Researchers developed DNA-based detection of herbicide resistance

Researchers in Dijon have developed DNA-based assays that can detect the onset of herbicide resistance in weed populations at a very early stage. This type of tool facilitates the managed use of herbicides and their inclusion in a diversified range of cultivation practices.

Herbicides are one of the keys to the intensification of farming that has guaranteed a degree of food security in Europe. Their use has nonetheless led to a reduction in the biodiversity of agricultural ecosystems by contributing to the elimination of the most herbicide-sensitive species, and resulted in the presence of residues in the environment. The need for substantial changes in cultivation practices was therefore acknowledged during the Grenelle de lEnvironnement (Environment Round Table). One of the major measures envisaged is a 50% reduction in the use of plant protection products by 2018 (Ecophyto 2018 Plan). In addition, the European Directive 91/414/EC led to the withdrawal of numerous active ingredients. As a result, the range of herbicide solutions available to growers is expected to become increasingly restricted. One consequence could be an increase in the proportion of herbicides combining excellent efficacy, a low dosage and a broad spectrum of action in herbicide-spraying programmes. The agents currently available that meet these criteria are mainly acetolactate-synthase (ALS) inhibitors, and especially sulfonylureas. However, the frequent application of herbicides with a limited number of modes of action to control weeds is doomed to favour the development of herbicide resistance.

Acetolactate-synthase (ALS) inhibitors are one of the herbicide families most widely employed at present. An ability to rapidly detect the presence of weed plants resistant to these herbicides will contribute to maintaining their efficacy. Most cases of resistance to ALS inhibitors are due to mutations in the ALS gene. Molecular assays have been developed for the major grass weeds of wheat, black-grass (Alopecurus myosuroides) and ryegrasses (Lolium spp.). Within 48 hours of samples arriving in the laboratory, these assays can detect any mutation in the ALS gene that is known to endow resistance. These tests were used to analyse samples of black-grass and ryegrass from fields where ALS inhibitor applications failed to control these weeds. They revealed the presence of ALS mutations at high frequencies in nine of the 22 samples analysed. ALS-related resistance appeared to be able to evolve rapidly in certain cases, especially when the weed control programme was mainly based on ALS inhibitors targeting grass weeds. These findings highlight the need for the reasoned use of these compounds and their inclusion in a diversified system of cultivation practices.