ACCase inhibitor herbicides – selectivity, weed resistance and fitness cost: a review

The worldwide application of the group of herbicides known as ACCase inhibitors is associated with the widespread appearance of resistant biotypes among weeds. Accordingly, ACCase inhibitor resistance has become the third most frequent type of weed resistance. ACCase (acetyl-coenzyme A carboxylase) inhibitors, which include aryloxyphenoxypropionate, cyclohexanedione and phenylpyrazolin herbicides, are applied postemergence to control weedy grasses. Their phytotoxicity is specifically attributed to the inhibition of lipid biosynthesis, while their selectivity is mainly due to the fact that they are able to block the eukaryote-type ACCase enzyme of Poaceae. Certain herbicides can be applied to cereals, because herbicide "safeners" allow the herbicides to be degraded metabolically. Resistance can evolve through both non-target and target-site processes, and many amino acid substitutions have been identified that result in resistance. Cross-resistance to different herbicides is also relatively common. Nevertheless, in many cases, it has been found that resistant biotypes show no reduction in fitness. Cycloxydim-tolerant maize, without genetic modification, is now used also in European farmland, and it can be a suitable alternative to transgenic herbicide tolerant crops when combined with herbicide rotation and monitoring for resistance.