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Abstract
European phytosanitary measures as applied to nurseries require that potential host plants within a radius of 2 m of a
Phytophthora ramorum-infected plant must be destroyed and that remaining host plants within a radius of 10 m cannot be traded until they are inspected and found to be pest free at further specific inspections. Despite the wide application and acceptance of these distances, they are not based on data regarding the in-field spread of this pathogen. Our previous study reported at the Fourth Sudden Oak Death Science Symposium demonstrated that direct aerial spread between potted plants in nurseries is rare and limited in distance. As an extension of this reported work, we have performed a study with two objectives: 1) to test the relative importance of direct versus indirect spread of
P. ramorum in nurseries, and 2) to test the movement of
P. ramorum from symptomatic plants to the root ball of neighboring plants via drain water film. Such movement could eventually lead to long-distance spread of the pathogen via the nursery trade in latently infected plants. Experiments were conducted at a mock nursery plot under specific biosafety conditions. The plot was lined with an impermeable film, a common practice in potted plant production in Europe.
Rhododendron was chosen as the test plant due to its susceptibility and its prevalence as a nursery host for
P. ramorum in Europe. Pathogen dispersal was monitored from individual infected potted plants placed in the middle of a circle of healthy detector plants. The rate at which the disease spread onto the detector plants was monitored in replicated experiments. Indirect splash dispersal (via the water film on the plastic ground cover and back to the leaves), as well as direct aboveground plant-to-plant dispersal (via air or via leaf-to-leaf splashing), were investigated by selective physical blocking of such pathways.
Parent Publication
Citation
Heungens, Kurt; Gehesquière, Bjorn; Van Poucke, Kris; Vercauteren, Annelies; Maes, Martine. 2013. Pathways of spread of
Phytophthora ramorum in a simulated nursery setting: an update. In: Frankel, S.J.; Kliejunas, J.T.; Palmieri, K.M.; Alexander, J.M. tech. coords. Proceedings of the sudden oak death fifth science symposium. Gen. Tech. Rep. PSW-GTR-243. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: p. 53.
