story to find out more.
The original 'Jefferson' American elm on the
National Mall in Washington, D.C.
Jefferson Trees Resistant to Dutch Elm Disease
June 13, 2006
A large-scale program to screen
American elm trees for resistance to Dutch elm disease may lead to trees that
can ward off this deadly disease, according to Agricultural Research Service
(ARS) scientists and cooperators.
The fungus that causes Dutch elm disease (DED)--Ophiostoma
ulmihas wiped out around 77 million American elms, decimating these
graceful trees along streets and in parks and gardens, since its introduction
to the United States in 1931.
To combat this exotic and deadly disease that originated in France,
researchers screened thousands of American elm trees for resistance. Thanks to
the efforts of ARS scientists with the
National Arboretum in Washington, D.C., and collaborators, enough old
specimens were located and kept alive to provide the germplasm necessary to
develop DED-tolerant trees.
The arboretum's tree-breeding project was led by ARS geneticist Denny
Townsend until his 2005 retirement. Townsend worked with horticulturalist
Bentz at the ARS Floral and Nursery Plants Research Unit (FNPRU)
in Glenn Dale, Md.
In 2005, the newest American elmnamed Jeffersonwas released
jointly by ARS and the National Park Service (NPS), after collaborative screening tests by
Townsend and James L. Sherald, NPS Natural Resource Officer, showed it to have
an outstanding level of DED tolerance. It was cloned in 1993 from the original
tree, a survivor of about 300 elms planted on the National Mall in Southwest
Washington in the 1930s.
Jefferson grows in the typical vase shape up to nearly 70 feet tall, has
broad U-shaped branch unions, and has leaves that turn dark-green earlier in
the springand stay dark later in the fallthan most other elms.
FNPRU research leader
Hammond regards Jefferson as a good "street tree" because it can
withstand pollution from city traffic and has wide adaptability, growing in
USDA hardiness zones 5 through 7.
While this durable, DED-tolerant elm may once again fill parks and grace
famous landmarks with true American elms, Jefferson wont be available to
consumers for about four years. But specimens can be seen on the National Mall,
next to the old Smithsonian building, and will soon be at the arboretum.
Efforts also are under way to propagate quantities for nursery cooperators.
more about the research in the June 2006 issue of Agricultural
ARS is the U.S. Department of
Agriculture's chief scientific research agency.