Plant Allelopathy in Response to Biotic and Abiotic Factors

The allelopathy definition accepted by the International Allelopathy Society is any process or phenomenon via which organisms such as plants, microorganism, viruses, and fungi release specific metabolites, known as allelochemicals, into the environment that affect the growth and development of other surrounding plants, resulting in mutual inhibition or promotion of the organisms. Allelopathy in donor plants is either self-induced or induced by specific external biotic and abiotic factors. The external factors may determine the types and quantities of allelochemicals released into the environment by a donor plants. Biotic factors inducing allelopathy include plant competition, herbivory by animals and insects, and soil-borne pathogens. For example, competing plants produce allelochemicals in response to competing weeds. Plants may emit signaling chemicals from their roots to induce the production of protective metabolites against organisms, herbivores, or competitors. Additionally, herbivory is a selection pressure that triggers defensive measures in plants, such as the synthesis of allelochemicals in response to injury. Moreover, some leaves release volatile substances that help the plant to deter or attract herbivores or pests that attack leaves. Likewise, root compounds may be produced in response to soil-borne pathogens. Furthermore, some abiotic factors, including light, temperature, drought, CO2, and nutrient deficiency, can also induce plants to release allelochemicals. Therefore, it is pertinent to understand this natural phenomenon in plants and how external factors lead plants to exert allelopathy to compete, defend themselves, and survive in a challenging environment.