Editing Dutch elm disease (section)

===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.