Usuario:Auró/sandbox1

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Acronecrosis del fresno[editar]

Hymenoscyphus fraxineus[editar]

The fungus Hymenoscyphus fraxineus was first identified and described in 2006 under the name Chalara fraxinea.[1]​ In 2009, based on morphological and DNA sequence comparisons, Chalara fraxinea was suggested to be the asexual stage (anamorph) of the ascomycete fungus Hymenoscyphus albidus.[1]​ However, Hymenoscyphus albidus has been known from Europe since 1851 and is not regarded as pathogenic.[2]​ In 2010, through molecular genetic methods, the sexual stage (teleomorph) of the fungus was recognized as a new species and named Hymenoscyphus pseudoalbidus.[1]​ Four years later it was determined that "under the rules for the naming of fungi with pleomorphic life-cycles", the correct name should be Hymenoscyphus fraxineus.[3]​ Hymenoscyphus fraxineus is "morphologically virtually identical" to Hymenoscyphus albidus, but there are substantial genetic differences between the two species.[4]​

Hymenoscyphus fraxineus[editar]

El hongo Hymenoscyphus fraxineus fue identificado y descrito por primera vez en 2006 bajo el nombre Chalara fraxinea[1]​En el 2009, comparaciones morfológicas y de Secuencia de ADN sugirieron que Chalara fraxineaera la fase sexual del hogo ascomycota Hymenoscyphus albidus[1]​ No obstante, este hongo se conocía en Europa desde 1851, y no es considerado patogénico.[5]​En el año 2010, utilizando técnicas de genética molecular la fase sexual de este hongo fue identificada como una nueva especie, dándosele el nombre de Hymenoscyphus pseudoalbidus.[1]​Cuatro años más tarde se determinó que siguiendo la normativa de nomenclatura para los hongos que tienen pleomorfismo el nombre correcto debía ser Hymenoscyphus fraxineus

Crown dieback in a mature ash tree

Hymenoscyphus fraxineus has two phases to its life-cycle: sexual and asexual.[6]​ The asexual stage (anamorph) grows in affected trees attacking the bark and encircling twigs and branches.[6]​ The sexual, reproductive stage, (teleomorph) grows during summer on ash petioles in the previous year's fallen leaves.[2]​ The ascospores are produced in asci and are transmitted by wind; this might explain the rapid spread of the fungus.[2]​ The origins of the disease are uncertain,[7]​ but researchers are investigating the theory that the fungus originated in Asia, where ash trees are immune to the disease.[8]​ Genetic analysis of the fungus Lambertella albida which grows harmlessly on petioles of the Manchurian ash (Fraxinus mandschurica) in Japan, has shown that it is likely to be the same species as Hymenoscyphus fraxineus.[9]​

Teams from The Sainsbury Laboratory (TSL) and the John Innes Centre in Norwich sequenced the genome of the fungus in December 2012. The sequence has been published on the website OpenAshDieBack and offers clues to how the fungus infects trees. The study has uncovered toxin genes and other genes that may be responsible for the virulence of the fungus. In the long term researchers aim to find the genes that confer resistance to the pathogen on some ash trees.[10]​

Ash dieback[editar]

Yellow to red-brown necrosis in a five-year-old ash tree

Trees now believed to have been infected with this pathogen were reported dying in large numbers in Poland in 1992,[11]​ and by the mid 1990s it was also found in Lithuania, Latvia and Estonia.[12]​ However, it was 2006 before the fungus’s asexual stage, Chalara fraxinea, was first described by scientists, and 2010 before its sexual stage was described.[11]​ By 2008 the disease was also discovered in Scandinavia, the Czech Republic, Slovenia, Germany, Austria and Switzerland.[13]​ By 2012 it had spread to Belgium, France, Hungary, Italy, Luxembourg,[14]​ the Netherlands, Romania, Russia, Britain and Ireland.[15]​[16]​

There are few official figures available, but the disease has caused a large-scale decline of ash trees across Poland,[17]​ and the experience there suggests that in the long term "15 to 20 per cent of trees do not die, and show no symptoms."[18]​ In 2012, the disease was said to be peaking in Sweden and Denmark, and in a post-decline (or chronic) phase in Latvia and Lithuania.[7]​ The disease was first observed in Denmark in 2002, and had spread to the whole country by 2005.[19]​ In 2009 it was estimated that 50 per cent of Denmark's ash trees were damaged by crown-dieback,[19]​ and a 2010 estimate stated that 60–90% of ash trees in Denmark were affected and may eventually disappear.[20]​ The disease was first reported in Sweden in 2003.[21]​ A survey conducted in Götaland in 2009 found that more than 50% of the trees had noticeable thinning and 25% were severely injured.[21]​

A Danish study found that substantial genetic variation between ash trees affected their level of susceptibility.[22]​ However, the proportion of trees with a high level of natural resistance seemed to be very low, probably less than 5%.[22]​ A Lithuanian trial based on the planting of trees derived from both Lithuanian and foreign populations of European ash found 10% of trees survived in all progeny trials to the age of eight years.[23]​

So far the fungus has mainly affected the European ash (Fraxinus excelsior) and its cultivars, but it is also known to attack the Narrow-leafed ash (Fraxinus angustifolia).[24]​ The Manna ash (Fraxinus ornus) is also a known host, although it is less susceptible than the other European ash species.[24]​ Experiments in Estonia have shown that several North American ash species are susceptible, especially the Black ash (Fraxinus nigra), and to a lesser extent the Green ash (Fraxinus pennsylvanica).[24]​ The White ash (Fraxinus americana) and the Asian species known as Manchurian ash (Fraxinus mandschurica) showed only minor symptoms in the study.[24]​

  1. ↑ a b c d e f «FRAXBACK – Category: Chalara». FRAXBACK. Archivado desde el original el 4 August 2014. Consultado el 31 October 2012.  Error en la cita: Etiqueta <ref> no válida; el nombre «fraxback1» está definido varias veces con contenidos diferentes
  2. ↑ a b c «Hymenoscyphus pseudoalbidus». ETH – Forest Pathology and Dendrology. 14 April 2010. Consultado el 31 October 2012. 
  3. ↑ Error en la cita: Etiqueta <ref> no válida; no se ha definido el contenido de las referencias llamadas baraletal
  4. ↑ Bengtsson, S. B. K.; Vasaitis, R.; Kirisits, T.; Solheim, H.; Stenlida, J. (2012). «Population structure of Hymenoscyphus pseudoalbidus and its genetic relationship to Hymenoscyphus albidus». Fungal Ecology 5 (2): 147-153. doi:10.1016/j.funeco.2011.10.004. 
  5. ↑ «Hymenoscyphus pseudoalbidus». ETH – Forest Pathology and Dendrology. 14 de octubre de 2010. Consultado el 4/02/2018.  |title= y |título= redundantes (ayuda)
  6. ↑ a b «Chalara dieback of ash». Forestry Commission. Consultado el 31 August 2015. 
  7. ↑ a b «Decline of Fraxinus excelsior in northern Europe (2010–2012)». SNS – Nordic Forest Research Co-operation Committee. Consultado el 31 October 2012. 
  8. ↑ «Are Europe's ash trees finished?». New Scientist. 31 October 2012. Consultado el 31 October 2012. 
  9. ↑ Zhao, Y.; Hosoya, T.; Baral, H.; Hosaka, K.; Kakishima, M. (2012). «Hymenoscyphus pseudoalbidus, the correct name for Lambertella albida reported from Japan». Mycotaxon 122: 25-41. doi:10.5248/122.25. 
  10. ↑ Ash fungus genetic code unravelled – BBC News
  11. ↑ a b Error en la cita: Etiqueta <ref> no válida; no se ha definido el contenido de las referencias llamadas forestrycomm
  12. ↑ «Ash decline in Nordic and Baltic countries». Metla. 3 July 2007. Consultado el 6 November 2012. 
  13. ↑ «Eschensterben alarmiert Forstexperten» (en german). Spiegel Online. 6 November 2008. Consultado el 29 October 2012. 
  14. ↑ Cf. p. 35-36 in: Garnier-Delcourt, M., G. Marson, Ch. Reckinger, B. Schultheis & M.-T. Tholl, 2013. Notes mycologiques luxembourgeoises. VII. Bull. Soc. Nat. luxemb. 114 : 35-54. (Pdf 6.5 MB)
  15. ↑ «Chalara fraxinea – Ash dieback». European and Mediterranean Plant Protection Organization. March 2012. Archivado desde el original el 17 July 2012. Consultado el 29 October 2012. 
  16. ↑ «Chalara ash dieback outbreak: Q&A». BBC News. 29 October 2012. Consultado el 31 October 2012. 
  17. ↑ Vasaitis, R.; Lygis, V. (2008). «Emerging forest diseases in south-eastern Baltic Sea region». Network of Climate Change Risks on Forests (FoRisk): SNS Workshop, Umea, Sweden.: 14-15. 
  18. ↑ Cole Moreton (11 November 2012). «Ash dieback: the ruined Polish forest where deadly fungus began». London: The Telegraph. Consultado el 17 December 2012. 
  19. ↑ a b «Udryddelse truer asketræet» (en danish). Naturstyrelsen. 6 June 2012. Consultado el 9 January 2013. 
  20. ↑ «Workshop on Chalara fraxinea – Oslo, Norway, 2010-06-30/07-02». European and Mediterranean Plant Protection Organization. 2010. Consultado el 6 November 2012. 
  21. ↑ a b «Den senaste om askskottsjukan». Svenska Trädföreningen. 2010. Consultado el 6 November 2012. Uso incorrecto de la plantilla enlace roto (enlace roto disponible en Internet Archive; véase el historial, la primera versión y la última).
  22. ↑ a b «Ash trees that can survive the emerging infectious die-back disease». NBforest.info. 9 February 2010. Consultado el 31 October 2012. 
  23. ↑ Pliūra, A.; Lygis, V.; Suchockas, V.; Bartkevičius, E. (2011). «Performance of twenty four European Fraxinus excelsior populations in three Lithuanian progeny trials with a special emphasis on resistance to Chlara fraxinea». Baltic Forestry 17 (1): 17-34. 
  24. ↑ a b c d «Update on ash dieback (Chalara fraxinea) in Europe: New confirmed hosts and description of the perfect state». North American Plant Protection Organisation. 10 November 2010. Consultado el 6 November 2012. 
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