Abstract:
The symbiosis Rhizobium-legume leads to the formation of root nodules fixing atmospheric nitrogen. This natural process has a considerable economic and agronomic interest. In Algeria, the production of food and forage legume is affected by environmental and climatic stresses (high temperature, water deficit...). In this study, total of 237 isolates were isolated from root nodules collected on lentil (Lens culinaris), proteaginous and forage peas (Pisum sativum) grown in the field in six sites representing two contrasting eco-climatic zones, sub humid and semi-arid in Eastern Algeria. The main objective was to determine the
degree of variability of the genetic structure of populations of Rhizobium nodulating among sites and isolated plants in different climatic conditions. Our isolates were characterized by PCR-restriction fragment length polymorphism (RFLP) of the 16S-23S rRNA intergenic region (IGS), and the nodD-F symbiotic region. The combination of these haplotypes allowed to clustered the isolates into 26 distinct genotypes. Phylogenetic analysis of 16S rDNA sequences allowed us to classify all isolates as Rhizobium leguminosarum. Results obtained showed that the variation of symbiotic marker (nodD-F) is low with the predominance of one
haplotype nod g, previously recovered at high frequency in Europe. Sequence analysis of IGS further confirmed its high variability in the studied strains. An AMOVA analysis showed highly significant differentiation in the IGS haplotype distribution between populations from both eco-climatic zones. This difference was reflected by differences in dominant genotype frequencies. Conversely we could not detect any host plant effect. The nodD gene sequence based phylogeny suggests that symbiotic gene diversity in pea and lentil nodulating rhizobial populations in Algeria is low compared to that reported elsewhere in the world.
