Question

Allelopathy is caused by the release of
(a) Poison
(b) Toxin
(c) Pheromone
(d) Chemicals

Answer 1

Hint: Allelopathy is the process by which plant growth is prevented by other species by the release of certain secondary bio-active metabolites or allelochemicals that function as poisonous substances in the plant.

Complete answer:
A toxin is a poison in cells or organisms that are formed in life. Allelopathy is a popular biological phenomenon in which an organism produces biochemicals that affect other organisms' growing, living, developing and reproducing. These biochemicals have beneficial and damaging effects on target organisms. These are called allelochemicals. Allelopathy is caused by the release of Toxin.

Additional Information: Biotic factors such as available nutrients and abiotic factors such as temperature and pH influence the production of allelochemicals.
Allelopathy is typical of various plants, algae, bacteria, coral, and fungus. Allelopathic interactions are an important factor in deciding the distribution, abundance, and success of many invasive plant populations. Potential use in farming of allelopathy. The possibility to use allelochemicals to encourage sustainable farming as growth regulators and natural herbicides. Many invasive plant species interfere through allelopathy with native plant species. Allelopathy is of vital importance for forests and to affect the composition of plant growth and also clarify trends for forestry recovery.
So, the answer is, “Toxin.”

Note: -Small molecules, peptides, or proteins that can lead to the disease on body contact or absorption, such as enzymes or cell-cell receptors, can be toxins that can interfere with the biological macromolecules. Toxins range from generally minor to virtually instantly lethal (such as botulinum toxin), and differ dramatically in their toxicity.
-Allelochemicals constitute subsets of secondary metabolites that are not essential for the allelopathic organism's metabolism (i.e., growth, development, and propagation). A significant aspect of herbivorous plant safety is allelochemicals with negative allelopathic effects.