PARENT SESSION
Oral Session # 33: Pathogens, Toxins, and Disease II: Plants.
Presiding: A Davelos
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 201.
Forest composition influences transmission of Phytophthora ramorum (Sudden Oak Death) in California oak woodlands.
Davidson, Jennifer*,1, 2, Maloney, Patricia2, Wickland, Allison2, Rizzo, David2, 1 Pacific Southwest Research Station, Albany, CA, USA2 University of California-Davis, Davis, CA, USA
ABSTRACT- Phytophthora ramorum, the causal agent of Sudden Oak Death, is now known to infect over twenty native plants in California oak woodlands. The potential for P. ramorum to spread in these forests depends on its ability to form reproductive spores on hosts during winter rains and to survive within hosts during hot, dry summer months. We have begun to investigate sporulation and survival of P. ramorum in two common forest types in Northern coastal California: mixed-evergreen forest (dominated by coast live oak (Quercus agrifolia) and bay laurel (Umbellularia californica)) and tanoak-redwood forest. To date, studies placing infected plant tissue in moist chambers show that spores are produced on bay leaves from mixed-evergreen forest, and bay leaves, tanoak (Lithocarpus densiflorus) leaves, and tanoak twigs from tanoak-redwood forest. We initiated additional studies on the survival of P. ramorum in bay leaves because the pathogen sporulates prolifically on this host, which may be key for spread of P. ramorum. Monitoring infected bay leaves in both forest types indicated that infected bay leaves were significantly more likely to abscise in drier mixed-evergreen forest as opposed to tanoak-redwood forest. Furthermore, leaf abscission and forest type influenced survival of P. ramorum. Recovery of P. ramorum from attached, infected bay leaves at the end of summer was 24% and 60% from a mixed-evergreen forest and a tanoak-redwood forest, respectively. In contrast, recovery of P. ramorum from abscised bay leaves collected during summer months from leaf litter in a mixed-evergreen forest was nearly zero. In tanoak-redwood forests, higher survival of P. ramorum in bay leaves throughout the summer and additional spore production from dominant hosts like tanoak may contribute to differences in levels and timing of inoculum produced in these two forest types during the winter rainy season.
Key words: plant disease, plant pathogen