Resistant Trees
Research to select resistant cultivars and varieties began in the Netherlands in 1928, followed by the USA in 1937. Initial efforts in the Netherlands involved crossing varieties of U. minor and U. glabra, but later included the Himalayan or Kashmir elm U. wallichiana as a source of antifungal genes. Early efforts in the USA involved the hybridization of the Siberian elm U. pumila with American red elm U. rubra to produce resistant trees. Resulting cultivars lacked the traditional shape and landscape value of the American elm; few were planted.
In 2005, the National Elm Trial (USA) began a 10-year evaluation of 19 cultivars in plantings across the United States. The trees in the trial are exclusively American developments; no European cultivars have been included.
Recent research in Sweden has established that early-flushing clones are less susceptible to DED owing to an asynchrony between DED susceptibility and infection.
Read more about this topic: Dutch Elm Disease
Famous quotes containing the word trees:
“One wonders that the tithing-men and fathers of the town are not out to see what the trees mean by their high colors and exuberance of spirits, fearing that some mischief is brewing. I do not see what the Puritans did at this season, when the maples blaze out in scarlet. They certainly could not have worshiped in groves then. Perhaps that is what they built meeting-houses and fenced them round with horse-sheds for.”
—Henry David Thoreau (1817–1862)