Evolution of Glyphosate-Resistant Crop Technology

New and improved glyphosate-resistant (GR) crops continue to be rapidly developed. These crops confer greater crop safety to multiple glyphosate applications, higher rates, and wider application timings. Many of these crops will also have glyphosate resistance stacked with traits that confer resistance to herbicides with other modes of actions to expand the utility of existing herbicides and to increase the number of mixture options that can delay the evolution of GR weeds. Some breeding stacks of herbicide resistance traits are currently available, but the trend in the future will be to combine resistance genes in molecular stacks. The first example of such a molecular stack has a new metabolically based mechanism to inactivate glyphosate combined with an active site-based resistance for herbicides that inhibit acetolactate synthase (ALS). This stack confers resistance to glyphosate and all five classes of ALS-inhibiting herbicides. Other molecular stacks will include glyphosate resistance with resistance to auxin herbicides and herbicides that inhibit acetyl coenzyme A carboxylase (ACCase) and 4-hydroxyphenyl pyruvate dioxygenase (HPPD). Scientists are also studying a number of other herbicide resistance transgenes. Some of these new transgenes will be used to make new multiple herbicide-resistant crops that offer growers more herbicide options to meet their changing weed management needs and to help sustain the efficacy of glyphosate.