Biodiv Sci

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Variation of Sym Plasmid and Symbiotic Effectiveness in Isolates of Rhizobium fredii


  1. Department of Microbiology, Huazhong Agricultural University, Wuhan, 430070
  • Received:1995-01-13 Revised:1995-03-31 Online:1995-12-20 Published:1995-12-20


The genetic diversity of symbiotic plasmids (pSyms) and symbiotic effectiveness was investigated in 11 isolates from one field population of Rhizobium fredii that had previously been characterized for plasmid content and serogroup polymorphisms. Two cloned DNA fragments from plas- mid pSA30 and pIJ1216 were used as nil HDK and nod DABC probes respectively to identify pSym variation. Although only a single plasmid hybridized to both nil and nod probes in each strain tested, pSym size variation was great ranging from 247 to 381 MDa. In addition to pSym, all of the R. fredii strains studied carried 1 - 5 other plasmids, of which one was approximately 500MDa cryptic megaplasmid. The strains with different size of pSym significantly varied in their symbiotic effectiveness determined by their chlorophyll content, total N. dry Weight of the plant and nitrogenase activity.