Herbicide resistance in rice weeds: Mechanistic insights into an evolving threat

Oryza sativa (rice) is an invaluable cereal food crop worldwide. It is cultivated in a wide range of environments and conditions across the globe. Nonetheless, sustainability of rice production systems can be impacted by various biotic and abiotic factors, such as insects, pathogens, and weed infestation. Among these, weed competition is a major challenge as it can lead to significant yield loss in any cropping system, including rice. Herbicides have played a crucial role in controlling a broad spectrum of weeds. Because of their effectiveness, ease of application, and convenience, use of herbicides has been the primary method of weed control by rice growers. However, extensive and/or exclusive use of the same mode of action group of herbicides resulted in evolution of resistance to herbicides in numerous weed accessions in rice globally. Echinochloa crus - galli (barnyardgrass), Cyperus difformis (smallflower umbrella sedge), Limnophila erecta (marshweed), Leptochloa chinensis (Chinese sprangletop), Oryza sativa var. sylvatica (red rice), and Sagittaria montevidensis (California arrowhead) are among the most troublesome weed species with evolved resistance to commonly used herbicides in rice. The purpose of this review is to summarize and provide an overview of resistance mechanisms conferred in herbicide-resistant weed accessions in rice. Knowledge of mechanisms of herbicide resistance is crucial to understand how weeds evolve resistance to herbicides and to develop alternative control strategies. This review also discusses some novel and emerging resistance mechanisms and strategies to delay resistance, extending herbicide effectiveness in rice systems.