Allelopathy

Allelopathy : It is a biological phenomenon by which an organism produces one or more biochemical compounds that influence the growth, survival or reproduction of other organisms. These compounds are known as chemical alleles and can lead to beneficial effects (positive allelopathy) or harmful effects (negative allelopathy) to recipient organisms. It was first used by Molisch (1937) to refer to the harmful or beneficial effects that are directly or indirectly the result of the action of chemical compounds that, released by one plant, exert their action on another.

Summary

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• 1 General
• 2 Types of Allelopathic control
  • 1 Accompanying plants
  • 2 Repellent plants
  • 3 Trap crops
• 3 Chemical nature of allelopathic agents
• 4 Biosynthesis of allelopathic agents
• 5 Mode of release of allelopathic agents
• 6 Sources

General

Allelopathy is a phenomenon that involves the direct inhibition of one species by another, be it plant or animal, using toxic or dissuasive substances. Organic farming makes good use of all this to protect crops from the attack of some insects- pests through the intercalation of aromatic plants within the crop. For example, by interspersing rue in potato crops. The allelopathic effect of a plant on another organism is not total for better or for worse, but is governed by manifestations of greater or lesser degree depending on the characteristics of the organisms involved. However, the potential of natural products that can be used for their particular biological properties as herbicides, pesticides, antibiotics, inhibitors or growth stimulants. These natural products has multiple effects as noted in the definition, effects from inhibition or stimulation of growth processes of neighboring plants, to the inhibition of germination of seeds, or they avoid the action of insects and leaf-eating animals, as well as the harmful effects of bacteria, fungi and viruses. Thus, natural products make up a very important part of plant defense systems with the advantage of being biodegradable.

Allelopathic control types

Organic control with plants has been used for a long time and its operation is based on repelling and attracting insects, worms and disease vector agents. The plants used for these purposes are vegetables , herbs, medicinal plants and the so-called “weeds”. In the association of crops by allelopathic principles, the types of control that are frequently used in allelopathy are made with companion plants, with repellent plants or with trap crops.

Accompanying plants

Plants called companions or related provide mutual benefit with other plants. This positive association can influence from seed germination, plant growth and development, to the final flavor and aroma of the vegetables obtained. For example, stinging nettle close to aromatic plants increases its aromatic quality. Companion plants should be planted alongside the rest of the crop so that the fumes are absorbed from one plant to another.

Repellent plants

Repellent plants are plants with a strong aroma that serve to keep insects away from the main crop. There are some that repel a specific insect and others can protect from different pests. They can be planted between crops, protecting specific plants, or bordering the garden as a protective barrier, covering their effect in an area that can be as much as 10 meters away.

Trap crops

Trap crops are plants chosen to attract harmful insects away from the main crop. Said plants are planted on the perimeter of the crop to be protected by removing harmful insects from it, or, interspersed among the rest, the plants to concentrate the pests and catch and eliminate them. Another way to use trap plants is to help reproduce parasites or predators of pests that attack the garden.

Chemical nature of allelopathic agents

Allelopathic agents are secondary metabolites and the known compounds were isolated from plants and soil. The chemical nature of allelopathic agents is highly varied. As research on the subject progresses, new groups of substances are added to which this biological activity was not attributed. Normally the specialized literature orders them into the following groups: 1. Aliphatic compounds: 2. Unsaturated lactones: 3. Lipids and fatty acids: 4. Terpenoids: 5. Cyanogenic glycosides: 6. Aromatic compounds:

Biosynthesis of allelopathic agents

Most allelopathic agents are secondary metabolites derived from the acetate-mevalonate or shikimic acid pathways. They come from the metabolic pathway of acetate-mevalonate terpenes, steroids, water-soluble organic acids, straight-chain alcohols, aliphatic aldehydes, ketones, simple unsaturated fatty acids, long-chain fatty acids, polyacetylenes, naphthoquinones, anthroquinones, complex quinones, and floroglucinol. . Simple phenols, benzoic acid and its derivatives, cinnamic acid and its derivatives, coumarins, sulfides, glycosides, alkaloids, cyanhydrins, some of the derivatives of quinones and hydrolyzable and condensed tannins, come from the metabolic pathway of the shikimic. There are also compounds (eg flavonoids) in whose synthesis metabolites of the two pathways participate. As expected, Tissue concentrations of these compounds vary according to the rate of biosynthesis, storage, and degradation. They are also affected by the internal balances of plant growth regulators and other biotic and abiotic factors. It is important to keep in mind that the details of the biosynthesis of these compounds are not always known.

Allelopathic agent release mode

A variety of allelopathic agents are synthesized and stored in different plant cells either in free form or conjugated to other molecules and are released into the environment in response to different biotic and abiotic stresses. In any case, it can be said that the mode of release of an allelopathic agent depends on its chemical nature. Higher plants regularly release organic compounds by volatilizing their surfaces and through leaf leachate and root exudates. Eventually, the chemical constituents of all organisms are released into the environment through decomposition processes, incorporating into the soil matrix. Therefore there are 4 main routes of release into the allelochemical environment 1. Volatilization 2. Leaching 3. Root exudates 4.