Global patterns and mechanisms of herbicide-resistance evolution in Conyza species: implications for sustainable weed management

Abstract

The genus Conyza comprises globally important weeds, with horseweed [ Conyza canadensis (L.) Cronquist; syn.: Erigeron canadensis L.], hairy fleabane [ Conyza bonariensis (L.) Cronquist; syn.: Erigeron bonariensis L.], and Sumatran fleabane [ Conyza sumatrensis (Retz.) E. Walker] repeatedly evolving resistance to multiple herbicide modes of action. This review provides an updated comparative synthesis of resistance evolution, resistance profiles, and mechanistic drivers among these three species. The earliest documented resistance cases occurred in both C. canadensis and C. bonariensis around 1980, including resistance to paraquat and photosystem II (PSII) inhibitors. Resistance subsequently expanded to glyphosate and, more recently, to multiple-herbicide resistance. Concerning resistance profiles, comparative analysis reveals species-specific patterns: C. canadensis has the largest number of reported resistance cases; C. bonariensis has evolved resistance to a broad range of herbicide modes of action; and C. sumatrensis exhibits some of the most complex multiple-resistance profiles, with populations resistant to up to five herbicide modes of action. Resistance dissemination has been facilitated by inheritance of resistance traits, gene flow, and, where documented, hybridization. Regarding mechanistic drivers, evolutionary trajectories involve both target-site (TSR) and non–target site resistance (NTSR) mechanisms. TSR typically arises through target-site mutations or increased target-site abundance. In contrast, NTSR is linked to altered herbicide transport, sequestration, and detoxification. ATP-binding cassette (ABC) transporter activity, cytochrome P450 monooxygenases, glutathione S -transferases, glycosyltransferases, and antioxidant enzymes may contribute to reduced herbicide sensitivity in some populations. These adaptations compromise long-term herbicide efficacy and highlight the limitations of herbicide rotation alone. The findings provide a mechanistic framework for predicting future resistance evolution and support integrated weed management strategies that reduce selection pressure and improve the sustainability of weed management.