Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 48-52). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Le Phytophthora ramorum Werres est responsable de la mort de dizaines de milliers de chênes sur la côte ouest-californienne depuis 1995. On nomme cette maladie l’encre des chênes rouges ou la mort subite du chêne. Cet organisme appartient au même genre que le Phytophthora infestans, agent causal de la famine irlandaise de la pomme de terre du 19e siècle. Il fut découvert en 1993, infectant des rhododendrons et des viornes en Europe. Depuis, il a été démontré qu’il pouvait infecter plus d’une centaine d’espèces de plantes, non seulement sur la côte ouest américaine, mais également au Canada et dans plusieurs pays d’Europe. Des mesures de quarantaine ont été mises en place, essentiellement en pépinières où sa prolifération est la plus efficace, afin d’éviter sa propagation dans d’autres États américains ou d’autres pays. Il est donc nécessaire de développer des outils de détection, et d’identification. La détection moléculaire et le génotypage peuvent être des outils importants pour découvrir et mieux comprendre la biologie de ces populations et les mouvements de cet agent pathogène. La disponibilité des séquences complètes du génome du P. ramorum, depuis 2004, apporte une nouvelle ressource pour l’identification de gènes portant du polymorphisme et la conception d’outils pour les études de populations. Les objectifs de ce projet de recherche proposés sont : de développer des outils moléculaires pour identifier le P. ramorum et le différencier des autres Phytophthora; de découvrir des loci différenciant le polymorphisme intra-spécifique du P. ramorum; de réaliser des études de populations entre les populations européennes et nord-américaines connues avec les différents marqueurs développés. Par le biais d’analyses bioinformatiques et de séquençage d’ADN, la méthodologie employée consiste au développement d’outils de diagnostic tels que la PCR en temps réel utilisant des sondes et amorces spécifiques au P. ramorum sur trois loci et de les distinguer des autres espèces de Phytophthora connues. D’ailleurs, ces analyses ont permis d’identifier plusieurs polymorphismes de nucléotides simples (SNPs) (Single Nucleotide Polymorphisms), dans treize gènes totalisant 6.3 kb utilisant la notion de volatilité des codons. Dans une collection d’isolats provenant d’Europe et d’Amérique du nord, des profils de SNPs distincts et fortement corrélés avec l’origine géographique ont été identifiés. Les populations du P. ramorum en Californie et Oregon, présentent généralement trois profils uniques de SNPs et semblent plus être dérivés d’un ou quelques clones, quelques individus nouvellement trouvés présentant des insertions et délétions. En Europe plusieurs génotypes ont été retrouvés et les gènes sélectionnés semblent avoir des homologies avec des protéines de la paroi cellulaire et donc pourraient jouer un rôle dans l’adaptation. Cette thèse présente donc l’utilisation et la découverte de nouveaux gènes présentant du polymorphisme permettant de détecter et différencier le P. ramorum des autres espèces de Phytophthora mais également de connaître les origines et une identification des individus par leurs polymorphismes. / Phytophthora ramorum Werres is responsible of mortality of ten thousand of oak trees on the California coast since 1995. This disease is called sudden oak death, Ramorum blight, canker. This organism is on the same genus than Phytophthora infestans, the causal agent of Irish potato famine on the 19th century. P. ramorum was discovered in 1993 infecting Rhododendron and Viburnum in Europe. Since, it was demonstrated that it could infect more than one hundred plant species, not only on the American west coast but also in Canada and many European countries. Quarantine measures were placed in effect, principally in plant nurseries where the spread is more efficient to prevent propagation in other American States or other countries. That is necessary to develop detection and identification tools. The molecular detection and genotyping could be important tools to discover and understand le biology of the population and movement of this pathogen. The availability of complete sequences from the P. ramorum genome since 2004 permitted to use new resources for identification of gene sharing potential polymorphism and conception of tools for population studies. The objectives of this research project were: to develop molecular tools for identification of P. ramorum and differentiate it from other Phytophthora species; to discover loci differentiating intra-specific polymorphism of P. ramorum; and finally to realize population studies between European and North American population known with the different markers developed. With utilisation of bioinformatics and DNA sequencing, the method used was to develop diagnosis tool with real-time PCR using specific probes and primers for P. ramorum on three different loci and distinguish it from the other Phytophthora species known. Moreover, these analyses allowed identification of multiple single nucleotide polymorphisms (SNPs), in thirteen genes for a total of 6.3 kb based on codon volatility. In a collection of isolates from Europe and North America, distinct SNPs profiles and correlated with the geographic origin were identified. P. ramorum populations in California and Oregon present generally three unique SNPs profiles and seem to drift from one or few clones, new individual newly discovered with insertion-deletion mutation. In Europe, many genotypes were found and the selected genes had homologies with proteins implicated in cell wall. This could have an implication on adaptation and evolution. This thesis presents utilisation and discovery of new genes sharing polymorphisms allowing to detect and differentiate P. ramorum form other Phytophthora species and moreover to known the origin and identification of individuals by their polymorphisms.

Thesis (M.E.S.)--The Evergreen State College, 2008. / Title from title screen viewed (4/7/2009). Includes bibliographical references (leaves 114-126).

The sudden oak death pathogen, Phytophthora ramorum, is present in southwestern Oregon, and while an eradication effort is underway, the potential impact of the polyphagous pathogen on surrounding vegetation is unknown. Plant communities in the area are substantially different from those affected in California, although tanoak (Lithocarpus densiflorus), evergreen huckleberry (Vaccinium ovatum) and Pacific rhododendron (Rhododendron macrophyllum) are hosts found in both areas. Other species are likely to be susceptible to the pathogen. Detached leaf and whole plant assays were used to test species commonly associated with tanoak, as well as three rare or endemic ericaceous species of the western Siskiyou Mountains and their associated taxa. Leaves and plants were challenged with zoospore suspensions that were capable of generating symptoms in the known hosts tanoak and evergreen huckleberry. Most (78%) of the previously unchallenged species developed necrotic lesions in detached leaf assays although severity (% leaf area necrotic) was variable. All three of the ericaceous species of conservation concern: Arctostaphylos hispidula, Kalmiopsis leachiana, and Leucothoe davisiae were susceptible in detached leaf assays. Factors important in determining whether or not these species will become infected in their native habitat are discussed. / Graduation date: 2004

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 87-92). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 58-61). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 69-72). Also available on the World Wide Web.

This PhD examined the epidemiology of two potentially devastating plant pathogens, Phytophthora ramorum and P. kernoviae, at Benmore Botanic Garden in Argyll & Bute and Brodick Castle Garden in Arran. Spore traps, river baiting, bait plants and soil sampling were used to both confirm the presence of, and measure the amount of inoculum in the environment in order to quantify the relationship between inoculum levels and disease development. P. ramorum was detected in spore traps at high levels under a sporulating host throughout the year at Benmore. Also, findings at sites where infected hosts had been removed before the study led to the conclusion that the low level spore traps detect inoculum from soil splash. Rhododendron and Vaccinium bait plants were also infected with P. ramorum via soil splash at sites within Benmore where there was no sporulating host present. P. kernoviae was detected in spore traps at Brodick throughout the year but only where there was a sporulating host overhead. P. kernoviae infected bait plants only where an infected host is overhead. Water baiting confirmed the presence of P. ramorum in two streams at Benmore but P. kernoviae was not detected using this method despite the large-scale P. kernoviae infection at Brodick. Inoculum continued to be detected in soil in areas of both gardens where infected hosts had been removed two years previously, confirming that both of these pathogens can survive in soil for a considerable period. A number of statistical models were produced to describe conditions required for P. ramorum sporulation and infection. Sporulation occurred during warmer and wetter conditions and infection of bait plants occurred in wet conditions and where an infected host is in close proximity. A statistical model was also used to produce a P. ramorum risk map, uniquely at the garden scale, to enable garden managers at Benmore to visualise the areas most at risk within their garden. The findings of this study have clear management implications for the control of disease establishment and spread within the garden setting.

Phytophthora ramorum, an exotic forest pathogen known as ‘sudden oak death’ (SOD), has received considerable attention in recent years because of its effects on vegetation structure, composition, and fire disturbance regimes in western U.S. coastal forests. This research examines differences in the importance (e.g., density, dominance, and frequency) and distribution of five host species of P. ramorum–– Umbellularia californica (California bay laurel), Quercus agrifolia (coast live oak), Pseudotsuga menziesii (Douglas fir), Sequoia sempervirens (Coast redwood), and Arbutus menziesii (Madrone)––in Soquel, California. A stratified random sampling design was used to select 66 plots surrounding a managed forest edge in Soquel Demonstration State Forest. Vegetation measurements were conducted in summer 2013. In each plot, all trees ≥3 cm diameter at breast height (DBH) were identified to species, counted, and DBH, height, and canopy position measured. Leaf area index (LAI) of bay laurel was measured to quantify the amount of leaves available for pathogen dispersal with a LiCOR 2200 Plant Canopy Analyzer. In addition, morning (9:00 am) and afternoon (1:00 pm) photosynthetically active radiation (PAR) were quantified using a quantum light sensor. This paper examines the influence of environmental variables, including distance to edge, aspect, slope, and light availability on host species spatial patterns in Soquel, CA. Studying P. ramorum host pattern and importance among managed forest edges is critical for determining hotspots most susceptible to infection and spread, thus relevant for implementing control measures.