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Black walnut allelopathy: implications for intercropping

Shibu Jose

School of Forest Resources and Conservation, University of Florida, 5988 Hwy 90, Bldg. 4900
Milton, FL 32583


Black walnut (Juglans nigra L.), an allelopathic tree, has been cited since the first century A.D. as having poisonous effects on other plants. The active agent causing growth inhibition was identified as a phenolic compound called juglone (5-hydroxy-1,4-napthoquinone) in the early twentieth century. In living tissues, juglone is present in a reduced nontoxic form called hydrojuglone. However, when exposed to the air, hydrojuglone is oxidized to its toxic form. Although the allelopathic effects of black walnut have been questioned due to the contradictory nature of species affected, a large body of evidence for black walnut allelopathy has accumulated over many years. Further, considerable progress has been made during the last two decades in extracting and quantifying juglone from black walnut plant parts and from the soil. With renewed interest in establishing intercropping systems with black walnut, it is important to determine the sensitivity of potential agronomic species that are planted with black walnut. Juglone uptake and disruption of normal physiological functions in sensitive plants have been demonstrated in solution cultures. Recent findings from a number of trials and the implications for intercropping will be discussed.

Media summary

Black walnut produces an allelochemical -juglone. With renewed interest in intercropping with black walnut sensitivity of agronomic species is being investigated


Allelochemical, black walnut, intercropping juglone

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