quality:correction
Hybrid cultivars

Owing to their innate resistance to DED, Asiatic species have been crossed with European species, or with other Asiatic elms, to produce trees that are both highly resistant to disease and tolerant of native climates. After a number of false dawns in the 1970s, this approach has produced a range of reliable hybrid cultivars now commercially available in North America and Europe. Disease resistance is invariably carried by the female parent.

Some of these cultivars, notably those with the Siberian elm (Ulmus pumila) in their ancestry, lack the forms for which the iconic American elm and English elm were prized. Moreover, several exported to northwestern Europe have proven unsuited to the maritime climate conditions there, notably because of their intolerance of anoxic conditions resulting from ponding on poorly drained soils in winter. Dutch hybridizations invariably included the Himalayan elm (Ulmus wallichiana) as a source of antifungal genes and have proven more tolerant of wet ground; they should also ultimately reach a greater size. However, the susceptibility of the cultivar 'Lobel', used as a control in Italian trials, to elm yellows has now (2014) raised a question mark over all the Dutch clones.

Several highly resistant Ulmus cultivars have been released since 2000 by the Institute of Plant Protection in Florence, most commonly featuring crosses of the Dutch cultivar 'Plantijn' with the Siberian elm to produce resistant trees better adapted to the Mediterranean climate.