Can weeds become resistant through gene flow from the herbicide tolerant crop to the weed?
To date all instances of weeds becoming resistant have resulted from the weed evolving its own biochemical mechanism and not by acquiring genes for resistance from the crop. Nonetheless, in certain circumstances it would be possible for herbicide resistance genes to flow from the crop to weeds. The most important variable affecting gene flow is the degree of relatedness between the crop and the weed, because gene flow is only possible if close relatives are growing near the crop. As a result the possibility of gene flow depends first and foremost on the presence of wild, weedy relatives. For example, gene flow from maize to wild relatives is only possible in certain areas of Central America. The occurrence of gene flow does not constitute an ecological or economic problem in and of itself. Additional factors play essential roles in determining the impact of gene flow. For a complete discussion of this issue, please see the Science Knowledge Topic, Gene Flow from Crops to Wild Relatives
