Pathways of spread of Phytophthora ramorum in Rhododendron nurseries

Kurt Heungens, Bjorn Gehesquière, Kris Van Poucke, Annelies Vercauteren, Els Pauwels, Martine Maes

    Onderzoeksoutput: Hoofdstuk in Boek/Rapport/CongresprocedureC3: Congres abstract


    Within the European nursery industry, the Oomycete Phytophthora ramorum has mostly been detected on Rhododendron cultivars. EU phytosanitary measures against the spread of this pathogen, which have been in place for 10 years, require that potential host plants within a radius of 2 m of an infected plant must be destroyed and remaining host plants within a radius of 10 m are put in quarantine. Although these measures and distances are widely applied and accepted, they are not based on data regarding the in-field spread of this pathogen. Determining the pathways of in-field spread and the associated distances were the main objectives of this research.
    Our study was conducted at a mock nursery plot under specific conditions to ensure biosafety. Pathogen dispersal was monitored from individual infected potted Rhododendron plants in the middle of a ring of healthy detector plants that were placed at varying distances of the source plant. The distance over which the disease spread was monitored in separate experiments during spring, summer and fall. Under normal weather conditions, aerial dispersal of the pathogen was usually limited, and plant-to-plant contact was an important factor for successful spread. This lack of aerial dispersal was confirmed with a Burkard spore sampler. During intense rain events however, aerial dispersal in the absence of plant-to-plant contact was observed, and the pathways of such spread were studied. Indirect splash dispersal, via the water film on the plastic ground cover to the leaves, as well as direct (via air or via leaf-to-leaf splashing) aboveground plant-to-plant dispersal, were investigated by selective physical blocking of such pathways. Results indicated that indirect dispersal via the drain water film is at least as important as direct dispersal, and can take place over larger distances. Contamination of the drain water film was confirmed using leaf baits and direct PCR-mediated detection. Separate experiments demonstrated that the water films contribute to contamination in three ways: 1) splash dispersal, 2) direct inoculation of leaves when plants are tipped over, and 3) latent movement of the pathogen from the water film into the root ball.
    These data suggest that in nurseries, direct aerial dispersal of P. ramorum is limited in occurrence and distance, but the pathogen can spread via drain water over several meters on an impermeable surface. Drain water plays an important role in plant-to-plant spread to aerial plant parts as well as to the roots. These findings have implications for practical pest management as well as quarantine measures.
    Oorspronkelijke taalEngels
    Titelabstractbook 2nd ISHS Symposium on Woody Ornamentals of the Temperate Zone
    PublicatiestatusGepubliceerd - 2012
    Evenement2nd ISHS Symposium on Woody Ornamentals of the Temperate Zone - Gent, België
    Duur: 1-jul-20124-jul-2012

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