Little is known about factors that affect the indigenous populations of rhizobia in soils. We compared the abundance, diversity and genetic structure of @entity14441 viciae populations in soils under different crop managements, i.e., wheat and @entity2829 monocultures, crop rotation, and permanent grassland. Rhizobial populations were sampled from nodules of @entity3587 - or vetch plants grown in soils collected at three geographically distant sites in France, each site comprising a plot under long-term @entity2829 monoculture. Molecular characterization of isolates was performed by PCR-restriction fragment length polymorphism of 16S-23S rDNA intergenic spacer as a neutral marker of the genomic background, and PCR-restriction fragment length 0polymorphism of a nodulation gene region, nodD, as a marker of the symbiotic function. The diversity, estimated by richness in types and Simpson's index, was consistently and remarkably lower in soils under @entity2829 monoculture than under the other soil managements at the three sites, except for the permanent grassland. The highest level of diversity was found under @entity3505 monoculture. @entity377 sequences of the main rDNA intergenic spacer types were determined and sequence analysis showed that the prevalent genotypes in the three @entity2829 fields were closely related. These results suggest that long-term @entity2829 monoculturing decreased the diversity of @entity14441 viciae populations and favored a specific subgroup of genotypes, but the size of these populations was generally preserved. We also observed a shift in the distribution of the symbiotic genotypes within the populations under @entity2829 monoculture, but the diversity of the symbiotic genotypes was less affected than that of IGS types. The possible effect of such changes on biological @entity1568 fixation remains unknown and this requires further investigation.

Long-term effects of crop management on XXXX viciae populations.

@entity1568 :: ('MESH:D009584', 'Chemical') :: ['nitrogen'] @entity2829 :: ('4577', 'Species') :: ['maize'] @entity377 :: ('CHEBI:36976', 'Chemical') :: ['Nucleotide'] @entity14441 :: ('384', 'Species') :: ['Rhizobium leguminosarum biovar', 'R. leguminosarum biovar'] @entity3505 :: ('4565', 'Species') :: ['wheat'] @entity3587 :: ('3888', 'Species') :: ['pea']
@entity14441 :: (384,Species) :: ['Rhizobium leguminosarum biovar']
