Treesearch

Over the past 14 years, a variety of native plant communities in northern California have been identified where introduced root-rotting Phytophthora species, most notably Phytophthora cinnamomi, P. cambivora, and P. cactorum, are causing decline and mortality of native species. In many older infested sites, the source(s) of the original Phytophthora introductions are not clear. Movement of contaminated soil is the most likely source in some sites that are located along roads and trails. In other cases, introductions are associated with plantings of nursery stock. In one site, a multi-specie...

To compensate for unavoidable impacts associated with critical water infrastructure capital improvement projects, the San Francisco Public Utilities Commission (SFPUC) restored over 2,050 acres of riparian, wetland, and upland habitat on watershed lands in Alameda, Santa Clara, and San Mateo Counties. Despite strict bio-sanitation protocols, plant pathogens (Phytophthora spp.) were detected at multiple restoration sites on SFPUC lands. SFPUC staff will provide an overview of various treatments employed to contain and treat the pathogens using multiple in-situ treatment techniques including...

Phosphite compounds have been used in the control of sudden oak death; however, their precise mode of action is not fully understood. To study the action of phosphite compounds in the context of naturally occurring host resistance, we first identified open-pollinated family groups that carried resistance, that is in which approximately 20% of offspring demonstrated a quantitatively resistant phenotype, with zero or little dieback post-inoculation. Then, multiple inoculations were performed on previously unchallenged members of these families, half of which had been treated with phosphite....

Rapid phenotypic diversification in clonal invasive populations is often observed, although the underlying genetic mechanisms remain elusive. Lineages of the sudden oak death pathogen Phytophthora ramorum are exclusively clonal, yet isolates of the NA1 lineage from oak (Quercus spp.) frequently exhibit hostdependent, unstable colony phenotypes called non-wild type (nwt, fig. 1) (Brasier and others 2006). This phenotypic variation is seen despite the fact that population genetic and host-specificity studies negate any host-driven population subdivision. We also found comparable nwt phenotype...

Sudden oak death, caused by the oomycete Phytophthora ramorum, was first discovered in California toward the end of the 20th century and subsequently emerged on tanoak forests in Oregon before its first detection in 2001 by aerial surveys. The Oregon Department of Forestry has since monitored the epidemic and sampled symptomatic tanoak trees from 2001 to the present. Populations sampled over this period were genotyped using microsatellites and studied to infer the population genetic history (Kamvar and others 2015). To date, only the NA1 clonal lineage is established in this region,...

It is now generally accepted that the four evolutionary lineages of Phytophthora ramorum (informally designated NA1, NA2, EU1, and EU2) are relatively anciently divergent populations, recently introduced into Europe and North America from different, unknown geographic locations; that recombinants between them are genetically unstable and probably unfit to survive, indicating reproductive isolation; and that they differ in growth rates and aggressiveness. EU1 lineage, for example, is on average faster growing in culture and more pathogenic on Quercus rubra bark than the NA1 lineage. Our...

Bloedel Reserve is a 150-acre botanical garden and nature preserve on the north end of Bainbridge Island in Washington on the Puget Sound. The grounds encompass undeveloped forest, pastures, a bird marsh, woodland plantings, and intensely maintained gardens within the limits of the City of Bainbridge Island. The garden is part of the Sentinel Plant Network, a partnership between the American Public Gardens Association and the National Plant Diagnostic Network that engages public garden professionals, volunteers, and visitors in the early detection of serious plant pests and diseases. With...

Studies have shown that nurseries are an important source for the spread of Phytophthora. Most surveys and studies focusing on the epidemiology of these pathogens in nurseries are based on sampling of symptomatic plants or on samples like water of different sources used for irrigation. There is little knowledge, however, on the survival and occurrence of Phytophthora in the different steps of commercial plant production. This information is necessary for the development of good management strategies for Phytophthora in nurseries. Therefore, within a 3-year project, detailed samples were...

The primary purpose of this program was to demonstrate proof of concept of certain mitigation approaches at a repeat P. ramorum-positive nursery site in Washington. Approaches included steam treatment of infested soil areas; creating a gravel “sandwich” above steam-treated and potentially infested soil surfaces; improving drainage systems; required sanitation of pots, flats, and other surfaces; monitoring host plants; and training of staff to identify potential problems and symptoms associated with the life cycle of P. ramorum. Various critical control points (CCPs) were sampled for...

Soilborne inoculum (infested leaf debris which has become incorporated into the soil) may be an important contributor to the persistence of the sudden oak death pathogen Phytophthora ramorum in recurrently positive nurseries. To initiate new epidemics, soilborne inoculum must not only be able to survive over time, but also be capable of producing sporangia during times favorable to infection of plant material at the soil surface. Current research has only assessed the recovery of this pathogen after being buried in soils. Two additional aspects of the disease cycle are being investigated...