| Abstract/Contents: | "The inhibitory effects of one plant on another, and the diminution of crops repeatedly grown in the same ground, are acient [ancient] observations (3). A scientific basis for these phenomena was proposed as early as 1832 by De Candolle (4) who stated that common crop plants were injured by excretions from plant roots. Unfortunately, this work was generally ignored because of the prevailing dogma that plants only competed for light, nutrients, and water. In the 1960's, well over a century after De Candolle's observations and ideas, McCalla and Haskins (5) found that new crops were inhibited by specific substances which came from decomposing residues of previous crops, thereby substantiating De Candolle's work. In 1937, Molisch (6) introduced the word "allelopathy," which he used to indicate both the detrimental and beneficial interactions between all classes of plants, including microbes. However, "pathy" indicates detrimental action, and allelopathy is now restricted to this usage. There is disagreement as to whether antibiotics should be included under this term. Thus, allelopathy (7) is "the direct or indirect deleterious effect of one plant on another through the production of allelochems." Allelochems include many substances, such as organic acids, lactones, phenolic compounds, quinones, steroids, flavonoids, alkaloids, and various other compounds. These materials are released into the environment by volatilization, leaching, exudation, and by decaying plants. Allelochems act by inhibiting mitosis, respiration, oxidative phosphorylation, photosynthesis, enzymatic acitivity [activity], and the uptake of nutrients. Whereas most of the interest in allelopathy in crops has dealt with cases where weeds produce allelochems which inhibit or reduce crop growth, it is known that some crop plants produce substances which inhibit weeds. For example, field stands of Kentucky-31 fescue (Festuca arundinacea) are often free of weeds; toxic materials have been isolated from fescue roots which in tests inhibit the growth of black mustard and trefoil (8). Additional work on allelopathy in grasses is reported in the literature (for example, see 9, 10, 11, 12, 13). In the future, plant biologists should give serious consideration to breeding crop plants which produce allelochems and thus exert control on target pest populations." |
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