Waterhemp [Amaranthus tuberculatus (Moq.) Sauer] is a dioecious weed that has evolved resistance to very-long-chain fatty-acid elongase (VLCFAE)–inhibiting herbicides via rapid metabolism. Although detoxification enzyme activities are associated with S-metolachlor resistance in two multiple herbicide–resistant (MHR) A. tuberculatus populations from Illinois, the genetic basis of resistance is unknown. Therefore, our goal was to investigate inheritance of S-metolachlor resistance in the Stanford, Illinois–resistant (SIR) population. Specifically, our research objectives were to: (1) generate a uniformly resistant, full-sib near-inbred line (DK3-2) via three generations of recurrent selection for resistance using preemergence S-metolachlor; (2) develop A. tuberculatus populations segregating for S-metolachlor resistance via reciprocal single-plant (one male × one female) full-sib mating of DK3-2 and a VLCFAE-inhibiting herbicide-sensitive population, SEN; (3) quantify S-metolachlor resistance levels in parental lines and their F1 progenies via greenhouse dose–response analysis; and (4) evaluate inheritance of S-metolachlor resistance in F2 progenies. Dose–response analysis using six to eight S-metolachlor concentrations (0.015 to 15.0 μM, varying per population) generated lethal dose (LD) estimates of 50% (LD50) and 90% (LD90) for SIR, SEN, DK3-2, and F1 progenies. LD estimates indicated DK3-2 has a higher magnitude of S-metolachlor resistance than the SIR population, demonstrating single crosses significantly increased S-metolachlor resistance in DK3-2. Levels of S-metolachlor resistance in F1 populations were intermediate compared with DK3-2 and SEN. Segregation of S-metolachlor resistance in F2 families from the paternal-derived lines fit a single-gene model (R:S = 3:1), indicating a single, dominant gene confers S-metolachlor resistance in SIR. However, F2 segregation results from the maternal-derived lines fit a duplicate recessive epistasis model (R:S = 9:7), indicating a second recessive gene may also modify S-metolachlor resistance in SIR. Results and germplasm derived from this research can assist in identifying the gene(s) conferring resistance to S-metolachlor in A. tuberculatus.

水麻 [ Amaranthus tuberculatus (Moq.) Sauer] 是一种雌雄异株杂草，通过快速代谢进化出了对超长链脂肪酸延长酶 (VLCFAE) 抑制性除草剂的抗性。尽管解毒酶活性与来自伊利诺伊州的两个多重除草剂抗性（MHR）结核菌群体中的异丙甲草胺抗性相关，但抗性的遗传基础尚不清楚。因此，我们的目标是调查伊利诺伊州斯坦福抗性（SIR）人群中异丙甲草胺抗性的遗传。具体来说，我们的研究目标是：（1）通过使用芽前异丙甲草胺进行三代抗性轮回选择，产生均一抗性的全同胞近交系（DK 3-2 ）；(2) 通过 DK 3-2 与 VLCFAE 抑制性除草剂敏感群体 SEN 的单株互惠（一雄 × 一雌）全同胞交配，开发对异丙甲草胺抗性分离的A. tuberculatus群体；(3)通过温室剂量反应分析量化亲本系及其 F 1后代中的异丙甲草胺抗性水平；(4)评价F 2后代中S-异丙甲草胺抗性的遗传。使用 6 至 8 个异丙甲草胺浓度（0.015 至 15.0 μM，每个群体不同）进行剂量反应分析，得出 SIR、SEN、DK 3的致死剂量 (LD) 估计值分别为 50% (LD 50 ) 和 90% (LD 90 ) -2和F 1后代。LD估计表明DK 3-2比SIR群体具有更高程度的S-异丙甲草胺抗性，表明单交显着增加了DK 3-2中的S-异丙甲草胺抗性。与DK 3-2和SEN 相比，F 1群体中的S-异丙甲草胺抗性水平处于中等水平。F 2家族中来自父本系的异丙甲草胺抗性分离符合单基因模型（R:S = 3:1），表明单个显性基因赋予SIR异丙甲草胺抗性。然而，来自母本系的F 2分离结果符合重复的隐性上位模型(R:S = 9:7)，表明第二个隐性基因也可能改变SIR中的S-异丙甲草胺抗性。这项研究的结果和种质可以帮助鉴定赋予抗性的基因结核菌中的异丙甲草胺。