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    Author(s): S. Denman; E. Moralejo; S.A. Kirk; E. Orton; A. Whybrow
    Date: 2008
    Source: In: Frankel, Susan J.; Kliejunas, John T.; Palmieri, Katharine M., tech. coords. 2008. Proceedings of the sudden oak death third science symposium. Gen. Tech. Rep. PSW-GTR-214. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. pp. 201-207
    Publication Series: General Technical Report (GTR)
    Station: Pacific Southwest Research Station
    PDF: View PDF  (253 KB)

    Description

    Phytophthora ramorum and P. kernoviae are newly discovered invasive Phytophthoras causing leaf necrosis, shoot tip dieback (mostly on ornamental and forest understorey host species) and bleeding cankers on tree trunks of a wide range of plant species. Both pathogens are now present in south-west England. Sporulation occurs on infected shoots and foliage but not on bleeding stem cankers; thus foliar hosts are key in disease epidemiology. During evaluation of a two-year field trial established to assess infection periods and infection incidence, we discovered that naturally infected, asymptomatic leaves supported sporulation of both pathogens. Asymptomatic leaves of 79 percent of rhododendron trap plants exposed to natural inoculum yielded P. kernoviae in the first year of field trials and 53 percent in the second year, whereas 36 percent of trap plants yielded P. ramorum in the first year and 33 percent in the second. We realized that sporulation occurred because asymptomatic leaves subjected to baiting remained asymptomatic for the duration of the baiting period, but the baits were positive for the pathogen. The foliage of approximately 20 percent of the positive trap plants remained asymptomatic for the duration of the trial and baiting period, indicating that asymptomatic infection can endure for at least 8 days but may be as long as 22 days. In laboratory trials artificially-inoculated leaves and fruits supported P. ramorum sporulation, sporangia were consistently observed on asymptomatic leaves and fruit of several Mediterranean species.

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    Citation

    Denman, S.; Moralejo, E.; Kirk, S.A.; Orton, E.; Whybrow, A. 2008. Sporulation of Phytophthora ramorum and P. kernoviae on asymptomatic foliage and fruit. In: Frankel, Susan J.; Kliejunas, John T.; Palmieri, Katharine M., tech. coords. 2008. Proceedings of the sudden oak death third science symposium. Gen. Tech. Rep. PSW-GTR-214. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. pp. 201-207

    Keywords

    P. kernoviae, P. ramorum, asymptomatic, artificially inoculated, foliage, fruit, natural inoculum, trap plants

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