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POSTERS: New and emerging diseases

Is an invasive forest pathogen moving into a new environment? Phytophthora ramorum found on chaparral plants in Coastal California.
Wolfgang Schweigkofler - Dominican University of California. Karen Suslow- Dominican University of California, Tomas Pastalka- Dominican University of California

Phytophthora ramorum, causal pathogen of Sudden Oak Death and ramorum blight, was discovered in California in the mid 1990ies, and spread quickly along a narrow band close to the coast characterized by mild temperatures and abundant year-long moisture. The foliar host California bay laurel (Umbellularia californica) is an essential driver for the spread of the disease to ‘dead-end hosts’, such as coast live oak (Quercus agrifolia). Recently, P. ramorum was detected on several chaparral plants (manzanita, Arctostaphylos spp.; chaparral pea, Pickeringia montana) on a high, sun-exposed ridge in Marin County. During 2018, a severe outbreak of disease was observed on Mt. Tamalpais, with symptoms including wilting, branch dieback and occasionally plant death. Several plants showed a positive reaction for Phytophthora spp. using immuno-strips; and P. ramorum was detected using PCR from a manzanita stem. In addition, Neofusicoccum australe (Botryosphaeriaceae) was isolated from a symptomatic plant. Potted rhododendron plants were placed near symptomatic plants on Mt. Tamalpais to monitor the possible spread of airborne inoculum and the effect of environmental parameters such as rainfall on the timing and appearance of disease symptoms. While it is still unclear whether the observed symptoms are caused by a disease complex, and which role P. ramorum has in it, mounting evidence indicates that P. ramorum is expanding its host range and moving into new environments.