Editing Chestnut blight (section)

==History==
[[File:Castanea dentata - blight 1.jpg|thumb|right|250px|Chestnut blight affecting a young American chestnut]]

===Infections in North America===

In 1904, the chestnut [[blight]] was accidentally introduced to North America.  ''Cryphonectria parasitica'' was introduced into the United States from [[East Asia]] via import of [[Castanea crenata|Japanese chestnut trees]]. Commercial breeding purposes motivated these imports.<ref name=Columbia/><ref name=Miller/> Infection of American chestnut trees with ''C. parasitica'' simultaneously appeared in numerous places on the East Coast, most likely from Japanese chestnuts, which had become popular imports.<ref name="American-chestnut"/>

Herman W. Merkel, a forester at the [[Bronx Zoo|New York Zoological Garden]] (Bronx Zoo) first found infected chestnut trees on the grounds of the zoo. 
In 1905, American mycologist [[William Murrill]] isolated and described the fungus responsible (which he named ''Diaporthe parasitica''), and [[Koch's postulates|demonstrated by inoculation into healthy plants]] that the fungus caused the disease.<ref>{{cite journal | vauthors = Rogerson CT, Samuels GJ | year = 1996 | title = Mycology at the New York Botanical Garden, 1985-1995 | url = https://zenodo.org/record/1232568| journal = Brittonia | volume = 48 | issue = 3| pages = 389–98 | doi=10.1007/bf02805308| s2cid = 32145426 }}</ref> By 1940, most mature American chestnut trees had been girdled by the disease.<ref name="American-chestnut"/> It took about 40 years to devastate the nearly four-billion-strong American chestnut population in North America.<ref>{{Cite web |url=http://www.acf.org/history.php |title=The American Chestnut Foundation - Mission & History |access-date=2009-03-08 |archive-date=2008-05-16 |archive-url=https://web.archive.org/web/20080516030808/http://acf.org/history.php |url-status=dead }}</ref> Only a few clumps of uninfected trees remained in [[Michigan]], [[Wisconsin]], and the [[Pacific Northwest]].

Japanese and Chinese chestnut trees<ref name="Blight-resistance" /> may resist an infection from ''C. parasitica''.<ref>{{Cite web |url=http://acf.org/history.php |title=History of The American Chestnut Foundation |access-date=2019-06-29 |archive-date=2008-05-16 |archive-url=https://web.archive.org/web/20080516030808/http://acf.org/history.php |url-status=dead }}</ref> Because of the disease, American chestnut wood almost disappeared from the market for decades, although it can still be obtained as [[reclaimed lumber]].<ref name=Edlin/>

It is estimated that in some places, such as the [[Appalachian Mountains]], one in every four [[hardwood]]s was an American chestnut. Mature trees often grew straight and branch-free for 50 feet and could grow up to 100 feet tall with a trunk diameter of 14 feet at a few feet above ground level. The reddish-brown wood was lightweight, soft, easy to split, very resistant to decay, and did not warp or shrink. For three centuries many [[barn]]s and homes near the [[Appalachian Mountains]] were made from American chestnut.<ref name=Salem /> Its straight-grained wood was ideal for building furniture and caskets. The bark and wood were rich in tannic acid, which provided tannins for use in the tanning of leather.<ref>[http://ecosystems.psu.edu/research/chestnut/information/conference-2004/conference/davis Davis Conference 2004], ecosystems.psu.edu</ref>

Chestnuts were an important cash crop and food source.  Many native animals fed on chestnuts, and chestnuts were used for livestock feed, which kept the cost of raising livestock low.<ref>American-Chestnut: Appalachian Apocalypse, Cornett Media, 2010.</ref>

Efforts started in the 1930s and are still ongoing, in [[Massachusetts]]<ref name="Thys"/> and many other places<ref name="dof.virginia.gov" /> in the United States, to repopulate chestnut trees.<ref name="acf">[http://www.tacf.org/ American Chestnut Foundation].</ref>  Surviving American chestnut trees are being bred for resistance to the blight, notably by [[The American Chestnut Foundation]], which aims to reintroduce a blight-resistant American chestnut to its original forest range within the early decades of the 21st century.<ref>{{cite web |url=http://www.fs.fed.us/r8/chestnut/qa.php |title=American Chestnut Restoration Project - USDA Forest Service - Southern Region |access-date=2013-09-11 |archive-url=https://web.archive.org/web/20121223044518/http://www.fs.fed.us/r8/chestnut/qa.php |archive-date=2012-12-23 }}</ref> [[Japanese Chestnut|Japanese chestnut]] and [[Castanea mollissima|Chinese chestnut]], as well as Seguin's chestnut and Henry's chestnut, have been used in these breeding programs in the US to create disease-resistant [[Hybrid (biology)|hybrid]]s with the American chestnut.<ref name="rhs">''New RHS Dictionary of Gardening''. By A. Huxley ed. 1992. Macmillan {{ISBN|0-333-47494-5}}.</ref>  Chinese chestnut trees have been found to have the highest resistance to chestnut blight;<ref name="Blight-resistance" /> however, individuals within the Chinese chestnut species may vary in blight resistance. Some individuals are still quite susceptible while others are essentially immune.<ref>Dr. Greg Miller, Empire Chestnut Company, FAQ http://www.empirechestnut.com/faqpests.htm {{Webarchive|url=https://web.archive.org/web/20160113045455/http://www.empirechestnut.com/faqpests.htm |date=2016-01-13 }} Retrieved January 13, 2016</ref>

Hypovirulence is not widespread in the US and attempts to commercially introduce CHV1 virus have not been widely successful {{citation needed|date=September 2024}}. Though CHV1 persists in applied trees, it does not spread naturally as it does in Europe {{why?|date=September 2024}}, preventing it from being an effective form of [[Biological pest control|biocontrol]].

===Infections in Europe===

In 1938, chestnut blight was first identified around [[Genoa]]. Infection quickly spread and was identified in France in 1946, Switzerland in 1951, and Greece in 1963. It has most recently been found in the UK. Due to genetic differences between the fungal populations (strains), it is likely that a second introduction of chestnut blight occurred in [[Georgia (country)|Georgia]] and [[Azerbaijan]] in 1938.<ref>{{Cite journal|last=Prospero |first=S |title=Discovery of a new gene pool and a high genetic diversity of the chestnut blight fungus ''Cryphonectria parasitica'' in Caucasian Georgia |journal=Infection, Genetics and Evolution|volume=20|date=December 2013 |pages=131–139|doi=10.1016/j.meegid.2013.08.009 |pmid=23994123 }}</ref><ref>{{Cite journal|last=Rigling|first=Daniel|date=December 2018|title=Genetic and Phenotypic Characterization of ''Cryphonectria hypovirus 1'' from Eurasian Georgia|url= |journal=Viruses|volume=10 |number=12|page=687|doi=10.3390/v10120687|pmid=30513977|pmc=6315935|doi-access=free}}</ref> The fungal infections initially caused widespread tree death in Europe. However, in the early 1950s trees were identified in Italy that survived fungal infection. On these trees, the fungus caused more superficial cankers, that appeared to be healing. The milder infection outcome was due to the presence of CHV1, an [[RNA virus]] that infects ''C. parasitica''. CHV1 spread naturally throughout Europe but is also spread artificially as a biocontrol measure (particularly in France). CHV1 is currently not present in the UK, Northern France, or Eastern Georgia but an introduction for biocontrol is being considered. {{Citation needed|date=January 2024}}