Mechanisms of Cross-Resistance to Multiple Herbicide Modes of Action in Amaranthus tuberculatus Populations

Abstract

Mechanisms of cross-resistance to multiple herbicide modes of action in Amaranthus tuberculatus populations were investigated to understand the evolutionary and biochemical basis of herbicide resistance in agronomic systems. Field populations exhibiting poor control under repeated herbicide applications were collected from intensive cropping regions, and resistance screening was conducted using representative herbicides from different mode-of-action groups. Results confirmed the presence of cross-resistant biotypes exhibiting survival across multiple herbicide classes, indicating complex resistance mechanisms. Physiological and biochemical assays suggested that enhanced metabolic detoxification, particularly increased activity of cytochrome P450 monooxygenases and glutathione S-transferases, played a central role in non-target-site resistance. Target-site mutations were also detected in certain populations, contributing to reduced herbicide binding efficiency and increased survival. Cross-resistance patterns varied among populations, reflecting independent evolutionary pathways driven by selection pressure from diverse herbicide regimes. Fitness assessments indicated that resistant biotypes maintained competitive growth under field conditions, facilitating persistence and spread in agricultural landscapes. The study highlights the synergistic interaction between target-site and non-target-site resistance mechanisms in shaping multi-herbicide resistance. These findings emphasize the urgent need for integrated weed management strategies combining herbicide rotation, diversified cultural practices, and non-chemical control measures to mitigate the spread of cross-resistant A. tuberculatus populations and sustain long-term weed control efficacy.