Genetic diversity of Bradyrhizobium japonicum within soybean growing regions of the north-eastern Great Plains of North America as determined by REP-PCR and ERIC-PCR profiling

摘要

While soybean (Glycine max [L.] Merr.) has been grown for several decades in several northern states in the United States, the introduction of early maturing cultivars of soybean in western Canada in the late 1990's has resulted in a exponential increase in soybean production in the region. Soybean grows in a symbiotic association with Bradyrhizobium japonicum [Kirchner] Jordan, which carries out biological nitrogen fixation within the plant roots. Previous studies have shown that rhizobia introduced from commercial inoculants tend to evolve quickly in soil. In this study, we examined the genetic diversity of 105 B. japonicum isolates from the soybean growing areas of the north-eastern Great Plains of North America by genomic fingerprinting techniques - REP-PCR and ERIC-PCR profiling. High genetic diversity was detected among the B. japonicum isolates sampled across various sites in North Dakota, South Dakota and Minnesota in the United States, and southern Manitoba in Canada. Analysis of the genetic diversity by the unweighted pair group method with an arithmetic mean algorithm (UPGMA) indicated an interesting segregation of isolates between US and Canadian sites. Results of this study also suggest a relatively rapid rate of genetic change within the B. japonicum populations and some evidence that soil texture may influence genetic diversity of the bacterium in the region.