Aims: In order to understand the genetic diversity of Acacia tortilis ssp. raddiana-rhizobia in Tunisia, isolates from nine geographical locations were obtained and analysed.
Methods and results: Characterization using restriction fragment length polymorphism analysis (RFLP) of PCR-amplified 16S rRNA gene and the intergenic spacer (IGS) between the 16S and 23S rRNA genes was undertaken. Symbiotic efficiency of the strains was also estimated. Analysis of the 16S rRNA by PCR-RFLP showed that the isolates were phylogenetically related to Ensifer ssp., Rhizobium tropicii-IIA, and Rhizobium tumefaciens species. Analysis of 16S-23S spacer by PCR-RFLP showed a high diversity of these rhizobia and revealed eleven additional groups, which indicates that these strains are genetically very diverse. Full 16S rRNA gene-sequencing showed that the majority of strains form a new subdivion inside the genera Ensifer, with Ensifer meliloti being its nearest neighbour. Nodulation test performed on the plant host demonstrated differences in the infectivity among the strains.
Conclusion: Rhizobial populations that nodulate specifically and efficiently Acacia tortilis ssp. raddiana in representative soils of Tunisia is dominated by E. meliloti-like genomospecies.
Significance and impact of the study: This paper provides the first clear characterization and symbiotic efficiency data of rhizobia strains nodulating A. tortilis in Tunisia.