title: Efficacy of hydrogen peroxide treatment for control of hairy root disease caused by rhizogenic agrobacteria.
abstract: OBJECTIVE
  Rhizogenic Agrobacterium strains are the causative agent of hairy root disease (HRD), an increasing problem in the hydroponic cultivation of tomato and cucumber in Europe. A previous study has demonstrated that different lineages of rhizogenic agrobacteria are able to form biofilms. Although hydrogen peroxide (H2 O2 ) is a frequently used biocide in hydroponic systems, until now its effectiveness to remove rhizogenic agrobacteria has not been unequivocally demonstrated. Therefore, the main objective of this study was to assess the efficacy of H2 O2 in controlling Agrobacterium-containing biofilms.
  
  
  RESULTS
  Using lab-scale experiments, we found a huge variation between different rhizogenic Agrobacterium strains in EC50 values, ranging from 18·8 to 600 ppm H2 O2 , representing the lowest and highest concentration tested respectively. Using pilot-scale experiments in which different H2 O2 concentrations were tested, treatment with 25 ppm H2 O2 was found to be ineffective. In contrast, treatment with 50 ppm significantly affected a catalase-negative Agrobacterium population, while a catalase-positive population was only marginally affected. For the catalase-positive Agrobacterium population, a treatment of 100 ppm H2 O2 was required to be effective. Finally, H2 O2 treatment of HRD in two commercial greenhouses was monitored, and showed that the H2 O2 concentration decreased considerably towards the end of the irrigation circuits. Further, a clear correlation was found between the actual concentration of H2 O2 and the incidence of HRD.
  
  
  CONCLUSIONS
  We showed that H2 O2 may be effective to reduce biofilm formation by rhizogenic bacteria. Nevertheless, it was clear from our results that the required H2 O2 concentration depends on the particular Agrobacterium strain(s) present in the greenhouse.
  
  
  CONCLUSIONS
  This is the first study that examined the effectiveness of H2 O2 to control HRD in hydroponic systems, and the effect of catalase activity on H2 O2 effectiveness. Our study has direct relevance for the highly intensive horticultural sector.
authors.affiliation: Laboratory for Process Microbial Ecology and Bioinspirational Management (PME&BIM), Department of Microbial and Molecular Systems (M2S), KU Leuven, Sint-Katelijne-Waver, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Bosmans
authors.affiliation: Research Station for Vegetable Production vzw, Sint-Katelijne-Waver, Belgium.
authors.forename: B
authors.initials: B
authors.lastname: Van Calenberge
authors.affiliation: Scientia Terrae vzw, Sint-Katelijne-Waver, Belgium.
authors.forename: A
authors.initials: A
authors.lastname: Paeleman
authors.affiliation: Research Centre Hoogstraten vzw, Meerle, Belgium.
authors.forename: R
authors.initials: R
authors.lastname: Moerkens
authors.affiliation: Research Station for Vegetable Production vzw, Sint-Katelijne-Waver, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Wittemans
authors.affiliation: Scientia Terrae vzw, Sint-Katelijne-Waver, Belgium.
authors.forename: S
authors.initials: S
authors.lastname: Van Kerckhove
authors.affiliation: Centre of Microbial and Plant Genetics, M2S, KU Leuven, Leuven, Belgium.
authors.forename: R
authors.initials: R
authors.lastname: De Mot
authors.affiliation: Laboratory for Process Microbial Ecology and Bioinspirational Management (PME&BIM), Department of Microbial and Molecular Systems (M2S), KU Leuven, Sint-Katelijne-Waver, Belgium.
authors.forename: B
authors.initials: B
authors.lastname: Lievens
authors.affiliation: Laboratory for Process Microbial Ecology and Bioinspirational Management (PME&BIM), Department of Microbial and Molecular Systems (M2S), KU Leuven, Sint-Katelijne-Waver, Belgium.
authors.forename: H
authors.initials: H
authors.lastname: Rediers
mesh_terms: D060054:Agrobacterium / Q000187:drug effects* / Q000502:physiology*; D018441:Biofilms / Q000187:drug effects; D002374:Catalase / Q000378:metabolism; D005060:Europe; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D018551:Solanum lycopersicum / Q000382:microbiology; D010935:Plant Diseases / Q000382:microbiology* / Q000517:prevention & control; D018517:Plant Roots / Q000382:microbiology
chemical_list: D006861:Hydrogen Peroxide; D002374:Catalase
keywords: biofilm; hairy root disease; hydrogen peroxide; pilot-scale system; rhizogenic Agrobacterium