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RESEARCH PRODUCT

How ALS-inhibitor herbicide-resistant cultivars impact on weed resistance occurrence and management ?

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As soon as herbicides inhibiting the acetolactate synthase (ALS, or AHAS) were commercially released, research on herbicide-resistance genes was launched by industry and resulted before the end of the 80s in a wide diversity of resistant crop germplasms. Herbicide-resistant material was obtained by all diverse kinds of breeding techniques, but mainly mutants were used as commercial cultivars. According to the mutation place along the herbicide-binding domain corresponding DNA sequence, resistance is conferred to sulfonylureas (SU) or imidazolinones (IMI), and in some instances to both with various degrees of efficiency. These herbicides are used against a large panel of annual and perennial weeds, di and monocotyledons, although pre- or post-emergence can affect their efficiency. Their repeated use already conducted to the appearance and spread of more than one hundred resistant weeds species in cereals, maize, soybean and orchards. The release of SU and IMI herbicide-resistant cultivars in other crops such as oilseed rape and sunflower would make the herbicide selection pressure continuous all along the crop rotation, thus certainly accelerating the occurrence of herbicide-resistant weeds. In addition, volunteers of oilseed rape and weedy sunflower would have resistance to the SU and IMI herbicides used in cereals and other crops of the rotation, which would make impossible to control these plants by these herbicides, thus causing yield losses and harvest troubles. However, these cultivars could help using ALS inhibitors to better control some damaging weeds poorly controlled with the usual selective herbicides, and to design appropriate strategies to prevent or to contain the spread of herbicide-resistant weeds (e.g. the simultaneous use of several products with different modes of action and mechanical control). The specific case of Ambrosia sp. deserves to be carefully examined.