title: Host Phenology and Leaf Effects on Susceptibility of California Bay Laurel to Phytophthora ramorum.
abstract: Spread of the plant pathogen Phytophthora ramorum, causal agent of the forest disease sudden oak death, is driven by a few competent hosts that support spore production from foliar lesions. The relationship between traits of a principal foliar host, California bay laurel (Umbellularia californica), and susceptibility to P. ramorum infection were investigated with multiple P. ramorum isolates and leaves collected from multiple trees in leaf-droplet assays. We examined whether susceptibility varies with season, leaf age, or inoculum position. Bay laurel susceptibility was highest during spring and summer and lowest in winter. Older leaves (>1 year) were more susceptible than younger ones (8 to 11 months). Susceptibility was greater at leaf tips and edges than the middle of the leaf. Leaf surfaces wiped with 70% ethanol were more susceptible to P. ramorum infection than untreated leaf surfaces. Our results indicate that seasonal changes in susceptibility of U. californica significantly influence P. ramorum infection levels. Thus, in addition to environmental variables such as temperature and moisture, variability in host plant susceptibility contributes to disease establishment of P. ramorum.
authors.affiliation: First, second, and fifth authors: Department of Biology, Sonoma State University, Rohnert Park, CA 94928; third author: Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, CA 94720; and fourth author: Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27606.
authors.forename: Steven F
authors.initials: SF
authors.lastname: Johnston
authors.affiliation: First, second, and fifth authors: Department of Biology, Sonoma State University, Rohnert Park, CA 94928; third author: Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, CA 94720; and fourth author: Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27606.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Cohen
authors.affiliation: First, second, and fifth authors: Department of Biology, Sonoma State University, Rohnert Park, CA 94928; third author: Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, CA 94720; and fourth author: Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27606.
authors.forename: Tamas
authors.initials: T
authors.lastname: Torok
authors.affiliation: First, second, and fifth authors: Department of Biology, Sonoma State University, Rohnert Park, CA 94928; third author: Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, CA 94720; and fourth author: Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27606.
authors.forename: Ross K
authors.initials: RK
authors.lastname: Meentemeyer
authors.affiliation: First, second, and fifth authors: Department of Biology, Sonoma State University, Rohnert Park, CA 94928; third author: Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, CA 94720; and fourth author: Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27606.
authors.forename: Nathan E
authors.initials: NE
authors.lastname: Rank
mesh_terms: D002140:California; D010838:Phytophthora / Q000502:physiology*; D010935:Plant Diseases / Q000382:microbiology*; D018515:Plant Leaves / Q000382:microbiology*; D012621:Seasons; D027422:Umbellularia / Q000382:microbiology*