• allozyme electrophoresis;
  • founder effect;
  • genetic structure;
  • linkage disequilibrium;
  • Rhizobium leguminosarum;
  • selection


The importance of genotype-specific selection between host and symbiont, founder effect, and clonal reproduction in Rhizobia leguminosarum biovar trifolii populations is relatively unknown. A field experiment was conducted to sample 1268 isolates of R. l. bv. trifolii from four genotypically distinct Trifolium pratense plants for allozyme variation at nine loci. Genetic and genotypic variation, population genetic substructure, and linkage disequilibrium were estimated. Of the 1268 isolates 188 genotypically distinct strains (electrophoretic types or ETs) were identified with an average of 11.04 different ETs per plant. Total genetic diversity in the plot was 0.346 and most of the variation was found within plants (= 80%). Our data suggests that genotype-specific selection between the rhizobia and the four host-plant genotypes tested does not influence local population structure, but evidence of founder effect was present. Significant linkage disequilibrium was observed and is most likely due to the clonal reproduction of R. l. bv. trifolii.