Group-specific differentiation of Rhizobium from clover species by PCR amplification of 23S rDNA sequences.

Two 20-bp primers that provide group-specific detection of Rhizobium spp. by polymerase chain reaction (PCR) have been used to differentiate strains that belong to different effectiveness groups within the Rhizobium-Trifolium cross-inoculation group. The target for DNA amplification was a 370-bp fragment of the 23S rDNA region. Analysis of additional root-nodule forming, as well as root-associated bacterial species by PCR-primer assay revealed that variability within this 20-bp segment of the 23S rDNA region may be widespread and provide an effective identification tool. Our data suggest that strains of Rhizobium isolated from the perennial clover Trifolium semipilosum may be phylogenetically more closely related to Rhizobium etli.