الفهرس 
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Abstract
A large number of Rhizobium isolates were collected from two different Governorates in Egypt, which isolated from soil rhizosphere and root nodules of Vicia faba L. plants. The isolates were characterized in the laboratory and in the field for biological nitrogen fixation parameters and the genetic diversity among promising isolates was assessed based on PCR methods. All rhizobial isolates showed a great variation in their growth biomass density at 620nm and in their ability to produce IAA during their growth in Ty medium. In pot experiments, all isolates nodulated successfully all the growing faba bean plants (Var. Giza 843) and registered a great variation in their symbiotic activities. The ability of conjugation of selected Rhizobium leguminosarum bv.viciae isolates with three strains of Pseudomonas fluorescens were assessed for possible gene transfer and its effects on nitrogen fixation criteria under normal and salt stress conditions. The filed experiment data showed that three transconjugant rhizobia could be considered promising, since they showed effectiveness in symbiotic nitrogen fixation performance. The results allowed selection of efficient salt-tolerant rhizobial isolates.
Five Rhizobium isolates (Rh 32, Rh 6-A, Rh 3-4, Rh RL3, and Rh 8-A) were selected according to their lab and field attributes and subjected to further characterizations. All isolates were found to produce higher nodulation efficieny, IAA, nitrogenase activity and increasing the root and shoot dry weight. The five selected Rhizobium isolates were identified by partial sequencing of 16S rRNA genes and were registered in the GenBank database with accession numbers LC593632.1, LC593633.1, LC593634.1, LC593635.1, and LC593636.1, respectively. The alignment and phylogenetic analyses of 16S rRNA sequences with closely related in the GenBank revealed that all isolates belonging to Rhizobium group. A molecular phylogenetic analysis was also done using six ISSR molecular markers. Amplification of bacterial genomic DNA of the five rhizobia isolates produced a total of 37 genomic loci, 54% of them were polymorphic and 46% were monomorphic. The average polymorphism rate was 83.85%. The ISSR approach was found to be suitable for detecting genetic diversity among rhizobial isolates. We concluded that the five rhizobia isolates will be promising as a source of genes for nitrogen fixation and plant growth-promotion.