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Abstract
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.
Parent Publication
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.
