Ulmus americana 'Jefferson'

The American Elm cultivar Ulmus americana 'Jefferson' was cloned from a tree that grows along the National Mall in Washington D. C. . Planted in the 1930s, it remains (2013) unscathed by Dutch elm disease, and was cloned (NPS 3487) by the U. S. National Park Service, which released it as 'Jefferson' in 2004. Early studies on this clone indicated triploid chromosome levels, suggesting it may be a hybrid between the tetraploid American Elm and a diploid species. A genetic study performed by the United States National Arboretum in 2004 confirmed the tree as Ulmus americana, despite its atypical features.[1] A later study by the USDA's Agricultural Research Service confirmed the tree as a triploid, but derived from a crossing of two American Elms, one a tetraploid, the other a rarer diploid.[2]

Ulmus americana 'Jefferson'
'Jefferson' elm in The Mall, Washington D. C.
SpeciesUlmus americana
Cultivar'Jefferson'
OriginNational Park Service, US

Description

'Jefferson' is distinguished by its low, spreading form with arching limbs and broad U-shaped crotches; the tree in the National Mall has attained a height of about 21 m (68 ft) after 80 years.[3] Ploidy: 2n = 42.

Pests and diseases

The tree proved highly resistant to Dutch elm disease in USDA trials (as clone N 3487/NA 62001),[4] and very resistant to the Elm Leaf Beetle Xanthogaleruca luteola.[5] No specific information is available, but the species as a whole is highly susceptible to Elm Yellows; it is also preferred for feeding by the Japanese Beetle Popillia japonica. [6] [7] U. americana is also the most susceptible of all the elms to verticillium wilt.[8] [9]

Cultivation
President G. W. Bush planting 'Jefferson' outside the White House, 2006.

'Jefferson' has not been widely tested beyond Washington D.C., although it is now being evaluated in the National Elm Trial coordinated by Colorado State University. The tree was introduced to the UK in 2010 by the Golden Hill Nursery in Kent, but remains rare in cultivation.

Accessions

North America

References
  1. Pooler, M. R. & Townsend, A. M. (2005). DNA Fingerprinting of Clones and Hybrids of American Elm and Other Elm Species with AFLP Markers. Journal of Environmental Horticulture, 23 (3): 113-117. September 2005.
  2. Kaplan, K. (2011). Hidden elm population may hold genes to combat Dutch elm disease. ARS News, 30 March 2011. USDA.
  3. Photographs of mature and young 'Jefferson' elms on the National Mall, Washington DC: 'Elms of the Monumental Core', James L. Sherald, National Park Service (2009), p.38
  4. Townsend, A. M., Bentz, S. E., and Douglass L. W. (2005). Evaluation of 19 American Elm Clones for Tolerance to Dutch Elm Disease Archived 2005-05-11 at the Wayback Machine. Journal of Environmental Horticulture, March 2005, Horticultural Research Institute, Washington, D.C.
  5. "Elm Leaf Beetle Survey". Archived from the original on 2011-07-19. Retrieved 17 July 2017.
  6. Miller, Fredric; Ware, George; Jackson, Jennifer (2001-04-01). "Preference of Temperate Chinese Elms ( Ulmus spp.) for the Adult Japanese Beetle (Coleoptera: Scarabaeidae)". Journal of Economic Entomology. Oxford University Press (OUP). 94 (2): 445–448. doi:10.1603/0022-0493-94.2.445. ISSN 0022-0493. PMID 11332837.
  7. "Elm Leaf Beetle Survey". Archived from the original on 2011-07-19. Retrieved 17 July 2017.
  8. Pegg, G. F. & Brady, B. L. (2002). Verticillium Wilts. CABI Publishing. ISBN 0-85199-529-2
  9. "Elm Leaf Beetle Survey". Archived from the original on 2011-07-19. Retrieved 17 July 2017.
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