Several phenotypic tests were used in this study to determine the biodiversity of rhizobial strains nodulating Medicago ciliaris L. Phenotypic characteristics of thirty-seven rhizobia strains isolated from root nodules of Medicago ciliaris L. growing in soils collected from Zerizer (north eastern Algeria) were studied. Tolerance to salinity, high temperatures, acid and alkaline pHs, drought and antibiotics and symbiotic and cultural characteristics allowed the description of a wide physiological diversity among tested isolates. Thirteen isolates from the total could grow at 45 degrees C. Only six isolates grew at 4% NaCl. Furthermore, the isolates that showed tolerance to salinity stress also showed tolerance to water stress, indicating direct relationships between these two physiological pathways. High salt- and water stress-tolerant strains were isolated and tested for their ability to fix biological nitrogen. Seven isolates were phenotypically categorised as Agrobacterium.
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