A single American elm tree in Findlay, Ohio --
the only survivor of a Dutch elm disease epidemic that killed all the others in its row -- is carrying the hopes of tree scientists to establish a new population of American elms that are resistant to the disease.
"It looks as if this tree happened to be one that had genetic resistance. We've taken cuttings from it, rooted them and we're testing to see whether they're resistant," said Lawrence R. Schreiber of the Agriculture Department's Agricultural Research Service (ARS) station in Delaware, Ohio.
Dutch elm disease first appeared in the United States in the 1930s and has been spreading ever since, killing nearly all of the huge, widely spreading shade trees that once graced the streets of many American cities and towns. The disease is caused by a fungus carried by beetles that bore under the elm's bark.
The newly propagated trees are two to three years old and have not succumbed to direct inoculations of the fungus. But, Schreiber cautions, young trees before have seemed resistant until they became four or five years old. Then they died.
"It looks good so far, but we'll have to wait a few years to be sure," Schreiber said. Even then it would be a few years more before the trees could be propagated in enough numbers to begin supplying commercial nurseries.
In the meantime, tree breeders at the ARS facility at the National Arboretum in Washington have been hybridizing Asiatic and European elms, both of which are resistant but which do not look much like the American elm, to try to create a new variety that has the American elm's shape. Their best bet so far is an elm that grows more slowly than the American and reaches only half its 100-foot height.