Thesis
A comparison of detection and quantification methods for Phytophthora ramorum in water and threshold levels of inoculum in irrigation water required for infection of rhododendron leaves
Washington State University
Master of Science (MS), Washington State University
2014
Handle:
https://hdl.handle.net/2376/105938
Abstract
The propagules of Phytophthora ramorum, the causal agent of sudden oak death (SOD) and ramorum blight, have been recovered from streams and irrigation runoff associated with SOD outbreaks in forests and nurseries. The potential for new infections exists if untreated water from infested sources is used for irrigation of P. ramorum hosts. Five detection methods were tested simultaneously using lab and creek water artificially inoculated with P. ramorum zoospores to determine the detection threshold for each method. In creek water, detection thresholds were found to be between 1 and 10 direct plate colony-forming units per liter (DP CFU/liter) for filtration and qPCR methods, between 1 and 35 DP CFU/liter for leaves and leaf disks and between 10 and 35 DP CFU/liter for pear baits. Filtration, qPCR and leaf disk baits were able to quantify P. ramorum zoospores in creek water up to 400 DP CFU/liter; however, v precision was lost at higher inoculum concentrations. Results indicate that filtration, qPCR and leaf disks can be used for both detection and quantification of inoculum while pear and leaf baits were most effective for detection only. The inoculum concentration of P. ramorum zoospores needed in irrigation water for infection of nursery hosts was investigated using a novel spray device designed to simulate over-head irrigation similar to that used in nurseries and greenhouses. Inoculum threshold concentrations were found to be 51 zoospores/ml for wounded detached leaves in laboratory assays and between 1,000 and 10,000 zoospores/ml for plant hosts in a simulated nursery study. The pressurization and spraying of P. ramorum zoospores out of the device did not appear to affect zoospore viability or infectivity on wounded detached rhododendron leaves, implying the device may be useful in other research involving P. ramorum zoospore inoculum. Results of this study will help researchers, government agencies and nursery operators assess the risk of using untreated water infested with P. ramorum for over-head irrigation of susceptible hosts.
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Details
- Title
- A comparison of detection and quantification methods for Phytophthora ramorum in water and threshold levels of inoculum in irrigation water required for infection of rhododendron leaves
- Creators
- Lucy Rollins
- Contributors
- Gary A. Chastagner (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Plant Pathology, Department of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; [Pullman, Washington] :
- Identifiers
- 99900525122601842
- Language
- English
- Resource Type
- Thesis