ALLELOPATHY: CHARACTERISTICS, TYPES AND APPLICATIONS - BIOLOGY - 2024

The allelopathy is the production and release of biochemical agents by an organism and affect the development of other organisms. The term comes from the Greek words allelon, which means one to the other, and pathos, which means to suffer and refers to the negative effect of one organism on the other.

The term was used for the first time in 1937 by the Australian professor Hans Molisch to refer to the detrimental effects on one plant due to metabolites released by another.

Walnut (Juglans regia) tree known for its allelopathic properties. Taken and edited from: Franz Eugen Köhler, Köhler's Medizinal-Pflanzen.

This phenomenon is widely used in agroecological crops to prevent, inhibit or stimulate the growth of other organisms. In this way, the use of artificial chemicals is reduced or completely eradicated.

History

Naturalists and scientists have known for several centuries that some plants could affect or favor the development of others, although they did not know the exact nature of these interactions.

In Ancient Greece Theophrastus (285 BC) and later Pliny recognized the existence of substances or attributes that caused interferences between plants. The latter attributed to the aromas and juices of some plants harmful properties for others. For example, radish and bay leaf affect the growth of the vine.

Pliny also assumed that the shade of other plants, such as pine and walnut, had the same properties. In the Middle Ages, in his Garden of Cyrus Bowne (1658) he suggested that "the good and bad smells of vegetables promote or weaken each other", highlighting the fact that the effect can be both harmful and beneficial.

The first to suggest that plants produced chemical compounds that were involved in interactions with other plants was the Swiss botanist Alphonse Louis Pierre Pyrame de Candolle in 1832. While the first evidence for allelopathic agents was found by Schneider and colleagues during the first decade 20th century.

Schneider's team found chemicals of unknown origin in depleted growing soils. These products had deleterious effects on many crop species.

Molish, for his part, was the first to use the term allelopathy to refer to the effects of chemicals produced by one plant on another plant. These chemicals are called allelopathic products or agents.

characteristics

Allelopathy is a biological phenomenon that involves two organisms, the emitter of the allelopathic agent and the one affected by it. It can occur between organisms of two different species or of the same species, in which case it is called autoalelopathy.

Allelopathic species are primarily plants, although fungi, protists, bacteria, and some invertebrates such as corals and sponges can produce allelopathic agents.

Allelopathic substances are metabolites that can be released by different means when the offending species feels threatened or has suffered some type of injury. These biochemical compounds have effects on the growth, survival, or reproduction of other organisms.

Cup coral (Tubastrea coccínea). This coral produces allelopathic agents that inhibit the growth of other organisms including other coral species. Taken and edited from: Nhobgood Nick Hobgood.

Types

Positive allelopathy

The product released by the allelopathic species directly or indirectly favors the other organism involved in the relationship. For example, when nettle grows close to peppermint, it causes an increase in the production of essential oils of the latter, but the allelopathic agent involved in the relationship is not yet known.

Negative allelopathy

In this, one species is negatively affected by metabolites released by the other species. For example, tomato, alfalfa, and many other species are affected by juglona, ​​an allelopathic agent produced by walnut.

Recently, the cause of some diseases that corals suffer have been attributed to an increase in the natural chemical activity of allelopathic agents released by marine macroalgae, due to the increase in the acidity levels of the oceans due to pollution.

Chemical nature of allelopathic agents

The secondary metabolites that have been identified as allelopathic agents in plants are quite diverse in chemical nature. Some of the groups identified include the following.

Aliphatic compounds

Among these compounds are acids such as acetic or succinic, as well as alcohols, among these are methanol, ethanol and butanol. These compounds inhibit the germination and growth of plants.

Unsaturated lactones

They have a strong plant growth inhibitory activity. Among these types of substances is protoanemonin, which is produced by different species of ranunculaceae. However, its use in nature as an allelopathic agent has not yet been proven.

Lipids and fatty acids

Various fatty acids, such as linoleic, palmitic and lauric, have plant growth inhibitory activity. Its role in allelopathy is unknown.

Terpenoids

Among these, monoterpenes are the main components of the essential oils of vegetables. Researchers have verified the allelopathic effect of monoterpenes from various plants, such as those of the genus Pinus and Eucalyptus, against weeds and crop plants.

Cyanogenic glycosides

Some of these compounds show allelopathic activity by inhibiting germination and / or growth, such as amygdalin and prunasin.

Aromatic compounds

They represent the most diverse group of allelopathic agents. These include phenols, benzoic and cinnamic acids and their derivatives, quinones, coumarins, flavonoids, and tannins.

Alkaloids

Compounds like cocaine, caffeine, quinine, and strychnine have germination-inhibiting effects. Other alkaloids can inhibit plant growth, and even be lethal, such as caffeine, which can eliminate various species of herbs without affecting some cultivated species.

Photograph of the soil where Casuarina litter trees grow, it can be seen how these trees inhibit the growth of other plants around them (allelopathy). Taken and edited from: Eric Guinther at English Wikipedia..

Applications

For many years, farmers have employed plants that produce allelopathic agents for their power to control or repel worms, insects, or microorganisms, as well as other unwanted plants.

In this order of ideas, such plants can be used as companions, repellants and even to attract some pests to them, thus distancing them from others.

Companion plants

It is based on the principle of positive allelopathy. In this case, the companion plant improves the yield or quality of its peer's products. It may also be that both species are of interest. For example, the onion improves its performance when it is accompanied in cultivation by tomato, beet or carrot.

Repellent plants

Aromatic plants generally produce metabolites that keep insects and other pests away. In agriculture this phenomenon is used by sowing aromatic plants with other crops to use them as a natural repellent. For example, oregano serves as a repellent agent for ants, flies, and aphids.

Trap plants

Contrary to the previous case, there are plants that are especially attractive to insects and other pests. Farmers use these species as decoys to attract such invaders away from other plants.

Once the pests are concentrated in the decoy plant they are easier to eradicate. Rue, for example, is highly attractive to flies and moths.

Other uses involve obtaining botanical extracts containing the allelopathic agents for use as natural insecticides. The methods and techniques to obtain these extracts are very diverse and can vary from simple maceration and decoction to more elaborate processes such as extraction by soxlet or percolation.

Some of these allelopathic agents are even obtained industrially and exploited commercially, but nevertheless they can present adverse effects similar to traditional commercial herbicides.

References

1. Allelopathy. On Wikipedia. Recovered from en.wikipedia.org.
2. J. Friedman & GR Walker (1985). Allelopathy and autotoxicity. Trends in Biochemical Sciences.
3. DA Sampietro (nd). Allelopathy: Concept, characteristics, study methodology and importance. Recovered from biologia.edu.ar.
4. MJ Roger, MJ Reigosa, N. Pedrol & L. González (2006), Allelopathy: a physiological process with ecological implications, Springer.
5. C. Cárdenas (2014). Allelopathic plants. University of the Armed Forces, Ecuador.
6. Allelopathy, ecological pest control. Recovered from horticultor.es.
7. C. Del Mónaco, ME Hay, P. Gartrell, PJ Murphy & G. Díaz-Pulido (2017). Effects of ocean acidification on the potency of macroalgal allelopathy to a common coral. Scientific Reports. Nature.