylands.

Synergistic use of biochar, compost and plant growth‐promoting rhizobacteria for enhancing cucumber growth under water deficit conditions

“…Inoculation of PGPR can also minimize the impact of water deficit stress on plant growth and development owing to their ability of ACC deaminase, EPS and osmolyte production . In the present study, it was observed that seed inoculation with P. fluorescens reduced water deficit‐induced growth suppression in cucumber, and significantly better shoot and root growth was observed than in un‐inoculated plants.…”

“…Various researchers have reported that inoculation with PGPR containing ACC deaminase activity can reduce the stress‐induced negative impact of ethylene on root growth by degrading its immediate precursor ACC . Moreover, the production of EPS by bacteria protects plants from desiccation . Therefore inoculation with P. fluorescens resulted in the development of a better root system, which subsequently affected shoot growth positively.…”

“…Exopolysaccharides (EPS) produced by bacteria protect plants from desiccation and indirectly affect phosphate solubilization by binding free phosphorus . PGPR can enhance plant growth under drought conditions by mitigating the negative impact of stress‐induced ethylene through their 1‐aminocyclopropane‐1‐carboxylic acid (ACC) deaminase activity, production of exopolysaccharides, up‐ or down‐regulation of stress‐responsive genes and accumulation of osmolytes …”

The role of biostimulants and bioeffectors as alleviators of abiotic stress in crop plants

“…Most documented growth enhancement determined by these bacteria is associated with high level of IAA, which has been proven to alleviate salt stress [88] and EPS production that may help in maintaining a film of hydration around the roots and/or help re-establishing favourable water potential gradients under water limitations. These functions have been proven useful under saline stress [89], extremes of temperature, pH, salinity, and drought [87,90]. Inoculation of maize with Azotobacter strains has been shown to have general positive effects under saline stress by facilitating uptake of K + and exclusion of Na + as well as increasing phosphorous and nitrogen availability [24].…”

Review on Drought Tolerance in Plants Induced by Plant Growth Promoting Rhizobacteria

“…Cellular dehydration induced biosynthesis of ABA, a stress hormone during water deficit condition (Kaushal and Wani, 2015). In addition to IAA, production of ABA by Azospirillum lipoferum alleviated drought stress in maize plants (Cohen et al, 2009).…”