Appraising the potential of EPS‐producing rhizobacteria with ACC‐deaminase activity to improve growth and physiology of maize under drought stress

Abstract

Rhizobacteria containing 1-aminocyclopropane-1-carboxylic aciddeaminase (ACC-deaminase) and exopolysaccharides (EPS) activity are important to induce stress tolerance in plants. The present study was conducted to screen and characterize plant growth-promoting rhizobacteria (PGPR) with ACC-deaminase and EPS-producing activity for improving maize growth under drought stress. Eighty-five rhizobacterial strains were isolated from the rain-fed areas, among those 69 isolates were able to utilize ACC and 31 strains were found positive for EPS production. These strains containing ACC-deaminase and/or EPS-producing activity were subjected to drought tolerance assay by inducing water stress in media using polyethylene glycol 6000. Based on results of the drought tolerance bioassay, 12 most prominent strains were selected to evaluate their growth-promoting abilities in maize under water-stressed conditions by conducting jar trial. The impact of strains on maize growth parameters was variable. Strains with coexistence of ACC-deaminase and EPS-producing activity showed comparatively better results than those with either ACC-deaminase or EPS-producing activity only. These strains were also significantly better in improving the plant physiological parameters including photosynthesis rate, stomatal conductance, vapor pressure, water-use efficiency and transpiration rate. The strain D 3 with co-existence of ACC-deaminase and EPS-producing activity was significantly better in colonizing maize roots, improving plant growth and physiological parameters. The strain was named as Bacillus velezensis strain D 3 (accession number MT367633) as confirmed through results of 16S rRNA partial gene sequencing. It is concluded that the strains with coexistence of ACC-deaminase and EPS-producing activity could be better suited for improving crop growth and physiology under drought stress.

Rhizobacteria from ‘flowering desert’ events contribute to the mitigation of water scarcity stress during tomato seedling germination and growth

“…This finding was likely due to the general synergistic effects that allow members of Consortium C to optimize the use of resources 45 . In addition, a protective effect against water stress has also been observed in maize, pea and vetch plants treated with EPS-producing rhizobacteria 53 – 55 . It is known that EPSs provide a microenvironment that holds water and dries more slowly compared with the surrounding environment, thus protecting bacteria and roots of agriculturally relevant vegetables against desiccation 56 .…”

Improving crop drought resistance with plant growth regulators and rhizobacteria: Mechanisms, applications, and perspectives

“…The EPS-producing bacteria Pseudomonas putida GAP-P45 can form a biofilm on the root surface, and plants inoculated with this strain show greater soil aggregation, more root-adhering soil, and high leaf RWC ( Sandhya et al., 2009 ). Nadeem et al. (2020) found that EPS-producing bacteria improved the photosynthetic rate, stomatal conductance, and other physiological characteristics of maize under drought stress.…”

“…Studies have shown that inoculation of tomato and pepper with Achromobacter ARV8, a PGPR that produces ACC deaminase, reduces ethylene levels and improves drought resistance of host plants ( Mayak et al., 2004 ). In addition, inoculation with ACC deaminase-producing PGPRs has positive effects on photosynthetic efficiency, stomatal conductance, water-use efficiency, transpiration rate, vapor pressure, chlorophyll content, and carbon content of maize plants under drought stress ( Danish et al., 2020 ; Nadeem et al., 2020 ). ACC deaminase-producing PGPRs also enhance osmotic adjustment and antioxidant defenses of host plants under drought stress ( Gowtham et al., 2020 ; Zarei et al., 2020 ).…”

“…(2020) found that EPS-producing bacteria improved the photosynthetic rate, stomatal conductance, and other physiological characteristics of maize under drought stress. Studies showed that the integrated use of ACC deaminase-producing bacteria and EPS-producing bacteria had more beneficial effects on plant drought resistance than the use of either bacteria separately ( Nadeem et al., 2020 ). Soil structure is very important for crop production.…”

Understanding drought tolerance in plants

“…Genome‐wide association studies (GWAS), used for studying natural genetic variations, can identify genes and alleles involved in drought tolerance and metabolic regulation, which will pave the way for mapping and cloning gene loci regulating drought tolerance through controlled hormonal regulation, seed development and maintenance of water relations. In addition to current management practices, such as mineral fertiliser application and the use of compost (Hafez et al, 2020), the exogenous application of biostimulants (Nadeem et al 2020) and phytohormones (Khan et al, 2020) has been tested for their efficacy in improving water use efficiency and the mitigation of drought‐induced oxidative effects. Molecular genetic approaches and physio‐biochemical evaluations have revealed several key avenues for improving drought tolerance in plants, especially food crops as discussed by several researchers (Jabeen et al, 2020; Razik et al, 2020; Aleem et al, 2020).…”