Genetic diversity of fast-growing rhizobia that nodulate soybean (<i>Glycine max</i> L. Merr)

Abstract

The fast-growing <i>Rhizobium</i> sp. strain NGR234, isolated from Papua New Guinea, and 13 strains of <i>Sinorhizobium fredii</i>, isolated from China and Vietnam, were fingerprinted by means of RAPD, REP, ERIC and ARDRA. ERIC, REP and RAPD markers revealed a considerable genetic diversity among fast-growing rhizobia. Chinese isolates showed higher levels of diversity than those strains isolated from Vietnam. ARDRA analysis revealed three different genotypes among fast-growing rhizobia that nodulate soybean, even though all belonged to a subcluster that included <i>Sinorhizobium saheli</i> and <i>Sinorhizobium meliloti</i>. Among <i>S. fredii</i> rhizobia, two strains, SMH13 and HH303, might be representatives of other species of nitrogen-fixing organisms. Although restriction analysis of the <i>nifD–nifK</i> intergenic DNA fragment confirmed the unique nature of <i>Rhizobium</i> sp. strain NGR234, several similarities between <i>Rhizobium</i> sp. strain NGR234 and <i>S. fredii</i> USDA257, the ARDRA analysis and the full sequence of the 16S rDNA confirmed that NGR234 is a <i>S. fredii</i> strain. In addition, ARDRA analysis and the full sequence of the 16S rDNA suggested that two strains of rhizobia might be representatives of other species of rhizobia.