The term allelopathy, literally meaning mutual harm, refers to the positive or negative influences of one plant with or without microbial action upon anotherthroughchemicalmeans other than nutritional. Allelopathy depends on chemical compounds mainly added to the environment from living plants or dead and decaying parts(Tang 1986). Thenumber and diversityofthe compounds involved in allelopathy are growing
rapidly. These chemicals may be produced by various parts of the plant such as roots and leaves (Horseley 1977), pollen (Ortega et al. 1988), seeds or fruits (Friedman et al. 1982), although roots and leaves are the main sources (Horseley 1977). Autotoxicity is apparently a negative feature of allelochemical production avoided by some species through excreting or sequestering of chemicals involved in structures. The
allelochemicals can be classified based on the nature of producers, systematics of donor and receiver, inhibitory and stimulatory activity or
upon the self or alien origin. During the last few years effortshave beenmade to exploitallelopathy for weed management, pest management,
comparison and rational cropping, agroforestry and other.