Mitigation of drought stress in rice crop with plant growth‐promoting abiotic stress‐tolerant rice phyllosphere bacteria

Abstract

In the search of effective drought‐alleviating and growth‐promoting phyllosphere bacteria, a total of 44 bacterial isolates were isolated from the leaf surface of drought‐tolerant rice varieties, Mattaikar, Nootripattu, Anna R(4), and PMK3, and screened for their abiotic stress tolerance by subjecting their growth medium to temperature, salinity, and osmotic stress. Only eight isolates were found to grow and proliferate under different abiotic stress conditions. These isolates were identified using 16S ribosomal DNA gene sequence and submitted to the NCBI database. All the bacterial isolates were identified as Bacillus sp., except PB24, which was identified as Staphylococcus sp., and these isolates were further screened for plant growth‐promoting (PGP) traits such as IAA production, GA production, ACC deaminase activity, and exopolysaccharide production under three different osmotic stress conditions adjusted using polyethylene glycol (PEG 6000). Additionally, mineral solubilization was measured under the normal condition. Bacillus endophyticus PB3, Bacillus altitudinis PB46, and Bacillus megaterium PB50 were found to have multifarious PGP traits. Consecutively, the performance of an individual strain to improve the plant growth was investigated under the osmotic stress (25% PEG 6000) and nonstress condition by inoculating them into rice seeds using hydroponics culture. Furthermore, the drought‐alleviating potency of bacterial strains was assessed in the rice plants using pot experiment (−1.2 MPa) through bacterial foliar application during the reproductive stage. Finally, as a result of seed inoculation and foliar spray, the application of B. megaterium PB50 significantly improved the plant growth under osmotic stress, protected plants from physical drought through stomatal closure, and improved carotenoid, total soluble sugars, and total protein content. Metabolites of PB50 were profiled under both stress and nonstress conditions using gas chromatography–mass spectroscopy.

Drought Stress Impacts on Plants and Different Approaches to Alleviate Its Adverse Effects

“…The Bacillus species assembles solutes that enable maize plants to cope with drought and prevent degeneration [208]. In rice plants, the biotic and abiotic stresses were mitigated through phyllosphere bacteria inoculation [209]. The inoculation of Bacillus amyloliquefaciens, Azospirillum brasilense, Rhizobium leguminosarum, Mesorhizobium cicero bacterials strains improved homeostasis in plants and increased growth, biomass and drought tolerance index [210].…”

The Impact of Drought Stress on Soil Microbial Community, Enzyme Activities and Plants

“…The plant growth-promoting rhizobacteria (PGPR) and fungi (PGPF) by colonizing the root areas are known to contribute towards the plant adaptive mechanism in order to help the plant to survive the adverse effects of drought stress, as shown in Table 5. Microorganisms associated with plant roots minimize the harmful effects of stresses by delaying wilt and drought-induced changes (stomatal conductance, photosynthesis, and leaf discoloration), increasing amino acid content and Pro production, reducing H 2 O 2 content, and increasing total phenolics in plants [1,[149][150][151][152][153], increase nitrogen fixation, nutrients uptake, siderophore, phytohormone and secondary metabolite production, synthesis of exopolysaccharides (EPS), and many other organic compounds, and enhance enzyme activities [154][155][156][157][158][159][160][161][162][163][164], and many more (Table 5). [166]…”

Phyllosphere microbiota: Community dynamics and its interaction with plant hosts

“…Further in vitro experiments that monitor the growth of pathogen and microbiota strains in leaf homogenates sprayed with buffer or SynCom microbiota suggest that microbial interaction and fertilization‐induced host status are both important for determining the strength of phyllosphere microbiota‐mediated pathogen protection (Berg and Koskella, 2018). In addition to disease protection, phyllosphere microbiota can influence many other plant traits, including nutrient acquisition (e.g., nitrogen fixation (Mattos et al, 2008; Miyauchi et al, 2008)), adaptation to abiotic stresses (e.g., drought, ultraviolet, and frost tolerance (Lindow, 1987; Kumar et al, 2016; Arun et al, 2020)), and plant metabolic functions (Gargallo‐Garriga et al, 2016) (Table 1).…”