Treesearch

Since the discovery of Phytophthora ramorum in southern Oregon forests in 2001, newly infested areas are located each year. We tracked the spread and dispersal using DNA fingerprinting. While among site genetic variance was low, we did find changes in genotype presence and frequency at the site level. These genotypic differences allowed us to map the spread of some individual genotypes demonstrating long and short distance dispersal of P. ramorum in Oregon Forests.

Phytophthora ramorum populations are clonal and consist of three clonal lineages: EU1 is the only lineage found in Europe with a few isolated nursery infections in the USA; NA1 is associated with natural infestations in California and Oregon as well as some nursery infections in North America, and NA2 has a limited distribution and has only been isolated from a few nurseries in the USA. Recent studies have shown that the clonal lineages may have varying degrees of aggressiveness on some host species, such as Quercus rubra. In this study, we examined virulence, sporulation, and elicitin...

Phytophthora ramorum can produce spores on dozens of native California plant species, but the most important vector for infection of oak (Quercus) is California bay laurel (Umbellularia californica). Presence of bay laurel is associated with increased infection of oaks and it is the most common tree species that co-occurs with coast live oak (Quercus agrifolia) in northern California woodlands. Understanding the interaction between P. ramorum and bay laurel is critical to predicting dynamics of disease establishment in mixed oak woodlands. Previous studies showed that P. ramorum lesion...

In Europe, Phytophthora ramorum has mostly been detected on rhododendron plants in nurseries. European Union (EU) phytosanitary measures state that potential host plants within a radius of 2 m of an infected plant must be destroyed, and remaining host plants within a radius of 10 m must be quarantined. Despite the lack of research on the spread characteristics of P. ramorum in nurseries, these distances have been generally accepted. To test the distances over which P. ramorum can spread between potted rhododendron plants in a nursery setting, dispersal was monitored from individual...

If a nursery plant infected with Phytophthora ramorum is introduced in a non-infested area, then it is important to understand what environmental conditions could lead spread and infection of new hosts. Once an infected nursery plant is introduced in a nursery or landscape, moving water sources, such as from rain and irrigation events, could provide an important means for dispersal and infection of new hosts. We evaluated seasonal environmental factors and associated rainfall and irrigation events that could support sporulation, dispersal, and infection of new hosts under field conditions.

Foliar hosts of Phytophthora ramorum are often susceptible to root infection, but the epidemiological significance of such infections is unknown. We used a standardized test system to study inoculum in runoff from root-infected Viburnum tinus cuttings.

Phytophthora kernoviae (Pk) and Phytophthora ramorum (Pr) are recently introduced pathogens in United Kingdom (U.K.) woodlands. Pk is also an emerging threat to coastal heathland where it infects Vaccinium myrtillus. In infested woodlands, an invasive plant, Rhododendron ponticum, supports sporulation of both pathogens, providing primary inoculum for infection of Fagus sylvatica. R. ponticum has been removed from several infested woodlands; however, the long term efficacy of R. ponticum removal for disease management is unknown. The epidemiology of Pk in infested heathland is not yet...

To obtain a better understanding of the potential risk of infection and colonization of living Douglas-fir (Pseudotsuga menziesii) and grand fir (Abies grandis) stems, the stems on over 150 trees of each species were inoculated at a Christmas tree farm near Los Gatos, California. This study had the following objectives: 1) Determine if inoculation timing affects the infection of living Douglas-fir and grand fir stems, 2) Characterize symptom development associated with inoculated stems, and 3) Determine what stem tissues were colonized by P. ramorum. Tanoak (Lithocarpus densiflorus) is...

Tanoak (Lithocarpus densiflorus) is highly susceptible to sudden oak death caused by Phytophthora ramorum. Symptoms include dying crowns, bleeding cankers, and, eventually, death of infected trees. The cause of mortality is not well understood, but we showed previously that naturally infected mature trees have reduced sap flow and reduced hydraulic conductivity. One possible mechanism for this is the presence of tyloses in xylem vessels formed in response to P. ramorum infection.

Many nursery plants are known to be hosts of Phytophthora ramorum or to be associated with this pathogen. These plants can be infected or merely infested by P. ramorum and with or without symptoms. The pathogen has been detected most frequently on container-grown nursery plants, and occasionally has been found in the container mix around these plants. Because of this close association with container-grown nursery plants, P. ramorum can be disseminated within a nursery, among local nurseries, and between nurseries in different states on infected plants or infested materials. Pathogen...