PARENT SESSION
Oral Session #7: Disturbance in Forests: Fire, wind, and other.
Presiding: G. Murray
Monday, August 5. 8:00 AM to 11:30 AM. Cochise Meeting Room, TCC.
Phytophthora ramorum (Sudden Oak Death) in California oak woodlands: expanded geographic and host ranges.
Davidson, Jennifer*,1,2, Maloney, Patricia2, Garbelotto, Matteo3, Wickland, Allison2, Tjosvold, Steve4, Slaughter, Garey2, Rizzo, David2, 1 Pacific Southwest Research Station, Berkeley, CA2 Plant Pathology, Davis, CA3 Environmental Science, Policy, and Management, Berkeley, CA4 University of California Cooperative Extension, Watsonville, CA
ABSTRACT- The newly discovered Phytophthora ramorum canker disease of oak (Sudden Oak Death) continues to threaten California woodlands where Quercus agrifolia (coast live oak), Lithocarpus densiflorus (tanoak), or Quercus kelloggii (black oak) are dominant species. The disease on oak and tanoak now spans a 600 km range, extending from Big Sur, California to southwest Oregon. In addition to oak and tanoak species, P. ramorum infects 11 other native hosts with varying levels of disease severity. Although viable spores have yet to be found on infected oak or tanoak bark, laboratory and field experiments indicate that foliar hosts, such as Umbellularia californica (bay laurel), Rhododendron spp., and L. densiflorus, may serve as sources of spores that are produced on leaves and dispersed in rain, thereby contributing to significant aerial transmission of P. ramorum. In 2001, we placed raintraps in a woodland next to infected Q. agrifolia and U. californica. Spores of P. ramorum recovered from raintraps increased in number as the rainy season progressed. Experiments are underway to determine the role of increasing numbers of infected U. californica leaves in leading to higher inoculum levels at later time points in the rainy season. Ultimately, aerial transmission of P. ramorum by sporulation from leaves of foliar hosts may help explain the rapid transmission of this emerging pathogen among oak and tanoak trees.
KEY WORDS: forest pathology, invasive pathogen