Multiple resistance of Conyza sumatrensis to three mechanisms of action of herbicides

ABSTRACT. Fleabane (Conyza spp.) is an important weed in grain production systems and is currently one of the most problematic weeds in Brazil. An important factor related to weeds such as fleabane is the characteristic of herbicide-resistant biotypes developed under selection pressure, with multiple resistance previously detected for Conyza spp. Thus, the aim of this study was to demonstrate the multiple resistance of Conyza sumatrensis to the herbicides paraquat, glyphosate, and chlorimuron. From the F2 seeds of biotypes with suspected resistance to paraquat, glyphosate, and chlorimuron, dose-response greenhouse experiments were conducted for the three herbicides. Herbicides were applied when the plants had 6-8 leaves that were at a height of 8 cm. At the end of the evaluations, 28 days after application, multiple resistance to paraquat, glyphosate, and chlorimuron was observed, with resistance factors (RF50) for the control of 7.43, 3.58, and 14.35 and for the reduction of dry mass of 2.65, 2.79, and 11.31, respectively. All the established criteria for demonstrating new cases of weed resistance were met; thus, the first case worldwide of a Conyza species with resistance to herbicides with three different mechanisms of action was confirmed.

摘要。小飞蓬（Fleabane，Conyza spp.）是粮食生产体系中的重要杂草，目前为巴西最具危害性的恶性杂草之一。与该类杂草相关的关键特征之一，是其在除草剂选择压下演化出的抗除草剂生物型特性，此前已有针对白酒草属（Conyza spp.）物种多重抗性的检出报道。本研究旨在验证苏白酒草（Conyza sumatrensis）对百草枯、草甘膦及氯嘧磺隆的多重抗性。实验以疑似对上述三种除草剂产生抗性的生物型的F₂代种子为材料，针对三种除草剂开展了温室剂量反应试验。当植株生长至6-8片叶、株高达到8 cm时喷施除草剂。施药后28天完成评估，结果显示该生物型对三种除草剂均表现出多重抗性：防效对应的抗性系数（RF₅₀）分别为7.43、3.58和14.35，干重抑制对应的抗性系数分别为2.65、2.79和11.31。本研究满足验证杂草抗药性新案例的全部判定标准，由此确认了全球首例白酒草属物种对三种不同作用机制除草剂产生抗性的案例。