Allelopathy: Principles, procedures, processes, and promises for biological control

Allelopathy can be defined as chemical interactions between and among both plants and microorganisms via releases of biologically active chemical compounds into the environment. During the past three decades this scientific field has received growing attention from soil scientists, microbiologists, ecologists, plant physiologists, biochemists, botanists, weed scientists, agronomists, and natural product chemists. Although a few studies are acknowledged to have demonstrated probable allelopathy in nature, many appeared limited to in vitro circumstances. This difficulty reflects the complexity of allelopathic interactions. Allelopathic effects are often modified by additional biotic and abiotic stress factors, uncertain meteorological events, or physical, chemical, and biological soil factors, all of which can influence the residence time, persistence, concentration, and fate of allelopathic compounds in the environment. Special emphasis is given to an overview of the allelopathic activities of weed and crop species, especially via crop residues in the agroecosystem, and to consideration of the biotic and abiotic factors which influence the expression of Allelopathy A brief discussion of secondary metabolites with allelopathic activities and of the mechanisms of action of allelopathic compounds is also provided. The allelopathic potential of certain weed and crop species can influence the growth and distribution of associated weed species and the yield of desired plants, and allelopathy has been employed successfully in biocontrol programs focusing on control of problematic weeds and plant diseases. Thus, it plays an important role in an agroecosystem and it is clear that a better understanding of allelopathy can help both in crop improvement and in developing more sustainable agriculture. © 1999 Academic Press Inc.