Phenotypic, genotypic, and symbiotic diversities in strains nodulating clover in different soils in Spain

Trifolium species are the most common legumes present in wild Spanish soils; however, there are no studies to date on the diversity of rhizobia nodulating clover in Spain. Twenty strains from different Spanish soils with acidic, neutral, and basic pH were selected to study their genotypic, phenotypic, and symbiotic features. The results showed that the isolates were genotypically diverse, displaying 12 different DNA fingerprint patterns and also 14 different plasmid profiles. Although they have 16S rRNA gene sequences that are nearly identical to that of the type strain of Rhizobium leguminosarum, their recA and atpD gene sequences were phylogenetically divergent from those of R. leguminosarum reference strains, and phenotypic divergence as well as different host ranges were also found. Although most of them nodulated both Trifolium and Phaseolus, only 5 strains were also able to nodulate Pisum. The results of the effectiveness analysis showed a high variability in the symbiotic characteristics of our strains and suggested that Pisum is the more restrictive host of this group. Interestingly, some of the Trifolium isolates showed an ability to promote growth of Pisum in the absence of nodulation.