1Soils, Water and Environment Research Institute, Agricultural Research Center, Giza, Egypt
2Plant Pathology Research Institute, Agricultural Research Center, Giza, Egypt
Abstract
A number of osmophilic diazotrophic bacteria was isolated from saline soil and studied for tolerance to osmotic stress generated by increased concentrations of NaCl (2 - 10 %). Bacterial growth, nitrogenase activity and production of indole acetic acid (IAA), gibbrelic acid (GA) and abscisic acid (ABA) under osmotic stresses were determined. Only one isolate that successfully showed high tolerance to NaCl was identified as Rhizobium radiobacter using Biolog (Microlog 3.70 database) and confirmed through PCR technique and 16SrRNA gene sequence analysis. The Rhizobium radiobacter strain showed an acetylene reduction activity of 1000.4 nmoles C2H4/100ml/hr in absence of salt, against 100.0 nmoles C2H4/100ml/hr in culture medium containing 6 % of NaCl. The highest amounts of IAA, GA and ABA were produced at 8 , 4 and 9 % NaCl, being 27.5, 4.9 and 2.2 µg/ml, respectively. The N2-fixation efficiency of candidate was very much saltdependent, where the record estimates dramatically decreased from 162 to 50 mg N fixed/g C oxidized as the salt level increased up to 9 %.
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