Allelopathy and its Role in Agriculture

What is Allelopathy?

It is a sub-domain of chemical ecology that deals with the impact of hazardous chemicals (called allelochemicals or allelochemicals) released by some plants to destroy the plant in their vicinity. These chemicals alter the genetic structure of the neighboring plants in order to cease their growth which is ultimately fatal for them. This phenomenon is common in plants as well as organisms. It can be observed in plant-plant interaction, plant-microbe interaction, and plant-animal interaction as well.

Allelopathic plants can hide their allelochemicals in their flowers, stem, leaves, or even roots. However, leaves are the most favorable places to store the allelochemicals by allelopathic plants. When the leaves fall, these allelochemicals are released to nearby places which are toxic to the other plants. In many cases, the trees exploit allelopathy to defend their territory by using their roots to draw more water from the earth, in order to inhibit the growth of other plants.

Allelopathy was explained in detail by Austrian scientist Hans Molisch back in 1937 in his book whose English translation reads “Effect of plants on each other”.

Allelopathic Effects on the Neighbouring Plant

Why some Plants are Allelopathic and how common is it?

Allelopathic plants release harmful chemicals in order to kill their competitor plants. It is a survival game. In doing so, allelopathic plants win the race to get more space and sunlight as well. Allelopathy is very common around us even more than we think. For example, the sunflower is also an allelopathic plant. After harvesting its crop, farmers need to wait for more than two weeks before going for the second crop in the same field in order to save the second crop from the allelopathic effect of the earlier crop.

Allelopathy in News:

In 2014, it was pointed out by Himachal Pradesh (HP) Forest Department that a deadly weed “Lantana” which is also called “Phool Lakri” in the regional language has drastically affected the forest biodiversity in more than 1800 square kilometers. Lantana was brought to India in 1809 in the Indian Botanic Garden, Kolkata. It has beautiful flowers which enable it to be an ornamental plant. It flowers throughout the year. It spreads easily and exhibits extensive seed production. It poses serious problems to plantation forestry owing to its dominance over other species. It also acts as a potential fire hazard as it is combustible even in its green form. HP witnesses forest fires each summer season which causes great losses to the state and environment.

Pros and Cons of Allelopathy:

In the garden, allelopathy can have a negative impact that halts plant development and seed germination. However, at the same time, allelopathic plants can be thought of as natural weed killers specially designed by nature.

Pros:

• Allelopathic plants can be used to obtain natural herbicides/pesticides
• Being a weed itself, it does not allow the growth of other weeds
• Proper use of allelopathy can result in the reduced use of pesticides/herbicides
• It can be used for intercropping and crop rotation

Cons:

• It is itself a weed and hence is unwanted
• The growth of allelopathic plants is difficult to control
• Allelopathic plants prevent the growth of healthy organisms around them
• In the race of survival, it competes for resources
• If not handled properly, they may turn out into invasive species

 Role of Allelopathy in Irrigated Agriculture:

• Allelopathy is a well-known natural process in ecological systems. Since ancient times, it has been utilized in agriculture.
• Allelochemicals have the potential to aid or prevent plant germination and development, allowing the growth of crops with low phytotoxic residue amounts in water and soil. This way allelopathy enables wastewater treatment and recycling.
• Allelopathic chemicals can be seen as suitable alternatives for non-natural herbicides owing to their non-residual effects. However, despite their promising potential as natural herbicides, they suffer certain issues such as low efficacy and specificity of many allelochemicals.

The Current focus of Research on the Allelopathy in Context of Agriculture:

Majorly, the current research on allelopathy in agriculture revolves around the following points:

• Application of the known allelopathic effects on agricultural production
• Its impact on decreasing the chemical pesticides’ intake
• Contribution of allelopathy to reducing the environmental pollution
• Assessing the advantages and disadvantages of allelopathy on the sustainable development of agricultural production and ecological systems.
• The effective use of the plant allelopathy to increase crop productivity and ecological sustainability through eco-friendly weed suppression, insect pests, and plant diseases, conservation of nitrogen in croplands, and the production of novel agrochemicals based on allelochemicals has drawn significant interest from scientists working on allelopathic research.

Relevance of Allelopathy to the Present Scenario of Agriculture Practices:

A. Reducing the use of pesticides and help in organic farming: Increasing the use of pesticides and insecticides is a big challenge as it is harmful to the crops, ecology, environment, and health. It is evident from the research and other public reports that heavy use of toxic pesticides and insecticides is giving rise to many deadly diseases. Numerous studies have shown a link between pesticide exposure and a higher incidence of chronic diseases like cancer, diabetes, Alzheimer’s disease, and Parkinson’s disease. Amyotrophic lateral sclerosis along with birth defects and reproductive problems are also among the major side effects of pesticides. These issues have been among the main reasons for farmers to turn away from traditional farming and adopt organic farming practices. As in organic farming, regularly used pesticides are avoided, and the natural allelopathy may help farmers to control pests and weeds.

B. Intercropping and crop rotation: As many crops are allelopathic, the knowledge of allelopathy can help the farmers in careful selection for intercropping with the minimal negative effect of one crop on the other. Similarly, it can definitely help in choosing the proper crop rotation cycle and keeping an appropriate time gap within any consecutive crops in order to avoid any bad effect of an earlier crop on the next crop.

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