Allelopathic Toxins and the Allelopathic Toxins and the Black WalnutBlack Walnut ((Juglans nigraJuglans nigra))

By: Kathleen A. TravisBy: Kathleen A. Travis

EcologyEcology

Fall 2000Fall 2000

HistoryHistory

• Pliny the Elder (A.D. 37) a Roman Pliny the Elder (A.D. 37) a Roman naturalist, noted the harmful effects of naturalist, noted the harmful effects of Black Walnut trees on the plants around Black Walnut trees on the plants around them. them.

• Native Americans would often use Native Americans would often use juices from the hull of the Walnut juices from the hull of the Walnut to poison and catch fish in to poison and catch fish in small streams and ponds.small streams and ponds.

LocationLocation

• Black Walnut trees are found in the Black Walnut trees are found in the Midwest and East in the United States.Midwest and East in the United States.

• Some varieties of the Black Walnut are also Some varieties of the Black Walnut are also found in Europe.found in Europe.

Plant AllelopathyPlant Allelopathy

• Plant allelopathy: the secretion or admission Plant allelopathy: the secretion or admission of a toxin or chemical from one plant in of a toxin or chemical from one plant in order to inhibit the growth of another plant order to inhibit the growth of another plant

• Allelopathic chemicals themselves are a Allelopathic chemicals themselves are a part of a diverse group of substances such part of a diverse group of substances such as alkaloids, terpenes, and organic as alkaloids, terpenes, and organic cyanides which can be naturally synthesize cyanides which can be naturally synthesize and released by plants.and released by plants.

Mechanisms of ReleaseMechanisms of Release

• Exuded through glands on roots or in Exuded through glands on roots or in leaves leaves

• Released by the decay of fallen leaves Released by the decay of fallen leaves and dead roots and dead roots

• Leached from the leaves when rain or Leached from the leaves when rain or fog passes over the leaf and drips offfog passes over the leaf and drips off

• Volatilized and then attached to soil Volatilized and then attached to soil particles particles

Jugalone ToxinJugalone Toxin

• Found in the roots, leaves, and in the Found in the roots, leaves, and in the husks surrounding the seeds of Black husks surrounding the seeds of Black Walnut trees Walnut trees

• Will not kill everything, but it Will not kill everything, but it does affect a variety of plants does affect a variety of plants commonly used for commonly used for landscaping and various landscaping and various garden vegetablesgarden vegetables

Symptoms Symptoms of Walnut Toxicityof Walnut Toxicity

• Symptoms begin with the wilting of the terminal shoots followed by an irreversible wilting of the rest of the plant. (callus build in xylem)

• If the plant has only a mild reaction to the toxin, poor flower development and stunted growth are noted.

Experimental ObjectiveExperimental Objective

• The objective of this experiment was to The objective of this experiment was to test the tolerance levels of some test the tolerance levels of some grasses used for landscaping purposes grasses used for landscaping purposes in this region to the jugalone toxins. A in this region to the jugalone toxins. A few other garden (tomatoes and few other garden (tomatoes and potatoes) and floral (hostas and day potatoes) and floral (hostas and day lilies) plants were also tested for lilies) plants were also tested for susceptibility. susceptibility.

ProcedureProcedure

• Grasses chosen: Alliance Rye, Annual Grasses chosen: Alliance Rye, Annual Rye, Kentucky Bluegrass, Wolfpack Tall Rye, Kentucky Bluegrass, Wolfpack Tall Fescue, and Creeping Red Fescue. Fescue, and Creeping Red Fescue.

• The grass seeds were planted and allowed The grass seeds were planted and allowed to grow in Bellarmine's Green House for to grow in Bellarmine's Green House for two weeks. Each variety of grass was two weeks. Each variety of grass was planted in a separate pot, and four pots of planted in a separate pot, and four pots of each type of grass were grown.each type of grass were grown.

Walnut Extract• Solution #1, one walnut : one liter HSolution #1, one walnut : one liter H22OO

• Solution #2, three walnuts : one liter HSolution #2, three walnuts : one liter H22OO

• Solution #3, five walnuts: one liter HSolution #3, five walnuts: one liter H22O O

• Husk cut up before soaking to increase the Husk cut up before soaking to increase the amount of surface area amount of surface area

• Soaked in a refrigerated room for two days with Soaked in a refrigerated room for two days with stirring every 12 hours stirring every 12 hours

• Walnuts removed and the solution was Walnuts removed and the solution was refrigerated until its use (3 days)refrigerated until its use (3 days)

• Solution #1, solution #2, and solution #3 Solution #1, solution #2, and solution #3 were each added to one of the pots were each added to one of the pots containing each variety of grass containing each variety of grass

• One tomato and one potato were treated One tomato and one potato were treated with solution #2, then solution #1 with solution #2, then solution #1

• One day lily and one hosta were both One day lily and one hosta were both treated with solution #3. treated with solution #3.

Problem!Problem!

• No response form the grass!No response form the grass!

• So...one whole walnut was added to each So...one whole walnut was added to each pot. pot.

• These Walnuts were allowed to naturally These Walnuts were allowed to naturally degrade over a period of two weeks.degrade over a period of two weeks.

• A clear response could be seen after two A clear response could be seen after two weeks.weeks.

ResultsResults

Plant Final Height of Controls Solution #1 Solution #2 Solution #3 Whole Walnut Alliance Rye 7-8 inches No reaction No reaction No reaction Inhibited Growth (3-5in)

Annual Rye 7-8 inches No reaction No reaction No reaction Inhibited Growth (3-5in

Kentucky Bluegrass 4-5 inches No reaction No reaction No reaction Inhibited Growth (3in) and half dead

Wolfpack Tall Fescue 10-12 inches No reaction No reaction No reaction Most grass dead remaining strands 5in

Creeping Red Fescue 5-6 inches No reaction No reaction No reaction dead

Tomato - Some yellowing dead - dead

Potato - Some yellowing dead - dead

Hosta - - - No reaction No reaction

Day Lily - - - No reaction No reaction

Plants Susceptible and Plants Susceptible and Resistant to the Jugalone ToxinResistant to the Jugalone Toxin

Susceptible to Jugalone Toxin Resistant to Jugalone ToxinApple Tomatoes Astibe HollyhocksAzaleas Wild Hydrangea Beans HostasBlackberries Black raspberry Jacob's ladderBlueberries Bugleweed Japanese mapleCabbage Canadian hemlock LungwortCotoneaster Carrots MelonsEvergreens Christmas fern Multiflora roseHydrangea Clematis PansiesLaurels Common Hyacinth Pot-marigoldMountain laurel Crocuses SnowdropsNorway spruce trees Daffodills SquashPeppers Darwin tulips Summer phloxPotatoes Dayliles Weeping forsythiaRhododendron EpimediumsSilver maple Grape hyacinths

Additional InformationAdditional Information• Some of the test subjects were also allelopathic Some of the test subjects were also allelopathic

plants plants • Many turf grasses are allelopathic including Many turf grasses are allelopathic including

Perennial Rye, Kentucky Bluegrass, and Perennial Rye, Kentucky Bluegrass, and Creeping Red Fescue. Creeping Red Fescue.

• Other allelopathic plants include Other allelopathic plants include Chrysanthemums, varieties of apples, Annual Chrysanthemums, varieties of apples, Annual Sunflowers (Sunflowers (Helianthus annusHelianthus annus), quack grass, ), quack grass, crabgrass, nut sedge, Canada thistle, and lamb's-crabgrass, nut sedge, Canada thistle, and lamb's-quarters.quarters.

ConclusionsConclusions• This experiment has examined one aspect This experiment has examined one aspect

of the jugalone toxin in Black Walnuts, its of the jugalone toxin in Black Walnuts, its toxicity. We have been able to deduce toxicity. We have been able to deduce which grasses of the test subjects are most which grasses of the test subjects are most conducive to life under a Black Walnut tree conducive to life under a Black Walnut tree and those that should be avoided. Perhaps and those that should be avoided. Perhaps in time, the inhibited grasses would be able in time, the inhibited grasses would be able to develop resistance to the toxin if allowed to develop resistance to the toxin if allowed to grow in its presence for a long duration.to grow in its presence for a long duration.

One Final NoteOne Final Note

• In recent years more work has been done In recent years more work has been done in the field of plant alleopathy. This work in the field of plant alleopathy. This work has lead to the discovery of medicinal has lead to the discovery of medicinal uses for the jugalone toxin. Jugalone is uses for the jugalone toxin. Jugalone is considered an antiseptic, a germicide, a considered an antiseptic, a germicide, a parasitic, and a laxative. Perhaps more parasitic, and a laxative. Perhaps more disease fighting uses can be found for disease fighting uses can be found for allelopathic chemicals, as they are allelopathic chemicals, as they are examined further.examined further.

Works CitedWorks Cited• Abraham, D. "The Green Thumb."

Consumer's Research Magazine. April 1992: 37-38. • "The Curse of the Black Walnut." Country Journal.

December 1997: 80.• Fuchs, Lucy. "Natural Connections." American

Horticulturist. February 1995: 14-16. • Meyer, P.W. "Underground Battles." Horticulture.

October 1990: 11-13. 5. • Orr, Tamra B. "Black Walnut." Better Nutrition. March

1999: 44-45.

The EndThe End