Synthetic auxin herbicides were developed and commercialized 60 yr before their mode of action was definitively elucidated. Although evolution of resistance to auxinic herbicides proceeded more slowly than for some other herbicide chemistries, it has become a major problem in the dicotyledonous weeds of many cropping areas of the world. With the molecular characterization of the auxin perception and signaling pathway in the mid-2000s came a greater understanding of how auxinic herbicides work, and how resistance may develop in weeds subjected to repeated selection with these herbicides. In wild radish (Raphanus raphanistrum L.) populations in southern Australia, resistance to multiple herbicides, including synthetic auxins such as 2,4-D, has reduced the number of chemical control options available. The aim of this study was to determine whether compounds involved in auxin biosynthesis, transport, and signaling are able to synergize with 2,4-D and increase its ability to control 2,4-D–resistant R. raphanistrum populations. Although some mild synergism was observed with a few compounds (abscisic acid, cyclanilide, tryptamine), the response was not large or consistent enough to warrant further study. Similarly, alternative auxinic herbicides applied pre- or postemergence were no more effective than 2,4-D. Therefore, while use of auxinic herbicides continues to increase due to the adoption of transgenic resistant crops, nonchemical control techniques will become more important, and chemical control of 2,4-D–resistant R. raphanistrum should be undertaken with alternative modes of action, using mixtures and good stewardship to delay the development of resistance for as long as possible.

合成植物生长素除草剂的开发和商业化早于 60 年，其作用方式才得到明确阐明。尽管对生长素除草剂的抗性进化比其他一些除草剂化学进展得慢，但它已成为世界许多种植区双子叶杂草的主要问题。随着 2000 年代中期生长素感知和信号通路的分子表征，人们对生长素除草剂的工作原理以及经过这些除草剂反复选择的杂草如何产生抗药性有了更深入的了解。在澳大利亚南部的野生萝卜 ( Raphanus raphanistrum L.) 种群中，对多种除草剂（包括 2,4-D 等合成生长素）的抗性减少了可用化学防治方案的数量。本研究的目的是确定参与生长素生物合成、运输和信号转导的化合物是否能够与 2,4-D 协同作用，并提高其控制 2,4-D 抗性萝卜种群的能力。尽管观察到一些化合物（脱落酸、环酰苯胺、色胺）有一些轻微的协同作用，但其反应不够大或一致，不足以保证进一步研究。同样，芽前或芽后施用的替代生长素除草剂并不比 2,4-D 更有效。因此，虽然由于转基因抗性作物的采用，植物生长素除草剂的使用持续增加，但非化学防治技术将变得更加重要，并且应采用替代作用模式对 2,4-D 抗性萝卜芥进行化学防治，使用混合物和良好的管理来尽可能长时间地延缓耐药性的发展。