الفهرس 
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Abstract
This study aimed to determine effects of changing DNA content on symbiotic efficiency of some Rhizobia species. The four wild types ; R. japonicum R leguminosarum
ٌ R. meliloti R. trifoloii and the three mutants; R . meliloti histidineless, R. meliloti threonineless and R. trifolii threonineless were used in the present study. Treatments with colchicines , extraction and characterization ( amount, Tm and G-C%)of DNA , effect of changing DNA quantity (evaluated from the UV spectra on 260 nm) on; symbiotic properties (on the hosts ; Glycine max , vicia faba, Triflium alexandainum L. and Trigonella foenum G. ) of strains under study, their conjugants and their transformants were investigated.