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Allelopathy



Allelopathy

Introduction:

Allelopathy is a process by which a plant releases chemicals that can either inhibit or competitors. Allelopathic plants do sometimes pose obstacles that are hard to overcome, however. Soil sickness, a general term for a problem that may well be caused by residues of allelochemicals that persist in the soil after the plant is gone, may make some sites unsuitable for growing other plants.
Allelopaths are plants that have an advanced weapon in their arsenal. The allelopathic plant competes with other species through "chemical warfare" by releasing chemicals that inhibit the growth of its neighboring  plants.

History

Theophrastus (ca. 300 B.C.E.), a student and successor to Aristotle, wrote about allelopathic reactions in his botanical works.  He has been called the "father of Botany", and wrote of how chickpea "exhausts" the soil and destroys weeds.

In 1 C.E., Gaius Plinius Secundus, also known as Pliny the Elder, a roman scholar and aturalist, wrote about how chick pea and barley "scorch up" corn land.  He also mentioned that Walnut trees are toxic to other plants.

Augustin Pyramus  De Candolle, a botanist and naturalist, in 1832, suggested that soil sickness was caused by chemicals released by the crop.

And, in 1907-1909, two researchers, Schreiner and Reed investigated the isolation of a number of phytotoxic chemicals from plants and soils.


What is Allelopathy?


The word allelopathy derives from two separate words.  They are allelon which means "of each other", and pathos which means "to suffer".  Allelopathy refers to the chemical inhibition of one species by another.  The "inhibitory" chemical is released into the environment where it affects the development and growth of neighboring plants.

Allelopathic chemicals can be present in any part of the plant.  They can be found in leaves, flowers, roots, fruits, or stems.  They can also be found in the surrounding soil.  Target species are affected by these toxins in many different ways.  The toxic chemicals may inhibit shoot/root growth, they may inhibit nutrient uptake, or they may attack a naturally occurring symbiotic relationship thereby destroying the plant's usable source of a nutrient.

 

Are all plants Allelopathic?

Not all plants have allelopathic tendencies.  Some, though they exhibit these tendencies, may actually be displaying aggressive competition of a non-chemical form.  Much of the controversy surrounding allelopathy is in trying to distinguish the type of competition being displayed.  In general, if it is of a chemical nature, then the plant is considered allelopathic.  There have been some recent links to plant allelotoxins directed at animals, but data is scarce.


Environmental Impact

Allelopathy is a form of chemical competition.  The allelopathic plant is competing through "interference" chemicals.  Competition, by definition, takes one of two forms--exploitation or interference.

Competition is used by both plants and animals to assure a place in nature.  Plants will compete for sunlight, water and nutrients and, like animals, for territory.  Competition, like parasitism, disease, and predation, influences distribution and amount of organisms in an ecosystem.  The interactions of ecosystems define an environment.

When organisms compete with one another, they create the potential for resource limitations and possible extinctions.  Allelopathic plants prevent other plants from using the available resources and thus influence the evolution and distribution of other species.  One might say that allelopathic plants control the environments in which they live.

Allelopathy is a process by which a plant releases chemicals that can either inhibit or benefit other plants. Since most allelopathic plants cause harm to other plants, that's the what I'll be discussing here. Species competition ensures the biodiversity of ecosystems. All plants and animals have developed techniques for out-competing other species for nutrients, water, territory, and other resources. For example, certain plants have extremely dense root systems.                                                           

Allelopaths are plants that have an advanced weapon in their arsenal. The allelopathic plant competes with other species through "chemical warfare" by releasing chemicals that inhibit the growth of its competitors.

Allelopathic substances work like herbicides, preventing the germination and growth of the seedlings of competing species. Plants that are under stress, such as those with pests, diseases, or less than optimum access to nutrients, sun, or moisture, are at an even higher risk for being eliminated by allelopaths.

Depending on the plant, allelopathic substances can be released from a plant's flowers, leaves, leaf debris and leaf mulch, stems, bark, roots, or soil surrounding the roots. Some of the chemicals biodegrade over time while others can be persistent in the soil.

Probably the most well-known allelopathic plant is the black walnut (Juglans nigra) tree. All parts of the tree-roots, bark, leaves, nuts, and even rainwater that falls off a leaf-release an allelopathic substance called juglone. Some species are affected by it and others aren't bothered at all

My great-aunt used to have a huge black walnut tree in her yard. I always thought it was bare underneath because we kids were always playing and horsing around underneath it! Maybe that was part of it, but the juglone must have been at work as well.

If you're wondering what to grow near your black walnut tree, try rviceberry/juneberry/shadbush (Amelanchier sp.), tulip Shasta daisy (Leucanthemum x superbum), speedwell (Veronica sp.), or American arborvitae (Thuja occidentalis), or one of many others. More information about plants that are affected by juglone, and those that are not, is available here.

Other common trees with allelopathic properties include eucalyptus, sugar maple, tree-of-heaven, hackberry, southern waxmyrtle, American sycamore, cottonwood, black cherry, red oak, black locust, sassafrass, and American elm.

Allelopathic study is in its infancy, but early research suggests that allelopaths can be used as effective herbicides for organic weed control. For example, an allelopathic crop might be used to control weeds by planting it in rotation with other crops.

I wonder if organic herbicides based on allelopaths are commercially available, or will be soon. It's interesting to think about the possibilities of allelopathic chemicals for the organic gardener

Though scores of plants are known to produce allelochemicals--Ailanthus (ailanthone), sorghum (sorgoline)--black walnut (Juglans nigra) is the poster plant for allelopathy.

Scientists were able to isolate the toxic compound in black walnut--juglone--by soaking various parts of the tree in water and then studying those solutions and their effects on other plants. Juglone, like all allelochemicals, is a secondary metabolite, meaning that it is produced as a by-product of chemical reactions that actually keep the plant alive. It has been found in the leaves, bark and wood of the walnut, as well as in the husks of walnut seeds. The highest concentration of juglone, however, is in the tree roots.

Juglone inhibits the growth of certain plants, especially those in the Solanaceae or nightshade family--as well as azaleas and rhododendrons, mountain laurel--even privet. Exactly how it does this--whether by interfering with photosynthesis or water uptake--is still a question biochemists are exploring. Whatever the mechanism, plants such as tomatoes, potatoes, blackberries and blueberries soon wilt and die if planted within the root zone of walnuts or mulched with the leaves or bark of walnut. Other members of the walnut family--pecans and hickories--have also been found to contain juglone and can also produce this effect.

Different strokes for different plants

Many plants, however, easily tolerate juglone; these include vegetables such as melons, beans and carrots and trees such as Eastern redbud and southern catalpa. In low concentrations, juglone even appears to stimulate growth in some species--an anomalous effect observed in other allelopathic associations. For instance, it appears to have this effect on Kentucky bluegrass, a cool-season grass that may also produce allelopathic chemicals.

How to cope with allelopathic plants

Dr. Thomas Green, a professor of urban forestry at Western Illinois University, has studied the effects that turf grass and ornamental trees have on each other. These groups of plants tend to have incompatible needs and compete with each other both above ground and below.

"What we tend to do as horticulturists is pick Plant A that we like and Plant B that we like and put them together," Green said. He points out, though, that some of the associations we come up with have never occurred in natural situations, where associated plant species have often co-existed over eons and have possibly even evolved to tolerate each other's chemical toxins.

Some grasses, and fescues in particular, are allelopathic. In many cases of tree-turf grass competition, Green has found it best for both the trees and the grasses to simply separate them by heavily mulching an area several feet out from the tree.

"Mulch will eliminate competition of the roots with grass. It also preserves moisture for the fine surface roots of the tree. With mulch we're emulating nature--exactly what happens in the forest." This way, what was taken up by the tree into its leaves is directly recycled. Also, both direct competition and allelopathy between turfgrass and the tree are avoided.

Using allelopathy to your advantage

Often the ways farmers and gardeners have dealt with allelopathy--whether they pegged the phenomenon by name or not--have been simple and practical: separate a plant that inhibits the growth of others, or else use that plant to the garden's advantage.

Rye has allelopathic properties, as do several other cover or "smother" crops--oats, wheat, barley and sorghum. In fact, Rice's Allelopathy cites a 1983 study that showed "populations of common purslane and smooth crabgrass were reduced 70 and 98 percent, respectively, by residues of sorghum."

"Reduce competition--that would be the primary objective," said Dr. Bill Klingeman, a professor of plant sciences at the University of Tennessee, about allelopathic plants. "But the other benefit would be that if they outcompete other plants, then you get a uniform stand. If the plant helps you out, that's an added benefit." Synthesizing allelochemicals for their herbicidal applications, or using certain allelopathic plants in crop rotations or as companion plants, is yet another burgeoning branch of allelopathic research.

Soil Sickness

Allelopathic plants do sometimes pose obstacles that are hard to overcome, however. Soil sickness, a general term for a problem that may well be caused by residues of allelochemicals that persist in the soil after the plant is gone, may make some sites unsuitable for growing other plants.

Rice cites a famous example where foresters tried to establish a birch arboretum on the site of a former black walnut grove at the Vermont Agricultural Experiment Station--a tale summarized by W. J. Gabriel in 1975: "an unusually large number of trees died within the boundaries of the old walnut plantation." Auto-toxicity, where a species chemically prevents germination of its own seeds, is another possible source of soil sickness that may plague apples and roses.

Through research as well as trial-and-error, it is usually possible to find some hardy plant that through chemical connivance or lucky immunity can manage to survive on such sites. Improving the soil by adding organic matter may also help to resolve the problem, as many allelochemicals more easily persist in poorly drained soil such as cla

  Allelopathic plants don't want any other plants near them. In fact, like Greta Garbo, they just want to be alone. But what plants are allelopathic and how do they affect other plants? Are their chemical attacks specific to one genus, or are they indiscriminate? What are the chemicals they use?

 There are many allelopathic plants. Some discriminate, and have a stronger effect on specific plants. Others are indiscriminate. They use a variety of chemicals. Some use phenols. Others use coumarins. Plants also use juglone, cyanogenic glycosides, and terpenoides. These chemicals affect plants in different ways. Some act on the plant's respiration, blocking it, and inhibiting the plant's transfer of energy. Some slow plant growth, or stop cell division, thereby interfering with seed germination. Some allelopathic chemicals interfere with a plant's ability to take in water and nutrients. In a few instances, the chemical can kill a plant, or prevent it from becoming established, or reduce plant growth.

Allelopathic plants spread their chemicals mainly through the soil (although some may also be absorbed directly from the air). How much chemicals accumulate there depends on how well the soil drains, how much aeration there is in the soil, temperature and a number of other factors. Chemicals accumulate in clay soils, because clay soils do not drain well. In sandy soils, however, they leach out quickly. So if you're planting near allelopathic plants, don't put plants sensitive to the chemicals in heavy clay soils.

Also, microorganisms may break down allelopathic chemicals .Allelopathy (from the Greek, allelon, meaning another and pathos, which means to suffer) is a way some plants deal with competition.

Allelopathic plants release chemical substances which literally make other plants suffer. Some of these allelopathic plants store toxins in their leaves. When the leaves fall to the ground, the toxins are released. These toxins leach through the soil and are taken up by other nearby plants.

Alternately, allelopathic plants can release chemicals through their roots. These toxins travel thr;ough the soil where they can be absorbed by the roots of other plants.

Some allelopathic plants use gas warfare by releasing allelochemicals through small pores in their leaves and gassing nearby species.

Plants like black walnut (Juglans nigra) have allelopathic chemicals in their leaves, bark and roots. This chemical (called juglone) is particularly toxic to members of the Solanacea family, which includes deadly nightshade, potatoes and tomatoes. It is also toxic to azaleas, rhododendrons, mountain laurel, blackberries and blueberries.

Pecans and hickories are relatives of the black walnut and also have fairly high levels of juglone.

Of course, black walnut is only one plant that is allelopathic. There are many others.

Other allelopathic plants include sagebrush (Artemesia grandiflora), red cedar, some species of pine and eucalyptus, some clovers, fescues and sunflowers to name a few.

Allelopathy refers to the beneficial or harmful effects of one plant on another plant, both crop and weed species, by the release of chemicals from plant parts by leaching, root exudation, volatilization, residue decomposition and other processes in both natural and agricultural systems.

First widely studied in forestry systems, allelopathy can affect many aspects of plant ecology including occurrence, growth, plant succession, the structure of plant communities, dominance, diversity, and plant productivity. Initially, many of the forestry species evaluated had negative allelopathic effects on food and fodder crops, but in the 1980s research was begun to identify forestry species that had beneficial, neutral, or selective effects on companion crop plants (Table 1). Early research grew out of observations of poor regeneration of forest species, crop damage, yield reductions, replant problems for tree crops, occurrence of weed-free zones, and other related changes in patterns of vegetation. Our purpose here is to introduce the concept of allelopathy, cite specific examples, and to mention potential applications as an alternative weed management strategy.

Nature of Allelopathy

Commonly cited effects of allelopathy include reduced seed germination and seedling growth. Like synthetic herbicides, there is no common mode of action or physiological target site for all allelochemicals. However, known sites of action for some allelochemicals include cell division, pollen germination, nutrient uptake, photosynthesis, and specific enzyme function.

Allelopathic inhibition is complex and can involve the interaction of different classes of chemicals like phenolic compounds, flavonoids, terpenoids, alkaloids, steroids, carbohydrates, and amino acids, with mixtures of different compounds sometimes having a greater allelopathic effect than individual compounds alone. Furthermore, physiological and environmental stresses, pests and diseases, solar radiation, herbicides, and less than optimal nutrient, moisture, and temperature levels can also affect allelopathic weed suppression. Different plant parts, including flowers, leaves, leaf litter and leaf mulch, stems, bark, roots, soil and soil leachates and their derived compounds, can have allelopathic activity that varies over a growing season. Allelopathic chemicals can also persist in soil, affecting both neighboring plants as well as those planted in succession. Although derived from plants, allelochemicals may be more biodegradable than traditional herbicides but may also have undesirable effects on non-target species, necessitating ecological studies before widespread use.

Selective activity of tree allelochemicals on crops and other plants has also been reported. For example, Leucaena leucocephala, the miracle tree promoted for revegetation, soil and water conservation and animal improvements in India, also contains a toxic, non-protein amino acid in leaves and foliage that inhibits the growth of other trees but not its own seedlings. Leucaena species have also been shown to reduce the yield of wheat but increase the yield of rice. Leachates of the chaste tree or box elder can retard the growth of pangolagrass but stimulate growth of bluestem, another pasture grass.

Allelochemical concentrations in the producer plant may also vary over time and in the plant tissue produced. Foliar and leaf litter leachates of Eucalyptus species, for example, are more toxic than bark leachates to some food crops.

Chemical Interaction among Plants

Black walnut trees kill almost anything you plant under them. In 1 C.E., Pliny the Younger attributed this to their heavy shade. Now we know they secrete a poison, called juglone. In 1937 Botanist Hans Molisch, president of the University of .Vienna coined the term "allelopathy," from Greek roots meaning "each other" and "sensitivity."

Some people use the term only to refer to inhibition of one plant by another's chemical residues. But a substance that inhibits growth at one concentration, commonly promotes it at a much smaller dose. Moreover concentrations in the wild are typically minute, so that the effect of one plant is less important than the interaction between the chemicals in a community of various plants. The same substance can also stimulate during one part of a plant's growth cycle, and inhibit at another stage or season.

Of course one plant can simply outcompete with another for sun, water, minerals ... even air. To rule out competition, scientists conduct experiments like one that grew grass and apple seedlings in two well-separated trays. Water drained from the grass was introduced into the apple tray; the seedlings wilted.

Grasses inhibit many woody plants, notably dogwood and forsythia. In turn, Sycamore inhibits kentucky bluegrass, bermudagrass, and annual ryegrass. Other trees which inhibit various plants include horse chestnut, firs, pines ... and hackberry, a sturdy native tree I was considering - until now - to replace my dying maple.

New England asters inhibit sugar maples; many native asters are allelopathic. (Hmm, what have the ones all over my garden affected?) Allelopathy orchestrates the phenomenon of plant succession in abandoned land; major players include asters, sunflowers and goldenrod.

Roses, lilacs, viburnums, mockorange, and barberry show considerable allelopathic activity. Strong allelotoxins persist from most plants of the Brassica (cabbage) family - including that old-fashioned, sweet-smelling annual, stock. (Dame's Rocket, too; maybe I don't want so much of it after all.)

Some invasive plants create allelopathic toxins in the ecosystem they've been introduced to, but not in their native one!

Peach, apple and citrus trees leave allelochemicals in the soil that prevent replanting the same kind of tree. Citrus trees actually kill themselves off - as well as two plants I've struggled with: chrysanthemums and clover. (I tried three times with Trifolium purpurascens, a bronze-leaved clover that makes lots of four-lobed leaves.

Table 1.  Examples of allelopathy from published research.

Allelopathic Plant

Impact

Rows of black walnut interplanted with corn in an alley cropping system

Reduced corn yield attributed to production of juglone, an allelopathic compound from black walnut, found 4.25 meters from trees

Rows of Leucaena interplanted with crops in an alley cropping system

Reduced the yield of wheat and tumeric but increased the yield of maize and rice

Lantana, a perennial woody weed pest in Florida citrus

Lantana roots and shoots incorporated into soil reduced germination and growth of milkweed vine, another weed

Sour orange, a widely used citrus rootstock in the past, now avoided because of susceptibility to citrus tristeza virus

Leaf extracts and volatile compounds inhibited seed germination and root growth of pigweed, bermudagrass, and lambsquarters

Red maple, swamp chestnut oak, sweet bay, and red cedar

Preliminary reports indicate that wood extracts inhibit lettuce seed as much as or more than black walnut extracts

Eucalyptus and neem trees

A spatial allelopathic relationship if wheat was grown within 5 m

Chaste tree or box elder

Leachates retarded the growth of pangolagrass, a pasture grass but stimulated the growth of bluestem, another grass species

Mango

Dried mango leaf powder completely inhibited sprouting of purple nut sedge tubers.

Tree of Heaven

Ailanthone, isolated from the Tree of Heaven, has been reported to possess non-selecitve post-emergence herbicidal activity similar to glyphosate and paraquat

Rye and wheat

Allelopathic suppression of weeds when used as cover crops or when crop residues are retained as mulch.

Broccoli

Broccoli residue interferes with growth of other cruciferous crops that follow


Chemical Warfare in the Plant Kingdom

 

Black Walnut

One of the most famous allelopathic plants is Black Walnut (Juglans nigra).  The chemical responsible for the toxicity in Black Walnut is Juglone (5 hydroxy-1,4 napthoquinone) and is a respiration inhibitor.  Solanaceous plants, such as tomato, pepper, and eggplant, are especially susceptible to Juglone.  These plants, when exposed to the allelotoxin, exhibit symptoms such as wilting, chlorosis (foliar yellowing), and eventually death.  Other plants may also exhibit varying degrees of susceptibility and some have no noticeable effects at all.  Some plants that have been observed to be tolerant of Juglone include lima bean, beets, carrot, corn, cherry, black raspberry, catalpa, Virginia creeper, violets, and many others.

Juglone is present in all parts of the Black Walnut, but especially concentrated in the buds, nut hulls, and roots.  It is not very soluble in water and thus, does not move very rapidly in the soil.  Toxicity has been observed in all soil with Black Walnut roots growing in it (roots can grow 3 times the spread of the canopy), but is especially concentrated closest to the tree, under the drip line.  This is mainly due to greater root density and the accumulation of decaying leaves and hulls.

 

Tree-Of-Heaven

The Tree-Of-Heaven, or Ailanthus (Ailanthus altissima) is a recent addition to the list of allelopathic trees.  Ailanthone, an allelotoxin extracted from the root bark of Ailanthus, is known for its "potent post-emergence herbicidal activity".  Ailanthus poses a serious weed problem in urban areas.

 

Sorghum

The major constituent of sorghum that causes allelopathic activity is sorgolene (2-hydroxy-5-methoxy-3-{(8'z,11'z)-8',11',14'-pentadecatriene}-p-benzoiquinone).  Sorgolene is found in the root exudates of most sorghum species and has been shown to be a very potent allelotoxin that disrupts mitochondrial functions .

  There are many other known allelopathic species, and many that are highly suspected of being allelopathic including various wetland species, grasses, and other woody plants such as Fragrant Sumac (Rhus aromaticus).   Tobacco (Nicotiana rustica), Rice (Oryza sativa), Pea (Pisum sativum), and many


Procedures and Protocol


Protocol 1. Learning To Identify Signs Of Allelopathy

The best way to study allelopathy is to find signs of it occurring in nature.  It is impossible to "see" the toxins at work, but it is possible to see the signs and symptoms caused by the chemicals on surrounding plants.  For example, very few plants grow under a Black Walnut and those that do often times look sickly and chlorotic.  This is a sign of the allelotoxin, Juglone, at work.

Along with recognizing the signs of allelopathy, one must also be able to identify the plants.  Some allelopathic plants, such as Black Walnut, grow in our backyards and on our streets and are easy to identify.  Others, like sorghum or chick pea, may be easier to find in rural areas where they are grown as crops or alongside farm land.  Some allelopathic plants, especially many of the wetland species, may require special field trips and extra time to find them first and then identify them.

 

Protocol 2. Harvesting Plants and Plant Parts

Many of the known allelotoxins are very expensive and not easy to come by.  Some companies such as Sigma Chemical and Caroline Biological may carry the chemicals, but in solid form that will require extra time and effort to bring to a soluble form that can be used in the lab.  However, not every class will have the funds or the access to these chemicals.  Thus, it may be that the only way to run the experiments is to have the class harvest their own allelotoxins.


Some research will be required to investigate what plant parts have the highest concentrations of allelopathic species.  For instance, the Juglone found in Black Walnut can be found throughout the plant but particularly within the nut hulls, leaves, and roots.  Therefore, a class project may be to break into groups and harvest each part and test them accordingly.

It is important when harvesting plants or plant parts to be sure that the plant is not endangered and to be sure that the procedure is carried out in such a way as to bring no harm to the plant or the surrounding area.  Of course, in the case of harvesting the entire plant, accommodations must be made.

This field exercise can be done when the class is identifying the allelopathic plants as described in Protocol 1, or can be done as a separate exercise.

Protocol 3. Testing for Allelopathy in the Lab

The effects of allelopathic toxins on sensitive plants can easily be tested in the lab or greenhouse setting.  Seeds are the easiest and least expensive to test.  Seeds that do not germinate in the presence of allelotoxins are probably displaying toxicity effects.  Plants that

become chlorotic and eventually die in the presence of allelotoxins are also showing signs of toxicity to the chemical.

Solanaceous crops, such as tomatoes and peppers, are most susceptible to juglone (the allelotoxin found in Black Walnut trees).  The laboratory setting is the perfect place to test the susceptibility of certain plants to various alleltoxins.

Other scientific or research based concepts, such as graphing, dilutions, and general lab protocol will also be covered when certain allelopathy activities are conducted in the lab or classroom setting.

 

Procedures

  1. Familiarize yourself with the allelopathic species in your area.  In particular, focus on mature species that are established.  These tend to have higher concentrations of the allelotoxin and thus will display better signs and symptoms on any susceptible surrounding plants.
  2. If possible, contact a local conservation organization or extension agency, that might have some insight about allelopathy.  Your research may be of interest to them and they may offer professional advice or important information.
  3. Decide which species and areas should be the focus of your survey.
  4. Decide on a survey method.  For instance, you may want to conduct the identification field trip one day and then follow up with the harvest field trip another, or you may want to conduct both on the same day.
  5. Learn how to identify the species that you will be studying.  There are many good Field Guides available, as well as many excellent web sites.
  6. Decide how to divide up the area you will be working in.
  7. Record what allelopathic signs and symptoms were found, and the species they were found by.
  8. Discuss ways to study allelopathy in the laboratory.
  9. Gather needed materials.  See the materials list at the end.


Lab & Classroom Exercises

A} Identifying Allelopathic Plant Parts: Black Walnut

Research Focus

Have the students discuss why they believe certain plant parts may be more allelopathic than others.  Have them conduct some research into this.  They can scan the web, be involved in personal communications with professionals in the field, or visit a library.

For Discussion:

  • Why are some parts more allelopathic than others?
  • How does this affect the organism's ability to out-compete other plants?
  • Does this change from season to season? Day to night?
  • How can we test these parts and their

Field Harvesting

Conduct a field trip to harvest parts of the Black Walnut tree.  These parts will be brought back to the classroom for further investigation and observation.

Students should collect the following:

 

1. Leaves

  • 5-10 leaves per group
  • Place them in paper bags with the group's name or number on them and where on the tree canopy the leaves were collected from.


2. Nut Hulls

  • 2-3 nut hulls per group
  • Note: Black Walnut nuts stain skin and clothes.


3. Roots

  • One bunch of roots for the entire class is sufficient
  • Dig a clean hole, CUT a small amount of roots by the drip line
  • Replace the soil
  • Removal of roots is invasive and should ONLY be done if the teacher and students are confident in their techniques and methods.

 

4. Soil

  • Have students remove soil from a range of areas starting at the trunk of the tree and moving out beyond the drip line.
  • One bucket-full per group will be sufficient

 

5. Other

Laboratory Procedures

Leaves:

  1. Prepare jars with tomato or pepper seeds
  • Place tissue in bottom jar
  • Make moist
  • Place seeds on moist towels (usually ten seeds per treatment)
  1. Crumble leaves and place in cheesecloth
  2. Rubber band or tie the cheesecloth closed and place into mouth of jar so that the leaf bundle dangles over, but does not touch, the seeds.
  3. Place jars in windowsill or under grow light.
  4. Observe


 Nut Hulls:

  1. Using a blender, food processor, or hammer, pulverize the nut
  2. Decide on whether to add water or leave as is (a comparison of both ways may be best)
  3. Place the nut juice in a petri dish that has been lined with paper towel.
  4. Place ten seeds into each prepared petri dish
  5. Observe.     

 

Roots:

See Nut Hulls Procedure Above

 

Soil:

  1. Place some potentially allelotoxic soil into containers.
  2. Place a known un-contaminated soil into other containers (control)
  3. Plant seeds into each
  4. Observe


  • Note: Tomato plants can be used instead of seeds where appropriate.
  • Solanaceous crops, such as tomatoes, peppers, eggplants, etc., are most susceptible to juglone and are thus best to use.
  • Tomato, eggplant, or pepper plants can be used instead of seeds where appropriate.


Juglone is generally non-toxic to humans but, as with any substance, individuals may be sensitive and might react.  It is recommended that pregnant women not come in direct contact with crystallized juglone.




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great information. You post

great information. You post about Allelopathy give me alot of knowledge. thanks for this great article.

 

regard


Please note that this is the opinion of the author and is Not Certified by ICAR or any of its authorised agents.