الفهرس 
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Abstract
The present study was carried out during the period from 2016 to 9102 at Microbiology Department, Faculty of Science, Ain Shams University (ASU) and Sugar Crops Research Institute (SCRI), Agricultural Research Centre (ARC), Giza.
Saline soil conditions have resulted in reduction of the value and productivity of considerable areas of land throughout the world. This study has aimed to monitor the effect of salt stress condition on sugarcane and Stevia growth parameters and the role of PGPR application in alleviation of applied salt stress using classical microbiological and molecular techniques.
Two characterized halophilic PGPR were isolated from the rhizosphere of halophytic plants grown in Nuweiba region located at South Sinai governorate and south of Port Said governorate and identified as Streptomyces variabilis and Streptomyces fradiae.
Pot experiment was carried out and divided into four sets according to irrigation with different levels of NaCl concentrations (0, 2000, 4000, and 6000 ppm) for sugarcane
and (0, 1000, 1500, and 2000 ppm) for Stevia.
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The potential of Streptomyces fradiae to promote sugarcane setts germination was higher than that of Streptomyces variabilis under saline condition except for 6000 ppm, while Streptomyces variabilis-inoculated stevia plantlets could ameliorate the adverse effect of salt stress better than Streptomyces fradiae -inoculated plants except for 2000 ppm.
Regarding sugarcane, under non-saline condition, the shoot height was improved by 26% and 31% for Streptomyces variabilis and Streptomyces fradiae-inoculated plants respectively in comparison to the non-inoculated plants. Under saline condition, the enhancement in shoot height was recorded to be 17, 30, and 110% at 2000, 4000 and 6000 ppm NaCl treatments for Streptomyces variabilis-inoculated plants and 12, 73 and 51% at 2000, 4000 and 6000 ppm NaCl treatments for Streptomyces fradiae inoculated plants.
Leaf number of PGPR-inoculated plants with no salt treatment was increased by 30 and 41% for Streptomyces variabilis and Streptomyces fradiae, respectively compared to the non-inoculated plants. While PGPR- inoculated plants under salt stress were increased non-significantly in the leaf number.
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Regarding Stevia plant, the selected halophilic streptomycetes isolates have promoted the growth of Stevia significantly under non-saline condition. Under saline condition, the Streptomyces variabilis-inoculated plants at 1500 ppm NaCl has recorded 159% increase in shoot height, while the Streptomyces fradiae-inoculated plants at 2000ppm NaCl has recorded 143% compared to the non-inoculated plants. Also in the case of the leaf number, the selected halophilic Streptomycetes isolates have increased the leaf number obviously under non-saline condition.
Total cellular proteins (TCPs) were extracted from 7- days old cultures of the two selected actinobacteria isolates and the three control organisms. Streptomyces variabilis and Streptomyces fradiae has harbored a unique and characteristic polypeptide running approximately at 200 kDa which was identified by nano HPLC-ESI-MS/MS as Elongation Factor Thermo Unstable (EF-Tu).
TCPs were extracted from 42-days old stevia leaves after application of salinity stress. A pronounced enhancement was detected in the SDS-PAGE patterns of the inoculated salt- stressed plants at ~53 kDa. This polypeptide was identified as the large subunit of ribulose- 1, 5-biphosphate
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carboxylase/oxygenase (RuBisCO) enzyme complex. RuBisCO is the major carboxylating enzyme used by all photosynthetic organisms to incorporate atmospheric CO2 into carbohydrates necessary for plant growth.