الفهرس 
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Abstract
In the present research work, twenty Rhizobium trifolii isolates were collected from different geographical regions of Middle and Upper Egypt. For diversity and relatedness determination between these isolates their growth characters, symbiotic effectiveness and genetical polymorphism at the DNA level were investigated.
1. Growth characters
a- Morphological and growth parameters
Twenty pure isolates of putative Rhizobium strains were isolated
from root nodules of Egyptian clover (Trifolium alexandrinum). Results of the phenotypic and growth characteristics examination (Growth
rapidity on YEM medium, gram staining, colony colors, motility, aerobic
growth, cell shape, sporulation, color in the presence of Congo red),
demonstrated the belonging of such strains to R. trifolii.
b. Sugars test The twenty isolates of Rhizobium trifolii were tested on YEM agar medium free of sugar source or supplemented with one of various
compounds (fructose, glucose, lactose, sucrose, starch, surbose and
mannitol) as a sole carbon source. The results of this test revealed that the
isolates of Rhizobium trifolii under study have varied in their ability to
utilize specific sugars as a sole source of carbon.
c. Antibiotic Resistant Antibiotic resistance of the twenty isolates of R. trifollii was tested on YEM media supplemented with one of 13 different antibiotics. Generally, the results indicated that all isolates were highly resistant to cefobid, however, they showed high sensitivity to amikacin, gentamicin and streptomycin. Concerning the other antibiotics, all of the isolates revealed a considerable variation in thier resistance. Cluster analysis on the basis of antibiotic resistance showed a greater diversity of antibiotic resistance among these Rhizobium isolates. d. pH test The results of growth rates will examined for all isolates under six levels of pH (5, 6, 8, 9, 10 and 7 as a control) on YEM agar medium were examined. Data indicated that, all isolates survived at pH 6, 8 and 9 similar to the control. Some isolates grew weakly at pH 10, and some isolates could grow well at pH 5.