|Forum topic by Planeman40||posted 11-01-2012 02:20 PM||1794 views||0 times favorited||15 replies|
11-01-2012 02:20 PM
Will this come to the USA?
Are Europe’s ash trees finished?
October 2012 by Andy Coghlan
A fungus deadly to ash trees has just reached Britain and Ireland, after emerging 20 years ago in Poland. Already it has devastated ash trees in mainland Europe, sweeping through more than 20 countries powerless to prevent its spread.
How did this fungus develop? And what, if anything, can be done to stop it in countries like the UK, where ashes account for around a fifth of all trees? By the sound of it, the outlook is not good. New Scientist investigates.
Just how many ash trees have been killed?
And now it’s reached the UK?
The alarm bells really started ringing last month when the disease was spotted in wild ash trees in East Anglia, one of the regions of England that is closest to mainland Europe. The likelihood is that the fungus must have spread here naturally.
How did it do that?
How does the fungus kill ash trees?
Can it be stopped?
“There’s very little you can do,” says Ottmar Holdenrieder of the Swiss Federal Institute of Technology in Zurich, who in 2010 helped uncover the fungus’s complete life cycle. “It’s a waste of time to chop down trees.” The infective material is all on the forest floor and cannot be removed or eradicated with fungicides without destroying countless other forms of forest life.
Which fungus causes the disease?
This did not solve the puzzle. Fungal species often exist in two forms: one that reproduces itself asexually, and one that multiplies sexually by producing spores. It turned out that Chalara fraxinea is asexual, so the real killer remained at large.
By 2009, Kowalski had found what he thought was the sexual form of C. fraxinea: Hymenoscyphus albidus, which produces spores from tiny toadstool-like growths on ash leaf litter (Forest Pathology, DOI: 10.1111/j.1439-0239.2008.00589.x). But this was something of a red herring. H. albidus has been growing on the decaying leaves of Europe’s ash trees for centuries, so was unlikely to be the culprit. It has been known in the UK, for example, since the mid-19th century.
The real killer was unmasked a year later, and produced toadstools identical to those of harmless old H. albidus. Using painstaking genetic analysis, Holdenrieder, Kowalski and others found that this doppelganger was actually a different, and lethal, species. They named it Hymenoscyphus pseudoalbidus (Forest Pathology, DOI: 10.111/j.1439-0329.2010.00645.x).
How did this killer emerge, apparently out of the blue?
The ideas that H. pseudoalbidus evolved from its close European relative, or that climate change made European ashes more vulnerable to a pathogen that was already there, have both been ruled out. In short, the fungus is new to Europe, and the serious money is on it arriving from the east.
Does our identification of the culprit help in combating the disease?
Alternatively, it might be possible to develop a vaccine, as was developed to protect elm trees against Dutch elm disease, but this is a distant goal.
Meanwhile, now that the fungus is in Europe, it is locked in an “arms race” with the ash trees. The fungus has the whip hand because it breeds far faster.
Can we do anything to stop the fungus evolving?
What’s the best hope for UK trees?
The best hope is that any fungus is present only in small pockets that can be cleared to prevent further spread. The worst case is that it is everywhere, in which case it’s probably goodbye to the English ash.
“If that’s the case, there’s nothing they can do about it,” says Jim Briercliffe, business development manager of the Horticultural Trades Association (HTA) in Reading, UK, which represents suppliers of plants, seeds and gardening equipment. The only option will be to replace dead ash with other kinds of tree.
The HTA warned the government in 2009 that the disease was rife in Danish nurseries and could easily reach the UK. “It is annoying that our warning was ignored,” he says.
How is mainland Europe coping?
Meanwhile, researchers are pooling their resources to see what can be done. A pan-European group of Chalara specialists called FRAXBACK is meeting for the first time in November in Uppsala, Sweden.
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