Conservation and utilisation

Elm species and Dutch elm disease The number and names of elm species is a bone of contention among taxonomists. If the specific rank is granted to major taxonomic variants only, there are about 30 elm species in the world, out of which ca 20 in Asia and 6 in north America. The number of European elm species is only 3 if the English elm (U. procera Salisb.) and other minor taxonomic variants are considered as varieties within the vast Field elms group (Ulmus minor Mill. sensu latissimo). The two Dutch elm disease (DED) pandemics that spread across Europe in the 1920s and 1970s have caused dramatic mortality in elm populations, and the disease still represents a great threat for each individual elm tree. It is estimated that more than 90 % of mature U. minor were lost to the disease. DED is also causing heavy losses to Wych elm populations (U. glabra Huds.), which are found in the mountains and in the northern part of Europe. The third elm species native to Europe, the European white elm (U. laevis Pall.), is less attractive to the elm bark beetles (Scolytus sp.) which spread the spores of the fungus causing the disease (Ophiostoma novo-ulmi Brasier). It is therefore less damaged by DED, but still endangered because of the disappearance of the riparian ecosystem where it thrives. Achievements of elm Breeding Elm breeding for resistance to DED has permitted to release several resistant hybrid cultivars to the European market (Mittempergher & Santini 2004). These hybrids involve crosses with at least one resistant Asiatic species (generally U. pumila L., U. japonica Sarg. or U. wallichiana Planch.)