Editing Dutch elm disease (section)

==Resistant trees==
[[File:Scripps College Elm Tree Lawn.jpg|thumb|Row of [[Princeton elm]] trees at [[Scripps College]] in [[Claremont, California]], resistant to Dutch elm disease<ref name="Scripps elm news">{{cite news |title=Elm Tree Lawn Begins New Life |url=https://www.scrippscollege.edu/news/features/elm-tree-lawn-begins-new-life |access-date=18 February 2021 |work=Scripps College News |publisher=[[Scripps College]] |date=14 April 2008 |language=en}}</ref>]]
Research to select resistant [[cultivar]]s and varieties began in the Netherlands in 1928, followed by the United States in 1937 (see [[Ulmus americana#Cultivars|''Ulmus americana'' cultivars]]). Initial efforts in the Netherlands involved crossing varieties of ''[[Ulmus minor|U. minor]]'' and ''[[Ulmus glabra|U. glabra]]'', but later included the Himalayan or Kashmir elm [[Ulmus wallichiana|''U. wallichiana'']] as a source of antifungal genes. Early efforts in the USA involved the hybridization of the Siberian elm ''[[Ulmus pumila|U. pumila]]'' with American red elm ''[[Ulmus rubra|U. rubra]]'' to produce resistant trees. Resulting cultivars lacked the traditional shape and landscape value of the American elm; few were planted.

In 2005, the [[National Elm Trial]] (USA) began a 10-year evaluation of 19 cultivars in plantings across the United States. The trees in the trial were exclusively American developments; no European cultivars were included. Based on the trial's final ratings, the preferred cultivars of the American elm (''Ulmus americana'') are 'New Harmony' and 'Princeton'. The preferred cultivars of Asian elms are the [[Morton Arboretum]] introductions and 'New Horizon'.<ref>(1) {{cite web|url=https://agsci.colostate.edu/agbio/national-elm-trial/|title=National Elm Trial|work=Bioagricultural Sciences & Pest Management|location=[[Fort Collins, Colorado]]|year=2018|publisher=[[Colorado State University College of Agricultural Sciences]]: [[Colorado State University College of Agricultural Sciences#Academic Departments|Department of Agricultural Biology]]|access-date=23 September 2021|archive-date=30 March 2018|archive-url=https://web.archive.org/web/20180330152322/http://bspm.agsci.colostate.edu/national-elm-trial/|url-status=dead}}.<br />(2) {{cite journal|first1=Jason J.|last1=Griffin|first2=William R.|last2=Jacobi, E.|first3=Gregory|last3=McPherson|first4=Clifford S.|last4=Sadof|first5=James R.|last5=McKenna|first6=Mark L.|last6=Gleason|first7=Nicole Ward|last7=Gauthier|first8=Daniel A.|last8=Potter|first9=David R.|last9=Smitley|first10=Gerard C.|last10=Adams|first11=Ann Brooks|last11=Gould|first12=Christian R.|last12=Cash|first13=James A.|last13=Walla|first14=Mark C.|last14=Starrett|first15=Gary|last15=Chastagner|first16=Jeff L.|last16=Sibley|first17=Vera A.|last17=Krischik|first18=Adam F.|last18=Newby|display-authors=4|url=https://webdoc.agsci.colostate.edu/bspm/NationalElmTrial/AUF2017.pdf|year=2017|title=Ten-Year Performance of the United States National Elm Trial|journal=Arboriculture & Urban Forestry|volume=43|number=3|pages=107–120|doi=10.17660/ActaHortic.2018.1191.5|oclc=7347020445|issn=0567-7572|publisher=[[International Society of Arboriculture]]|access-date=February 7, 2021|quote=Based on the ratings, the preferred cultivars of American elm were 'New Harmony' and 'Princeton', and the preferred cultivars of Asian elm were The [[Morton Arboretum]] introductions and 'New Horizon'.}}</ref>

Recent research in [[Sweden]] has established that early-flushing clones are less susceptible to DED owing to an asynchrony between DED susceptibility and infection.<ref name=Ghelardini>Ghelardini, L. (2007) ''Bud Burst Phenology, Dormancy Release & Susceptibility to Dutch Elm Disease in Elms (Ulmus spp.)''. Doctoral Thesis No. 2007:134. Faculty of natural Resources and Agricultural Services, Swedish University of Agricultural Sciences, Uppsala, Sweden</ref>

===Testing for disease resistance===
Elms are tested for resistance by inoculation with the fungal pathogen in late May when the tree's growth is at its annual peak. Clones raised for testing are grown to an age of 3 or 4 years. In Europe, the [[wikt:inoculum|inoculum]] is introduced into the cambium by a knife wound. However this method, developed in the Netherlands, was considered too severe in America, where the principal disease vector is the bark beetle ''[[Scolytus multistriatus]]'', a far less effective vector than the larger beetle [[endemicity|endemic]] to Europe, ''[[Scolytus scolytus]]'', which is unknown in America. In the method devised by the [[USDA]], the inoculum is introduced to the cambium via a 2&nbsp;mm-diameter hole drilled through the bark in the lower third of the tree. This method was further refined by the [[University of Wisconsin]] team, which drilled holes in the branches to simulate natural infection by the bark beetles feeding in the twig crotches, but results from this method were found to exaggerate the genetic resistance of the host. Consequently, tests were conducted on specimens in a controlled environment, either in greenhouses or customized plant chambers, facilitating more accurate evaluation of both internal and external symptoms of disease.

Another variable is the composition of the inoculum; while an inoculum strength of 10<sup>6</sup> spores / &nbsp;ml is standard in both continents, its composition reflects the different ''Ophiostoma'' species, subspecies and hybrids endemic to the two continents. In Italy for example, two subspecies, ''americana'' and ''novo-ulmi'', are present together with their hybrid, whereas in North America, ssp. ''novo-ulmi'' is unknown.<ref name=Mittempergher>{{cite journal|last1=Mittempergher|first1=L|last2=Santini|first2=A|journal=Investigacion Agraria: Sistemas y Recursos Forestales|title=The history of elm breeding|volume=13|issue=1|pages=161–177|date=2004|url=http://www.inia.es/gcontrec/Pub/161-177-(14)-The_history_1161943529015.pdf|access-date=9 February 2017|archive-date=11 February 2017|archive-url=https://web.archive.org/web/20170211155148/http://www.inia.es/gcontrec/Pub/161-177-(14)-The_history_1161943529015.pdf|url-status=dead}}</ref> The differences in method and inocula possibly explain why the American cultivar [[Ulmus americana 'Princeton'|'Princeton']], displaying high resistance in the US, has often succumbed to Dutch elm disease in Europe.<ref name=Brookes>{{cite web|last=Brookes |first=A.H. |title=Disease-resistant elm cultivars, Butterfly Conservation trials report, 3rd revision |date=2013 |publisher=Butterfly Conservation |location=Lulworth UK |url=http://www.hantsiow-butterflies.org.uk/conservation/2013%20Elm%20Report%20Sept%202013.pdf |url-status=dead |archive-url=https://web.archive.org/web/20140529181302/http://hantsiow-butterflies.org.uk/conservation/2013%20Elm%20Report%20Sept%202013.pdf |archive-date=2014-05-29 }}</ref>

===Hybrid cultivars===
[[File:Artificial inoculation of virulent strains of Ophiostoma in elm cambium Wageningen - DORSCHKAMP Institute for forestry and landscape planing 1984.06.19.jpg|thumb|right|Inoculation of virulent strains of ''Ophiostoma'' in elm cambium, Dorschkamp Institute for Forestry and Landscape Planning, [[Wageningen]], 1984]]
Many attempts to breed disease-resistant cultivar hybrids have involved a genetic contribution from Asian elm species that are demonstrably resistant to this fungal disease. Much of the early work was undertaken in the Netherlands. The Dutch research programme began in 1928, and ended in 1992. During those 64 years, well over 1000 cultivars were raised and evaluated. Still in use are cultivars such as 'Groeneveld', 'Lobel', 'Dodoens', 'Clusius' and 'Plantijn', although the resistance levels in these trees aren't high enough to confer good protection. The programme had three major successes: [[Ulmus 'Columella'|'Columella']], [[Ulmus 'Nanguen'|'Nanguen' {{tdes|Lutèce|caps}}]], and [[Ulmus 'Wanoux'|'Wanoux' {{tdes|Vada|caps}}]],<ref name="Institut">Institut National de la Recherche Agronomique. Lutèce, a resistant variety, brings elms back to Paris [http://www.international.inra.fr/research/some_examples/lutece_r_a_resistant_variety_brings_elms_back_to_paris], Paris, France</ref> all found to have an extremely high resistance to the disease when inoculated with unnaturally large doses of the fungus. Only 'Columella' was released during the Dutch programme's lifetime—-in 1987. Patents for the {{tdes|Lutèce|caps}} and {{tdes|Vada|caps}} clones were purchased by the French Institut National de la Recherche Agronomique (INRA), which subjected the trees to 20 years of field trials in the [[Bois de Vincennes]], [[Paris]], before releasing them to commerce—-in 2002 and 2006, respectively.

Asian species featured in the American DED research programs were the Siberian elm [[Ulmus pumila|''U. pumila'']], Japanese elm [[Ulmus davidiana var. japonica|''U. davidiana'' var. ''japonica'']], and the Chinese elm [[Ulmus parvifolia|''U. parvifolia'']], which gave rise to several dozen hybrid cultivars resistant not just to DED, but also to the extreme cold of Asian winters. Among the most widely planted of these, both in North America and in Europe, are [[Ulmus 'Sapporo Autumn Gold'|'Sapporo Autumn Gold']], [[Ulmus 'New Horizon'|'New Horizon']] and [[Ulmus 'Rebona'|'Rebona']]. Some hybrid cultivars, such as [[Ulmus 'Regal'|'Regal']] and [[Ulmus 'Pioneer'|'Pioneer']] are the product of both Dutch and American research.  Hybridization experiments using the slippery (or red) elm [[Ulmus rubra|''U. rubra'']] resulted in the release of [[Ulmus 'Coolshade'|'Coolshade']] and [[Ulmus 'Rosehill'|'Rosehill']] in the 1940s and 50s; the species last featured in hybridization as the female parent of [[Ulmus 'Repura'|'Repura']] and [[Ulmus 'Revera'|'Revera']], both patented in 1993, although neither has yet appeared in commerce.

In [[Italy]], research was initiated at the Istituto per la Protezione delle Piante, Florence, to produce a range of disease-resistant trees adapted to the warmer Mediterranean climate, using a variety of Asiatic species crossed with the early Dutch hybrid [[Plantyn (elm hybrid)|'Plantyn']] as a safeguard against any future mutation of the disease.<ref>{{cite journal|last1=Santini |first1=A. |last2=Fagnani |first2=A. |last3=Ferrini |first3=F. |last4=Mittempergher |first4=L. |last5=Brunetti |first5=M. |last6=Crivellaro |first6=A. |last7=Macchioni |first7=N. |title=Elm breeding for DED resistance, the Italian clones and their wood properties |journal=Invest Agrar: Sist Recur for |volume=13 |issue=1 |pages=179–184 |year=2004 |url=http://www.inia.es/gcontrec/pub/179-184-(15)-Elm_breeding_1161943564468.pdf |url-status=dead |archive-url=https://web.archive.org/web/20071026213739/http://www.inia.es/gcontrec/pub/179-184-%2815%29-Elm_breeding_1161943564468.pdf |archive-date=2007-10-26 }}</ref> Two trees with very high levels of resistance, [[Ulmus 'San Zanobi'|'San Zanobi']] and [[Ulmus 'Plinio'|'Plinio']],<ref>{{cite journal |last1=Santini |first1=A. |last2=Fagnani |first2=A. |last3=Ferrini |first3=F. |last4=Mittempergher |first4=L. |title=San Zanobi and Plinio elm trees |journal=HortScience |volume=37 |issue= 7|pages=1139–41 |year=2002 |publisher=American Society for Horticultural Science |doi=10.21273/HORTSCI.37.7.1139 |doi-access=free }}</ref> were released in 2003. [[Ulmus 'Arno'|'Arno']] and [[Ulmus 'Fiorente'|'Fiorente']] were patented in 2006 and entered commerce in 2012. All four have the Siberian elm ''U. pumila'' as a parent, the source of disease-resistance and drought-tolerance genes. [[Ulmus 'Morfeo'|'Morfeo']] was released in 2011; it arose from a crossing of the Dutch hybrid clone '405' (female parent) and the [[Ulmus chenmoui|Chenmou Elm]], the latter a small tree from the provinces of [[Anhui]] and [[Jiangsu]] in eastern China, The '405' clone is a crossing of an English [[Ulmus × hollandica|''U.'' × ''hollandica'']] and a French [[Ulmus minor|''U. minor'']].

In the Netherlands a new program has been initiated. From the old proving grounds of the Dorschkamp Research Institute, 10 fourth-generation hybrids survive in a DED-ridden area. These have been tested and some have a very high level of resistance. At Noordplant Nursery new hybrids have been tested since 2013.

===Species and species cultivars===

====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.

====Europe====
Among European species, there is the unique example of the European white elm [[Ulmus laevis|''U. laevis'']], which has little innate resistance to DED, but is eschewed by the vector bark beetles and only rarely becomes infected. Recent research has indicated it is the presence of certain organic compounds, such as [[triterpenes]] and [[sterols]], which serves to make the tree bark unattractive to the beetle species that spread the disease.<ref>{{cite journal|last1=Martín-Benito |first1=D. |last2=García-Vallejo |first2=M. |last3=Pajares |first3=J. |last4=López |first4=D. |title=Triterpenes in elms in Spain |journal=Can. J. For. Res. |volume=35 |pages=199–205 |year=2005 |issue=1 |url=http://pubs.nrc-cnrc.gc.ca/rp/rppdf/x04-158.pdf |doi=10.1139/x04-158 |bibcode=2005CaJFR..35..199M |url-status=dead |archive-url=https://web.archive.org/web/20070628155809/http://pubs.nrc-cnrc.gc.ca/rp/rppdf/x04-158.pdf |archive-date=2007-06-28 }}</ref>

In Europe the testing of clones of surviving [[field elm]]s for innate resistance has been carried out since the 1990s by national research institutes, with findings centrally assessed and published.<ref>''Screening European Elms for resistance to 'Ophiostoma novo-ulmi' '' (''Forest Science'' 2005)
[https://docs.google.com/viewer?a=v&q=cache:1oVZGFxowNAJ:www.researchgate.net/publication/229069171_Screening_European_Elms_for_resistance_to_Ophiostoma_novo-ulmi/file/d912f504c3964093f0.pdf+RESGEN+European+research+Project+CEMAGREF+ulmus&gl=uk&pid=bl&srcid=ADGEESgtD-wbjfEf61vnrZUHJUkixffKnW_OVe1DctErEzdv7YodqbRJgf3DVGNpOrLjMCCZSXp1-p1hQiPBgC_zRkhaH2KVLAq-kCpz12VUq4DWyze4zotrHdq6RPYdcjlXKRtqaojb]</ref> The first results of this ongoing project suggest that in some countries a very small number of native [[field elm]] genotypes have comparatively high levels of tolerance to DED. In Spain, for example, of around 5,000 native elms evaluated to 2013, some 25 genotypes (0.5% of those tested) fall into this category; and it is now hoped that the controlled crossing of the best seven of these (genetically and aesthetically) will produce ''Ulmus minor'' hybrids with effective 'field resistance' and market appeal.<ref>[http://www.resistantelms.co.uk/spanish-clones/ 'Spanish Clones' (Oct. 2013) resistantelms.co.uk]</ref> Similar results are beginning to emerge in trials on surviving field elms in Greece.<ref>''Δoκιμή ανθεκτικότητας ελληνικών γενoτύπων πεδινής φτελιάς'' (Ulmus minor) ''κατά της Oλλανδικής ασθένειας'', Σ. Διαμαντής και X. Περλέρου (:Resistance test of Greek Field Elm against Dutch Elm Disease, by S. Diamantis and H. Perlerou) [https://docs.google.com/viewer?a=v&q=cache:5ZGvqMoPUZIJ:www.forestry.gr/userfiles/file/pdf/PROSTASIA_DASON/DIAMANTIS.pdf+%CE%A6%CF%84%CE%B5%CE%BB%CE%B9%CE%AC+Ulmus+'Vegeta'&gl=uk&pid=bl&srcid=ADGEESjTpMYBDIz5PzGLEC_Q2UBC2LfzUYXW3XvmIOvhm29DSV8uq83WsOvtXpwsDmklzsYHgR403yvC6z-xiPHmGCQnlvIJsxMSFQVlDrET9b-lJkyJyfSr87QmoqoZ5YOoR72fb25p]</ref>

===== United Kingdom =====
Much of the work in the United Kingdom is by the Forestry Commission's research arm, which has had Dutch elm disease on its agenda since the 1920s.  In 1994 a Research Information Note (no 252) was published, written by John Gibbs, Clive Brasier and Joan Webber, and in 2010 a Pathology Advisory Note, as well as throughout the period a stream of more academic papers: notable results have been the observation that the progress of the disease through Scotland has been quite slow, and that genetic engineering has been tried to improve the resistance of the [[English elm]].

In England the [[Conservation Foundation, UK|Conservation Foundation]] had been propagating, distributing and planting clones of surviving indigenous elms, including field elms (but not the highly susceptible [[English elm]]), as part of a scheme to return elms to city and countryside.<ref>[https://web.archive.org/web/20150109162043/http://www.conservationfoundation.co.uk/content.php?id=178 Fifteen source-trees in England cloned for the Conservation Foundation's 'Great British Elm Experiment'; conservationfoundation.co.uk]</ref><ref>[https://conservationfoundation.co.uk/the-great-british-elm-experiment-update/ Update on new clones in the Conservation Foundation's 'Great British Elm Experiment'; conservationfoundation.co.uk/the-great-british-elm-experiment-update]</ref><ref>{{cite web | title="Super tree" from Northamptonshire helping to fight Dutch Elm Disease and repopulate woodlands | website=northamptonchron.co.uk | url=http://www.northamptonchron.co.uk/news/local/super-tree-from-northamptonshire-helping-to-fight-dutch-elm-disease-and-repopulate-woodlands-1-5685342 | archive-url=https://web.archive.org/web/20160305165821/http://www.northamptonchron.co.uk/news/local/super-tree-from-northamptonshire-helping-to-fight-dutch-elm-disease-and-repopulate-woodlands-1-5685342 | archive-date=2016-03-05}}</ref><ref>{{Cite web |url=http://www.conservationfoundation.co.uk/news_article.php?id=251 |title='Young elms return to London', conservationfoundation.co.uk |access-date=2013-11-16 |archive-url=https://web.archive.org/web/20131202223517/http://www.conservationfoundation.co.uk/news_article.php?id=251 |archive-date=2013-12-02 |url-status=dead }}</ref> The Foundation was running two elm programmes: the 'Great British Elm Experiment' and 'Ulmus londinium', an elm programme for London – these use saplings cultivated through micropropagation from mature parent elms found growing in the British countryside: parent trees are monitored for disease, while saplings were offered free to schools and community groups, who are asked to monitor their trees' progress on the Foundation's online elm map; in London, places with 'elm' in their name were offered a sapling – in an attempt to find out why some elms have survived while others succumbed to Dutch elm disease. Both these projects have been discontinued.

The spread of DED to Scotland has focussed attention on a small number of wych elms [[Ulmus glabra|''U. glabra'']] surviving in areas of high infectivity, prompting the [[Royal Botanic Garden Edinburgh]] to begin a programme of selecting trees, with a view to determining innate resistance (2009).<ref>Coleman, Max, ed.: ''Wych Elm'' (Royal Botanic Gardens Edinburgh, 2009; ISBN 978-1-906129-21-7), p.76</ref> The Garden is raising and distributing in Scotland seedlings derived from controlled crosses of rare survivors in these areas (2023).<ref>Russell Blackstock, ''[[The Sunday Post]]'' (Dundee), 6 August 2023, p.8</ref><ref>[https://stories.rbge.org.uk/archives/37449 'Scottish Plant Recovery: Next gen elms', Botanics Stories (RBGE Personal & Project Stories), stories.rbge]</ref><ref>[https://www.futurewoodlands.org.uk/wp-content/uploads/2022/04/2022-RBGE-Elm-Report.pdf Clarkson, R. & Coleman, M. (2022)] 'Propagating healthy mature elms that have survived in areas severely impacted by Dutch elm disease: a scoping study for a wych elm project in Scotland.' Royal Botanic Garden Edinburgh.</ref>

In 2001–2004, English elm [[Ulmus minor 'Atinia'|''U. minor'' 'Atinia']] was genetically engineered to resist disease, in experiments at [[Abertay University]], [[Dundee]], [[Scotland]], by transferring antifungal genes into the elm genome using minute DNA-coated ball bearings.<ref>[http://www.unisci.com/stories/20013/0828015.htm 'First Genetically Modified Dutch Elm Trees Grown', unisci.com]</ref><ref>[http://www.resistantelms.co.uk/faqs/ resistantelms.co.uk, FAQ 'Disease Control']</ref> However, owing to reservations to GM developments, there are no plans to release the trees into the countryside.

===== Spain =====
In Spain, the Escuela Técnica Superior de Ingenieros de Montes, [[Universidad Politecnica de Madrid]], charged with discovering disease-resistant elms for use in forestry, has raised and patented seven cultivars of the field elm ''Ulmus minor,'' although two have subsequently been found to have Siberian elm ''U. pumila'' DNA, the species introduced to Spain in the 16th century.  Although none have been released to commerce (2020), the clone [[Ulmus minor 'Ademuz'|'Ademuz']], pure ''U. minor'', has been imported into the UK since 2014, and widely planted there.