Editing Chestnut blight (section)

===Hybrid chestnut trees===
Current efforts are underway by the Forest Health Initiative to use modern breeding techniques and genetic engineering to create resistant tree strains, with contributions from [[SUNY College of Environmental Science and Forestry]], [[Pennsylvania State University]], the [[University of Georgia]], and the [[United States Forest Service]]. One of the most successful methods of breeding is to create a [[Backcrossing|back cross]] of a resistant species (such as one from China or Japan) and American chestnut. Researchers identified two or three genes that allow for blight resistance, and are focusing on giving the American chestnut hybrids only those genes from the Chinese or Japanese chestnut.<ref>{{Cite web|url=http://www.acf.org/pdfs/about/restoration.pdf|archive-url=https://web.archive.org/web/20071108102851/http://www.acf.org/pdfs/about/restoration.pdf|archive-date=2007-11-08|title=Restoring the American Chestnut|website=The American Chestnut Foundation}}</ref>

The two species are first bred to create a 50/50 hybrid. After three backcrosses with American chestnut, the remaining genome is approximately 1/16 that of the resistant tree and 15/16 American. The strategy is to [[Selection (biology)|select]] blight-resistance genes during the backcrossing while preserving the more wild-type traits of American chestnut as the dominant [[phenotype]]. Thus, the newly bred hybrid chestnut trees should reach the same heights as the original American chestnut. Many of these 15/16 American chestnut hybrids have been planted along the East Coast, including in the Jefferson National Forest and on the [[Flight 93 National Memorial]]. Some of these sites have had researchers check on the saplings that have been planted to see their survival rate. For the hybrids to do well, they need areas with decent drainage and abundant sunlight.<ref>{{Cite web |title=The American Chestnut Foundation - Mission & History |url=https://tacf.org/about-us/ |archive-url=https://web.archive.org/web/20080516030808/http://acf.org/history.php |archive-date=2008-05-16 |access-date=2016-11-13 |website=www.tacf.org}}</ref> Meeting these needs can be hard to do, so not all restoration areas have been successful with hybrid survival.