Engineering Cotton Resistance to Dicamba and Glufosinate Herbicides

The development of glyphosate resistant weeds has increased the need for additional weed control options for Roundup Ready® crops.  One mechanism for weed resistance management is the use of herbicides with alternative modes of action.  In cotton the choices of effective alternatives is significantly limited and additional options would be beneficial.  Dicamba and glufosinate are herbicides that can provide effective post-emergence weed control to complement Roundup® herbicide in glyphosate resistant cotton.  Dicamba is a synthetic auxin herbicide which provides broad spectrum broadleaf weed control; glufosinate targets the glutamine synthetase enzyme and is considered a non-selective herbicide with activity on essentially all grasses and broadleaf weeds.  Conventional cotton is sensitive to these herbicides however genes are available that confer resistance to these products.  Cotton plants were transformed with two microbial genes encoding for a mono-oxygenase enzyme that deactivates dicamba and a phosphinothricin N-acetyltransferase enzyme that deactivates glufosinate.  Cotton plants expressing these genes withstood high rates of dicamba (1 lb ai/A) and glufosinate (1 lb ai/A) showing little to no visible injury in greenhouse and field trials.  The option of combining glyphosate, dicamba and glufosinate resistant traits would permit late burndown as well as in-crop applications of glyphosate, dicamba and/or glufosinate as additional options for weed control in cotton and would provide strategies for weed resistance management.  Monsanto’s efforts to develop cotton with resistance to both dicamba and glufosinate are in the proof-of-concept stage.