• Frequently Asked Questions about The Liberty Elm

• What is the Liberty Elm?

Technical Info about
the Liberty Elm

Technical Data on Development of The American Liberty Elm
(Based on disclosure from Univ. of Wisconsin)

ABSTRACT Screening for a disease-resistant American elm began when Cornell University collected American elms from various northern regions of the U.S. in 1933. These seedlings were grown and screened for resistance to Dutch elm disease. In the mid 1940's surviving trees were moved to Ithaca, NY where screening continued until 1965. All surviving trees were inoculated more than seven times in at least five different years with the live C. ulmi fungus.

In the 60's, Elm Research Institute began funding universities in search of a typical, vase-shaped elm resistant to Dutch elm disease. The product is American Liberty elms; a group of hardy elms from breeding and selection programs possessing an upright vase-shape, disease-resistance and a vigorous growth habit. They constitute a genotypically diverse, multi-clone variety with similar phenotypes for use in urban areas as a replacement for lost elms killed by Dutch elm disease.

Five of the six individuals were derived from control-pollinations made in the late 60's between C. ulmi resistant parents. Parents include superior survivors from the screening program which began in the 1950's, as well as individuals from the New York program. The American Liberty parent elms are survivors of over 60,000 which survived repeated inoculations of live C. ulmi collected from many locations over the northern range of the American elm. The Liberty elms are resistant survivors of control-pollinations which involved more than 43 families and over 3,000 individuals. The sixth individual was the single survivor of about 1,000 inoculated seedlings obtained from Kansas in the 1950's. Demonstration plantings of the parent trees showed a vigorous upright main trunk in youth with older branches tending to become more horizontal at maturity. They developed the typical vase-shape of the traditional American elm. Growth of American Liberty elms is vigorous and typical of cross-pollinated seedlings of American elms. General leaf, size, shape and color, bark color and texture and other growth characteristics generally typical of Ulmus americana.

American Liberty elms exhibit unusual resistance to C. ulmi following screening for D.E.D. resistance using methods previously described. Selected survivors, after inoculation, which exhibited less than 10% crown damage were vegetatively propagated. In all cases C. ulmi inoculum consisted of a mixed conidial suspension from 10 different North American locations.

Clones comprising American Liberty elms possess superior resistance to C. ulmi when contrasted with non-selected susceptible American elms. Their resistance to C. ulmi represents the highest level thus far achieved by selection and breeding with Ulmus americana.

In practical urban plantings we do not anticipate major losses from Dutch elm disease in young American Liberty elms, because of their limited attractiveness to elm bark beetles at this stage of growth.

Vigorously growing ramets which are not infected during the first six years of growth will generally fail to become infected in later years after reaching maturity. Parents of the American Liberty elms have survived for many years in situations of severe disease and bark beetle pressure. Research for the physiological basis for juvenile susceptibility and mature resistance shows a causal relationship in the host's capability to elicit antifungal phytoalexins in response to C. ulmi spores which increases with plant age, both seasonally and with developing maturity caused by inhibitions of mycelia growth of fungal pathogens of elm by the elm phytoalexin mansonone E.

The multi-clone approach to the release of American elms for urban planting may counter problems inherent in wide-scale plantings of identical genotypes with limited genes resistance to D.E.D.

The Liberty elm's history and testing for resistance spans over 40 years. With this kind of track record, we are convinced of the tree's high resistance and ability to survive D.E.D. For this reason, each Liberty elm comes with a 10 year warranty against D.E.D.

There is no substitute for an American elm. We must insist that American Liberty elms be used as replacements for those that have been lost to D.E.D. This tree should not be confused with Asian or European hybrids.

What is the Liberty Elm?

Frequently Asked Questions about The Liberty Elm

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