Scientific Opinion on the Pest Categorisation of Cryphonectria Parasitica (Murrill) Barr

Scientific Opinion on the Pest Categorisation of Cryphonectria Parasitica (Murrill) Barr. Baker, R., Bragard, C., Candresse, T., Gilioli, G., Grégoire, J., Holb, I., Jeger, M. J., Karadjova, O. E., Magnusson, C., Makowski, D., Manceau, C., Navajas, M., Rafoss, T., Rossi, V., Schans, J., Schrader, G., Urek, G., Vloutoglou, I., van der Werf, W., & Winter, S. 12(10):n/a.

Paper doi abstract bibtex

The European Commission requested the EFSA Panel on Plant Health to perform a pest categorisation of Cryphonectria parasitica (Murrill) Barr, the fungal pathogen responsible for chestnut blight, a highly destructive disease that kills trees through bark cankers. The pathogen is listed in Annex IIAII of Directive 2000/29/EC. Its identity is clearly defined as C.parasitica (Murrill) Barr and methods exist for its discriminative detection. Several hosts are known, but the main hosts are species of Castanea and Quercus, particularly C.sativa and Q.petraea. These two host species are present in all the EU Member States and the disease has been recorded in most parts of the risk assessment area. C.parasitica is absent in Denmark, Estonia, Finland, Ireland, Malta, Iceland and Norway. No information is available on the presence of the pathogen in Latvia, Lithuania or Luxembourg. In the Czech Republic and Poland, C.parasitica has been eradicated. There are no recognised ecological or climatic factors limiting the potential establishment of the pathogen in the EU Member States where the pathogen is not known to occur. The pathogen can spread by propagules (mainly conidia, but also ascospores and mycelium) that are dispersed by wind, rain or vectors, as well as via the movement of infected or contaminated host plants for planting and bark, particularly asymptomatic ones. Control methods used against C.parasitica include exclusion and eradication, chemical control, host genetic resistance and biological control (hypovirulence). The most successful control methods of C.parasitica in the EU are exclusion and eradication, and hypovirulence. Potential consequences of the damage caused by C.parasitica include yield losses of fruit and wood, reduction in biodiversity and habitat loss for associated organisms. [Excerpt: Biology of Cryphonectria parasitica] [...] C. parasitica can be found on all the species of the genus Castanea and on other species, particularly several oak (Quercus) species, and, occasionally, on other genera, e.g. Acer, Fagus and Eucalyptus. However, on species other than Castanea spp., only virulent isolates of the fungus are able to form cankers, which are occasionally lethal, but the pathogen can survive on those species as a saprobe (Roane et al., 1986; Minervini et al., 1993; Gryzenhout et al., 2009). [] [...] C. parasitica infects the host through wounds of woody tissue or growth cracks, and quickly colonises the bark to the depth of the cambium, thus forming the bark canker. Dying tissues might also function as entry points for the pathogen (Roane et al., 1986; Prospero et al., 2006). Hail storms (Cortesi, unpublished data), forest fires and drought conditions can enhance the occurrence of infections (Prospero and Rigling, 2013). As the fungus continues to grow, the cankers expand, girdling and killing the trees. [] [...] [Uncertainty] The main sources of uncertainties of this pest categorisation are listed below: [::] Uncertainty on the current distribution of the pest in the risk assessment area. [...] [::] Uncertainty about the role of ascospores in disease epidemiology [...] [::] Uncertainty on natural spread by arthropods, birds, etc. [...] [::] Uncertainty on spread rate. [...] [::] Uncertainty on the spread of the pathogen through soil and growing media. [...] [::] Uncertainty on the current status of biocontrol in the EU MSs. [...] [::] Uncertainty about the distribution of minor hosts. [...] [::] Uncertainty on the current impact of the disease in the risk assessment area. [...] [Conclusions] [...] Cryphonectria parasitica is a clear taxonomic entity and sensitive and reliable methods exist for its detection and identification, as well as for its discrimination from other related fungal plant pathogens [] [...] The pest is absent in the Czech Republic (eradicated), Denmark, Estonia, Malta, Poland (eradicated) and Finland, and no information is available for Cyprus, Latvia, Lithuania, Luxembourg, Iceland and Norway [...] The pest is present in the risk assessment area [...] [] [...] There are no obvious eco-climatic conditions limiting the establishment and spread of C. parasitica in the risk assessment area. The main host species are present in the risk assessment area [...] Plants for planting are a pathway for the introduction and spread of C. parasitica [...] [] [...] C. parasitica primarily attacks chestnut trees (Castanea spp.) but can also cause damage to oak trees (Quercus spp.) and other hardwood tree species in forests and orchards. It produces cankers, causing wilting and diebacks, eventually killing the trees or relevant tree portions. Disease incidence ranges from less than 1\,% in the recently infested areas (such as Germany) to more than 90\,% in the countries where the pathogen has existed for a long time (e.g. Italy, France, Switzerland, Portugal, etc.). However, there is no direct relationship between disease incidence and disease severity (and therefore between disease incidence and impact) because of several factors, including hypovirulence. In areas where the fungal population has a low diversity of vegetative compatibility (vc) types, the natural spread of hypovirulence lowers the disease severity (and impact). In these populations, the introduction of new vc types may increase vc type population diversity, therefore lowering the hypovirulence efficacy Potential environmental impacts of damage caused by C. parasitica include reductions in biodiversity, food and wood resources and habitat for associated organisms [...] The pathogen was introduced into the USA in 1876 on imported Japanese chestnut trees (Castanea crenata). By 1900, many mail-order nurseries in the USA offered Japanese chestnut trees for sale throughout the country, thus contributing to the spread of the disease. In eastern USA, the disease has had a devastating impact on the American sweet chestnut (C. dentata) since its first detection in 1904. By 1940, 3.5 billion American chestnut trees had been killed by the pathogen throughout the natural range of C. dentata [...] [] [...] C. parasitica is a clear taxonomic entity and reliable methods exist for its detection and identification. C. parasitica is reported to be present in 15 MSs and absent in six MSs; its status in Cyprus, Latvia, Lithuania, Luxembourg, Iceland and Norway is unknown because of a lack of information. There are no obvious eco-climatic conditions limiting the establishment and spread of C. parasitica in the non-infested part of the risk assessment area, where the main hosts (Castanea spp. and Quercus spp.) are present. C. parasitica causes cankers, wilt and diebacks, resulting in the death of its hosts. No direct relationship exists between disease incidence and disease severity or impact because of several factors, including hypovirulence. In areas where low vc type diversity exists within the pathogen's population, the natural spread of hypovirulence decreases the disease severity and, thus, the impact. However, the introduction of new vc types into those areas may increase the diversity of vc types resulting in lower hypovirulence efficacy. Potential environmental impacts of C. parasitica in the risk assessment area include reductions in biodiversity, food and wood resources and habitat for associated organisms. [...] C. parasitica is a clear taxonomic entity and reliable methods exist for its detection and identification. The pest is present in the risk assessment area and is listed in Council Directive 2000/29/EC. The pathogen is present in part of the risk assessment area. Plants for planting are a pathway for the introduction into and spread within new areas of C. parasitica. The first introduction of the pathogen in the USA was on host plants for planting that had been imported from infested areas. Since then, C. parasitica has had a devastating impact on the American sweet chestnut (C. dentata), killing 3.5 billion American chestnut trees in the natural range of C. dentata within approximately 40 years [...] [] [...]

@article{bakerScientificOpinionPest2014,
  title = {Scientific Opinion on the Pest Categorisation of {{Cryphonectria}} Parasitica ({{Murrill}}) {{Barr}}},
  author = {Baker, Richard and Bragard, Claude and Candresse, Thierry and Gilioli, Gianni and Grégoire, Jean-Claude and Holb, Imre and Jeger, Michael J. and Karadjova, Olia E. and Magnusson, Christer and Makowski, David and Manceau, Charles and Navajas, Maria and Rafoss, Trond and Rossi, Vittorio and Schans, Jan and Schrader, Gritta and Urek, Gregor and Vloutoglou, Irene and van der Werf, Wopke and Winter, Stephan},
  date = {2014-10},
  journaltitle = {EFSA Journal},
  volume = {12},
  pages = {n/a},
  doi = {10.2903/j.efsa.2014.3859},
  url = {http://mfkp.org/INRMM/article/14425714},
  abstract = {The European Commission requested the EFSA Panel on Plant Health to perform a pest categorisation of Cryphonectria parasitica (Murrill) Barr, the fungal pathogen responsible for chestnut blight, a highly destructive disease that kills trees through bark cankers. The pathogen is listed in Annex IIAII of Directive 2000/29/EC. Its identity is clearly defined as C.parasitica (Murrill) Barr and methods exist for its discriminative detection. Several hosts are known, but the main hosts are species of Castanea and Quercus, particularly C.sativa and Q.petraea. These two host species are present in all the EU Member States and the disease has been recorded in most parts of the risk assessment area. C.parasitica is absent in Denmark, Estonia, Finland, Ireland, Malta, Iceland and Norway. No information is available on the presence of the pathogen in Latvia, Lithuania or Luxembourg. In the Czech Republic and Poland, C.parasitica has been eradicated. There are no recognised ecological or climatic factors limiting the potential establishment of the pathogen in the EU Member States where the pathogen is not known to occur. The pathogen can spread by propagules (mainly conidia, but also ascospores and mycelium) that are dispersed by wind, rain or vectors, as well as via the movement of infected or contaminated host plants for planting and bark, particularly asymptomatic ones. Control methods used against C.parasitica include exclusion and eradication, chemical control, host genetic resistance and biological control (hypovirulence). The most successful control methods of C.parasitica in the EU are exclusion and eradication, and hypovirulence. Potential consequences of the damage caused by C.parasitica include yield losses of fruit and wood, reduction in biodiversity and habitat loss for associated organisms.

[Excerpt: Biology of Cryphonectria parasitica] [...] C. parasitica can be found on all the species of the genus Castanea and on other species, particularly several oak (Quercus) species, and, occasionally, on other genera, e.g. Acer, Fagus and Eucalyptus. However, on species other than Castanea spp., only virulent isolates of the fungus are able to form cankers, which are occasionally lethal, but the pathogen can survive on those species as a saprobe (Roane et al., 1986; Minervini et al., 1993; Gryzenhout et al., 2009).

[] [...] C. parasitica infects the host through wounds of woody tissue or growth cracks, and quickly colonises the bark to the depth of the cambium, thus forming the bark canker. Dying tissues might also function as entry points for the pathogen (Roane et al., 1986; Prospero et al., 2006). Hail storms (Cortesi, unpublished data), forest fires and drought conditions can enhance the occurrence of infections (Prospero and Rigling, 2013). As the fungus continues to grow, the cankers expand, girdling and killing the trees.

[] [...]

[Uncertainty]

The main sources of uncertainties of this pest categorisation are listed below: [::] Uncertainty on the current distribution of the pest in the risk assessment area. [...] [::] Uncertainty about the role of ascospores in disease epidemiology [...] [::] Uncertainty on natural spread by arthropods, birds, etc. [...] [::] Uncertainty on spread rate. [...] [::] Uncertainty on the spread of the pathogen through soil and growing media. [...] [::] Uncertainty on the current status of biocontrol in the EU MSs. [...] [::] Uncertainty about the distribution of minor hosts. [...] [::] Uncertainty on the current impact of the disease in the risk assessment area. [...]

[Conclusions]

[...] Cryphonectria parasitica is a clear taxonomic entity and sensitive and reliable methods exist for its detection and identification, as well as for its discrimination from other related fungal plant pathogens

[] [...] The pest is absent in the Czech Republic (eradicated), Denmark, Estonia, Malta, Poland (eradicated) and Finland, and no information is available for Cyprus, Latvia, Lithuania, Luxembourg, Iceland and Norway [...] The pest is present in the risk assessment area [...]

[] [...] There are no obvious eco-climatic conditions limiting the establishment and spread of C. parasitica in the risk assessment area. The main host species are present in the risk assessment area [...] Plants for planting are a pathway for the introduction and spread of C. parasitica [...]

[] [...] C. parasitica primarily attacks chestnut trees (Castanea spp.) but can also cause damage to oak trees (Quercus spp.) and other hardwood tree species in forests and orchards. It produces cankers, causing wilting and diebacks, eventually killing the trees or relevant tree portions. Disease incidence ranges from less than 1\,\% in the recently infested areas (such as Germany) to more than 90\,\% in the countries where the pathogen has existed for a long time (e.g. Italy, France, Switzerland, Portugal, etc.). However, there is no direct relationship between disease incidence and disease severity (and therefore between disease incidence and impact) because of several factors, including hypovirulence. In areas where the fungal population has a low diversity of vegetative compatibility (vc) types, the natural spread of hypovirulence lowers the disease severity (and impact). In these populations, the introduction of new vc types may increase vc type population diversity, therefore lowering the hypovirulence efficacy Potential environmental impacts of damage caused by C. parasitica include reductions in biodiversity, food and wood resources and habitat for associated organisms [...] The pathogen was introduced into the USA in 1876 on imported Japanese chestnut trees (Castanea crenata). By 1900, many mail-order nurseries in the USA offered Japanese chestnut trees for sale throughout the country, thus contributing to the spread of the disease. In eastern USA, the disease has had a devastating impact on the American sweet chestnut (C. dentata) since its first detection in 1904. By 1940, 3.5 billion American chestnut trees had been killed by the pathogen throughout the natural range of C. dentata [...]

[] [...] C. parasitica is a clear taxonomic entity and reliable methods exist for its detection and identification. C. parasitica is reported to be present in 15 MSs and absent in six MSs; its status in Cyprus, Latvia, Lithuania, Luxembourg, Iceland and Norway is unknown because of a lack of information. There are no obvious eco-climatic conditions limiting the establishment and spread of C. parasitica in the non-infested part of the risk assessment area, where the main hosts (Castanea spp. and Quercus spp.) are present. C. parasitica causes cankers, wilt and diebacks, resulting in the death of its hosts. No direct relationship exists between disease incidence and disease severity or impact because of several factors, including hypovirulence. In areas where low vc type diversity exists within the pathogen's population, the natural spread of hypovirulence decreases the disease severity and, thus, the impact. However, the introduction of new vc types into those areas may increase the diversity of vc types resulting in lower hypovirulence efficacy. Potential environmental impacts of C. parasitica in the risk assessment area include reductions in biodiversity, food and wood resources and habitat for associated organisms. [...] C. parasitica is a clear taxonomic entity and reliable methods exist for its detection and identification. The pest is present in the risk assessment area and is listed in Council Directive 2000/29/EC. The pathogen is present in part of the risk assessment area. Plants for planting are a pathway for the introduction into and spread within new areas of C. parasitica. The first introduction of the pathogen in the USA was on host plants for planting that had been imported from infested areas. Since then, C. parasitica has had a devastating impact on the American sweet chestnut (C. dentata), killing 3.5 billion American chestnut trees in the natural range of C. dentata within approximately 40 years [...]

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