rep-PCR of tropical rhizobia for strain fingerprinting, biodiversity appraisal and as a taxonomic and phylogenetic tool.

Abstract

With more than 30 million doses of rhizobial inoculants marketed per year, it is probable that Brazilian agriculture benefits more than any other country from symbiotic N₂ fixation. As a result of strain-selection programs, 142 strains of rhizobia are officially recommended for use in commercial inoculants for ninety-six leguminous crops. In this study, sixty-eight of these elite strains were characterized by rep-PCR with the BOX-primer. Reproducibility of the DNA profiles was confirmed, suggesting efficacy of BOX-PCR both for control of quality of inoculants and for preliminary characterization of rhizobial culture collections. Strains of different species never showed similarity higher than 70% in the BOX-PCR analysis, however, some strains of the same species fit into more than one cluster, and correlation between BOX-PCR products and 16S rRNA sequences was low (7.6%). On the other hand, a polyphasic approach - 20%:80% of BOX-PCR: 16S rRNA which correlated well with the 16S rRNA analysis (95%), and provided higher definition of the genotypes, resulting in clearer indications of the taxonomic groups - might expedite rhizobial diversity studies.