A selected rhizobial strain isolated from wild-grown Medicago monspeliaca improves productivity of non-specific host Trifolium alexandrinum

Abstract

The rhizobium-legume symbiosis fixes atmospheric nitrogen (N) to form organic N. This can eventually reduce the need for inorganic N fertilizers which are potentially more detrimental to the environment. The objectives of this work were to study the ability of the rhizobial strain NHBTR71, isolated from root nodules of Medicago monspeliaca, to improve the productivity of Trifolium alexandrinum L. var. Miskawi (berseem clover) and to identify this strain to the molecular level. Field inoculation experiments were carried out during two successive winter seasons on a clay loamy soil to evaluate the yield of berseem clover inoculated either with strain NHBTR71 or with the commercial Rhizobium leguminosarum bv. trifolii strain ARC100 (as inoculated control). Five cuttings were obtained at 50, 100, 150, 190 and 225 days after planting. The sequences of the 16S rRNA and the nodC genes of strain NHBTR71 have been looked for. At the forth cutting, clover plants dry matter, inoculated with strain NHBTR71, out-yielded those of the control plants; uninoculated or ARC100-inoculated plants by 21% and 19%, respectively. At the end of the growth period, the N content was two-fold greater in plants treated with strain NHBTR71 than in the control plants. 16S rRNA and nodC sequences of the strain NHBTR71 showed that it was closely related to members of genus Ensifer of Alphaproteobacteria, with E. meliloti USDA 1002T being the closest relative type strain. Infectivity test for strain NHBTR71 gave effective association with its original host, T. alexandrinum and Melilotus officinalis. It could be concluded that strain NHBTR71 effectively nodulated T. alexandrinum and improved its productivity. Also strain NHBTR71 proved to be closely related to members of genus Ensifer of Alphaproteobacteria. This is the first time to report the tendency of T. alexandrinum to establish a symbiotic association with members of the genus Ensifer.