Diversités taxonomique et moléculaire des rhizobiums nodulant le pois chiche (Cicer arietinumL.), dans l’Est Algérien.
Ben Guedouar, Ammar
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Nodulating chickpea bacteria were examined for their diversity and biogeography taking three winter varieties into account as host plants. The study included nine sites in eastern Algeria with different climates and physicochemical characteristics. In order to operate these sites, the most efficient nodulation partners from these regions are sought after. Bacterial isolations were performed using trapping protocols in greenhouse with each varieties and soil samples from each site. A molecular study was carried out on the analysis of the sequences of five DNA fragments (DNA r16S, recA, IGS 16S-23S, nodC and nifH), showed that the nodules were occupied by rhizobia and non rhizobia, with a high degree of diversity within each. Four genera of rhizobia are present: Ensifer (46%), Rhizobium / Agrobacterium (23%), Mesorhizobium (21%) and Burkholderia (10%). Large differences are noted between sites and varieties for their ability to induce nodules and to involve a specific rhizobial genus or species as a symbiot. Specificity is detected between the genera of Mesorhizobium and Burkholderia associated with the site of Jijel as well as between the genus Ensifer and Biskra and between the genus Rhizobium and Tebessa. With this latter pair, variety II resulted in the greatest nodulation level while the nodulation efficiency of variety III is much more striking with the three other genera. Despite these variations, no correlation was found between the chemical and physical characterizations of the soil samples and those of the plant genotype. Within the Mesorhizobium genus, at least 5 different known genospecies are present (M.ciceri, M. amorphae, M. gobiense, M. opportunistum and M. Tamayadense), whereas some isolates could probably represent at least one new species of Mesorhizobium, closely related to the M.ciceri / M.loti cluster. Conversely to the significant genetic diversity shown by 16S rDNA, IGS 16S-23S and recA, symbiotic diversity represented by nodC and nifH was low. This may reflect acquisition of the symbiotic genes by lateral transfer. To our knowledge, this study is the first systematic evaluation of chickpea rhizobia in Algeria. For the first time it is shown that the species M. gobiense and M. tamadayense are symbiotic bacteria of chickpea. Also for the first time it is revealed that the genus Mesorhizobium is not dominant and the nodulation of chickpea is not limited to the genus Mesorhizobium and can be carried out by different species and genera of rhizobia, although it should be confirmed by more studies. This certainly opens up a broad spectrum for the selection of reliable symbiotic partners for the cultivation and yield of chickpea in Algeria.