Editing Chestnut blight (section)

===Transgenic blight-resistant chestnut trees===
A 1983 study on [[hypovirulence]] had shown that chestnut blight infected with hypovirus produced less oxalic acid when attacking the [[cambium]].<ref name="Havir-Anagnostakis-1983" /><ref name="Chen-et-al-2010" /> Meanwhile, a [[plant pathologist]], Dr. William Powell, had been trying to figure out how to transfer all of the Asian chestnut's resistance genetics to its American relatives. In the 1990s, he had the idea to give up on the more complicated and larger job, and instead look around for a single gene elsewhere.<ref name="Sierra-Club-transgenic" /> (In related work, in 2001 Liang, Mayard, Allen, and Powell successfully inserted an [[oxalate oxidase]] (OxO) gene from [[wheat]] into ''[[Populus × canadensis|Populus × euramericana]]'' ("Ogy") for ''[[Septoria musiva]]'' resistance.<ref name="Liang-et-al-2001" /> This enzyme breaks down the [[oxalic acid]] secreted by the fungus into carbon dioxide and hydrogen peroxide.) In 2007, Welch, Stipanovic, Maynard, and Powell showed that transgenic ''C. dentata'' expressing a wheat OxO indeed had lower [[lignin]] degradation by oxalic acid, and suggested this was the path to take.<ref name="Welch-et-al-2007" /><ref name="Chen-et-al-2010" />

A few years later this line of research culminated in the final product: Powell<ref name="Templeton-Powell" /><ref name="Plantopia" /><ref name="Plantopia-Powell" /> and another plant pathologist, Dr. Charles Maynard, working at the [[State University of New York College of Environmental Science and Forestry]] developed [[American chestnut]]s which had heightened [[blight resistance]]. Heightened resistance was attained by introducing a wheat OxO gene into the American chestnut genome. (Because an unrelated gene was transferred, this did not make the chestnut trees produce [[gluten]], and the nuts remain [[gluten-free diet|gluten free]].)<ref name="Cornell-Powell-gluten" /> The [[transgenic]] trees have blight resistance either equal to or surpassing that of ''[[Castanea mollissima]]'', Chinese chestnuts.<ref name="Zhang-et-al-2013" /> 
In 2013, SUNY ESF had over 100 individual events being tested, with more than 400 slated to be in the field or in the lab for various assay tests in the next several years.  By 2014, more than 1,000 trees were growing in several field sites.<ref>{{cite web|url=http://www.geneticliteracyproject.org/2015/06/04/government-approval-next-step-in-approving-gm-revival-of-american-chestnut/|title=Government approval next step in GM revival of American chestnut - Genetic Literacy Project|date=2015-06-04|website=www.geneticliteracyproject.org|access-date=9 November 2018}}</ref> Government approval will be required before returning any of these blight resistant trees to the wild.<ref>{{cite web|url=http://theplate.nationalgeographic.com/2015/06/02/can-we-engineer-an-american-chestnut-revival/|archive-url=https://web.archive.org/web/20160722024438/http://theplate.nationalgeographic.com/2015/06/02/can-we-engineer-an-american-chestnut-revival/|url-status=dead|archive-date=July 22, 2016|title=Can We Engineer an American Chestnut Revival?|date=2 June 2015|website=nationalgeographic.com|access-date=9 November 2018}}</ref> The [[New York Botanical Garden]] has planted several of the transgenic trees for public display.<ref>{{cite web|url=http://phenomena.nationalgeographic.com/2013/03/11/resurrecting-a-forest/|archive-url=https://web.archive.org/web/20130314024548/http://phenomena.nationalgeographic.com/2013/03/11/resurrecting-a-forest/|url-status=dead|archive-date=March 14, 2013|title=Resurrecting A Forest|date=11 March 2013|website=nationalgeographic.com|access-date=9 November 2018}}</ref> 
At the start, there were few such engineered chestnut trees. For seed multiplication, [[grafting]] could work.<ref name="Plantopia" /> Normal tree growth requires 6, 7, or even 8 years before a chestnut will flower.<ref name="Plantopia" /> However [[orchard]] management may accelerate pollen production to 2–3 years (although still without fruiting).<ref name="Plantopia" /> Powell's lab had been able to use [[Environmental chamber|growth chamber]]s with higher light inputs to get duration to pollen production down to less than a year.<ref name="Plantopia" />

[[The American Chestnut Foundation]] (TACF) once worked close with SUNY ESF to utilize the [[Darling 58]] in their mission to restore the American chestnut to its native range in the eastern United States.<ref>{{Cite web |title=Darling 58 |url=https://tacf.org/darling-58/ |access-date=2023-08-25 |website=The American Chestnut Foundation |language=en-US}}</ref> However, in December 2023, TACF withdrew its petition for use as a restorative species due to poor performance and high mortality in Darling 54 saplings. <ref>{{Cite web |title=Press Release: TACF Discontinues Development of Darling 58 |url=https://tacf.org/tacf-discontinues-development-of-darling-58/ |access-date=2023-12-08 |website=The American Chestnut Foundation |date=8 December 2023 |language=en-US}}</ref>