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    Author(s): S. Rooney-Latham; C.L. Blomquist; A. Williams; E. Gunnison; T. Pastalka
    Date: 2017
    Source: Proceedings of the sudden oak death sixth science symposium. Gen. Tech. Rep. GTR-PSW-255. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 83-84.
    Publication Series: General Technical Report (GTR)
    Station: Pacific Southwest Research Station
    PDF: Download Publication  (179.0 KB)

    Description

    Phytophthora ramorum causes stem and bole cankers (sudden oak death) and foliar and twig dieback (ramorum blight) of susceptible plants. To date, more than 100 tree, shrub and herbaceous hosts of P. ramorum have been identified. In March 2015, plant samples were submitted to the CDFA Plant Pest Diagnostics Lab from the Marin Municipal Water District for disease analysis. The samples were collected near Bolinas Ridge in Marin County, CA in a maritime chaparral-live oak woodland forest with a history of P. ramorum and P. cinnamomi. The collectors noticed a large amount of unusual die-back in many plant species earlier in the drought year and were concerned that the plants were infected with P. cinnamomi or other Phytophthora root pathogens. Manzanita species (Arctostaphylos canescens, A. sensitiva, A. virgata), chinquapin (Chrysolepis chrysophylla) and chaparral pea (Pickeringia montana) were submitted for diagnosis. Isolation from the roots onto PARP media from samples was attempted even though the roots appeared healthy. No Phytophthora sp. grew on isolation plates and no Phytophthora spp. were detected from the roots using the Agdia Phytophthora spp. specific immunoassay. The Arctostaphylos and Pickeringia montana samples contained foliar tissue with leaf spot, vein necrosis and stem canker symptoms which were tested separately for Phytophthora. Phytophthora spp. was detected from the leaf spots and stem cankers from the Pickeringia montana and some of the Arctostaphylos spp. by immunoassay. In addition, P. ramorum was detected in culture and confirmed by sequence analysis from the symptomatic foliage of these hosts.

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    Citation

    Rooney-Latham, S.; Blomquist, C.L.; Williams, A.; Gunnison, E.; Pastalka, T. 2017. Identification of five new hosts of Phytophthora ramorum in an infested forest in California. In: Frankel, Susan J.; Harrell, Katharine M., tech. coords. Proceedings of the sudden oak death sixth science symposium. Gen. Tech. Rep. GTR-PSW-255. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 83-84.

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