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Published on: January 22, 2018
Ulmus americana (Ulmaceae) is a polyploid complex
Alan T Whittemore1, Richard T Olsen
1U.S. National Arboretum, 3501 New York Ave NE, Washington, DC 20002-1958, USA. Alan.Whittemore@ars.usda.gov
American Journal of Botany
|May 27, 2011
Summary
American elm (Ulmus americana) populations exhibit genetic diversity, with 21% of wild trees found to be diploid, a previously unconfirmed ploidy level. This finding is crucial for understanding disease resistance in this important tree species.
Area of Science:
- Botany
- Genetics
- Forestry
Background:
- Exotic diseases pose significant threats to North American tree species, necessitating a deeper understanding of host-pathogen biology for effective management.
- American elm (Ulmus americana), a dominant and widely planted tree, has experienced substantial population decline due to Dutch elm disease, a fungal infection.
- While generally considered tetraploid, the existence of triploid American elms in cultivation prompted an investigation into potential lower ploidy levels in wild populations.
Purpose of the Study:
- To survey wild populations of American elm (Ulmus americana) across its native range to determine the nuclear DNA content and identify existing ploidy levels.
- To investigate the distribution and prevalence of different ploidy levels within Ulmus americana populations.
- To assess the genetic heterogeneity of American elm concerning ploidy for future disease resistance research.
Main Methods:
- Nuclear DNA content was quantified in 81 wild individuals of Ulmus americana and four cultivated trees using flow cytometry.
- Geographic locations of sampled wild trees spanned the entire known range of the species.
- Ploidy levels were analyzed and compared to existing species-wide data.
Main Results:
- The majority of Ulmus americana specimens analyzed were tetraploid, consistent with previous reports.
- A significant finding was the confirmation of diploid individuals (21% of wild trees sampled), a ploidy level not previously documented in wild populations.
- Diploid populations were predominantly found along the Atlantic coastal plain, Cumberland Plateau, and in southern Ohio, with scattered occurrences in Texas, Oklahoma, and Missouri. No wild triploids were detected.
Conclusions:
- Ulmus americana exhibits considerable genetic heterogeneity, with the presence of both diploid and tetraploid individuals confirmed in wild populations.
- Further research is required to elucidate the evolutionary origins and interrelationships of the different ploidy levels within the species.
- Understanding the ploidy variation in American elm is vital for identifying and developing genotypes with enhanced resistance to Dutch elm disease.
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