Weed Resistance to Herbicides in Mexico: A Review

Herbicide resistance in weeds has become a critical challenge in worldwide and Mexican agriculture. Many of these cases involve single, cross and multiple resistance to herbicides that inhibit Acetyl CoA Carboxylase (ACCase), Acetolactate Synthase (ALS), Hydroxyphenyl Pyruvate Dioxygenase (HPPD), and Enolpyruvyl Shikimate Phosphate Synthase (EPSPS) enzymes, as well as auxin mimic herbicides. Documented resistance mechanisms include both target-site resistance (TSR) mutations and various forms of non-target-site resistance (NTSR). In wheat and barley, biotypes with resistance to ACCase, ALS, EPSPS and auxins have been confirmed. Maize–sorghum systems show resistance to ACCase, ALS and EPSPS, and in cotton there are glyphosate-resistant populations of Amaranthus palmeri. Citrus orchards remain the focus of glyphosate resistance. Of concern is the advance of multiple resistance in cereals, exemplified by Avena fatua (ACCase + ALS) and Brassica rapa (EPSPS + ALS + auxin mimics). Unique cases, such as EPSPS resistance in Leptochloa virgata and Bidens pilosa and to HPPD in Setaria adhaerens, are unique to Mexico. These resistance patterns underline the need for robust monitoring and detailed study of molecular and physiological mechanisms, where this has not been done, to inform integrated weed management strategies and curb the spread of weeds.