Diversity of Rhizobium Bacteria Isolated from the Root Nodules of Leguminous Trees

Sixty rhizobial strains isolated from the root nodules of Acacia senegal and Prosopis chilensis in the Sudan were compared with 37 rhizobia isolated from woody legumes in other regions and with 25 representatives of recognized Rhizobium species by performing a numerical analysis of 115 phenotypic characteristics. Nineteen clusters were formed below the boundary level of 0.725 average distance, which was the level that separated the reference Rhizobium and Bradyrhizobium species. Our results indicated that tree rhizobia are very diverse with respect to their cross-nodulation patterns, as well as their physiological and biochemical properties, since 12 of the clusters formed consisted of tree rhizobia alone. Two distinctive features of tree rhizobia isolated in the Sudan were their high maximum growth temperature and their high salt tolerance.