Location: Horticultural Crops Research
Project Number: 2072-22000-041-26-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Aug 1, 2019
End Date: Sep 30, 2022
Phytophthora ramorum, the cause of sudden oak death (SOD), is of continuing national and international regulatory concern to the horticultural and forest product industries. In Southern Oregon Douglas-fir, grand fir, Sitka spruce, and western hemlock are all at risk from this exotic disease. The export of Douglas-fir, Christmas trees, and nursery products are threatened by the continued spread of SOD in Oregon forests. Recently, the more aggressive European lineage EU1 of P. ramorum was discovered in Oregon forests. Since the initial discovery of a single tanoak tree in 2015, several hundred acres at several locations have become infested with the European lineage. In order to mitigate the damage caused to date and improve management of this disease it is essential to develop a better understanding of the biology and ecology of this invasive forest pathogen. The overall aim of this proposal is to conduct basic and translational research on the sudden oak death pathogen P. ramorum in Oregon. The specific objectives of this project are to: Objective 1. Characterizing the epidemiology and ecology of SOD in Curry County, Oregon. Objective 2. Conduct genotypic and phenotypic characterization of EU1 and NA1 lineages of P. ramorum. Objective 3. Develop methods for control of SOD. Objective 4. Characterizing the genomes and populations of P. ramorum.
In order to meet the objectives described above a range of molecular, evolutionary, genomic, epidemiological, horticultural, and plant pathological approaches will be used to characterize the epidemic of the Sudden Oak Death (SOD) pathogen Phytophthora ramorum in Oregon. Objective 1: A combination of field and growth chamber experiments will be conducted to develop a better understanding of how far and how fast P. ramorum spreads on the landscape. Field experiments will consist of measuring sporulation and rates of infection in forest stands infested with P. ramorum. Growth chamber experiments will consist of measuring the environmental conditions which trigger sporulation and quantify the amount of sporulation from different host plants and different strains of the pathogen. This information will then be used to develop a model that can be used to predict the spread of the pathogen on the landscape and fine tune management. Objective 2: Using inoculated plants in the growth chamber we will use a combination of next-generation sequencing and transcriptomics to understand how P. ramorun infects and kills trees. We will quantify the genetic and phenotypic differences between host plants and strains of the pathogen. Objective 3: We will explore and evaluate the use of resistant host plants, eradication of infected trees in the forest, biotechnology, and chemical control to manage P. ramorum and reduce the spread of the disease. Evaluations of treatments will be conducted by a combination of ground surveys, canopy drip baiting, stream baiting, and soil sampling at several sites over the course of the project. The ground surveys will be conducted twice yearly. Symptomatic vegetation will be collected, and isolations made to determine the cause of the symptoms. Soil samples from within each site will be collected in a grid pattern and baited to determine if P. ramorum persists in the forest soil. Objective 4: Approximately 6,000 geo-referenced isolates of P. ramorum have been collected since 2001. We will re-sequence these isolates and use population genetics models to better understand the spread of the pathogen and the sources of the introductions into Oregon Forests. Population genetic analysis will be focusing on: (i) identifying patterns between the NA1 outbreak and the EU1 outbreak to estimate the number of introductions, rates of spread, and mutation rates; (ii) test the hypothesis that introductions can go from forest to nursery and from nursery to forest. Evidence of bi-directional introductions would allow us to determine the risk of the continued spread of EU1 to the Oregon nursery industry and predict the potential impact of seeing NA1-EU1 hybrid introductions into the nursery industry.