Isolation, Screening, Identification, and Salinity and Drought Stress Tolerance of Selected Plant Growth Promoting Rhizobacteria (PGPR) of Pistachio (Pistacia vera). Trees

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Three hundred isolates from rhizosphere of pistachio (Pistacia vera) trees of Kerman province were isolated. Isolates were examined for salinity tolerance at 0, 100, 200, 400 and 600 mM concentration of sodium, calcium and magnesium chloride salts (SAR=13). One hundred and four bacterial isolates were initially selected based on their salinity tolerance and morphological diversities. They were then screened for their Plant Growth Promoting (PGP) characteristics as phosphate solubilization, utilization of ACC as sole nitrogen source, as well as production of siderophore and indoleacetic acid (IAA)-like substances. Eleven isolates with strong tendency for one or more PGPR traits were exposed to stimulated drought stress by adding polyethylene glycol 6,000 (PEG-6,000) to the NB medium. The concentrations of PEG were 0, 202.13, 295.75, 428.38 and 548.80 gr PEG/kgNB media, respectively equal of 0, -5, -10, -20 and -30 bar. Of the 300 isolates, more than 80% were able to grow at 600 mM of salinity level. Of the 104 isolates, about 80% showed tendencies for one or more of the PGPR traits tested, 46% were able to produce siderophore, 47% produced IAA, 33% solubilized nonsoluble phosphates, and 22% produced ACC-deaminase. Polyethylene glycol reduced growth significantly (measured as optical density (OD600nm)), but only one isolate at -20 and two isolates at -30 bar were not able to grow. The isolates were morphologically, biochemically and physiologically tested for partial identification.

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