Editing Dutch elm disease (section)

====North America====
[[File:Results of artificial inoculation of Ophiostoma strains in elm cambium Arlington Experimantal Station Wisconsin 1987.06.14.jpg|thumb|right|Results of artificial inoculation of ''Ophiostoma'' strains in elm cambium, Arlington Experimental Station, [[Wisconsin]], 1987]]
Ten resistant American elm cultivars are now in commerce in North America. No cultivar is immune to DED; even highly resistant cultivars can become infected, particularly if already stressed by drought or other environmental conditions where the disease prevalence is high.  With the exception of 'Princeton', no trees have yet been grown to maturity; trees cannot be said to be mature until they have reached an age of 60 years.

Notable cultivars include:
* 'Princeton', is a cultivar selected in 1922 by [[Princeton Nurseries]] for its landscape merit.  By coincidence, this cultivar was found to be highly resistant in inoculation studies carried out by the [[USDA]] in the early 1990s.  As trees planted in the 1920s still survive, the properties of the mature plant are well known. However, 'Princeton' has not proven resistant in Europe, where the main vector of the disease—the larger elm bark beetle, ''Scolytus scolytus''—is capable of introducing far more fungal spores into the tree; many of the 50 trees planted at [[Highgrove House]] in the south-west of [[England]] in 2006 had died from Dutch elm disease by 2011.<ref name=Brookes/>
* [[Ulmus americana 'American Liberty'|'American Liberty']], is, in fact, a set of six cultivars of moderate to high resistance produced through selection over several generations starting in the 1970s.  Although 'American Liberty' is marketed as a single variety, nurseries selling the "Liberty Elm" actually distribute the six cultivars at random and thus, unfortunately, the resistance of any particular tree cannot be known. One of the cultivars, [[Ulmus americana 'Independence'|'Independence']], is covered by patent (U. S. [[Plant patent]] 6227). The oldest 'American Liberty' elm was planted in about 1980.
* 'Valley Forge', released in 1995, has demonstrated the highest resistance of all the clones to Dutch elm disease in controlled USDA tests.
* [[Ulmus americana 'Lewis & Clark'|'Lewis and Clark']] = {{tdes|Prairie Expedition TM|caps}}, released in 2004 to commemorate the bicentenary of the Lewis & Clark expedition, was cloned from a tree found growing in [[North Dakota]] which had survived unscathed when all around had succumbed to disease.

In 2007, the Elm Recovery Project of the [[University of Guelph Arboretum]] in Ontario, Canada, reported that cuttings from healthy surviving old elms surveyed across Ontario had been grown to produce a bank of resistant trees, isolated for selective breeding of highly resistant cultivars.<ref>{{cite web|archive-url=https://web.archive.org/web/20191122175021/https://www.uoguelph.ca/arboretum/researchandstewardship/elmrecovery|archive-date=22 November 2019|url=http://www.uoguelph.ca/arboretum/collectionsandresearch/elmrecovery|title=Elm Recovery Project|location=[[Guelph]], [[Ontario]], Canada|publisher=[[University of Guelph Arboretum]]|access-date=22 November 2019}}</ref>

The University of Minnesota USA is testing various elms, including a huge now-patented century-old survivor known as [[Ulmus americana 'St. Croix'|"The St. Croix Elm"]], which is located in a Minneapolis-St. Paul, MN suburb (Afton) in the St. Croix River valley—a designated National Scenic Riverway.

The slippery or red elm [[Ulmus rubra|''U. rubra'']] is marginally less susceptible to Dutch elm disease than the other American species, but this quality seems to have been largely ignored in American research. No cultivars were ever selected, although the tree was used in hybridization experiments (see above).

In 1993, Mariam B. Sticklen and James L. Sherald reported the results of NPS-funded experiments conducted at [[Michigan State University]] in [[East Lansing, Michigan|East Lansing]] that were designed to apply [[genetic engineering techniques]] to the development of DED-resistant strains of American elm trees.<ref>{{cite book|first1=Mariam B.|last1=Sticklen|first2=James L.|last2=Sherald|url=https://books.google.com/books?id=avvxBwAAQBAJ&pg=PA171|title=Chapter 13: Strategies for the Production of Disease-Resistant Elms|work=Mariam B.; Sherald, James L. (eds.). Dutch Elm Disease Research: Cellular and Molecular Approaches|pages=171–183|year=1993|location=New York|publisher=Springer-Verlag|oclc=851736058|lccn=93017484|isbn=9781461568728|via=[[Google Books]]|access-date=22 November 2019}}</ref> In 2007, AE Newhouse and F Schrodt of the [[State University of New York College of Environmental Science and Forestry]] in [[Syracuse, New York|Syracuse]] reported that young [[Transgene|transgenic]] American elm trees had shown reduced DED symptoms and normal [[mycorrhiza]]l colonization.<ref>{{cite journal|last1=Newhouse|first1=AE|last2=Schrodt|first2=F|last3=Liang|first3=H|last4=Maynard|first4=CA|last5=Powell|first5= WA|title=Transgenic American elm shows reduced Dutch elm disease symptoms and normal mycorrhizal colonization|journal=Plant Cell Rep.|year=2007|volume=26|number=7|pages=977–987|pmid=17310333|doi=10.1007/s00299-007-0313-z|bibcode=2007PCelR..26..977N |s2cid=21780088}}</ref> By 2013, researchers in both [[New York State]] and [[North Carolina]] were conducting field trials of [[Genetic engineering|genetically engineered]] DED-resistant American elms.