Editing American chestnut (section)

===Hypovirulence===
[[Hypovirus]] is the only [[genus]] in the family [[Hypoviridae]]. Members of this genus infect fungal pathogens and reduce their ability to cause disease (hypovirulence).<ref name=fungus>[http://www.dpvweb.net/notes/showgenus.php?genus=Hypovirus "Notes on Genus: Hypovirus"] {{Webarchive|url=https://web.archive.org/web/20160304093422/http://www.dpvweb.net/notes/showgenus.php?genus=Hypovirus |date=March 4, 2016 }}. ''www.dpvweb.net.'' Retrieved October 14, 2015.</ref> In particular, the virus infects ''Cryphonectria parasitica'', the fungus that causes chestnut blight, which has enabled infected trees to recover from the blight. The use of hypovirulence to control blight originated in [[Europe]] where the fungal virus spread naturally through populations of [[European chestnuts]]. The reduced ability of the fungus to cause disease allowed the European chestnut to regenerate, creating large stands of trees. Hypovirulence has also been found in North America, but has not spread effectively.<ref name=spread>[http://www.tacf.org/FAQ.php "Frequently Asked Questions"] {{Webarchive|url=https://web.archive.org/web/20151020065031/http://www.tacf.org/FAQ.php |date=October 20, 2015 }}. ''www.tacf.org.'' Retrieved November 1, 2015.</ref> The "Arner Tree" of [[Southern Ontario]] is one of the best examples of naturally occurring hypovirulence. It is a mature American chestnut that has recovered from severe infections of chestnut blight. The cankers have healed over and the tree continues to grow vigorously. Scientists have discovered that the chestnut blight remaining on the tree is hypovirulent, although [[Genetic isolate|isolates]] taken from the tree do not have the fungal viruses found in other isolates.<ref name=healed>[http://www.canadianchestnutcouncil.ca/index.cfm?page=hypovirulence "Hypovirulence"]. ''www.canadianchestnutcouncil.ca.'' Retrieved October 14, 2015.</ref> Trees inoculated with isolates taken from the Arner tree have shown moderate canker control.<ref name=control>[http://ecosystems.psu.edu/research/chestnut/meetings/crees-ne-projects/minutes-pdfs/minutes-2001 "NE-140 Technical Committee Meeting Biological Improvement of Chestnut (''Castanea'' spp.) and Management of Pests"]. ''www.ecosystem.psu.edu'', October 20, 2001. Retrieved October 14, 2015.</ref> The cankers of hypovirulent American chestnut trees occur on the outermost tissues of the tree but the cankers do not spread into the growth tissues of the American chestnut tree, thereby providing it with a resistance.<ref>{{Cite journal|last=Griffin|first=Gary |title=Blight Control and Restoration of the American Chestnut |journal=Journal of Forestry |volume=98 |issue=2 |date=February 2000 |pages=22–27 |doi=10.1093/jof/98.2.22 |doi-access=free|url=https://academic.oup.com/jof/article/98/2/22/4614209}}</ref>