Resistance to acetyl‐CoA carboxylase (ACCase)‐inhibiting herbicides in Lolium multiflorumLam. populations of Argentina

Abstract BACKGROUND Italian ryegrass ( Lolium multiflorum Lam.) is one of the most troublesome grass weeds in Argentina. The extensive and repetitive use of acetyl‐CoA carboxylase (ACCase)‐inhibiting herbicides has induced resistance in this weed species. The objectives of this study were to quantify the resistance levels to ACCase‐inhibiting herbicides in two resistant populations and to identify the target‐site mutations associated with their resistance. RESULTS Two resistant Italian ryegrass populations, Roldán and H2, were studied. Roldán was a suspected haloxyfop‐resistant population, located in a wheat field from Santa Fe province with a history of ACCase‐inhibiting herbicide use. The H2 population was obtained from the susceptible Hernandarias population (H0) after two cycles of selection with the herbicide quizalofop‐ethyl. Whole‐plant dose–response assays revealed that the resistant populations exhibited a high resistance to haloxyfop, with resistance factors (RF) exceeding 97‐fold. Additionally, both populations showed a moderate resistance to pinoxaden (RF > 7), while maintaining susceptibility to clethodim. Partial chloroplastic ACCase sequences revealed isoleucine‐to‐asparagine substitution at position 2041 (Ile‐2041‐Asn) in both resistant populations. CONCLUSION This work provides a better understanding of cross‐resistance to ACCase‐inhibiting herbicides in L. multiflorum populations and represents the first report of the target‐site mutation Ile‐2041‐Asn conferring resistance in populations from Argentina. © 2024 Society of Chemical Industry.