title: Colonization of the developing rhizosphere of sugar beet seedlings by potential biocontrol agents applied as seed treatments.
abstract: OBJECTIVE
  Poor colonization of the rhizosphere is a major constraint of seed treatment biological control. The objectives of this study were to; examine the colonization of the rhizosphere of sugar beet seedlings by selected rhizobacteria; determine the influence of the host rhizosphere and percolating water on the distribution of the bacteria; and deliver two biological control agents (BCAs) by co-inoculation.
  
  
  RESULTS
  Rifampicin-resistant bacterial strains (Rif +) applied as single treatments to seed sown in columns of field soil produced persistent populations of 5-9 log10 cfu g-1 in the infection court of the damping-off pathogen Aphanomyces cochlioides in a controlled environment. However, isolates varied in their ability to colonize the lower rhizosphere. Percolating water significantly increased the colonization of the upper rhizosphere. Bacterial populations in the soil profiles of "non-rhizosphere" controls declined markedly with time. There was no interaction between the two selected BCAs applied as a seed treatment mixture.
  
  
  CONCLUSIONS
  The distribution of the bacteria resulted primarily from root colonization although percolating water may modify the colonization profiles. Co-inoculation of the sugar-beet rhizosphere is a viable proposition.
  
  
  CONCLUSIONS
  Potential BCAs were successfully delivered to the known infection court of A. cochloides and persisted for the infection period. This bioassay can be used as a tool for the selection of BCAs for field trials.
authors.affiliation: IACR-Broom's Barn, Higham, Bury St Edmunds, Suffolk, IP28 6NP, UK. richard.walker@bbsrc.ac.uk
authors.forename: Richard
authors.initials: R
authors.lastname: Walker
authors.forename: S
authors.initials: S
authors.lastname: Rossall
authors.forename: M J C
authors.initials: MJ
authors.lastname: Asher
mesh_terms: D001410:Bacillus megaterium / Q000254:growth & development; D001419:Bacteria / Q000254:growth & development* / Q000302:isolation & purification; D027461:Beta vulgaris / Q000196:embryology / Q000254:growth & development / Q000382:microbiology*; D018546:Hypocotyl / Q000382:microbiology; D010572:Pest Control, Biological / Q000379:methods*; D027343:Rhizome / Q000254:growth & development / Q000382:microbiology*; D012293:Rifampin / Q000494:pharmacology; D012639:Seeds / Q000382:microbiology*; D012988:Soil Microbiology
chemical_list: D012293:Rifampin