DED-RESISTANT AMERICAN ELMS AND HYBRIDS

CULTIVARS

In recent years, botanical researchers have made available to the public American elms that are not only resistant to DED, but also have at least some of the tree's familiar growth characteristics. Several different "cultivars" or "cultivated varieties" have been obtained. The studies involved in producing them have generally been done over extended periods of time in scientific laboratories. Furthermore, several years of testing were usually required before the varieties were considered appropriate for public plantings.

In all cases, the perpetuation of the "cultivars" requires the technique of cloning, or vegetative propagation. "Cuttings" are taken from the parent variety and planted in a manner that will be conducive to root growing. The tree then proceeds through its seedling and sapling stages to maturity. All of the clones thus produced will have the same characteristics as the parent plant.

DED-RESISTANT AMERICAN ELM HYBRIDS

One approach, taken at the U.S. National Arboretum by researchers in the Agricultural Research Service (ARS) of the United States Department of Agriculture (U.S.D.A.), especially plant geneticist Dr. Alden Townsend, has been to seek a "hybrid" elm by cross-pollinating certain DED-resistant Asian and European elm species with selected "wild" American elms that were natural "survivors" of the DED onslaught.

A number of hybrid species have been produced, one of which has been named Patriot. Other species have been given the names of Prospector, Frontier, Homestead, Pioneer, Ohio, Pathfinder and Dynasty. The form of these hybrid trees varies, but they are usually smaller than American elms and have a more upright stature. However the ARS has reported that, for the most part, the hybrids are highly DED-resistant.

DED-RESISTANT AMERICAN ELMS

The Princeton Elm

This variety originated when a certain American elm was discovered that apparently had some degree of natural resistance to DED, since it had not succumbed to the disease. The original tree has simply been propagated by cloning at Princeton Nurseries in Princeton, NJ, and the clones have been sold for many years to the general public. Recent testing by the U.S.D.A. has established that the Princeton clones are highly DED-resistant.

The last remaining American elm in the Arnold Arboretum in Jamaica Plain, MA (near Boston) is a 60 year old tree of the "Princeton" variety.

U.S.D.A. Elms

The U.S.D.A. has sponsored additional research at the National Arboretum which has been led by Alden Townsend. This work has involved finding wild elm "survivors" of DED, deriving clones from them, injecting these clones with the DED fungus, and then "screening out" those plants which showed signs of DED infection after a certain number of months had passed. Two of the original trees generated repeated sets of clones that were relatively unaffected by fungus inoculations. These two varieties, now considered appropriate to sell to the general public, are known as "Valley Forge" and "New Harmony"- the latter name derived from an Indiana town. To date, however, the U.S.D.A. elms have been distributed mainly to wholesale nurseries, where mass propagation of them is taking place. Small nurseries will obtain the clones within the next few years, and make them available to the public

The Liberty Elm Program

The Elm Research Institute (ERI) is a non-profit organization headed by J. P. Hansel. It is presently located in Westmoreland, NH.

In the past, the ERI has funded American elm research conducted by Eugene Smalley, Raymond Guries, and Donald T. Lester at the University of Wisconsin. In this work, certain cloning and fungus injection procedures were used, but in 1969-71, trees that appeared DED-resistant were grown to maturity and cross-pollinated, so as to achieve genetic diversity. Seeds from these "matings" were then planted, the resulting seedlings were grown to sapling stages, and additional cloning and fungus injections were done. The final screenings resulted in 5 clones that are considered to be DED-resistant. These 5 clones and another more adequately DED-resistant clone from the parent generation have been mass-cloned by the ERI. They are currently being sold to the public under the name of "American Liberty Elms".

ERI-derived elms are growing in numerous communities and the ERI has involved the Boy Scouts of America in many of these plantings. An ERI goal is to re-elm Route 1, a coastal highway stretching from Maine to Florida.


PERTINENT LINKS

HOME