Treesearch

The genus Phytophthora comprises over 70 described species, however many new species have been reported recently as a result of the discovery of previously undetected species or by the hybridization of known species. Phytophthora ramorum, one of the new Phytophthora species, is considered a high phytosanitary risk because it is currently responsible for large-scale oak mortality in coastal California forests. In Europe, the disease occurs mainly in nurseries on Rhododendron, Viburnum and Camellia. However, in landscapes, infected trees of Quercus rubra, Q falcata, Q. ilex, Aesculus...

Sudden oak death, caused by Phytophthora ramorum, is a severe disease that can affect numerous species of trees and shrubs. This pathogen has been spread via nursery stock, and quarantine measures are currently in place to prevent further spread. Molecular assays have been developed to rapidly detect and identify P. ramorum, but one difficulty encountered with some of these assays is the inability to reliably distinguish between P. ramorum and closely related species. To increase redundancy and therefore confidence, ß-tubulin and elicitin regions from a collection of Phytophthora species...

Phytophthora ramorum is the pathogen that causes sudden oak death, which was first detected on tanoak in Marin County, California in 1995. The identification of several conifers as hosts of P. ramorum and the increased spread of this pathogen via shipment of ornamental nursery stock has the potential to severely impact the Christmas tree, conifer nursery and forestry industries if this pathogen spreads into major production areas. Four conifers (Douglas-fir, grand fir, yew and coast redwood) are among the naturally infected hosts that have been reported for this pathogen. There are large...

The comparative risk to trees posed by European (E.U.) versus North American (U.S.) isolates of Phytophthora ramorum, the possible risk posed by genetic recombination between them, and whether European versus North American isolates represented discrete sub-populations was investigated. Population samples of E.U. and U.S. isolates were compared for growth rate across different environments (gene x environment tests), phenotypic stability, host range, pathogenic aggressiveness and sexual behaviour.

Phytophthora ramorum is a recently introduced plant pathogen causing a range of diseases including sudden oak death, Ramorum shoot dieback and Ramorum blight (Rizzo and others 2002, 2004; Werres and others 2001). P. ramorum also attacks several nursery crops including viburnum and rhododendron (Werres and others 2001). Since its discovery P. ramorum has been shown to have a remarkably wide host range including many nursery crops (Parke and others 2002; Linderman and others 2002). It is well established that the ornamental plant Viburnum plicatum var. tomentosum cv. Mariesii and other...

Phytophthora ramorum, a previously unknown pathogen, was first seen in Europe on ornamental nursery stock in the early 1990s (Werres and others 2001). It has since been implicated in the death of thousands of oaks (Quercus agrifolia and Q. kelloggii) and tanoaks (Lithocarpus densiflorus) in the western United States (Rizzo and others 2002). Although populations of P. ramorum in Europe and the United States are largely distinct from one another, the organism is considered invasive in both locations with an operating hypothesis that it was introduced on both continents (Brasier and others...

Phytophthora ramorum and P . kernoviae sp. nov are recently introduced, invasive pathogens in woodlands in southern Britain. P. kernoviae is a newly discovered taxon, previously referred to as Phytophthora taxon C. Both species aggressively infect foliage and shoots of understory rhododendrons, especially Rhododendron ponticum. From there they can spread aerially to attack the inner bark of tree stems, especially European beech (Fagus sylvatica) and some Quercus species, causing bleeding lesions (Brasier and others 2004). Both species of Phytophthora are under investigation as scheduled...

Until now there has been little scientific information available about the susceptibility of different Rhododendron species and cultivars to Phytophthora ramorum. However, growers could use this knowledge as part of their control strategy. In our susceptibility screening we first optimized different inoculation methods on stem and leaf material. Four methods were chosen for the actual screening: two on detached leaves and two on detached stems, each time involving either wounded or non-wounded tissues. Finally, 63 Rhododendron species and hybrids were screened and the correlation between...

Non-destructive magnetic resonance imaging (MRI) revealed pathological anatomical features of coast live oak trees (Quercus agrifolia) that were naturally infected with Phytophthora ramorum. Fresh excised whole slices showing typical macroscopic cankers and bleeding were examined. Infected areas (i.e. cankers) were compared to presumed healthy sections. Various infected tissues were revealed and the depth of infection into the xylem could be estimated. Discontinuous distribution of water in the outer layer of sapwood was observed and high water concentrations appeared in the cankers. MRI...

Bay laurel (Umbellularia californica) is an important foliar host in terms of spore production and transmission of disease. We designed a bioassay to screen for variation in susceptibility to Phytophthora ramorum among populations of bay laurel collected along the coast of California to southern Oregon and also from Yosemite. Mature leaves of bay laurel were inoculated with zoospores and nine days later lesions and infection percentage were measured. Results indicated that each population comprises trees of different susceptibility. Data from three separate trials indicated that trees from...