Allelopathic Toxins and the Black Walnut (Juglans nigra)

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Allelopathic Toxins and the Black Walnut (Juglans
nigra)

• By Kathleen A. Travis
• Ecology
• Fall 2000

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History

• Pliny the Elder (A.D. 37) a Roman naturalist,
  noted the harmful effects of Black Walnut trees
  on the plants around them.
• Native Americans would often use juices from the
  hull of the Walnut to poison and catch
  fish in small streams and ponds.

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Location

• Black Walnut trees are found in the Midwest and
  East in the United States.
• Some varieties of the Black Walnut are also found
  in Europe.

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Plant Allelopathy

• Plant allelopathy the secretion or admission of
  a toxin or chemical from one plant in order to
  inhibit the growth of another plant
• Allelopathic chemicals themselves are a part of a
  diverse group of substances such as alkaloids,
  terpenes, and organic cyanides which can be
  naturally synthesize and released by plants.

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Mechanisms of Release

• Exuded through glands on roots or in leaves
• Released by the decay of fallen leaves and dead
  roots
• Leached from the leaves when rain or fog passes
  over the leaf and drips off
• Volatilized and then attached to soil particles

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Jugalone Toxin

• Found in the roots, leaves, and in the husks
  surrounding the seeds of Black Walnut trees
• Will not kill everything, but it does
  affect a variety of plants commonly used
  for landscaping and various
  garden vegetables

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Symptoms of 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.

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Experimental Objective

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

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Procedure

• Grasses chosen Alliance Rye, Annual Rye,
  Kentucky Bluegrass, Wolfpack Tall Fescue, and
  Creeping Red Fescue.
• The grass seeds were planted and allowed to grow
  in Bellarmine's Green House for two weeks. Each
  variety of grass was planted in a separate pot,
  and four pots of each type of grass were grown.

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Walnut Extract

• Solution 1, one walnut one liter H2O
• Solution 2, three walnuts one liter H2O
• Solution 3, five walnuts one liter H2O
• Husk cut up before soaking to increase the amount
  of surface area
• Soaked in a refrigerated room for two days with
  stirring every 12 hours
• Walnuts removed and the solution was
  refrigerated until its use (3 days)

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• Solution 1, solution 2, and solution 3 were
  each added to one of the pots containing each
  variety of grass
• One tomato and one potato were treated with
  solution 2, then solution 1
• One day lily and one hosta were both treated with
  solution 3.

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Problem!

• No response form the grass!
• So...one whole walnut was added to each pot.
• These Walnuts were allowed to naturally degrade
  over a period of two weeks.
• A clear response could be seen after two weeks.

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Results
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Plants Susceptible and Resistant to the Jugalone
Toxin
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Additional Information

• Some of the test subjects were also allelopathic
  plants
• Many turf grasses are allelopathic including
  Perennial Rye, Kentucky Bluegrass, and Creeping
  Red Fescue.
• Other allelopathic plants include Chrysanthemums,
  varieties of apples, Annual Sunflowers
  (Helianthus annus), quack grass, crabgrass, nut
  sedge, Canada thistle, and lamb's-quarters.

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Conclusions

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

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One Final Note

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

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Works 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.

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The End