Characterization of rhizobia from legumes of agronomic interest grown in semi-arid areas of Central Spain relates genetic differences to soil properties.

A study of symbiotic bacteria from traditional agricultural legumes from Central Spain was performed to create a collection of rhizobia from soils differing in physicochemical, analytical and/or agroecological properties which could be well-adapted to the environmental conditions of this region, and be used for sustainable agricultural practices. Thirty-six isolates were obtained from root-nodules of fifteen legume species (including Cicer arietinum, Lathyrus sativus, Lens culinaris, Lupinus spp., Medicago sativa, Phaseolus vulgaris, Pisum sativum, and Vicia spp.) from three agriculture areas with soils of different pHs and from a forest area with undisturbed soils. Phenotypical characterization revealed uniformity across the thirty-six isolates, with important exceptions in terms of environmental tolerance (three isolates survived at high temperatures, three at high salinity and three at acid pH). The molecular analysis of 16S rRNA gene showed a close relationship of twenty-nine isolates to Rhizobium leguminosarum, one to Rhizobium gallicum, one to Mesorhizobium ciceri, two to Sinorhizobium (Ensifer) meliloti and three to Bradyrhizobium canariense. The sequence analysis of a symbiosis-specific gene, nod C, showed a correlation with the plant host and grouped twenty-six isolates with Rhizobium leguminosarum bv. viciae, establishing the diversity in relation to legume-host. The 16S-23S rRNA intergenic spacer (IGS) region allowed for intraspecific differentiation, so that strains with equal 16S rRNA were grouped by means of their soil origin. These results indicated that phenotypical and genetically related strains may be widely distributed in this region and that soil abiotic characteristics could have a substantial bearing on the selection of the strains living in each environment.