Epidemiology and Ecology of Phytophthora ramorum in Redwood/Tanoak Forest Ecosystems of the California Coast Range
P. E. Maloney1, S. F. Kane2, C. E. Jensen2,and D. M. Rizzo2
A total of 120 plots have been established in the redwood/tanoak forest type along the California coast range to study the epidemiology and ecology of Phytophthora ramorum in this forest ecosystem. Our plots represent a north-south gradient of Phytophthora ramorum populations in this forest community from Sonoma to Monterey Counties. At each site, we have collected disease, environmental, forest structure and composition data. From this data, relationships will be made between disease incidence and a number of key biological and environmental parameters. Hosts present in this forest type include redwood (Sequoia sempervirens), tanoak (Lithocarpus densiflora), bay laurel (Umbellularia californica), madrone (Arbutus menziesii), huckleberry (Vaccinium ovatum), toyon (Heteromeles arbutifolia), bigleaf maple (Acer macrophyllum), and Douglas fir (Pseudotsuga menziesii). From the 120 plots, approximately 2150 symptomatic trees (of all species) were sampled and 35% of those trees were P. ramorum positive. Because rain is a key factor in pathogen dispersal, raintraps were placed in 5 plots at Jack London State Park to determine levels of inoculum and dispersal in these forests during the winter of 2001-2002. We recovered P. ramorum from rainwater throughout the rainy season with a large increase in inoculum during a May rain event. Soil/litter collections were made somewhat in concert with rainwater collections. Recovery frequency of inoculum from soil during the rainy season was approximately 20% from Sonoma and Marin county sites. Summer soil collections show a dramatic decline in inoculum recovery, to 0%, of P. ramorum. In the spring 2002, lines with mesh bags containing rhododendron leaves, as a P. ramorum bait, were placed across 2 streams in three locations at Jack London SP and adjacent property. P. ramorum was recovered throughout the spring and summer months in these streams, regardless of any rain event. During 2002-2003, weather monitoring stations will be used to determine specific environmental conditions (i.e., relative humidity, temperature, rainfall amount and duration) on these sites that favor inoculum production. Raintraps will be stratified in the canopy to determine local dispersal (within the canopy) and long distance dispersal (inoculum leaving the canopy).
1Department of Plant Pathology, University of California, One Shields Ave., Davis, CA 95616; (530) 754-9894; tbntm@telis.net
2Department of Plant Pathology, University of California, One Shields Ave., Davis, CA 95616
|
