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Fifth Meeting of the IUFRO Working Party S07-02-09, Phytophthora Diseases in Forests and Natural Ecosystems - supplement to Volume 41
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Application of phosphonate to prevent sudden oak death in south-western Oregon tanoak (Notholithocarpus densiflorus) forests
Kanaskie, A., Hansen, E., Sutton, W., Reeser, P., & Choquette, C.
Kanaskie et al. (pp. S177-S187) evaluated the effectiveness of phosphonate application to prevent sudden oak death in tanoak trees. All the treatments reduced visible symptoms but did not prevent seedlings from becoming infected.Published Online - 25/11/2011. [1.2 MB] (pdf).We conducted four experiments to evaluate the effectiveness of phosphonate application to tanoak (Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S.H.Oh) forests in south-western Oregon: (1) aerial application to forest stands; (2) trunk injection; (3) foliar spray of potted seedlings; and (4) foliar spray of stump sprouts. We compared aerial spray treatments: (1) no treatment (unsprayed); (2) low-dose (17.35 kg a.i. ha-1); and (3) high dose (34.5 kg a.i. ha-1), applied by helicopter in a carrier volume of 188 L ha-1 to 4-ha treatment plots. Treatments were applied in November 2007, in May 2008, and in December 2008 and May 2009 (double treatment). At the same time as the aerial application we injected phosphonate into the trunk of nearby mature tanoak trees at the standard label rates of 0.43 g a.i. cm-dbh-1. We used three different biological assays to measure uptake of phosphonate: (1) canopy twig dip in zoospore suspension; (2) in situ bole inoculation with Phytophthora gonapodyides (Petersen) Buisman; and (3) laboratory inoculation of log bolts with Phytophthora ramorum S. Werres, A.W.A.M. de Cock & W.A. Man in ‘t Veld and P. gonapodyides. We also simulated an aerial spray of potted seedlings, comparing an untreated control, a low dose (2.9 kg a.i. ha-1 applied in 935 L spray solution ha-1), and a high dose (17.35 kg a.i. ha-1applied in 187 L spray solution ha-1).Aerial spray with phosphonate consistently resulted in smaller bole lesions on trees challenge inoculated with Phytophthora gonapodyides in situ and in logs inoculated with P. ramorum. This effect persisted for 18 months post treatment. Results from detached canopy twig assays were variable and showed only small treatment effects. Trunk injection consistently reduced bole lesion size in trees and logs, but gave inconsistent results in the canopy twig assay, possibly due to the twig assay methodology. In the spring and autumn trunk injection treatment, canopy twig lesion length was reduced by 32 percent compared to untreated controls, indicating that trunk-injected phosphonate was mobilised to the outer twigs of the tree crown. Trunk injection with phosphonate resulted in a greater reduction in bole lesion area than aerial spray. Spray application of phosphonate to tanoak seedlings did not protect them from infection when exposed to artificial or natural inoculum of P. ramorum. Foliar application of phosphonate to stump sprouts reduced lesion length by 44% of control in a shoot-dip assay three months post-treatment.
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Progress of the Phytophthora ramorum eradication programme in south-western Oregon forests, 2001 - 2009
Kanaskie, A., Hansen, E., Michaels Goheen, E., Osterbauer, N., McWilliams, M., Laine, J., Thompson, M., Savona, S., Timeus, H., Woosley, B., Sutton, W., Reeser, P., Schultz, R., & Hilburn, D.
Kanaskie et al. (pp. S169-S175) monitored the spread of Phytophthora ramorum in Oregon forests between 2001 and 2009. During this period, the area quarantined expanded from 23 km2 to 420 km2.Published Online - 24/11/2011. [3.9 MB] (pdf).Sudden Oak Death (SOD) disease caused by Phytophthora ramorum Werres, de Cock & Man in ‘t Veld was first discovered in Oregon forests in July 2001. Since then, an interagency team has been attempting to eradicate the pathogen though a programme of early detection (aerial and ground surveys, stream baiting) and destruction (herbicide treatment, felling and burning) of infected and nearby host plants, which has evolved over time. Post-treatment monitoring has indicated that although the disease has been eliminated from many of the sites and spread of inoculum may have been reduced, the disease continues to spread slowly. The quarantine area has expanded from 23 km2 in 2001 to 420 km2 in 2009. We attribute continued spread of the disease to the slow development of recognisable symptoms and to delays in treatment application associated with inconsistencies in funding. -
Forest Phytophthora diseases in the Americas: 2007 - 2010
Frankel, S. J., & Hansen, E. M.
Frankel & Hansen (pp. S159-S167) review recent findings, policy, regulation, and management relating to tree disease caused by Phytophthora species in wildlands and nurseries of North and South America.Published Online - 23/11/2011. [892.0 KB] (pdf).Recent findings, policy, regulation, and management relating to tree disease caused by Phytophthora species in wildlands and nurseries of North and South America are reviewed. These include the isolation of Phytophthora alni uniformis Brasier & S.A.Kirk in Alaska, and detection of population shifts in NA1, NA2 and EU1 clonal lineages of Phytophthora ramorum Werres, de Cock, & In’t Veld. The dissemination of Phytophthora ramorum from infested nurseries in water run-off presents a challenge for forest and plantation management. In the United States, forest Phytophthoras are viewed as a biosecurity threat and are monitored by the United States Department of Agriculture, Animal and Plant Health Inspection Service but tools designed to protect forests and nurseries need refinement. In Mexico, Phytophthora cinnamomi Rand is recognised as a threat to Quercus forests. The Phytophthora pinifolia Alv. Durán, Gryzenh. & M.J.Wingf. epidemic in Chilean Pinus radiata D.Don plantations has receded. Work with Phytophthora austrocedrae Gresl. & E.M.Hansen continues in Argentina. -
Quercus suber - Phytophthora cinnamomi interaction: a hypothetical molecular mechanism model
Coelho, A. C., Horta, M., Ebadzad, G., & Cravador, A.
Coehlo et al. (pp. S143-S157) have designed a hypothetical model that illustrates the initial events of the interaction between Quercus suber and Phytophthora cinnamomi.Published Online - 17/11/2011. [4.9 MB] (pdf).Phytophthora cinnamomi Rands is involved in the decline and mortality of Quercus suber L. and Quercus ilex L. in Southern Europe, in particular in Portugal and Spain. The presence and spread of P. cinnamomi in these regions is a severe threat to these oak ecosystems leading to expectable severe consequences for the production of cork and acorns in the near future.Molecular mechanisms underlying oomycete-host interactions are poorly understood. As a first step to identify transcripts involved in the Quercus suber - Phytophthora cinnamomi interaction, we applied complementary deoxyribonucleic acid-amplified fragment length polymorphism (cDNA-AFLP) methodology to cork oak seedlings infected with zoospores or mycelium of P. cinnamomi.
Forty-four Quercus suber genes that were differentially expressed when exposed to Phytophthora cinnamomi were selected and sequenced. Several of these genes were fully sequenced and the deduced aminoacid sequences showed consistent homology with proteins involved in the defence mechanism of other plant species. These findings led to the design of a simplified hypothetical model that illustrates the initial events of the interaction between Q. suber and P. cinnamomi.
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Tracking populations of Phytophthora ramorum within trees and across the South-western Oregon tanoak (Notholithocarpus densiflorus) forest with DNA fingerprinting and the relative fitness of dominant and rare individuals
Britt, J., & Hansen, E.
Britt and Hansen (pp. S133-S141) used DNA fingerprinting to investigate the spread of Phytophthora ramorum in south-western Oregon forests. Their results indicate that there was a single founder genotype, which is being progressively diluted by new genotypes arising through mutation. They also found that P. ramorum populations in Oregon forest are genetically distinct from those in nurseries and in California forests.Published Online - 11/11/2011. [1.3 MB] (pdf).Since the discovery of Phytophthora ramorum Werres, De Cock & Man In’t Veld in south-western Oregon forests in 2001, newly infected areas are detected each year. Yet, there are still gaps in our knowledge about how the pathogen spreads or where new infections come from. Our study aims to track the spread of P. ramorum in Oregon forests and within individual trees using DNA fingerprinting. We examined the genetic diversity of 1589 samples collected from 2001 to 2008 on several temporal and spatial scales. We identified 60 novel multilocus genotypes (MGs) with 9 to 44 MGs found in each year. While the majority of MGs were present in very low numbers (< 1%) one MG was dominant in all years representing 39 to 73% of isolates. The dominance of one MG was not attributable to higher fitness by any measure examined. Frequency of the dominant MG declined with time. This supports the hypothesis that it represents the founder genotype, and is being progressively diluted by new genotypes that arise through mutation. Our data also demonstrate that P. ramorum populations in Oregon forest are genetically distinct from those in nurseries and in California forests. -
A review of the catchment approach techniques used to manage a Phytophthora cinnamomi infestation of native plant communities of the Fitzgerald River National Park on the south coast of Western Australia
Dunne, C. P., Crane, C. E., Lee, M., Massenbauer, T., Barrett, S., Comer, S., Freebury, G. J. C., Utber, D. J., Grant, M. J., & Shearer, B. L.
Dunne et al. (pp. S121-S132) summarise a range of management techniques that have been used to contain an infestation of Phytophthora cinnamomi to the Fitzgerald River National Park on the south coast of Western Australia.Published Online - 03/11/2011. [2.3 MB] (pdf).The Fitzgerald River National Park (FRNP) is an International Biosphere Reserve on the south coast of Western Australia. The National Park is recognised for its high biodiversity with over 2000 plant species (including many endemics), threatened ecological communities and rare fauna. In contrast with many other areas of high biodiversity value in the region, the FRNP remains largely free of the introduced plant pathogen, Phytophthora cinnamomi Rands, with less than 0.1% of the Park currently infested. -
Comparing virulence of Phytophthora plurivora and P. pseudosyringae towards Fagus sylvatica seedlings using a method ensuring equal growth of both pathogens
Dalio, R. J. D., Fleischmann, F., & Oßwald, W.
Dalio et al. (pp. S115-S119) found that the greater aggressiveness of Phytophthora plurivora compared with P. pseudosyringae cannot be explained by its faster growth at a given temperature.Published Online - 02/11/2011. [905.9 KB] (pdf).Phytophthora plurivora T.Jung & T.I.Burgess and P. pseudosyringae T.Jung & Delatour exhibit different potential to colonise host plants. In order to clarify whether P. plurivora is more aggressive than P. pseudosyringae simply because of its faster growth and sporulation, a method for root infection was developed ensuring equal growth and sporulation for both pathogens during infection of F. sylvatica L. seedlings. Infection with P. plurivora strongly reduced CO2 uptake of seedlings and five out of eight seedlings died by the end of the experiment. In contrast, P. pseudosyringae did not alter physiology of infected plants and no mortality was recorded. The DNA contents of roots infected by either pathogen were similar at the end of the experiment, which indicated that a similar amount of fungal material was present for each species. This indicates that the greater aggressiveness of P. plurivora in comparison to P. pseudosyringae cannot be explained by its faster growth compared to P. pseudosyringae at a given temperature. -
Phytophthora ramorum research at the National Ornamentals Research Site at the Dominican University of California
Johnson-Brousseau, S., Henkes, M., Kosta, K., Suslow, K., Posadas, A. & Ghosh, S.
Johnson Brousseau et al. (pp. S101-S113) describe the establishment and operation of the National Ornamentals Research Site (NORS) at the Dominican University of California (DUC). This special facility allows nursery research to be performed on quarantine pests and pathogens (such as Phytophthora ramorum) while safeguarding plant health and the environment.Published Online - 01/11/2011. [3.7 MB] (pdf).Phytophthora ramorum Werres, De Cock & Man in‘t Veld, causal agent of sudden oak death (SOD) and ramorum blight, has been detected in container-grown plants, soil and irrigation ponds in various United States’ nurseries. Phytophthora ramorum has also been detected in runoff water from some nurseries and adjoining streams. Despite emergency regulatory actions, there is concern that P. ramorum infected nursery stock may further spread the disease in the United States of America (USA), particularly to previously unaffected wildlands. If established in the south-eastern USA, it could cause damage similar to that occurring in the coastal forests of California and Oregon. To develop solutions for nurseries that trade plants susceptible to P. ramorum, a quarantine nursery was established in Marin County, California, to investigate pathogen eradication and disease management. More than four years of collaborative efforts between the California Department of Food and Agriculture, California county Agriculture Commissioners, the California Oak Mortality Task Force, US National Plant Board, United States Department of Agriculture Animal and Plant Health Inspection Service Plant Protection and Quarantine and nursery industry resulted in locating a suitable site for developing the National Ornamentals Research Site (NORS) at the Dominican University of California (DUC). Funding to set-up and run the research nursery was awarded in 2008 through congressionally approved, Farm-bill (Section 10201) funding. The site is designed to perform research on quarantine pests and pathogens while safeguarding plant health and the surrounding natural environment. Research initiatives on P. ramorum have commenced at the NORS-DUC. Research grants are awarded to undertake research at the NORS-DUC and proposals can be submitted through www.dominican.edu/norsduc. -
Histology of Phytophthora ramorum in Notholithocarpus densiflorus bark tissues
Giesbrecht, M., Hansen, E., & Kitin, P.
Using various microscopic techniques, Giesbrecht et al. (pp. S89-S100) show that nearly all tanoak bark tissues are capable of being colonised by Phytophthora ramorum that this host responds to infection with callose deposition, tissue discoloration, and cell collapse; and that elicitins are present in cell walls of hyphae in infected bark tissues.Published Online - 25/10/2011. [5.7 MB] (pdf).Using various microscopic techniques, Giesbrecht et al. (pp. S89-S100) show that nearly all tanoak bark tissues are capable of being colonised by Phytophthora ramorum that this host responds to infection with callose deposition, tissue discoloration, and cell collapse; and that elicitins are present in cell walls of hyphae in infected bark tissues.Colonisation of Notholithocarpus densiflorus (Hook. and Arn.) Rehder tissues by Phytophthora ramorum Werres, De Cock & Man in’t Veld is not well understood. The pathogen is able to colonise nearly all tissues of this host but it is unclear how a tree is ultimately killed. In this research, P. ramorum infected N. densiflorus bark tissues were examined using various microscopic techniques to better understand the role of bark infection in killing a tree. Host responses to infection were detected by histological methods in conjunction with examining P. ramorum colonisation. Results of this work indicate that the pathogen can colonise nearly all N. densiflorus bark tissues but that phellogen and parenchyma of the inner bark are the most frequently and densely colonised. Pathogen specific elicitin labelling of P. ramorum-infected N. densiflorus sprouts caused hyphal cell walls to fluoresce in plant tissues, allowing specific identification of hyphae. Findings of this research show that nearly all bark tissues are capable of being colonised, that this host responds to infection with callose deposition, tissue discoloration, and cell collapse; and that elicitins are present in cell walls of hyphae in infected bark tissues