The allelopathic effects of juglone containing nuts ()

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Abstract Allelopathy is the inhibition of the growth of

a plant by the allelochemicals, produced by a

nearby plant, into their shared environment.

It is a form of chemical warfare used by plants

to defend their territory and resources, thus

reducing interspecifc competition1. Although

some allelopathic plants produce agents that may

beneft rather than harm surrounding species,

the majority release chemicals that are toxic to

others. To explore this biological phenomenon,

the effects of allelopathic nuts of the family

Juglandaceae, containing the novel allelopathic

agent juglone, were tested on the germination of

plants sensitive to allelopathy and those shown to

be resistant. Based on previous studies examining

allelopathy, it is expected that sensitive plants

treated with this agent would cause negative

affects on germination, while the seeds that are

known to be resistant, would undergo relatively

normal germination. The results of these

experiments are generally consistent with thismodel of allelopathic toxicity and resistance.

Allelopathy is a unique phenomenon in nature

that is relatively new to the scientifc community,

and the results of this experiment are not only

relevant to basic botanical research, but also

have real world applications.

Introduction Allelochemicals can be found in all parts of the plant,

the greatest amounts are most often located in theroots and leaves. Plants release their allelochemicals

in several different ways: volatilization, leaching, orexudation. In volatilization, the toxic chemicals arereleased in the form of a gas from the leaves and thenare absorbed by another plant, causing it to die. Inleaching, the chemicals that are stored in the plant’sleaves seep into the soil, either by the littering and

decomposition of the leaves, or via runoff rain, fog,or dew that comes into contact with the leaves. Inexudation, the chemicals are released into the soilthrough the plant’s roots1. Allelochemicals can act on

plants in a variety of ways: inhibiting germination bydisrupting cell division, interfering with mechanisms ofenergy transfer such as respiration, and limiting

water and nutrient uptake1. The overall effect is toseverely impede the growth of the plant. Examples ofplant species that exhibit allelopathy include many trees(sugar maple, eucalyptus, and oak), shrubs, (sumacrhododendron, and elderberry), agricultural crops(tobacco and rice), and various grasses and ferns1. Eachreleases its own type of allelochemical.

In this study, the vegetable seeds examined thatare known to be sensitive to allelopathic toxins werepecan ( Carya illinoinensis ), English walnut ( Juglans regia )black walnut ( Juglans nigra ), tomato ( Solanum lycopersicum )cabbage ( Brassica oleracea ), and Wisconsin Fast Plants®( Brassica rapa ). The seeds that are known to be resistantto allelopathic toxins, bean ( Phaseolus vulgaris ) and corn( Zea mays )were compared with the sensitive plants, inorder to test the phenomena of allelopathy. One ofthe most well-known allelopathic chemical toxins is

known as juglone. Juglone negatively affects the growth

of many plants, including pine, birch, blueberry, andtomato, often times killing very sensitive species. Theallelopathic properties of Juglans nigra , Juglans regia , andCarya illinoinensis are due to the production of juglone3

For our experiment, we decided to use the fruit –the actual nut – of each nut tree, as opposed to theroots, leaves, or branches because nuts are the easiest

to obtain and handle. Previous research has shownthat tomato and cabbage are sensitive to black walnut while vegetables such as bean and corn do not seem tobe4. Hence, we decided to use tomato, cabbage, beanand corn as our test subjects. In addition WisconsinFast Plant® ( Brassica rapa ) were tested for allelopathicsensitivity/resistance, because it is closely related tocabbage.

Various studies have been written on the

allelopathic effects of certain plants, though none havehad the same focus and scope of experimentation asours. A study by Shibu Jose and Andrew R. Gillespiein 1998, showed the effects of juglone on the growthand physiology of corn versus soybean. The ndings

The allelopathic effects of juglone containing nutsCatherine Qin, Manavi Nagai, Whitney Hagins, and Reginald Hobbs*Department of Science AP Biology Lexington High School, 251 Waltham Street, Lexington, MA 02421

*Correspondence: rhobbs@sch.ci.lexington.ma.us

of the study were that although both crops weresensitive to juglone, soybean showed more of a

negative impact than corn5. These results led to thehypothesis that the germination of corn would berelatively unaffected by nut allelochemicals at the

concentrations that we would be testing. In anotherstudy, “Allelopathic effects of Squash ( Cucurbita pepo

L. cv. Scarlette ) on certain common weed species in Jordan” (Qasem, J.R., et al., 2010), the allelopathiceffects of squash on several different weed species

was investigated. The ndings of the study showed

that even 1ml of squash extract caused reducedgermination and growth in all of the weeds, and theseeffects were amplied with increased concentrations

of squash extract6. Although the focus of this study was on the allelopathic effects of squash on weeds

as opposed to nuts on vegetable seeds, they used asimilar experimental design: using a variety of testsubjects, and testing various concentrations of the

extract.Another study, “Phytotoxic effects of

Parthenium hysterophorus residues on three Brassica

species” (Singh, H.P., et al., 2005), the phytotoxiceffects of Parthenium hysterophorus , was investigatedon three different Brassica species. The ndings

of the study were that P. hysterophorus does in factnegatively impact the early growth of the three crops

by allelopathy, and that there was a direct correlationbetween the degree of inhibition of growth and theamount of P. hysterophorus residue in the soil7. Otherstudies have investigated the allelopathic effects of a variety of other plants, such as sour orange, red maple,eucalyptus, mango, Tree of Heaven, rye, wheat, andbroccoli; each of these allelopathic plants interfered with the growth of surrounding plants. In the currentexperiment, the allelopathic effects of Juglone,

contained in the nuts of the Juglandaceae family, was

tested on the germination of garden vegetables seeds. The relevance of our experiments to real world

applications is obvious. In agriculture, gardening,and landscaping, the growth of various plants may be affected when they are exposed to allelochemicalsproduced by these nuts. Knowing this, susceptibleplants should be grown far away from where nut trees

are growing. However, plants that are not as sensitiveto allelochemicals can be planted in proximity tothe nut trees and grow mostly unaffected. The

Results The data shows that tomato seed germination waseverely slowed down by the allelochemicals (Figure 1)

and that the black walnut was extremely detrimental toits germination. Brassica rapa (Figure 2) and cabbage

seeds (Figure 3) also showed intense susceptible tojuglone containing nuts/nut extracts; the cabbageseeds took until Day 11 to completely germinateBean seeds are only resistant to a certain extent to theallelochemicals - germination was slightly inhibited(Figure 4), whereas corn germination seems to be

enhanced by juglone (Figure 5). English walnut andpecan treated seeds also germinated at a slower ratethan in the original procedure when exposed to jugloneextracts (all gures).

Catherine Qin, Manavi Nagai, Whitney Hagins, and Reginald Hobbs Page 2 of 5

allelopathic effects of these nuts on certain plants canalso be used to an advantage; trees of the Juglandaceae

family can be used as natural herbicides on weeds andother unwanted plant growth.

Materials and Methods Approximately 10-20 nuts of each nut species (pecan

English walnut, and black walnut) were ground upinto a ne powder. A solution with a ratio of 7g nu

powder: 50ml water was refrigerated for 24 hours, andthen ltered to remove insoluble material. 2g of nu

powder was placed into the corresponding small petrdishes for that nut, on top of 3 wet paper towels, andcovered with one wet paper towel. 4g of nut powder was placed into large petri dishes, again on top of 3

wet paper towels, and covered by one paper towel

4.5ml of each nut solution was pipetted into the smalpetri dishes and 7ml of each nut solution was pipettedinto the large petri dishes. For the controls, 4.5ml or7ml of water was used instead of nut solution. 10 vegetable seeds(tomato, cabbage, Brassica rapa , beanand corn) were then placed individually into each oftheir corresponding petri dishes. To the small petrdishes 0.5ml of water was added each day and 1.5m

of water was added to the large petri dishes. The dishes were kept at room temperature in the dark in a coveredbox, and were only taking out for observation. The

seeds in each dish were watered until ~100% of thecontrol seeds germinated. The percentage of seedsgerminated of both the control and treated seeds foreach vegetable were recorded daily and then averagedand graphed after three trials.

Figure 1. The Effects of Various Allelopathic Nuts on the Germination of Tomato Seeds: The black walnut treated tomato seeds underwent almosno germination. The English walnut and pecan treated seeds also germinated at a slower rate.

Figure 2. The Effects of Various Allelopathic Nuts on the Germination of Cabbage Seeds: The germination of cabbage seeds were negativel

impacted by allelochemicals; these seeds took until Day 11 to completely germinate.

Figure 3. The Effects of Various Allelopathic Nuts on the Germination of B. rapa Seeds: In Brassica rapa seeds, germination was inhibited by juglone

containing nuts/nut extracts. This was most prevalent in the black walnut treated Brassica rapa seeds - they never nished germinating.

Figure 4. The Effects of Various Allelopathic Nuts on the Germination of Bean Seeds: Germination in bean seeds was slightly inhibited, contraryto our hypothesis that bean would be resistant. This is shown in the graph by the slightly lower rates of germination of all of the treated

seeds, as compared to the control. However, due to our small sample size, it is not known if this slight inhibition is signicant.

Figure 5. The Effects of Various Allelopathic Nuts on the Germination of Corn Seeds: The germination of the treated corn seeds was actuallyenhanced by juglone. This data suggests that the allelochemicals of these nuts may actually be helping corn to germinated faster, as

opposed to negatively impacting the seeds.

Discussion This study supported our predictions that allelopathic sensitive plants would show decreased germination, and that

allelopathic resistant plants would not. We showed that tomato, cabbage, B. rapa , and bean showed negatively affected

germination in the presence of nut allelochemicals, while corn germination became more enhanced. Tomato and Brapa germination were the most negatively affected, followed by cabbage, though to a lesser extent. Our result thatcorn seed germination was not negatively affected but rather enhanced by the presence of nut allelochemicals issurprising, but concurs with our hypothesis. The results obtained from this study showed correlations with the resultsof past work conducted in the eld of allelopathy. Experiments conducted by Shibu Jose and Andrew R. Gillespie

in 1998, showed that corn was less negatively affected by juglone than soybeans 5. This supports our conclusionthat corn is more tolerant of nut allelochemicals than other vegetable varieties. Our result that cabbage and B. rapa

seeds showed signicant inhibition in germination by the presence of nut allelochemicals correlated with the results

of the study conducted by Harminder Pal Singh, et. al. in 2005; they found that the residues of the allelopathicplant P. hysterophorus severely reduce the growth of Brassica species, including cabbage and B. rapa 7. Another study whose results correlated with ours was conducted by Jamal R. Qasem and Nabil N. Issa in 2010, which found

that allelopathic effects on plants are amplied with

increased concentrations of allelochemicals6. Ingeneral, the results of our experiment seem to agree with the previous research that has been done in this

Therefore, after experimentation and dataanalysis, we can conclude that the results of ourexperiment support our hypothesis, and concur withpast work conducted in the eld of allelopathy.

References1 Allelopathy: “Chemical warfare” among plants.

Trees and turf: Are they compatible? University of Minnesota. nd.

2 Brown, C. Allelopathic plants: Nature’s weed

killers.Earth friendly gardening. 2006, November 30.

3 Appleton, B., Berrier, R., Harris, R., Alleman, D.,& Swanson, L. Trees for problem landscape sites

- the walnut tree. Allelopathic effects and tolerantplants. 2009, May 1.

4 Smith, C. W. Walnut tree allelopathy. New MexicoState University. 2004, October 9.

5 Jose, S., & Gillespie, A. R. Allelopathy in black

walnut (Juglans nigraL.) alley cropping. II.Effects of juglone on hydroponically grown corn

(Zea maysL.) and soybean (Glycine maxL. Merr.)

growth and physiology. Plant and Soil, 1998, 203,

199-206.

6 Qasem, J. R., & Issa, N. N. Allelopathic effects

of squash (Cucurbita pepo L. cv. scarlette) on

certain common weed species in Jordan. TheRegional Institute. 2010.

7 Singh, H. P., Batish, D. R., Pandher, J. K., &Kohli, R. K. Phytotoxic effects of Parthenium

hysterophorus residues on three Brassica species. Weed Biology and Management, 2005, 5,105-109.

8 Ferguson, J. J., & Rathinasabapathi, B. Allelopathy:

How plants suppress other plants. HorticulturalSciences Department, Florida Cooperative ExtensionService, Institute of Food and Agricultural Sciences,University of Florida. 2009.

The allelopathic effects of juglone containing nuts ()

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