Evaluation of genetic diversity of rhizobial strains nodulating soybean (Glycine max L.) isolated from Serbian fields

Among various legumes in Serbia, soybean (Glycine max L.) is widely grown and plays a central role as food and forage crops. However, the diversity of native rizobial strains in Serbia that can nodulate soybean is poorly understood. Diversity and phylogeny of 50 mainly slow-growing strains, isolated from root nodules of soybean in different geographical regions of Serbia, were studied using rep-PCR, 16S rDNA and recA gene sequencing. On the basis of 16S rRNA gene sequences, the majority of rhizobia were affiliated to the genus Bradyrhizobium, with B. japonicum as the closest related species. Phylogenetic analysis of recA sequences revealed high diversity of strains nodulating soybean. These isolates according to recA sequences clustered into at least 6 distinct groups within the genus Bradyrhizobium. One group of isolates was identified as B. japonicum and one strain was identified as B. liaoningense (100% similarity). The four other Bradyrhizobium groups may represent new species. Additionally, two strains isolated from soybean belong to the genus Rhizobium, showing low similarity (89.9%) to R. rhizogenes and they may form new Rhizobium species, too.