Allelopathy act as a natural herbicide by releasing chemicals which control the weed growth and in this way the nutrients and water up taken by weeds become available to plant and effective for their growth.
Allelopathy is the biological act by which one living body release chemicals and suppress the growth, development, reproduction, and survival of other body. These chemicals termed as allelochemicals which play an important role in sustainability of agriculture also these are environment friendly.
Positive role of allelochemicals provide support and maintenance to crop yield. Allelochemicals belongs to various chemical groups such as; terpenoids, strigolactones, triketones, benzoquinones, flavonoids, terpenes, phenolic acids, coumarins, fatty acids, tannins lignin and non-protein amino acids.
Allelopathy and Allelochemicals
Formerly, the word allelopathy used, people noticed the depressing effect of one plant on other plant. The first definition was made by Molish in 1937 who indicate all direct and indirect effects. The term was sophisticated by Rice to describe any direct and indirect, harm and beneficial effects of chemicals release to environment by one plant on another plant. In 1996 its broad definition refers to a procedure including secondary metabolites made by plants that stimulus the development and growth of plant.
Mechanism of action of Allelopathy
Allelochemicals which are non-nutritious chemicals, are the dynamic media of allelopathy which are produce by plants. Allelochemicals release from different parts of plant body such as rhizomes, roots, leaves and stem. Allelochemicals affect the other plant growth by disturbing their physiological functions such as photosynthesis, water and nutrient balance and respiration. Allelochemicals comprise of many families of chemicals, discus above, they are classified into 10 different groups in accordance with their properties and structure
- Simple lactones
- Water soluble organic acid, straight chain alcohol, ketone and aliphatic aldehydes
- Long chain fatty acid and polyacetylenes
- Quinines (anthraquinones, benzoquinones and complex quinines
- Cinnamic acid & its derivatives
- Steroids and terpenoids (diterphenes, sesquiterpene lactones & triterpenoids)
A natural herbicide for sustainable agriculture
Weeds are antagonist for crops, restrict their development and lessen their growth and functions. 34% crop yield losses are caused by weeds present in main crops. Some Pests and insects also cause harm to crop but the yield losses by weeds are much higher than the losses caused by pest. Sustainable agriculture supervision should be adopted to overcome the crop outcome losses.
There are so many ways by which weeds growth is under control but some of them are dangerous for environment. Allelopathy; as an herbicide does not have environmental hazards. Many studies have explained the signifiicane of allelopathy method in weed control. Rice, ray, wheat, sorghum, sunflower, and rape seed have been reported as important allelopathic crops. These crops express their potential and release chemicals which not even decrease the weeds growth but also grant microbial activities. Allelochemicals are either totally or partially soluble to water that’s why it’s easy to apply. Allelochemicals are more environmental friendly then manmade herbicides. First of all allelochemicals isolated from the plant.
Screeing of allelochemicals for their competitiveness
Purify extract, select the most attractive compound then determine their mode of action. Check their activity, chemical structure and their way to work. The most significant thing before allelochemical use as herbicide the few things should be studied such as; their mode of action in different plants, their chemicals nature, their tie to retain in soil, impact on ecology of soil, adverse effect on other plants, toxicity and profitability. In addition, several kinds of plants can be grown in lines known as intercropping could also reduce weeds growth.
Cropping a normal crop with allelopathic crops is another way to suppress weeding growth. Alternatively, allelochemicals are used for weeding management; the extract taken from the allelopathic plants could be foliar spray as herbicides. It decreases the cost of weed management and improve the crop yield. Best example of bioherbicides are extract of sorghum’s herbage (sorgaab) & rice (sunfaag) both can be used effectively without causing damage to crop yield.
Competition is the main action between two crops or between crop and weeds for nutrients, water and so many other things. Allelopathy is the easy, useful and efficient way to suppress the weeds growth. Legume crops can also be used as allelochemicals for the inhibition of weeds. Cover of dead pea crop also use in controlling weeds. Mugwort is a weed which can be control by alfalfa. By growing alfalfa it inhibit the mugwort growth to 86% in field condition. While it has been observed that by using alfalfa extract it decreased the growth upto 83% in petri dishes analyze. Function of plant extract in pre-emergence as a herbicide can control the amount of herbicide chemicals use.
Though not all the extract (phytotoxin) useful enough to suppress the weed growth and their germination when use as mist even when they use as cover crop or mulch, intercropping system. This inability of bioherbicide is due to the disguise of extract with water and may be due to no penetration through cuticle. Another opportunity for effective use of bioherbicide is to take pure extract of each allelochemical separately and compare with the artificial herbicide.
Though, as mentioed above, not all the ways are cost-effective and appropriate in field condition. To overcome this effect, investigator focused on the single application for specific weed management also isolation. Many isolated allelochemicals, then use for inhabitation of weed-seed germination. These allelopathins suppress the weed growth by lower and higher power.
Effect of changing chemical properties on effectiveness of allelopathin
We can make allelopathin more effective by altering their chemical properties. For example, herein, which is purified allelopathins also act as herbicide. There are so many chemical and biochemical methods which describes their mode of action and by this way we can easily use this application. Though we already known the chemical properties, structure and their mode of action in different plants but unluckily only thousands of them are under use in agriculture.
Synthesis of allelochemicals give triple profit then man made herbicides. Firstly, it help to increase the allelopathic potential of plant and make it strong against weeds, it make the plant extract more active and thirdly it make compound collection at adequate amount make it more effective. Allelochemicals which produce by roots may obtain from hairy roots. Allelochemicals production can improve by different genetic methods on large scale such as recombinant DNA expertise. As like crop production improve by different breeding methods allelopathic plants can also improve to increase the potential.
All above mention ways give adequate awareness about allelopathy. In spite of this, by knowing the complicated relation among these different phenomenon able to move one step onward for the expansion of novel strategies for weed control and management.
In advance biological sciences, the phenomenon of interaction between plants and allelopathy is strongly expanding. All elochemicals also known as bio communicators, seem to be productive task for associated traditional agriculture system and novel methodology in pest control management approaches. Allelochemicals used to protect crop against insects, pathogens, nematodes and use to control weeds. Other agricultural occupation includes cover crops, living and dead plant mulches and crop rotation. In both agriculture and natural environment, the interaction of allelopathy, include plant growth also play role in suppressant. The earliest knowledge about toxic features of liquid extract of allelopathic plants provide us base to production of new way to weed control.
Allelochemicals specifically act as the beginning point for novel herbicides but recognizing their mode of action is still rising. Till recently, more studies on phytotoxicity organized in laboratory conditions due to capability to eradicate environmental factors as temperature, physical and chemicals properties of soil, soil texture, which elaborate their direct effects. Still there is need of applying laboratory data in fields. New way adopted to make it effective to cope the problems of weeds.