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

A collection of 468 rhizobial isolates was obtained from different ecologic al areas of Tunisia by trapping them on Medicago sativa cv. Gabes, Medicago scutelleta cv. Kelson, Medicago truncatula, and Medicago ciliaris. A subsa mple 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. Twent y-five representatives from these isolates were evaluated for their nodulat ion and nitrogen fixation capacities. MLEE studies revealed two groups with highly heterogeneous host specificity and geographical origin. The discrim inatory power was found to be slightly better with the amplified ribosomal intergenic region, than the nifKD genes. Divisions detected by nifKD amplif ied DNA analysis matched those established by ribosomal PCR-RFLPs. The comp arison between different analyses revealed that MLEE illustrated better phe notypic properties of isolates than PCR-RFLP or plasmid content analysis. C lear distinction between Sinorhizobium meliloti and Sinorhizobium medicae w ere 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 inoculati on group which was more closely related to isolates trapped from M. truncat ula than those trapped from M. ciliaris.