Combating Dutch Elm Disease

New research into a previously hidden population of elms shows the trees carry genes resistant to Dutch elm disease, which continues to affect U.S. trees.

| April 8, 2011

  • Diploid elms - elm trees with only two copies of chromosomes - have been found by themselves and intermixed with the expected tetraploid elms (four copies of chromosomes).
    Diploid elms - elm trees with only two copies of chromosomes - have been found by themselves and intermixed with the expected tetraploid elms (four copies of chromosomes).
    courtesy Agricultural Research Service
  • ARS scientists have found American elm trees that may be the source of genes for resistance to Dutch elm diseases.
    ARS scientists have found American elm trees that may be the source of genes for resistance to Dutch elm diseases.
    courtesy Agricultural Research Service

  • Diploid elms - elm trees with only two copies of chromosomes - have been found by themselves and intermixed with the expected tetraploid elms (four copies of chromosomes).
  • ARS scientists have found American elm trees that may be the source of genes for resistance to Dutch elm diseases.

Two U.S. Department of Agriculture (USDA) scientists may have discovered "the map to El Dorado" for the American elm – a previously hidden population of elms that carry genes for resistance to Dutch elm disease. The disease kills individual branches and eventually the entire tree within one to several years.

It has been accepted for 80 years that American elms (Ulmus americana) are tetraploids, trees with four copies of each chromosome. But there have also been persistent but dismissed rumors of trees that had fewer copies – triploids, which have three copies of chromosomes, or diploids, which have two copies.

Now botanist Alan T. Whittemore and geneticist Richard T. Olsen with USDA's AgriculturalResearch Service (ARS) have proven beyond question that diploid American elms exist as a subset of elms in the wild. Their findings were published in the April edition of the AmericanJournal of Botany. Whittemore and Olsen work at the U.S. National Arboretum operated by ARS in Washington, D.C.

American elms once lined the country's streets and dominated eastern forests until they succumbed by the millions after Dutch elm disease arrived in the United States in 1931. Yet elms are still one of the most important tree crops for the $4.7 billion-a-year nursery industry, especially since the introduction of a very few new trees with some tolerance to the disease. American elms remain popular because of their stately beauty, their rapid leaf litter decay and their ability to stand up to city air pollution.



It was one of the disease-tolerant elm trees – Jefferson, released jointly by ARS and the National Park Service in 2005 – that put Whittemore and Olsen on the trail of the diploid.

"Jefferson is a triploid. To get a triploid elm, we thought there had to be a diploid parent out there somewhere in the wild that had crossed with a tetraploid," Whittemore says.

Lois
4/8/2011 7:41:30 AM

I have a wild American Elm on my property.






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