A conceptual framework for assessing allelochemicals in the soil environment

Abstract

There has been a surge of interests in recent years on the phenomenon of allelopathy, the chemical agents involved in allelopathy, and the role of allelopathy in crop production (Chou and Waller, 1983; Rice, 1984; Thompson, 1985; Waller, 1987). Studies have generally concentrated either on the symptoms and severity of the adverse effects on affected plants or on the production and identification of the allelochemicals from producing organisms. Few reports have considered the mechanisms and processes involved in the overall relationship from the production of the allelochemicals to the actual occurrence of allelopathy. To be sure, a number of chemicals have been implicated in allelopathic relationships, the phytotoxic nature of these chemicals has been demonstrated, and these chemicals have been isolated from the surroundings of affected plants. Invariably the relationship has been established by inference rather than by direct evidence showing that the isolated chemicals actually caused the allelopathic effects. As Fisher (1979) remarked: ‘It seems unlikely that the allelochemicals that may be extracted from plant material are actually those that reach the host plant, yet all our information on allelopathic compounds is derived from extracts that have never been exposed to the soil.’