Symbiotic and phylogenetic diversity of rhizobia associated with native and introduced Acacias in Algeria

In the arid zones were crop production is reduced due to drought combined to low soil fertility, the use of symbiotic native legume trees adapted to such harsh conditions could enhance the productivity of agroforestry systems. In North Africa, Acacia species are good candidates for this purpose since they can grow on N-deficient soils and improve their N balnce due to their symbiotic association with rhizobia, nitrogen-fixing soil bacteria. In order to identify and select. Efficient acacia-rhizobia symbiotic associations, soil samples and root nodules from seven Acacia species, five native (A ehrenbergiana, A laeta, A. niIotica, A. seyal, A. tortimis) and two introduced (A. karroo, A. saligna). were collected in arid and semi-arid regions of Algeria from Oran to Tamanrasset. A collection of 22 bacteria1 strains was obtained after trapping on Acacia seedlings inoculated with soil samples originating from nine geographic sites. 16S rDNA sequencing revealed that the new strains represented different species in Sinorhizobium and Rhizobium. This genetic diversity was confirmed by phenotypic characterisation through biochemical assays and host spectrum. Some strains were particularly tolerant to low pH and high NaCl concentrations. temperature and osmotic stress in vitro conditions. In a next step, selection of efficient rthizobia displaying a high nitrogen-fixing potential under stress conditions will be carried out in controlled conditions before testing them in field conditions. (Texte integral)