Characterization of plant growth-promoting rhizobacteria (PGPR) in Persian walnut associated with drought stress tolerance

Abstract

There is a lack of information on the rhizosphere of nut-bearing trees where microbial populations can benefit roots and tree growth. The current research aimed at discovering plant growth-promoting rhizobacteria (PGPR) in the rhizosphere of soil samples from around the root zone of six walnut trees, each of which was considered as a genotype, i.e. ‘TT1’, ‘TT2’, ‘SS2’, ‘ZM1’, ‘Chandler’ and ‘Haward’. The trees grew in different arid and semiarid regions of Iran and Turkey. The strains were isolated and identified based on different morphological and biochemical markers. Drought-stress tolerance was assessed in the case of each isolate through their transfer to culture medium, containing polyethylene glycol (PEG6000) at 0 and 373.80 g L−1. Resilient strains were analyzed for measuring their ability to produce siderophore, hydrogen cyanide (HCN), Indole-3-acetic acid (IAA) and Gibberellic acid (GA3). In sum, 211 isolates were identified, of which a large number belonged to the Bacillus genus and, specifically, 78% of the strains were able to grow under drought stress conditions. The genus Arthrobacter was only detected in the rhizosphere of ‘ZM1’, ‘Haward’ and ‘TT1’ genotypes. In 4% of the strains, IAA production exceeded 53 mg L−1, while a high level of phosphorus solubility was verified in 6% of the strains. No strain was found to have the capability of producing HCN. The strains were screened for drought-tolerance, which resulted in the discovery of two promising strains, i.e. ZM39 and Cha43. Based on molecular identification through amplification and sequencing of the 16S rDNA gene, these two strains seemed to belong to Bacillus velezensis and Bacillus amyloliquefaciens, respectively. The discovery of new PGPR strains could probably assist walnut trees in improving their mechanisms of adaptation to drought stress.

Osmolyte-producing microbial biostimulants regulate the growth of Arachis hypogaea L. under drought stress

“…Many bacterial genera exhibit plant growth- promoting traits in different crops [ 63 , 64 ]. The drought-tolerant PGPR ameliorates drought stress through PGP attributes [ 65 ]. Production of rhizobacterial IAA is a direct mechanism to enhance plant development, which was efficiently produced by the selected bacteria of the present work.…”

Improving Tree Seedling Quality Using Humates Combined with Bacteria to Address Decarbonization Challenges through Forest Restoration

“…The ability of rhizosphere bacteria to stimulate plant growth is well known, intensively studied, and increasingly used in agriculture [ 23 ]. However, information on the impact of bacteria on woody plants is sparse [ 19 , 24 ]. Our experiments demonstrated species specificity of the action of bacterial preparations.…”

Biocontrol potential and action mechanism of Bacillus amyloliquefaciens DB2 on Bipolaris sorokiniana

“…Amylase, protease, and cellulase activities were determined by starch agar, skim milk agar, and carboxymethylcellulose agar, respectively ( Waithaka et al, 2017 ; Khalil et al, 2021 ; Xu et al, 2022 ). Plant growth-promotion (PGP) tests include indole acetic acid (IAA) production, siderophores production, and phosphate solubilization ( Shcherbakova et al, 2018 ; Lotfi et al, 2022 ; Mirskaya et al, 2022 ). The ability of bacterium to produce IAA was determined by Salkowski’s colorimetric method.…”