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Deriving from the Greek words allelon meaning “of each other” and pathos meaning “to suffer”, allelopathy is a process by which one organism affects (generally inhibiting) another through the release of biochemicals, known as allelochemicals (Ferguson, Rathinasabapathi, & Chase, 2003; Pratley, 2012).  Allelopathy is a phenomenon mostly commonly observed in plants, and may serve as a potential means of reducing competition from surrounding neighbors (Pratley, 2012). 


Examples of AllelopathyEdit

The Black Walnut (Juglans nigra) is one example of an allelopathic organism.  Black Walnuts are a medium-size, deciduous tree found extensively throughout the eastern and mid-western United States (Coladonato, 1991).  Although rich woodlands are the preferred habitat of the Black Walnut, this species is very intolerant and favors poorly amongst high competition (USDA, 2003).  In response to this challenge, the walnut has adapted by developing an allelopathic toxin known as “Juglone” which inhibits the growth of surrounding plants, thus, reducing competition (USDA, 2003).

Other examples of plant allelopathy are listed in the table below:



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 m (~14 ft) from trees

Rows of Leucaena interplanted with crops in an alley cropping system

Reduced the yield of wheat and turmeric 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

Wood extracts inhibited 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 (~16.5 ft)

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 nutsedge tubers.

Tree of heaven

Ailanthone, isolated from the tree of heaven, has been reported to possess non-selective postemergence herbicidal activity similar to glyphosate and paraquat

Rye, fescue, 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

Jungle rice

Inhibition of rice crop

Forage radish

Cover crop residue suppression of weeds in the season following the cover crop

Jerusalem artichoke

Residual effects on weed species

Sunflower and buckwheat

Cover crop residues reduced weed pressure in fava bean crop

Tifton burclover

Growth inhibition in wheat and autotoxicity in burclover

Sunn hemp

Growth inhibition of smooth pigweed and lettuce and inhibition of vegetable seed germination

Desert horsepurslane (Trianthema portulacastrum)

Growth promotion of slender amaranth (Amaranthus viridis)

Rhazya stricta

Growth inhibition of corn

Rough cocklebur (Xanthium strumarium)

Growth inhibition of mungbean

Garlic mustard

Inhibition of arbuscular mycorrhizal fungi colonizing on sugar maple

Barbados nut (Jatropha curcas)

Extracts of leaves and roots inhibited corn and tobacco

Chicory

Inhibition of Echinochloa crusgalli and Amaranthus retroflexus

Swallow-worts

Invasive species in northeastern United States and southeastern Canada; inhibited several weed species

Vogel's tephrosia (Tephrosia vogelii)

Growth inhibition of corn and three narrow-leaf weed species

Green spurge

Inhibition of chickpea

Crabgrass

Inhibition of corn and sunflower but no inhibition of triticale when dry crabgrass residue was incorporated into soil

Silver wattle (Acacia dealbata)

Inhibition of native understory species in northwest Spain

Sticky snakeroot (Ageratina adenophora)

Volatiles were inhibitory to plants in non-native ranges but not inhibitory to plants in the native range

Santa Maria feverfew (Parthenium hysterophorus)

Aqueous extracts had inhibitory effects on cereal crops

Teak wood

Leaf extracts inhibited jungle rice and sedge, but not cultivated rice

Rabbitfoot grass

Leaf extracts and mulch inhibited wheat

Table 1. Examples of allelopathy from published research (copied from Ferguson, Rathinasabapathi, & Chase, 2003, p. 5)

ReferencesEdit

Coladonato, M. (1991). Juglans nigra. In: Fire Effects Information System, [Online]. Retrieved from http://www.fs.fed.us/database/feis/

Ferguson, J. J., Rathinasabapathi, B., & Chase, C.A. (2003). Allelopathy: How plants suppress other plants. Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Publication #HS944 , pp. 1-5. Retrieved from: http://edis.ifas.ufl.edu/hs186


Pratley, J. E. (2012). Allelopathy -- a fancy name or a potential weed management tool?. Plant Protection Quarterly, 27(4), 131-137.

USDA NRCS (2003). Plant guide: black walnut. Retrieved from http://plants.usda.gov/plantguide/pdf/cs_juni.pdf   

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