The history of elms in Europe goes back a long way: the holy elm of Ephesus is famous, and in the Edda elm and ash represent woman and man. But also the wood and even leaves were of high importance throughout the past 3000 years. It is like a paradox: This tree species struggles for its survival. If you look around in your neighbourhood most of the elms have vanished or are in a deplorable state. This is true for most of Europe and North America. Where there had been beautiful majestic elms in parks and along avenues hardly any are left. There seems to be only one strategy – to plant highly disease resistant varieties.
 

deadly partnership between a fungus and a beetle

There is no doubt about the cause for the elm disease: The fungus Ophiostoma ulmi is killing the elm. It is not yet clear how this pathogen found its way to Europe and America. For its distribution, however, the large European elm beetle (Scolytus scolytus) and the small elm bark beetle (Scolytus multistriatus) are almost exclusively responsible. These beetles bring the spores of the fungus to the elm trees. They live under the bark of the tree. In spring they leave their tree to fly to the crown of another elm. There they feed on young shoots where the spores are left. The infection can then take place. The fungus interrupts the liquid transport system and blocks the vessels - the leaves start to wilt. Eventually the branches dry out, and during the following year most of the trees die completely.

 

successful teamwork between scientist and nurseryman

Briefly after detecting and identifying the fungus in 1920 scientists searched for methods to fight against this disease and to look for elms with natural resistance. Many paths did not lead to satisfactory results. No chemical was found to be effective. Screening of existing elm species did not bring results. And even breeding new varieties encountered many problems: The new trees had disappointing growth, shape or form. Or the disease resistance was not good enough to resist any of the different strains of the fungus. 1958 Prof. Eugene B. Smalley of the Madison University in Wisconsin/USA took over the task to develop disease resistant elms. He travelled many countries in Asia, Europe and America to collect all elms he could find: Ulmus parvifolia, U. pumila, U. wallichiana, U. japonica, U. laciniata, U. villosa, U. wilsoniana, U. carpinifolia, U. glabra, U. laevis, U.. americana, U. rubra, U. thomasii. U. alata, U. serotina, and U. crassifolia

Seedlings and crosses of these elms were grown and artificially infected to test their resistance against many different strains of the deadly fungus. Finally several hundred highly resistant varieties were found. These then had to be screened for adaptability to different environments, growth habits, health and aesthetics.

Thoroughly tested breeder’s quality

Professor Smalley entrusted WARF (Wisconsin Alumni Research Foundation) of Madison, Wisconsin/USA to distribute his new varieties to the public. This foundation chose Eisele GmbH & Co KG of Darmstadt, Germany to test, produce and distribute these elms in Europe. In 1981 an extensive testing program was launched in collaboration with the official Federal Institute for Pest Control. At the same time more than a hundred new varieties were screened for growth, adaptability to the environment and architecture. The few varieties finally selected had to go through an official testing program for registration under the breeder’s rights law, first in Germany, then on E. U. level. At the end of this long process marketing began under the umbrella of the registered trademark RESISTA®.









Resistance solid and profound

World wide genetic resources have given Resist® elms their vitality and high disease resistance, not only against the elm disease (Ophiostoma ulmi and novo-ulmi) but also against other diseases such as Verticillium, Stegophoa and others. They prove themselves by fast growth, tolerance to drought, water logging, salt, wind, stress of many kinds, a great variation of soils. All this is partly due to the fact that all Resista® elms grow on their own roots. A side effect of this method of production is that incompatibility between the two species of grafted trees cannot occur.



Reliability in practice for more than 20 years

For more than 20 years many thousands of Resista® elms planted all over Europe to testify their qualities, especially their DED resistance. Year after year under the supervision of the German Federal Institute for Pest Control, tests with the most virulent strains of the disease are made. The results confirm: The varieties ‘New Horizon’ and ‘Rebona’ have an outstanding resistance against Dutch Elm Disease (DED – Ophiostoma ulmi and novo-ulmi) Since 2003 the identity of every young tree of a Resista® variety is secured by an implanted chip. By reading this chip the tree can be identified and its origins found. Only selected partner nurseries provide Resista® elms to the market. When delivered every tree shows a special label and the shipment is covered by a special Certificate of Authenticity.

The elm is back

By way of controlled breeding and testing for almost half a century this species could be saved. Even the insect world is happy – many species only live on elms. They also have back their feeding grounds.