Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 16, 2003
Publication Date: February 1, 2004
Citation: Mahan, J.R., Dotnay, P.A., Light, G.G. 2004. Thermal dependence of enzyme function and inhibition; implications for, herbicide efficacy and tolerance. Physiologia Plantarum. 120(2): 187-195. Interpretive Summary: The presence of weeds in agricultural fields reduces crop yields and as a result producers incur significant dollar costs to eliminate and/or control them with herbicides. Of the many factors that affect the ability of a herbicide to control weeds, environmental conditions before, during, and after herbicide use are most difficult to control. Temperature is known to affect herbicide effectiveness and its affects on herbicides have been well described. Recently a novel effect of temperature on herbicide function was identified and methods for determining its importance were described. Recent efforts to create herbicide resistant crop plants have been successful though the effects of temperature on the resistance mechanisms have yet to be considered. Failure to understand the role of temperature could result in reduced effectiveness of the herbicide and in extreme cases, herbicide damage to the crop itself. In this paper we describe the theoretical basis for temperature effects on bioengineered herbicide resistance in a crop plant and herbicide effectiveness in a crop and a weed. The relationship between resistance and effectiveness and temperature will ultimately determine the usefulness of a crop with engineered herbicide resistance. This information will be used by a producer to determine the most optimal temperatures for herbicide application. The insights discussed in this paper will provide the basis for studies of the effect of environmental temperature on various weed, crop, and herbicide combinations. A more complete understanding of temperature limitations on herbicides will increase the efficiency of their use, reduce production inputs and reduce the need for repeated herbicide applications.
Technical Abstract: Most crops experience periods of thermal stress related to seasonal patterns of temperature and periodic water deficits. These stresses affect many plant processes and often result in decreased crop productivity. Because losses in crop productivity related to weed populations can be substantial, significant costs are often incurred for weed control by the application of herbicides. Herbicide applications that fail to control weeds result in increased costs to the producer, unnecessary introduction of chemicals into the environment and failure to alleviate the negative effects of weeds on the crop. An improved understanding of the role of environmental temperature on the efficacy of herbicides will help to optimize herbicide function in crops subjected to variable thermal environments. Several sources of temperature limitations on herbicide function are well documented and have been accounted for in the formulations and application procedures of many herbicides. Recently the effect of temperature on the inhibition of enzymes by herbicides has been proposed as another source of thermal limitations on herbicide efficacy. The development of herbicide tolerant crops through the introduction of novel enzymes and/or the modification of enzymes already present in the plant presents the possibility that thermal limitations on tolerance and efficacy could effect the utility of such plants in environments characterized by extreme thermal variation. Sources of such limitations and methods for their analysis are described.