Research
Plant health risk and monitoring evaluation (PHRAME)
Research Status:completed
PHRAME developed improved pest risk analysis techniques for quarantine pests, using pine wood nematode, Bursaphelenchus xylophilus, in Portugal as a model system.
Final report and summary of conclusions
This research is now continued by the REPHRAME project.
Detection of pine wood nematode in Portugal has increased the threat to the EU from this extremely dangerous pest. The key objective for this project was to develop an improved Pest Risk Analysis methodology that can be used at both local and regional scales to assess the significance of a plant health threat and, by use of a core model, to assess the consequences of outbreaks.
This programme was funded by the European Union – Framework Programme FP5.
There were partners in six countries: Austria, France, Germany, Portugal, Spain and UK.
Forest Research co-ordinated this project.
The project ran from 2003 to 2006.
Co-ordinator: Hugh Evans, Forest Research
Contract: QLK5-CT-2002-00672, Quality of Life and Management of Living Resources, FP5.
The main aim of the research programme is to develop scientifically verifiable methods to enable the current high levels of uncertainty in Pest Risk Analysis (PRA) to be reduced, thus giving confidence in proposing quarantine measures that are justifiable and minimise recourse to the Precautionary Principle.
Thus, the research programme addresses the twin objectives of:
The combined experimental and observational approach proposed by this project is based on the unique opportunity that has arisen with the discovery, in 1999, of B. xylophilus in Portugal. This will enable the partnership in this proposal to address known weaknesses in PRA technology arising from the lack of direct knowledge of the ecological and socio-economic aspects of the introduction of a new pest. Integration of more traditional techniques of survey and gathering of biological information with new techniques such as molecular identification, Geographic Information Systems and use of ecological models provides an approach that will enhance the prospects of producing the key deliverables from this proposal.
The building blocks of the PRA approach that is central to this research programme are reliable quantitative data on the pest organisms Bursaphelenchus xylophilus and its vectors Monochamus spp. Surveys and detailed ecological studies will be critical components of the work and will take maximum advantage of the new pest association in Portugal. An understanding of the inter-relationships between the nematode, its vectors and the host tree is, therefore, essential to the study.
Schematic representation of the inter-relationships between pine wood nematode, Bursaphelenchus xylophilus, and its vectors in the genus Monochamus
The links in the diagram display (pop-up) photographs of:
The approach adopted enables the consortium to address weaknesses in PRA technology arising from the lack of direct knowledge of the ecological and socio-economic aspects of the introduction of a new pest. In the case of B. xylophilus in Portugal, there is an opportunity to develop Plant Health and regional pest management strategies at the same time as fundamental knowledge of the new pest-host plant association is gathered.
This has four principal, inter-related, benefits:
The research programme is co-ordinated through a series of groupings that will work individually and collectively to deliver the main expected output:
Key: Pn indicates the Partner number
Clockwise from top, then centre:
Professor Manuel Mota, University of Evora.
Increased volumes of traded goods consequent on rapid transport systems by air, land and sea have brought with them associated risks from the transportation of pests between countries and ecosystems. Some of these pests are carried on plants or plant products and range from those that are visible on the substrate and others that are cryptic and well hidden from cursory inspection.
Although essential in making decisions to safeguard against international movement of plant pests, development of Pest Risk Analysis (PRA) techniques is still in its infancy, despite international collaboration within the context of the International Plant Protection Convention (IPPC) and Regional Plant Protection Organisations (RPPOs) world-wide.
This uncertainty is emphasised further when dealing with new pest infestations where knowledge of the risk factors may be limited and, hence, decisions on pest management are constrained and may not be the most appropriate. This is the case in Portugal where the discovery of pine wood nematode, Bursaphelenchus xylophilus, has led to development of rapid pest management strategies that have, of necessity, been based on limited information and which make the task of managing the threat very difficult.
Refinements in the PRA process will aid this management requirement and increase confidence in assessing further risks and consequences of management actions applicable to Portugal and the rest of Europe.
Close-up of needle wilting of pines caused by pine wood nematode
The key deliverable of the project is the development of an improved pest risk analysis methodology that can be used at local and regional scales to assess the scale of a potential plant health threat and, by use of models, to assess the consequences of a range of pest management options.
The Consortium will aim to achieve this by:
See the description of the work packages for further information.
Progress report for Year 1 (PDF-113K)
Summary:
Progress report for Year 2 (PDF-110K)
Summary:
The principal objective is to determine the distribution of Monochamus spp. (vectors of the pine wood nematode) in the Iberian Peninsula, and to collect information about their biology, especially the flight period and any Bursaphelenchus spp. carried by the beetles.
Sampling in the Setubal region of Portugal will aim to detect vector(s) active in the current B. xylophilus infestation, with emphasis on M. galloprovincialis. This information will be used for elaboration of control measures against the beetles that should prove to be the most effective means of managing Bursaphelenchus. Moreover, the distribution of Monochamus and the presence of B. mucronatus on the vector will provide a means to indicate the highest risk regions for establishment of B. xylophilus. The number of B. xylophilus carried by the longhorn beetles is an important indicator for a possible epidemic spread of pine wilt.
Other wood- and bark-breeding beetles, especially bark beetles may also play a role as vectors of B. xylophilus and will be investigated.
The principal objective is to evaluate the extent of establishment of B. xylophilus in the Iberian Peninsula. Since Portuguese wood is mainly exported to Spain, there is a high probability of dissemination of B. xylophilus to Spain. Eco-climatic conditions in Spain are favourable for pine wilt disease, and the proximity to Portugal could permit natural spread of the nematode between the two countries. Since other Bursaphelenchus species may also possess a phytopathogenic potential, their distribution and host preferences will also be recorded. Partner 7 will make Bursaphelenchus samples collected during the EU surveys in France available for inclusion in the investigations.
The association between the severity of nematode attack and underlying ecological parameters will be thoroughly investigated and correlated. National forest services will supply important and accurate information on the ecosystem. Specific biotic and abiotic parameters in the region, such as high summer temperatures, low precipitation, extensive fire outbreaks and the reduction of forest land, necessitates immediate studies in relation to their roles on Bursaphelenchus and Monochamus occurrence in Mediterranean forests.
The main objective will be to investigate ecological variables that explain the nematode’s presence in Portugal, in order to establish an ecological optimum for the nematode and its vectors. Meteorological variables will be thoroughly investigated; also landscape variables and land use will be considered.
The objective of this work package is the development of methods for early detection of Bursaphelenchus nematodes in living trees. To prevent spread of nematodes and attack of nematode-infested trees by egg-laying longhorn beetles, infested trees should be removed as early as possible. However, nematode distribution within trees is very irregular initially and difficult to detect by sampling. The increase of the nematode population in xylem and the collapse of the cambium-phloem zone will lead to a change in the water regime and resin flow of the infested tree. This could be measured by different instruments and methods.
To obtain detailed information on the pathogenicity of the Portuguese isolate(s) of B. xylophilus in comparison to known provenances of the nematode, pathogenicity data will be obtained in climate chambers under variable temperatures and under outdoor conditions in Portugal using various European pine species.
The objective is to obtain information on the area of origin and the pathway of introduction of the B. xylophilus strain detected in Portugal. It is very important to determine the potential pathways for introduction of this serious pest to Europe because efforts to eradicate the nematode in Portugal will be in vain if introductions occur repeatedly. This issue is also very important in order to better protect other EU countries from introduction of the nematode.
Identification of the pathway will also enable existing risk reduction measures within EU legislation to be assessed for efficacy and, if necessary, recommend more stringent measures in relation to future imports from the country of origin of the nematode.
To carry out a new literature review and to update an information database on B. xylophilus and Monochamus spp. in a world-wide context. Special attention will be paid to information from China where the nematode is a relatively new arrival and is still spreading, and to quantitative information on the phenologies of B. xylophilus and Monochamus spp. Information will be prepared in a form suitable for inclusion in GIS and CLIMEX predictive models.
Development of refined Pest Risk Analysis (PRA) tools using B. xylophilus and its inter-relations with native Monochamus spp. in Europe as a model system. This includes:
The project was formally completed in 2007 and the final report is available for download:
Plant health risk and monitoring evaluation (PHRAME) final report (PDF-6270K)
There is no doubt that Bursaphelenchus xylophilus is a significant threat to the pine forests of Europe and this is confirmed by the considerable tree mortality that has already been observed in the affected zone in Portugal.
For example, surveys carried out in the affected zone during the winter of 2006 revealed around 200,000 symptomatic trees and, of the trees sampled for presence of pine wood nematode (PWN), approximately 22% were positive for B. xylophilus (Report of FVO Mission to Portugal, May 2007). Such data indicate that the scale of the problem is large and, therefore, access to definitive information on the interactions between PWN, its vectors and its host trees in a European context is essential. The results presented in this report provide a solid basis from which to determine optimised methods for management of this important new pest to Europe.
In relation to identification of the source of the B. xylophilus populations in Portugal, a combination of sophisticated molecular techniques have indicated that at least one race of the nematode originating in Asia has arrived in the country. There are indications that two sources of origin are included in the Portuguese population of PWN which suggests either multiple introductions or a single introduction of a mixed population of the nematode.
While of academic interest, this information is valuable in assessing potential future pathways of arrival of further incursions of the pest to Europe. Extensive surveys of trees in the countries represented within the project have revealed no further findings of B. xylophilus outside the affected zone in Portugal. However, the surveys have revealed many other species of Bursaphelenchus, including the closely related B. mucronatus and B. fraudulentus, which are difficult to differentiate morphologically. The data provide encouragement that B. xylophilus itself is still restricted to the affected zone in Portugal. New molecular techniques from this research programme will aid rapid and accurate identification of the members of the genus Bursaphelenchus in future.
A key factor in the survival and spread of PWN in the field is association with a vector insect species. Extensive studies were made of the potential of members of the xylophagous insect fauna associated with PWN-affected trees to act as vectors of the nematode for further spread of the organism. A clear conclusion from the studies is that only M. galloprovincialis has taken on the role of vector in Portugal.
Although there are nematodes associated with a number of bark and wood-boring beetles in Austria, Portugal and Spain, none of these has been shown to successfully transmit B. xylophilus to host trees.
A further significant finding from the project is that despite clear demonstration of the presence of PWN in the roots of affected trees, there was no evidence of transmission of the nematode to adjacent trees either through root grafting or by direct migration through the soil. This information confirms the widely demonstrated results from international literature on PWN that it is only adult beetles in the genus Monochamus that act as effective vectors of the nematode.
Information on the biology and pathogenesis of PWN in relation to tree species potentially likely to exhibit wilt expression following introduction of the nematode to the crowns of trees during maturation feeding by Monochamus spp is critical and essential to understanding and predicting likelihood of wilt expression.
Correlative studies in regions of the world where pine wilt disease has been demonstrated all indicate a close relationship with average summer temperatures, including hypotheses that monthly isotherms must exceed 24oC to give rise to extensive tree mortality (Rutherford & Webster, 1987). While of general practical value, such correlations cannot account for local variation in eco-climatic conditions and it was recognised that more detail on the nature of pathogenesis of PWN in living susceptible trees was needed.
Results from studies carried out in Germany, Portugal and Japan within this project have thrown considerable light on the nature of the process of wilt expression when B. xylophilus is introduced to living trees by maturation feeding. Of particular significance is the knowledge that movement of nematodes from the site of introduction is immediate and rapid, with some nematodes being found in the root area within days of inoculation. Such patterns of invasion can be explained by the ability of the nematodes to exploit living tissues both for nutrition and reproduction and also to move into less well defended areas of the affected trees. This matches with previous histopathological examination of nematode invasions that linked their rapid movement downwards to exploitation of the cambial zone, leading to breakdown of tissue integrity and the opening of cavities that facilitated free movement of nematodes.
Lodging of nematode populations in particular parts of the tree was also shown to provoke local defence reactions, which contributed to embolism and cavitation of the xylem. Presence of large numbers of nematodes in xylem cells also confirmed the ability of B. xylophilus to breed successfully in the living trees. Such data are essential building blocks in developing process-based predictive models for wilt expression.
With the demonstration that M. galloprovincialis is the only known vector in Portugal, data on the biology and dispersal of the vector have been gathered, starting from a low knowledge base on this insect prior to the appearance of PWN in Portugal. Results from the project studies have shown that the vector has a single generation per year, with clearly defined emergence, flight and oviposition peaks around mid-summer in Portugal.
The proportion of adults carrying viable B. xylophilus dauer larvae emerging from trees killed by PWN can be high (ca. 75%), indicating a close relationship between tree mortality from PWN and subsequent exploitation of those trees for breeding by the vector. Such data confirm the cause and effect relationship between PWN, its host trees and the breeding success of the vector, the combination forming a feedback loop leading to increasing tree mortality and availability of breeding resources.
The Portuguese strategy of early identification and removal of PWN affected trees before emergence of vectors insects that may have used them for breeding is, therefore, sound.
Methods to increase the efficacy of sampling for vector insects are part of such an approach and considerable progress has been made in identifying and improving trap and chemical lure designs for use in both monitoring and, potentially, reduction of vector populations. Within this approach, attempts have been made to develop methods for early detection of infestation and potential wilt expression in PWN-affected trees. A simple method to measure oleoresin flow from a punch hole system, proved to be quite reliable for larger trees (> 20 cm DBH) and gave early warning of subsequent wilt and tree mortality, but this was dependent also on the time of year and month of infestation by the nematode. Electrical conductivity methods did not provide sufficient warning of likely tree mortality.
Bringing together the detailed and more general information on the interactions between PWN and its host trees in an eco-climatic context, significant progress has been made in predictive modelling of wilt expression.
Two main approaches have been adopted, namely use of correlative heuristic and empirical models to link to tree suitability parameters and a process-based modelling strategy that links directly to tree physiology in relation to local eco-climatic conditions. This complementary approach has started to yield valuable predictive tools for improved risk assessment in the future.
The main conclusions from the correlative modelling approach were:
The process-based models employed and adapted existing tree growth models that have already been validated for pine species in Europe. Addition of PWN as a factor compromising the evapotranspiration models has allowed direct prediction of the effects of the nematode using moisture and temperature as key driving variables. Simulations carried out under a range of conditions in Portugal and in the UK as a contrast, indicated that high mortality can be expected in the Setubal region of Portugal, which confirms the situation observed in P. pinaster trees in this area.
The model also predicted when mortality can be expected in relation to month of infestation in the field and, here, there were some surprising predictions in that some trees in the main affected area are predicted to die in the second year after infestation. This has profound implications for survey strategies based on symptomatic trees; some trees may be infested by the nematode but not be declared symptomatic during a winter survey and could be missed.
Current work includes field trials with inoculated standing trees to verify the predictions of the models. This work is ongoing, but early results confirm the mortality and timescales arising from PWN infestation of susceptible trees.
In final conclusion, the combined data from this study have advanced knowledge on the interaction of PWN, its vectors, host trees and eco-climatic factors in both a regional and global context. Much has been learned about the PWN system and there are real prospects of using the advanced knowledge to provide customised Pest Risk Analysis predictions of PWN impact in any location in Europe. This will commence with use of the process-model to provide country and region specific predictions of likelihood of wilt expression.
We are Forest Research
| Partner | Principal Scientist |
Contact details | |
|---|---|---|---|
| 1 | H. F. Evans Coordinator |
Forest Research Alice Holt Lodge Farnham Surrey GU10 4LH, UK E-mail: hugh.evans@forestresearch.gov.uk www.forestresearch.gov.uk |
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| 2 | T. Schröder | Federal Biological Research Centre for Agriculture and Forestry Department for National and International Plant Health (BBA/AG) Messeweg 11-12 D-38173 Braunschweig Germany |
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| 3 | M. M. Mota | Departamento de Biologia Universidade de Évora 7000 Évora Portugal Tel: +351-266-760800 Fax: +351-266-711231 E-mail: mmota@uevora.pt |
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| 4 | M. Arias | Departamento de Agroecologia Centro de Ciencias Medioambientales (CCMA) Consejo Superior de Investigaciones Científicas (CSIC) Serrano 115 dpdo E-28006 Madrid Spain |
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| 5 | C. Tomiczek | Institute of Forest Protection Seckendorff-Gudent-Weg 8 A-1131 Wien, Austria Tel: +43-1-87838-0 Fax: +43-1-87838-1250 E-mail: christian.tomiczek@bfw.gv.at |
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| 6 | W. Burgermeister | Federal Biological Research Centre for Agriculture and Forestry Institute for Plant Virology, Microbiology and Biosafety (BBA/PS) Messeweg 11-12 D-38104 Braunschweig Germany |
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| 7 | P. Castagnone- Sereno |
INRA Interactions Plantes-Micro-organismes et Santé Végétale BP2078 123 Bd Francis Meilland 06606 Antibes Cedex France |
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| 8 | E. Sousa | INIA, Instituto Nacional de Investigação Agrária Quinta do Marquês 2780 Oeiras Portugal |
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