Treesearch

In early 2006 we implemented a series of comparative silvicultural treatments aimed at managing the spread of Phytophthora ramorum Werres, de Cock & Man in?t Veld by reducing inoculum densities in isolated infestations on one public and three private properties in southern Humboldt County. These treatments, which took place on over 56 forested ha, are the first attempts at large-scale, stand-level silvicultural management of P. ramorum in California. As part of first-year post treatment monitoring, we compare a number of issues related to operational effectiveness of the treatment installat...

The mitochondrial genomes of Phytophthora infestans, P. ramorum and P. sojae have been sequenced and comparative genomics has provided an opportunity to examine the processes involved with genome evolution in the genus Phytophthora. This approach can also be useful in assessing intraspecific genome evolution and identification of cytoplasmic markers that will be useful in population studies. Polymorphisms have been observed in the mitochondrial genomic sequences of P. ramorum isolates from North America and Europe (13 single base changes and an insertion of 180 bp in the European isolate)....

There is widespread concern among scientists and land managers that Phytophthora ramorum may be accidentally introduced into oak-dominated eastern U.S. forests through the transfer of the pathogen from infected nursery plants to susceptible understory forest species (for example, Rhododendron spp.) at the forest-urban interface. Inspection programs can be made more efficient by identifying locations throughout the U.S. that are most likely to receive infected nursery stock. e develop a spatial network model framework utilizing potential interstate nursery stock movements on a bipartite...

In effort to eradicate Phytophthora ramorum from Oregon forests, tanoak over its entire range in southwestern Oregon is surveyed intensively for stem disease. Pieces of bark from the leading edge of tanoak stem cankers were plated on cornmeal agar amended with 10 ppm natamycin, 200 ppm a-ampicillin, and 10 ppm rifamycin SV (CARP) to favor the isolation of Phytophthora. Phytophthora ramorum was usually identified on the isolation plates based on the presence of characteristic hyphae, chlamydospores, and sporangia. Hyphae from the leading edge of other colonies resembling Phytophthora were...

Phytophthora ramorum and P. kernoviae are newly discovered invasive Phytophthoras causing leaf necrosis, shoot tip dieback (mostly on ornamental and forest understorey host species) and bleeding cankers on tree trunks of a wide range of plant species. Both pathogens are now present in south-west England. Sporulation occurs on infected shoots and foliage but not on bleeding stem cankers; thus foliar hosts are key in disease epidemiology. During evaluation of a two-year field trial established to assess infection periods and infection incidence, we discovered that naturally infected,...

Rates of disease incidence and tree mortality in redwood-tanoak forests were determined by repeated sampling across a system of 120 plots at five long-term research sites from 2001 through 2006. Plots were located within the known geographic area of Phytophthora ramorum in California, ranging from Monterey to Sonoma counties. All overstory species were monitored, but analysis was restricted to three important host species: California bay laurel (Umbellularia californica), tanoak (Lithocarpus densiflorus), and redwood (Sequoia sempervirens). Infection in bay laurel and tanoak varied among...

The complete genomes of Phytophthora ramorum and P. sojae have recently been sequenced. Of the 19,027 predicted genes in P. sojae and 15,743 gene models in P. ramorum, 9,768 are predicted to have the same function. These two genomes both revealed a rapid expansion and diversification of many protein families associated with plant infection including different classes of pathogen effectors. Two protein motifs (RxLR and dEER) are shared by the four known effectors in plant pathogenic oomycetes. Genome analyses identified a diverse superfamily of approximately 350 genes in P. ramorum that...

For a scientist, my title may seem a little sensationalist in tone. This is deliberate - to draw attention to my issue. And here?s the issue. About six years ago the previously unknown invasive pathogen P. ramorum sp. nov. was found spreading on trees and shrubs in North America and Europe. Almost simultaneously in the U.K. we found another previously unknown invasive Phytophthora on trees and shrubs, P. kernoviae sp. nov. Shortly efore that we found the previously unknown invasive P. alni sp. nov. spreading on alders; and a decade before that the invasive P. ilicis on holly? Four invasive...

Phytophthora ramorum is an oomycete pathogen that causes sudden oak death in several species of Fagaceae including tanoak (Lithocarpus densiflorus). Symptoms on tanoak include stem cankers and crown death. Stem infection was thought to be restricted to bark and cambium, but has recently been shown to include sapwood. Woody tissue colonized by fungal pathogens often has a greater abundance of tyloses than non-infected tissue, and tyloses have been interpreted as a host defense response to infection. In this study, we are investigating the spatial and temporal development of tyloses in...

The effectiveness of 19 fungicides in protecting noble fir, grand fir, and Rhododendron x ?Nova Zembla? foliage from P. ramorum was tested. The tops of conifer seedlings with newly emerging shoots and mature rhododendron leaves were collected from treated plants 7 days after drench applications or 1 day after foliar applications. Detached seedling tops and leaves were then placed on moistened filter paper in Petri dishes and inoculated. Zoospores from three European genotype isolates of the A1 mating type (EU1 lineage) and three NA1 lineage isolates of the A2 mating type were mixed to...