The present study focused on the characterization of plant growth promoting rhizospheric (R) and endophytic (E) bacteria and their impact on wheat cultivars growth. In this study, 400 strains were isolated from the rhizosphere soil (250 isolates) and surface-sterilized roots (150 isolates) of wheat and screened for their ability to plant growth promotion (PGP) traits. Four R isolates and four E isolates with different ability were selected to investigate the interaction between R and B bacteria associated with wheat cultivars under in vitro and greenhouse conditions. Plant growth parameters were found to be enhanced by the combined inoculation of two groups of R and E bacteria compared to individual inoculations (respectively 33.7 and 37.8% increase in root and shoot dry weight), suggesting that PGP rhizobacteria acted synergistically with PGP endophytes in phosphate solubilization. Compared to inoculation with phosphate-solubilizing bacteria (PSB) or indole-3-acetic acid producer bacteria (IAA-PB), inoculation by bacteria with multiple PGP properties (PSB and IAA-PS) showed higher promotion capacity. Also, in greenhouse assay, bacterial inoculation had a positive effect on the soil dehydrogenase (70.2%) and phosphatase (52.2%) activity. It seems PGP traits do not work independently of each other but additively as it was suggested in the "synergistic hypothesis" that multiple mechanisms are responsible for the plant growth promotion and increased yield. Findings of this study could improve the current bio-fertilizer production procedure in research and related industries.
Keywords: Endophyte; IAA production; Phosphate solubilization; Rhizobacteria.