Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2005
Publication Date: 1/1/2006
Citation: Mahan, J.R., Light, G., Dawson, K., Dotray, P. 2006. Thermal dependence of bioengineered glufosinate tolerance in cotton. Weed Science. 54:1-5. Interpretive Summary: Weeds compete with crop plants for water, nutrients and sunlight and as a result the presence of weeds in a crop results in reduced yield and/or quality. Agricultural producers invest significant resources to control weeds. The use of crops that are resistant to herbicides allows the producer to apply the herbicide to both the weed and the crop. When the herbicide is applied to the crop there is the potential for damage to the crop if the resistance mechanism is not fully effective. It is known that environmental temperature can alter the ability of a herbicide to kill a plant by changing the interaction between the herbicide and the plant enzyme that is its target. Herbicide resistance can be produced in a crop plant by introducing an enzyme that degrades the herbicide into an inactive form before it can harm the plant. This degradation of the herbicide will be affected by temperature and it is possible that under certain conditions the herbicide could damage the crop itself. Damage to the crop would be very costly to the producer. In this laboratory we have previously shown that knowledge of the thermal dependence of herbicide function can be used to develop recommendations for producers on how to optimize herbicide effectiveness. In this study the thermal dependence of the herbicide Liberty was determined in normal and herbicide resistant cotton. It was determined that a naturally occurring kinetic tolerance and the introduced resistance to Liberty were affected by temperature in such a way that is can be concluded that Liberty resistant cotton will not be damaged by the herbicide across a range of temperatures typical for environments in which cotton is commonly grown. While similar information can be obtained with field studies of herbicide applications under a variety of environmental conditions over the course of several growing seasons, the approach used in this study can produce similar information in a matter of weeks. This time saving may prove useful in the development of herbicide resistance crops in the future.
Technical Abstract: Herbicidal weed control is an integral part of modern agricultural production, and applications must be efficacious regardless of the environmental conditions. The thermal dependence of enzymatic herbicidal action can limit their efficacy in some thermal environments and can be used to explain and predict tolerance under specific conditions. Additionally, availability of herbicide resistant crops has provided producers with a wider range of options for weed control within a crop. In this study, the effect of temperature on the resistance of cotton to the herbicide glufosinate was determined in both glufosinate-resistant cotton and a non-transgenic, glufosinate sensitive variety. The thermal dependence of the introduced glufosinate resistance, assessed with respect to the apparent KM of phosphinothricin acetyl transferase, was predicted to be optimal between 15 C and 40 C. The I50 of glufosinate for glutamine synthetase varied with temperature, and reduced efficacy was predicted at temperatures <25 C and >35 C. The combined effects of the I50-based kinetic tolerance and the introduced glufosinate resistance produce an aggregate tolerance to glufosinate in cotton that would be expected to function well over the temperature range experienced by cotton on the Southern High Plains of Texas. This laboratory approach to the characterization of the effects of temperature on herbicide tolerance may prove useful in the future development of herbicide resistant crops.