Epidemiological Framework Development for Management of Phytophthora Ramorum in Nursery Systems
Horticultural Crops Research
2013 Annual Report
1a.Objectives (from AD-416):
1. Parameter estimation of transmission rates and dispersal kernels for foliar Phytophthora spp. on Rhododendron in nursery settings.
a. Parameter estimation for P. ramorum at NORSDUC
b. Parameter estimation for P. citricola at Corvallis
2. Development and validation of spatially-explicit epidemiological model for invasion.
within nurseries to screen potential management scenarios
3. Evaluation of different management scenarios for control of P. ramorum in nursery settings.
1b.Approach (from AD-416):
We propose to use a combination of small-scale ‘challenge experiments’ with which to estimate transmission probabilities, percolation thresholds and incubation periods that are then used to parameterize models from which to predict efficient methods for control. The challenge experiments will be complemented by population experiments to test and modify the model predictions for invasion and disease control. Simple percolation and network models will be parameterized to estimate biologically meaningful parameters such as transmission rates and dispersal kernels for both Phytophthora species within nurseries. The simple susceptible-infected model will be refined to give spatially explicit models based on the SIR (susceptible, infected, removed) family of modeling approaches, but with several important adaptations for plant disease.
Phytophthora ramorum is an emerging pathogen that has received worldwide attention as the causal agent of Sudden Oak Death (SOD). Epidemiological theory provides a useful toolbox to identify criteria for invasion of the pathogen in nursery settings. Using a combination of intensive experimentation and established epidemiological theory – rather than de novo modeling - the current project aims to develop and test the epidemiological framework necessary for evaluating different management scenarios within nurseries. Experiments will be conducted both in California and Oregon. In order to replicate experiments at sites we are exploring the use of several species of Phytophthora and how suitable they may be as surrogates for the sudden oak death pathogen P. ramorum. A number of species have been retrieved from our culture collection, have been maintained on antibiotic containing media to ensure they are not contaminated and are now being maintained on antibiotic free media. We are currently exploring the relative performance of infection and disease spread for several species (e.g., P. citrophthora, P. cactorum, P. hibernalis). We have developed protocols for monitoring spread of Phytophthora spores from a source of sporulating lesions to neighboring host leaves. This research was conducted in support of NP 303 objective 2C of the parent project.