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''Hymenoscyphus fraxineus'' is an Ascomycete fungus that causes ash dieback, a chronic fungal disease of ash trees in Europe characterised by leaf loss and crown dieback in infected trees. The fungus was first scientifically described in 2006 under the name ''Chalara fraxinea''. Four years later it was discovered that ''Chalara fraxinea'' was only the asexual (anamorphic) stage of a fungus that was subsequently named ''Hymenoscyphus pseudoalbidus'' and then renamed as ''Hymenoscyphus fraxineus''. Trees now believed to have been infected with this pathogen were first reported dying in Poland in 1992. It is now entrenched in Europe. It is closely related to a native fungus ''Hymenoscyphus albidus'', which is saprotrophic and grows on the dead leaves of ash trees. == ''Hymenoscyphus fraxineus'' == The fungus ''Hymenoscyphus fraxineus'' was first identified and described in 2006 under the name ''Chalara fraxinea''. 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''.〔 However, ''Hymenoscyphus albidus'' has been known from Europe since 1851 and is not regarded as pathogenic. In 2010, through molecular genetic methods, the sexual stage (teleomorph) of the fungus was recognized as a new species and named ''Hymenoscyphus pseudoalbidus''.〔 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''.〔 ''Hymenoscyphus fraxineus'' is "morphologically virtually identical" to ''Hymenoscyphus albidus'', but there are substantial genetic differences between the two species. ''Hymenoscyphus fraxineus'' has two phases to its life-cycle: sexual and asexual.〔(【引用サイトリンク】accessdate=31 August 2015 )〕 The asexual stage (anamorph) grows in affected trees attacking the bark and encircling twigs and branches.〔 The sexual, reproductive stage, (teleomorph) grows during summer on ash petioles in the previous year's fallen leaves.〔 The ascospores are produced in asci and are transmitted by wind; this might explain the rapid spread of the fungus.〔 The origins of the disease are uncertain,〔(【引用サイトリンク】title=Decline of Fraxinus excelsior in northern Europe (2010–2012) )〕 but researchers are investigating the theory that the fungus originated in Asia, where ash trees are immune to the disease. 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''. 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.〔(''Ash fungus genetic code unravelled'' – BBC News )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hymenoscyphus fraxineus」の詳細全文を読む スポンサード リンク
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