Crops resistant to oxynils: From the laboratory to the market

Herbicide resistance was one of the first traits introduced to crops by transgenic methods. The main reason for this was the fact that it is generally controlled by a single gene and that a large body of biochemical information is available on the mode of action, mechanisms of resistance and metabolism of herbicide molecules. Oxynil herbicides, such as bromoxynil and ioxynil, destroy dicot plants. In order to extend the selectivity of these herbicides to some of the major dicot crops such as cotton and oilseed rape, a gene coding for a nitrilase which specifically detoxifies these herbicides was isolated in collaboration with Calgene (Davis, CA, USA). The coding region of the gene was linked to regulatory DNA sequences for expression in plants and transferred into various dicotyledonous species, such as tobacco, tomato, cotton, oilseed rape, carrot, potato and eggplant. All plants containing the bacterial nitrilase gained resistance to oxynil herbicides. Field experiments have already been conducted with cotton, oilseed rape, tobacco and potato. They show the transgenic cultivars behave identically as the non-transgenic ones and that herbicide resistance at the agronomic level has been achieved. Experiments are in progress for the commercial development of some of these lines.