 More recently, field elms "Ulmus minor" highly resistant to DED have been discovered in Spain, and form the basis of a major breeding programme.Owing to their innate resistance to Dutch elm disease, Asiatic species have been crossed with European species, or with other Asiatic elms, to produce trees which 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.