Symbiotic competence, genetic diversity and plasmid profiles of Egyptian isolates of a Rhizobium species from Leucaena leucocephala (Lam.) Dewit

L.D. KUYKENDALL, D.M. SWELIM, F.M. HASHEM, S.M. ABDEL‐WAHAB AND N.I. HEGAZI. 1996. There is considerable interest in improving nitrogen fixation in tropical legume trees to increase soil fertility, particularly in developing countries. To provide information needed for the development of improved strains, characterization of strains of Leucaena‐nodulating Rhizobium was performed. Thirteen strains were isolated from root nodules of Leucaena leucocephala grown in different geographical regions in Egypt. Plasmid DNA profile groups, including identification of symbiosis‐controlling plasmids, were defined. Symbiotic competence was determined in plant tests and some strains were perhaps more symbiotically proficient at fixing nitrogen with L. leucocephala than were reference strains. The genetic diversity of these strains was determined by RFLP analysis of total DNAs using, as probes, six arbitrarily selected cosmid clones from a gene library of strain TAL 1145, a well‐characterized reference strain. There were four plasmid profile groups which did not correlate with either symbiotic competence or RFLP analysis. RFLP analysis, unlike plasmid profiles, permitted a determination that all 13 Egyptian strains were evidently homogeneous and quite distinct from previously studied Leucaena‐nodulating Rhizobium as represented by reference strains.