| Susceptibility of some eastern oak species to sudden oak death caused by Phytophthora ramorum. P. W. TOOLEY (1) and K. L. Kyde (2). (1) USDA-ARS, Ft. Detrick, MD 21702; (2) University of Rhode Island, Kingston, RI 02881. Phytopathology 93:S84. Publication no. P-2003-0614-AMA. To evaluate susceptibility of eastern oak species to P. ramorum,
2- to 3-year-old seedlings of white oak (Quercus alba), Northern red oak (Q. rubra), chestnut oak (Q. prinus), cherrybark oak (Q. falcata var pagodifolia), and coast live oak (Q. agrifolia) were inoculated with P. ramorum. Agar plugs from 10-14 day old P. ramorum colonies on 20% V8-juice agar were placed in stem wounds 5 cm above the soil line. Trees were incubated at 20°C in a greenhouse cubicle for 9 weeks, then debarked and lesion areas were traced and measured. P. ramorum caused significantly more (P < 0.01) disease than the controls on all five oak species in two replicated experiments (25 trees/species/experiment). White and chestnut oak sustained the largest lesions, followed by Northern red oak, cherrybark oak, and coast live oak The results suggest that, following wound-inoculation, P. ramorum can infect seedlings of eastern oak species under greenhouse conditions. Whether these species would serve as hosts of P. ramorum in nature is unknown.
Detection and identification of Phytophthora ramorum, the causal agent of sudden oak death by real-time PCR.
G. BILODEAU (1), C. A. Lévesque (2), A. W. A. M. De Cock (4), G. Kristjansson (3), J. McDonald (3), and R. C. Hamelin (1). (1) Natural Resources Canada, CFS, QC, Canada; (2) Agriculture and Agri-food Canada, ON, Canada; (3) Pest DNA Diagnostics Laboratory, CFIA, ON, Canada; (4) Centraalbureau voor Schimmelcultures, Utrecht, Netherlands. Phytopathology 93:S8. Publication no. P-2003-0056-AMA. Phytophthora ramorum causes severe damage on oak trees in California and Oregon. This pathogen is spreading rapidly and a quarantine is currently in effect to prevent spread. New molecular assays are being developed to detect and identify P. ramorum reliably in order to implement this quarantine. However most assays cannot distinguish between P. ramorum and P. lateralis. In order to overcome
this cross reaction, Beta-tubulin and other regions were sequenced and used to find polymorphisms between P. ramorum and other Phytophthora spp. Specific primers for Allelic Specific Polymerase Chain Reaction, molecular beacons, Taqman and SybrGreen assays were developed to detect and identify this pathogen. The real-time assays and primers differentiated P. ramorum from all Phytophthora spp., including P. lateralis. Official survey of Oregon agricultural commodities for Phytophthora ramorum. N. K. OSTERBAUER, L. Rehms, and J. Hedberg. Oregon Dept. of Agriculture, Salem, OR 97301. Phytopathology 93:S68. Publication no. P-2003-0493-AMA. Phytophthora ramorum is established in 12 counties in California and has been detected (and targeted for eradication) in Curry County, Oregon. This pathogen infects at least 19 host species in 11 plant families. Many of these hosts are important parts of Oregon's agricultural commodities. Thus, we have conducted an annual survey for P. ramorum in Oregon nurseries, plantations, and other high risk sites since 2001. Following the USDA protocol, hosts at each site were examined and samples collected from symptomatic plants. The samples were processed using standard laboratory techniques and analyzed for the presence of P. ramorum.
Since 2001, 167 sites have been surveyed with a total of 6,584 samples collected and analyzed. No P. ramorum was detected, although other Phytophthora species were recovered in both years. As of 2002, Oregon's agricultural commodities remain apparently free of P. ramorum. Surveys will continue in 2003, pending available funding. Phytophthora ramorum: An emerging forest pathogen.
M. GARBELOTTO (1), D. M. Rizzo (2), J. M. Davidson (2,3), K. Ivors (1), P. E. Maloney (2), D. Hüberli (1), K. Hayden (1), T. Harnik (1), and S. T. Koike (4). (1) Department of ESPM, 151 Hilgard Hall, University of California, Berkeley, CA 94720; (2) Department of Plant Pathology, 1 Shields Ave., University of California, Davis, CA 95616; (3) Pacific Southwest Research Station, USDA Forest Service,
P.O. Box 245, Berkeley, CA 94710; (4) Cooperative Extension Service, University of California, 1432 Abbott St., Salinas, CA 93901-4507. Phytopathology 93:S28. Publication no. P-2003-0203-AMA. Aided initially by taxon specific PCR primers, we have determined that Phytophthora ramorum, cause of Sudden Oak Death, is not restricted to oaks, but has a host range
encompassing at least 11 families and 18 plant species, including dominant tree species such as redwood and Douglas-fir, as well as understory shrubs, and herbaceous plants. This pathogen can infect all of the dominant woody species in coastal woodlands of Central California. While forest Phytophthora species are commonly known to cause root diseases, P. ramorum in California appears to exclusively be causing above ground disease symptoms, and can be dispersed aerially. Analysis of North American isolates of P. ramorum using amplified fragment length polymorphisms (AFLPs) indicates largely a clonal population with no subdivisions based on geography or host of origin. The AFLP data also indicate that the European and North American populations are quite distinct. The finding of P. ramorum on many host species in a relatively short time frame, underlines the power of DNA-based diagnostic approaches, and has important consequences for determining the epidemiology, ecological impact and management of this important new forest pathogen.
Use of single strand conformation polymorphism of PCR-amplified ribosomal DNA for detection of Phytophthora ramorum in plant tissues. P. KONG, P. A. Richardson, and C. X. Hong. Virginia Tech., Hampton Roads AREC, Virginia Beach, VA. Phytopathology 93:S47. Publication no. P-2003-0340-AMA. Phytophthora ramorum, causal agent of Sudden Oak Death, is an important quarantine pathogen for most parts of the United States and many other countries. Rapid and accurate detection is important to prevent the spread of this pathogen. Single strand conformation polymorphism (SSCP) analysis is an effective technique for species differentiation in the genus Phytophthora. In this study, we assessed SSCP
technique for detection of P. ramorum in plant tissues. DNA samples from plant tissues were provided by Dr. Garbelotto's lab at University of California Berkeley and were amplified using ITS6 and ITS7 primers. PCR protocol was optimized using various DNA concentrations prior to SSCP analysis (previously described). While yielding consistent results with P. ramorum-specific PCR, the SSCP analysis also detected other pythiaceous species in the plant samples. These results
indicate that SSCP analysis can be an effective alternative method for diagnosing plant samples infected by P. ramorum alone or mixed with other pythiaceous pathogens. Factors influencing growth and sporulation of Phytophthora ramorum, causal agent of 'Sudden Oak Death'. M. Browning (1), L. ENGLANDER (1), and P. W.
Tooley. (1) Dept. Plant Sciences, University of Rhode Island, Kingston, RI 02881. Phytopathology 93:S12. Publication no. P-2003-0085-AMA. Phytophthora ramorum has emerged as a new, lethal pathogen on oaks in the U.S. Further, numerous cultivated and wild plants support growth of this pathogen. Little is known about the environmental parameters which influence fungal biology. We investigated the influence of incubation temperatures and illumination regimes on growth and spore production at two research facilities. Cultures were incubated on clarified V-8 agar with sterol, at temperatures ranging from 4-30°C, under 12-hr diurnal light (cool white and near-UV) or darkness. Colony diameters were measured periodically, and number of chlamydospores were counted after 14 days. Sporangia production was assessed on mycelial plugs transferred to autoclaved soil extract and subjected to various temperatures and light regimes. Results with American isolates of P.
ramorum, from Lithocarpus densiflorus, Quercus agrifolia, and Rhododendron sp. were compared with those obtained using the type culture isolate (Germany). Chemical treatment strategies for control of sudden oak death in oaks and tanoaks. M. M. GARBELOTTO (1), D. J. Schmidt (1), S. Tjosvold (2), and T. Y. Harnik (1).
(1) University of California, Berkeley and (2) University of California Cooperative Extension, Santa Cruz and Monterey Counties. Phytopathology 93:S28. Publication no. P-2003-0202-AMA. Field experiments were conducted in Marin, Alameda, and Santa Cruz counties to evaluate the effectiveness of chemical treatments for controlling Sudden Oak Death. Nursery-grown saplings
as well as native populations of mature coast live oak (Quercus agrifolia) and tanoak (Lithocarpus densiflora) were tested. Trees were infected by placing a small amount of mycelium of Pytophthora ramorum under the bark. A variety of commercially available chemicals that have been used on other Phytophthora species were evaluated in at least 10 different trials. Application methods included trunk injections, soil drenches, topical applications, and foliar sprays. Treatments with phosphonate
compounds significantly and consistently reduced lesion size in both oaks and tanoaks. Injecting the chemicals into the trunk of the tree was found to be the most effect method. Treatment of the tree prior to infection was found to be significantly more effective at controlling the disease than treatment after infection. Phosphonate treated trees remained resistant to new P. ramorum infections for at least three months. However, mature trees may require a longer period following chemical
treatment to become resistant to infection. Development of a molecular marker system for detection of Phytophthora spp. and diagnosis of species associated with Sudden Oak Death in California. F. N. MARTIN (1), P. Tooley (2), and R. Frederick (2). USDA-ARS, (1) Salinas, CA 93905; (2) Ft. Detrick, MD 21702. Phytopathology 93:S58.
Publication no. P-2003-0418-AMA. A molecular marker system using mitochondrial sequences has been developed for detection of Phytophthora spp. in diseased tissue and identification of P. ramorum (the causal agent of sudden oak death) and an additional species that is morphologically similar to P. ilicis that is commonly recovered from diseased trees in California. The first multiplex amplification included a primer pair to amplify plant sequences (to serve as a positive control) and a Phytophthora genus-specific primer pair. This amplification was diluted and followed by a second amplification with a nested species-specific primer pair. The primers developed for P. ramorum and the P. ilicis-like
isolates exhibited a high degree of species specificity and did not amplify any of the 27 other Phytophthora species evaluated thus far. Some aspects of this marker system have been modified for use with the TaqMan real-time PCR system. Potential for Phytophthora ramorum to infect tanoak-associated vegetation in southwestern Oregon.
J. W. ZANZOT, J. L. Parke, and E. M. Hansen. Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR. Phytopathology 93:S93. Publication no. P-2003-0685-AMA. Phytophthora ramorum, the causal agent in sudden oak death and related diseases, is being actively extirpated from southwestern Oregon. The tanoak communities where the
pathogen has been found in Oregon are substantially different from infested areas in California, with a new suite of potential host species present. We have screened more than 30 species of native shrubs and herbs for susceptibility to foliar infection by the pathogen using detached leaf assays. Most species screened appear susceptible to some degree in these tests when compared to known hosts, though evidence from field-collected material or whole-plant inoculations are needed to confirm the
disease phenotype. Phytophthora diseases of oaks. E. M. HANSEN. Oregon State University, Corvallis, OR. Phytopathology 93:S102. Publication no. P-2003-0035-SSA. Phytophthora first impressed pathologists as the cause of potato late blight. Today sudden oak death presents disquieting parallels. Phytophthora is known as a genus of agricultural pathogens, but we are increasingly aware of the important roles it plays in forests of the world. P. ramorum is new, and the unknown is frightening. It is killing some oak species and oak relatives in western North America and seems to have the potential to wreak havoc in some other parts of the world as well. P. ramorum is stealing the headlines oday, but that other invasive, P. cinnamomi,
has already established itself broadly across oak forests of the world. P. cinnamomi arrived unannounced in the Northern Hemisphere 200 or more years ago and we are still discovering its many impacts on oaks. By contrast, indigenous Phytophthoras are widespread in many oak forests, usually in the absence of dramatic disease. In continuing work at least 13 species are now known from oak forests. Eight of these are described since 1995 or remain unnamed. The research and management challenges are many, from containing the acute threat of known and unknown invasive pathogens, to understanding the effects of indigenous species, including their roles in chronic diseases like oak decline.
Protecting our world's forest ecosystems from exotic pathogens. S. D. COHEN. USDA APHIS, University of Minnesota, St. Paul, MN. Phytopathology 93:S119. Publication no. P-2003-0154-SSA. Exotic forest pathogens are
moving worldwide in commercial trade of seed, nursery stock, logs, chips, and solid wood packing materials. Pathogen interception records published by various countries and new exotic outbreaks worldwide attest to the mobility of forest pathogens. Insect-vectored pathogens (e.g., Ophiostoma ulmi), wind-disseminated pathogens (e.g., Melampsora spp.), facultatively-saprophytic pathogens (e.g., Heterobasidion annosum), seed borne pathogens (e.g., Pythium spp.), and pathogens that are carried with living plant material (e.g., Cronartium ribicola,Phytophthora
ramorum) are known to be transported in commercial trade. Potential risks posed by forest pathogens may be reduced thorough improved detection methods, worldwide shared knowledge through interception databases and forest pest databases, use of effective treatment protocols, pathway risk evaluations and international plant protection standards. Overview of the challenges and conflicts of a new pathogen Phytophthora ramorum between researcher, regulator, the public and politicians.
M. STANLEY. California Dept. of Forestry and Fire Protection & CA Oak Mortality Task Force Chair, Sacramento, CA. Phytopathology 93:S121. Publication no. P-2003-0166-SSA. Significant challenges exist in dealing with a new pathogen that is killing trees in a very visible populated area. Efforts to allow scientist and researchers to continue unrestricted while at
the same time satisfy the needs of the regulatory community and still answer to the public who demands action can be problematic. The politicians act as not only friend from a funding standpoint, but as foe demanding information and actions that are not supported or known by science. All parties want the same thing, eradication, treatments or controls, but each has unique demands that conflict with most of the others, either in timing or scope. In many cases the decision makers are either not
knowledgeable or are not even in the same world of those that deal with a new disease on a daily basis. This will be a case study of how we are walking that fine line in an attempt to keep everyone working together while satisfying each groups needs. This has been done with some success and those techniques will be discussed. Disease threats to oaks worldwide: an introduction.
J. JUZWIK. USDA Forest Service, St. Paul, MN. Phytopathology 93:S101. Publication no. P-2003-0033-SSA. Oaks (Quercus spp.) are an ecologically and economically significant species group found in widely disparate areas around the world. During the second half of the 20th century extensive threats to oaks surfaced on three continents in the Northern Hemisphere. Oak Wilt and Sudden Oak Death are currently associated with significant oak mortality in the USA, while reports of widespread oak decline have emanated from Europe and North America. The cause of massive mortality of oaks in Japan has recently been elucidated. Potential for these disease problems to spread to other continents is a continuing concern in the 21st century. The association of insects with three of these diseases increases this concern, as well as the potential for spread and intensification within affected continents. Major disease disturbance in oak habitats may have broad regional impacts, e.g. ecosystem instability, reduced economic viability, and increased risk of catastrophic fire. Understanding these diseases and conveying relevant information to both practitioners and are of immediate importance.
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