During the 2017 to 2019 growing seasons, samples of waterhemp and Palmer amaranth that had reportedly survived field-rate applications of protoporphyrinogen oxidase (PPO)–inhibiting herbicides were collected from the American Midwest and tested for target-site mutations known at the time to confer resistance. Target-site resistance was identified in nearly all (135 of 145) tested common waterhemp populations but in only 8 of 13 Palmer amaranth populations. Follow-up research on one population of Palmer amaranth (W-8), which tested negative for all such mutations, confirmed it was resistant to lactofen, with a magnitude of resistance comparable to that conferred by the ΔG210 PPO2 mutation. Gene sequences from both isoforms of PPO (PPO1 and PPO2) were compared between W-8 and known PPO inhibitor–sensitive sequence. A glycine-to-alanine substitution at the 399th amino acid position (G399A) of PPO2, recently identified to reduce target-site herbicide sensitivity, was observed in a subset of resistant W-8 plants. Because no missense mutation completely delimited resistant and sensitive sequences, we initially suspected the presence of a secondary, non-target-site resistance mechanism in this population. To isolate G399A, a segregating F2 population was produced and screened with a delimiting rate of lactofen. χ2 goodness-of-fit analysis of dead/alive ratings indicated single-locus inheritance of resistance in the F2 population, and molecular markers for the W-8 parental PPO2 coding region co-segregated tightly, but not perfectly, with resistance. More research is needed to fully characterize Palmer amaranth PPO inhibitor–resistance mechanisms, which appear to be more diverse than those found in common waterhemp.

中文翻译：

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Amaranthus tuberculatus 和 Amaranthus palmeri 对 PPO 抑制剂耐药性的分子确认，以及 A. palmeri 中 G399A PPO2 取代的分离

在 2017 年至 2019 年的生长季节，从美国中西部收集了据报道在原卟啉原氧化酶 (PPO) 抑制性除草剂的田间施用中幸存下来的水麻和苋菜样本，并测试了当时已知的靶点突变以赋予反抗。在几乎所有（145 个中的 135 个）测试的常见水麻种群中都发现了目标位点抗性，但在 13 个 Palmer 苋种群中只有 8 个。对所有此类突变均呈阴性的帕尔默苋菜 (W-8) 种群的后续研究证实，它对乳多芬具有抗性，其抗性程度与 ΔG210 PPO2 突变所赋予的抗性相当。在 W-8 和已知的 PPO 抑制剂敏感序列之间比较了来自 PPO 的两种同种型（PPO1 和 PPO2）的基因序列。在抗性 W-8 植物的一个子集中观察到 PPO2 的第 399 个氨基酸位置 (G399A) ​​处的甘氨酸到丙氨酸取代，最近发现它可以降低目标位点除草剂敏感性。因为没有错义突变完全界定了抗性和敏感序列，我们最初怀疑该人群中存在次要的非靶位点抗性机制。为了分离 G399A，分离 F2以乳芬的定界率产生和筛选种群。χ2死/活评级的拟合优度分析表明 F 中抗性的单基因座遗传2种群和 W-8 亲本 PPO2 编码区的分子标记与抗性紧密但不完美地共同分离。需要更多的研究来充分描述帕尔默苋菜 PPO 抑制剂的抗性机制，这似乎比常见的水麻中发现的更多样化。