Genetic diversity of rhizobia associated with alfalfa in Serbian soils

We have evaluated the genetic diversity and phylogeny of alfalfa rhizobia isolated from different types of soils in Serbia and their ability to establish an effective symbiosis with alfalfa. About 80 strains isolated from nodules of Medicago sp. were characterised by rep-PCR analyses, partial and complete 16S rDNA gene sequencing and recA gene sequencing. Symbiotic effectiveness (nodulation and shoot dry weight) of rhizobia was evaluated in glasshouse experiments. The results of the sequence analyses revealed that Sinorhizobium meliloti is the dominant species in alfalfa nodules. One strain was identified as S. medicae while three other strains were identified as Rhizobium sp. According to current data these Rhizobium sp. strains can be recognized as a new species, however, further analyses are needed to clarify the taxonomic identity of these strains. Despite the fact that the majority of the strains were identified as S. meliloti, a high genetic diversity at strain level was detected. Almost all isolates shared the ability to nodulate and fix nitrogen with Medicago sp., except 12 of them that were not capable of fixing nitrogen with this plant. This was the first systematic study of rhizobia isolated from Serbian soil