Dr. Stephen Duke, USDA-ARS Research Leader at Oxford, MS, published an excellent summary on the current status of research on allelopathy and the possible implications for agriculture. His commentary article was published in 2010 in Vol. 25 of the Allelopathy Journal. Below are my summary points taken from this article.

●          Results of past research with allelopathy most often have demonstrated correlative rather than cause and effect relationships.

●          Effects often attributed to allelopathy may actually be a result of competition for resources between/among plants.

●          There is evidence that chemical detection of a competing plant species can trigger the production of an allelochemical.

●          Past research has often shown that many plants produce compounds that, in high enough concentrations, are toxic to other plants in the absence of soil. Such experiments suggest the potential for but do not prove allelopathy in a natural setting.

●          Extrapolation of results from experiments conducted in a lab setting in the absence of soil is virtually impossible.

●          Allelochemicals from living plants and dead plant matter are constantly entering the soil environment and this is almost impossible to measure. Also, these allelochemicals are either absorbed in the water portion of the soil or are adsorbed to soil particles, so the amount of the allelochemical that is available at any one time is difficult to measure or predict.

●          Reputed allelochemicals are often inactivated in a soil environment due to their instability, degradation by soil microbes, or other interactions with soil. Also, those that are water-soluble leach away from the root zone of potential target species.

●          Methods that are being developed can be used to determine if the loss of allelochemicals from the soil due to the above processes is offset by the producing plant’s exuding or secreting more of the allelochemical.

●          Allelochemicals that are steadily produced by a donor plant and released into the soil may not seem too significant, but may become so if this steady release and subsequent accumulation of the allelochemical by the receiving plant is in an amount to cause an adverse reaction. In other words, a steadily produced source of an allelochemical that is toxic to a receiving plant is more important than the static concentration of the toxic allelochemical in the soil at any measurement period.

●          Determining/understanding the mechanisms of allelopathic activity, followed by utilizing that information to manage weeds in agricultural systems, is the challenge that is faced by scientists.

●          Transgenically imparting or enhancing allelopathy in crop species will be a positive step toward utilizing allelopathy in agriculture.

●          Research is needed to ascertain soil microbial involvement in allelopathy; e.g. do soil microbes transform allelochemicals to more or less toxic forms, does exposure of soil microbes to a particular allelochemical over a period of time increase their activity on the allelochemical, do allelochemicals change the soil microbial makeup.

●          Increased interest in allelopathy is fueled by the need to reduce synthetic herbicide use in agriculture, and the desire to find or identify natural products or allelopathic processes to control herbicide-resistant weeds.

●          Using transgenics to produce crop cultivars that have enhanced allelopathic properties is being undertaken, but this area of research is insignificant compared to that of using transgenics to develop herbicide resistance in crop species.

●          In the near future, there is little reason to expect the development of allelochemicals for use as natural herbicides.

In subsequent blogs, I will present results from research on allelopathy or perceived allelopathy that pertain to corn, grain sorghum, and wheat, crops that are often rotated with soybeans in the Midsouth.

Composed by Larry G. Heatherly, Oct. 2012, larryheatherly@bellsouth.net