Agricultural Research/July 19964

New American ElmsRestore Stately Trees

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lden M. Townsend has beenon a quest for the last 20years—a quest to find and

develop disease-tolerant Americanelms and return these prized trees toU.S. towns, yards, and landscapes.

“American elms have been the na-tion’s main urban landscape tree,”says Townsend. “Just about everycity and town has an Elm Street.American elms were planted every-where until the early 1940’s, whenDutch elm disease spread rapidly.”

Townsend is an AgriculturalResearch Service plant geneticist atthe U.S. National Arboretum’s GlennDale, Maryland, laboratory. He saysthat USDA scientists began screeningelm trees for Dutch elm disease(DED) tolerance in 1937.

Shipments of elm tree logs fromFrance to Cleveland, Ohio, acciden-tally introduced the fungus into theUnited States in 1931. Within 4 to 5years, scientists could trace the logs’trip inland by looking at elm treesalong the railroad route. The deathtrail ran all the way to furnituremanufacturers in Cleveland andColumbus, where the imported elmswere used for making veneer.

By 1980, Ophiostoma ulmi—thefungus that causes Dutch elm dis-ease—had virtually wiped out 77million American elms. The loss ofthose prized shade trees denudedhundreds of tree-lined streets intowns and cities across the country.

Leaves on a DED-infected treefirst turn yellow, then brown, as wilt-ing symptoms gradually move upbranches to the main trunk. The nextyear, dieback is very noticeable. Andin just a short time—often by the sec-ond year—the disease becomes fatal.

Townsend says, “The loss of theseAmerican elms has not been justeconomic. Their loss was alsopsychological, with a negative effecton people’s psyches.”

American elms have been prizedfor their graceful stature and otheraesthetic attributes. But their superioradaptability, inherent vigor, hardi-ness, and tolerance to stresses—especially in urban settings—areunsurpassed in comparison with mosttree species. “Trees planted on citystreets take a lot of abuse,” saysTownsend. “Landscape trees likemaple, ash, and oak aren’t nearly asadaptable as the American elm inwithstanding such adverse environ-mental conditions.”

Finding Pockets of Resistance

Dutch elm disease was first foundin the Netherlands. “But, ironically,”says Townsend, “the American elm,Ulmus americana, is the elmspecies most susceptible tothe European disease. Itsfast spread was probablydue to the trees’ overusehere, since they were easy toplant and grow.”

About 20 years ago,Townsend and plant patholo-gist Lawrence R. Schreiber(now retired), along withARS technician Warren O.Masters, started screeningthousands of American elms,searching for DED-tolerantspecimens to propagate at thearboretum’s research site atDelaware, Ohio. Masters is nowin the ARS Root Disease andBiological Control Re-search Unit at Pullman,Washington.

“We would getnumerous cuttingsfrom people whobelieved they had

an ancient survivor growing in theiryard,” says Schreiber. “But we soondiscovered that most of those treeswere just lucky. They had simply notbeen attacked by the elm bark beetlethat spreads the disease.”

Adds Townsend, “It is not uncom-mon to find a single elm surviving bychance where others have died.”

He estimates that only 1 in100,000 American elm trees is DED-tolerant. “Most of the thousands wetested turned out simply to haveescaped exposure.”

The procedure the scientists usedto find and screen trees for built-inDED tolerance is exacting.

When a survivor tree is selectedfor study, fresh shoots are cut from as

At the U.S. National Arboretum’s GlennDale, Maryland, field site, plant geneticistAlden Townsend (left) and gardenerThomas Abell observe growth of youngAmerican elm selections. (K7314-2)

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Agricultural Research/July 19966

near the top as possible. Back in thegreenhouse, the shoots are rootedusing a growth hormone. Those thattake root and grow are deliberatelyinoculated with the DED fungus tosee which naturally resist the disease.

Recently, Townsend introducedtwo new American elms—ValleyForge and New Harmony. Theyrepresent a culmination of work heand Schreiber, along with severalother colleagues, have done overmore than 20 years. “These will bethe first commercially available newDED-tolerant American elm trees,”Townsend says.

Last year, several hundred rootedcuttings of Valley Forge and a fewNew Harmony were officiallyreleased—or introduced—to nurser-ies, experiment stations, and arbore-tums. Wholesale nurseries willpropagate the trees for sale by late1997 or 1998; retail nurseries shouldhave them in 1999.

Townsend says the new cultivarsare easy to propagate by softwoodcuttings using conventional propaga-tion techniques. Rooting generallyoccurs in less than 4 weeks.

They are products of the arbore-tum’s tree genetics program. Thisresearch is directed toward develop-ing improved tree cultivars withsuperior characteristics for nurseryproduction and for urban, suburban,and rural use, says ARS botanistThomas S. Elias, director of thearboretum. ARS moved the elmprogram there from Ohio in 1984 butretained established planting materialat the Ohio location.

Elias says, “The disease toleranceand superior horticultural characteris-tics of these two new cultivars makethem ideal candidates to replace themillions of trees that have died as aresult of Dutch elm disease.” OnJune 6, 1996, one of them wasplanted on the grounds of the U.S.Capitol in Washington, D.C.

Making a Commercial Comeback

Interest in restoring Americanelms is evident in several grass-rootsmovements.

Since 1993, Cincinnati business-man Bill Monroe has made elmresearch part of his business interest.Monroe’s passion for restoringAmerican elms has him networkingnationally with fellow enthusiasts—federal, state, city, and local. He has

spoken extensively with over 20scientists, including Townsend, all ofwhom are specialists in variousaspects of elm research.

Monroe says that when it comes todeveloping new American elms withDED tolerance, the U.S. NationalArboretum and USDA’s ForestService Forestry Sciences Laboratoryat Delaware, Ohio, are the keyresearch locations in this country.

For the last 3 years, Townsend andMasters have been collaborating withForest Service biologists JosephKamalay and Steve Eshita at the Ohiolab. All four have worked together tomake controlled genetic crosses withthe two new American elms andseveral other American elm selec-tions. About 500 seedlings from thesecrosses have been planted for futureevaluation.

Kamalay has been using DNAfingerprinting to search for DED-tolerance markers in the new elms.He says, “We are looking for a better,faster way to screen for tolerance.”

According to Townsend, “Monroehas done a lot of good for elm treerestoration by getting the word outabout the two new cultivars. Hehelped start the Cincinnati DED-tolerant American elm program. It’sthe first and only DED-tolerantAmerican elm nursery and marketingprogram under professional manage-ment in a major metropolitan area.”

The Cincinnati program involves acommercial tree nursery, the city’surban forestry department, andseveral hundred garden club memberswho plan to plant the new Americanelms in and around the city. Monroesays that pivotal in their program isthe work of Richard Ammon ofAmmon Nurseries in Burlington,Kentucky, who is raising and propa-gating the new elms for the program.

To check elms for tolerance, geneticistAlden Townsend inoculates a tree througha small predrilled hole with Ophiostomaulmi, the fungus that causes Dutch elmdisease. (K7311-1)

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American elm, Ulmus americana L.Photo by Scott Bauer (K7319-17)

Congress Honors ArboretumThe many research accomplish-

ments of the U.S. NationalArboretum were acknowledged ata tree-planting ceremony held inWashington, D.C., on June 6,l996. Installed on the grounds ofthe U.S. National Capitol at thattime was a disease-tolerant ValleyForge American elm developedby arboretum plant geneticistAlden M. Townsend.

Congressional recognition ofthe arboretum’s nearly 70-yearcontribution to horticulturalscience was initiated by MissouriSenator Christopher S. Bond. Hejoined arboretum director ThomasS. Elias and members of theFriends of the National Arbore-tum at the planting ceremony.

Agricultural Research/July 1996 7

Besides Valley Forge and New Harmony,geneticist Alden M. Townsend has introduced—or officially released to nurseries for propaga-tion—seven other new elm trees. They wereselected and bred from Asian and Europeanspecies that normally resist the Dutch elm disease(DED) fungus. An eighth has been introduced byARS geneticist Frank S. Santamour, Jr., who isTownsend’s colleague at the U.S. NationalArboretum.

All eight elms were released over the past 12years as part of the arboretum’s plant introduc-tion program. Developed to provide superiortrees for city conditions, they require less mainte-nance, have higher survival rates, and need lesspesticide than most other trees.

• Prospector originated from selected seed-lings of the Wilson elm from China. It has a V-shaped crown like the American elm but isshorter and resistant to Dutch elm disease and theelm leaf beetle.

• Frontier was developed by crossing thelacebark elm, Ulmus parvifolia, with a Europeanspecies. It has a pyramidal crown, with moderateresistance to the beetle and good DED resistance.

• Homestead is a cross between a Siberian elmand a complex hybrid of two Dutch elms. A rapidgrower, it has a pyramidal crown, high level ofDED resistance, and excellent tolerance toenvironmental stresses.

• Pioneer is a globe-shaped hybrid crossbetween two European species. It is quite DED-resistant but, like Homestead, has some suscepti-bility to the elm leaf beetle. Its crown is denseand provides deep shade.

• Patriot is a cross between Prospector andUrban elms. Its moderately V-shaped crownresembles that of a more upright American elm. Itis highly resistant to disease and resists insectinfestations.

• Ohio is a lacebark elm selection that ismoderately V-shaped, with excellent resistance tothe elm leaf beetle and Dutch elm disease.

• Pathfinder is a lacebark elm with a singletrunk and has both high insect and diseaseresistance.

• Dynasty is a lacebark elm of Korean parent-age that was released by Santamour because of itssmaller stature and potential use under powerlines along city streets.—By Hank Becker, ARS.

Arboretum Releases Elm Hybrids

Agricultural Research/July 19968

Interest in the new American elmsis shared by Roy Klehm of KlehmNursery in South Barrington, Illinois,whose nursery is 1 of 17 propagatingValley Forge, New Harmony, andother elm hybrids previously releasedby the arboretum.

Klehm says, “Chicagoans are inlove with them, and the city forestersare asking for large numbers for parkand street planting.”

While at the Ohio lab, Townsendworked with Masters and Schreiberin carrying out intensive diseaseinoculations of scores of Americanelms. Later, at the arboretum’s Floraland Nursery Plant Research Unit’sGlenn Dale lab, Townsend continuedthat work with ARS horticulturistSusan E. Bentz and arboretumgardener Tom Abell.

Since 1986, they have screened 10of the most DED-tolerant Americanelms for superior tolerance. ValleyForge and New Harmony resultedfrom this last, intensive effort.

“Compared with other Americanelm selections and seedlings, thesetrees showed significantly lowerfoliar symptoms and crown diebackafter being intensively inoculatedwith the fungus,” Townsend says.

Although neither Valley Forge norNew Harmony is completely immuneto the Dutch elm disease, both haveunusually high levels of tolerance.

Of the thousands of Americanelms that have been screened, ValleyForge is the most tolerant, and NewHarmony is a close runner-up. Anunnamed third—at least as tolerant asNew Harmony—may become thethird introduction to be released bythe arboretum, after further testing.

Townsend has also workedcooperatively with Richard Hall ofOhio State University screening elmsfor elm leaf beetle tolerance. Morerecently, he has supplied leaves ofValley Forge trees to ARS plantpathologist Ing-Ming Lee at the

Molecular Plant Pathology Laborato-ry in Beltsville, Maryland.

Lee screened the leaves for thepresence of elm yellows, a diseasecaused by a phytoplasma—a tinybacterium-like organism. Lee hasdeveloped a new tool to detect theminute organism. The test usespolymerase chain reaction, or PCR, toidentify the presence of the phyto-plasma organism, to determine if thetree is infected.

Since an outbreak of elm yellowsdisease occurred in the Delaware,Ohio, site while the new Americanelms were being tested, Townsendbelieves there is a possibility the newelms may also have some tolerance toelm yellows. None of the ValleyForge and New Harmony treesshowed the disease, while about 15percent of other American elmsacquired it. However, further testingwill be needed to confirm this appar-ent tolerance.

Both of the new cultivars have theclassic elm shape that made theirpredecessors so desirable as shadetrees. Valley Forge has an upright,arching, broadly V-shaped branchingstructure with a full, dense canopy ofleaves. After 12 growing seasons inOhio, cuttings from the parent treeare 26 feet tall, with an averagecrown spread of 30 feet. Leaves 4.6

inches long and 2.9 inches widegradually turn yellow in autumn. Thebark divides into grayish, rough-textured ridges separated by dia-mond-shaped fissures that are typicalof elm species.

New Harmony has a broadly V-shaped crown with the main trunkdividing nearly 30 feet from theground into several erect limbs thatare strongly arched and terminate innumerous slender, often droopingbranches. New Harmony’s parenttree is 68 feet tall with an averagecrown spread of 72 feet. Its leavesare 4.2 inches long and 2.5 incheswide and turn yellow in autumn.

In adaptability tests, Valley Forgehas performed well in Ohio, Mary-land, and the District of Columbiaand can be considered adaptable inplant hardiness zones 5 through 7.New Harmony has grown well inGeorgia, Maryland, Minnesota, NewJersey, Ohio, Oklahoma, Pennsylva-nia, and Tennessee. It is also adapt-able in zones 5 to 7, with possiblecold hardiness into zone 4.—ByHank Becker, ARS.

Alden M. Townsend is at theUSDA-ARS U.S. National Arboretum,11601 Old Pond Dr., Glenn Dale,MD 20769; phone (301) 344-4175,fax (301) 344-3441. ◆

Horticulturist Susan Bentz and gardener Thomas Abell plant cuttings from disease-tolerant elms. (K7315-1)

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