Evaluation of Plant Growth Promoting of Salt-tolerant Rhizobacteria Isolated from Egyptian Saline Soils

Abstract

Plant growth promoting rhizobacteria (PGPR) are alternative strategy for mitigating the negative impacts of salinity stress on plants. The aim of this study was to isolate native PGPR with high plant growth promoting traits from Egyptian soils which could be used as an environmentally eco-friendly technique for alleviating salinity stress. Twenty-five Azotobacter spp. were isolated from Most Probable tubes, then all isolates were tested to grow in different concentrations of NaCl for salt tolerance. The highest tolerant Azotobacter spp. were seven isolates which then were tested for their ability to fix nitrogen in vitro using acetylene reduction technique. The most active Azotobacter isolate was (No. AZ 1) which recorded 27.70 nmoles C2H4/ml/h. On the other side, twenty-five phosphate solubilizing bacteria were isolated from Pikovskaya's agar plates. All isolates were tested for salt tolerance and four isolates were selected for further understanding the mechanism of phosphate solubilization and its relationship to pH in liquid Pikovskaya's medium supplemented with tri-calcium phosphate. The highest quantity of released phosphorus in the culture (16.31 mg p /100 ml) was for the isolate PSB 14 which selected for further studies. As well as isolates AZ 1 and PSB 14 showed high effectiveness in the production of indole acetic acid (67.87 and 8.99 µg/ml), respectively. Based on the 16S rRNA sequence analysis, AZ 1 and PSB 14 were identified as Azotobacter salinstris ON809700 and Bacillus amyloliquefaciens ON818999. Based on this study, these salt-tolerant isolates could add benefits to plant grown in saline conditions.

Potential Impacts of Certain N2-Fixing Bacterial Strains and Mineral N Doses for Enhancing the Growth and Productivity of Maize Plants

“…These results agreed with the authors of [26,27], who stated that the Azotobacter isolate was found to be Na + -dependent, N 2 -fixing, and plant growth promoter strains. On the other hand, [28] found that some of the isolated bacteria showed remarkable plant growth-promoting traits, including high salt tolerance, N 2 fixation, P solubilization, and IAA production.…”