Failure to control Palmer amaranth with glyphosate and protoporphyrinogen IX oxidase (PPO)-inhibitor herbicides was reported across southwestern Nebraska in 2017. The objectives of this study were to 1) confirm and 2) validate glyphosate and PPO-inhibitor (fomesafen and lactofen) resistance in 51 Palmer amaranth accessions from southwestern Nebraska using genotypic and whole-plant phenotypic assay correlations and cluster analysis, and 3) determine which agronomic practices might be influencing glyphosate resistance in Palmer amaranth accessions in that location. Based on genotypic assay, 88% of 51 accessions contained at least one individual with amplification (>2 copies) of the 5-enolypyruvyl-shikimate-3-phosphate synthase (EPSPS) gene, which confers glyphosate resistance; and/or a mutation in the PPX2 gene, either ΔG210 or R128G, which endows PPO-inhibitor resistance in Palmer amaranth. Cluster analysis and high correlation (0.83) between genotypic and phenotypic assays demonstrated that EPSPS gene amplification is the main glyphosate resistance mechanism in Palmer amaranth accessions from southwestern Nebraska. In contrast, there was poor association between genotypic and phenotypic responses for PPO-inhibitor resistance, which was attributed to segregation for PPO-inhibitor resistance within these accessions and/or the methodology that was adopted herein. Genotypic assays can expedite the process of confirming known glyphosate and PPO-inhibitor resistance mechanisms in Palmer amaranth from southwestern Nebraska and other locations. Phenotypic assays are also a robust method for confirming glyphosate resistance but not necessarily PPO-inhibitor resistance in Palmer amaranth. Moreover, random forest analysis of glyphosate resistance in Palmer amaranth indicated that EPSPS gene amplification, county, and current and previous crops are the main factors influencing glyphosate resistance within that geographic area. Most glyphosate-susceptible Palmer amaranth accessions were found in a few counties in areas with high crop diversity. Results presented here confirm the spread of glyphosate resistance and PPO-inhibitor resistance in Palmer amaranth accessions from southwestern Nebraska and demonstrate that less diverse cropping systems are an important driver of herbicide resistance evolution in Palmer amaranth.

中文翻译：

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内布拉斯加州西南部棕榈苋（Amaranthus palmeri）基因型和表型草甘膦和 PPO 抑制剂抗性的分布和验证

2017 年在内布拉斯加州西南部报告了用草甘膦和原卟啉原 IX 氧化酶 (PPO) 抑制剂除草剂未能控制苋菜。本研究的目的是 1) 确认和 2) 验证草甘膦和 PPO 抑制剂（氟磺胺草醚和乳托芬）抗性在来自内布拉斯加州西南部的 51 个 Palmer 苋菜种质中，使用基因型和全植物表型分析相关性和聚类分析，以及 3) 确定哪些农艺实践可能会影响该地区 Palmer 苋菜种质的草甘膦抗性。根据基因型分析，51 份种质中的 88% 含有至少一个具有 5-烯丙基丙酮酸-莽草酸-3-磷酸合酶扩增（>2 拷贝）的个体。每股收益) 基因，赋予草甘膦抗性；和/或突变PPX2基因，无论是 ΔG210 还是 R128G，它赋予了帕尔默苋菜的 PPO 抑制剂抗性。基因型和表型分析之间的聚类分析和高度相关性 (0.83) 表明，每股收益基因扩增是内布拉斯加州西南部帕尔默苋种质的主要草甘膦抗性机制。相比之下，PPO 抑制剂抗性的基因型和表型反应之间的关联性较差，这归因于这些种质中 PPO 抑制剂抗性的分离和/或本文采用的方法。基因型分析可以加快确认内布拉斯加州西南部和其他地区的 Palmer 苋菜中已知的草甘膦和 PPO 抑制剂抗性机制的过程。表型分析也是确认草甘膦抗性的可靠方法，但不一定是帕尔默苋菜对 PPO 抑制剂的抗性。此外，帕尔默苋菜草甘膦抗性的随机森林分析表明，每股收益基因扩增、县、当前和以前的作物是影响该地理区域内草甘膦抗性的主要因素。大多数对草甘膦敏感的帕尔默苋属植物种质是在作物多样性高的地区的几个县发现的。此处提供的结果证实了内布拉斯加州西南部帕尔默苋种质中草甘膦抗性和 PPO 抑制剂抗性的传播，并证明较少多样化的种植系统是帕尔默苋菜除草剂抗性演变的重要驱动因素。