Genetic diversity of Sinorhizobium populations recovered from different Medicago varieties cultivated in Tunisian soils

A collection of 468 rhizobial isolates was obtained from different ecological areas of Tunisia by trapping them on Medicago sativa cv. Gabes, Medicago scutelleta cv. Kelson, Medicago truncatula, and Medicago ciliaris. A subsample of 134 rhizobia was chosen to determine their plasmid profile, and 89 isolates were subjected to multilocus enzyme electrophoresis (MLEE) and PCR/RFLP analysis using 16S, IGS (inter genic spacer), and nifKD probes. Twenty-five representatives from these isolates were evaluated for their nodulation and nitrogen fixation capacities. MLEE studies revealed two groups with highly heterogeneous host specificity and geographical origin. The discriminatory power was found to be slightly better with the amplified ribosomal intergenic region, than the nifKD genes. Divisions detected by nifKD amplified DNA analysis matched those established by ribosomal PCR-RFLPs. The comparison between different analyses revealed that MLEE illustrated better phenotypic properties of isolates than PCR-RFLP or plasmid content analysis. Clear distinction between Sinorhizobium meliloti and Sinorhizobium medicae were observed by analysis of the IGS symbiotic regions between nifD and nifK genes. Were able to distinguish three inoculation groups; isolates trapped from M. sativa cv. Gabes and M. scutelleta cv. Kelson formed one inoculation group which was more closely related to isolates trapped from M. truncatula than those trapped from M. ciliaris.