Allelopathy refers to all the biochemical interactions among plants, or between plants and microorganisms.

The origin of the word comes from the Greek allelo (“of each other’’ or ‘’mutual”) and pathos (“suffering”). Thus the etymology of the word implies that these interactions are negative and gather competition for resources or defence mechanisms. The current understanding of allelopathy also includes positive interactions, such as cooperative phenomena or microorganism stimulation. These interactions are done by allelochemical compounds, released by the plant into its environment. Most often, these compounds are secondary metabolites and belong to a wide variety of biochemical families. They can be released by the roots (exudation), the aerial parts (leaching, volatilization) or residue decomposition of dead plants.

Allelopathy has been known for over 2000 years. Observed in forest systems, especially through games of dominance and succession of tree species, it has been given a name and defined in the 1930s. Before long it was found that interactions also existed throughout the plant world, and especially in many cultivated plants, hence the current research on allelopathy in agriculture.

Nowadays, allelopathy is mainly recognized for its interest in weed management (inhibitory effect on the germination and growth of weeds). It is used in crop rotations, intercropping with cover crops, mulching or through bio herbicides.

With a view to an agroecological crop management approach, allelopathy is particularly interesting because it allows  weeding control, and might also play a role in the fight against pests and phytopathogenic agents (practice of biofumigation).