Department of Crop Sciences, University of Illinois, Urbana, IL, United States of America.
PLoS One. 2023 Dec 22;18(12):e0295927. doi: 10.1371/journal.pone.0295927. eCollection 2023.
Resistance to preemergence (PRE) soil-applied herbicides, such as inhibitors of very-long-chain fatty acid (VLCFA) elongases, was documented in two waterhemp [Amaranthus tuberculatus (Moq.) J.D. Sauer] populations (SIR and CHR) from Illinois, USA. To limit the spread of resistant weed populations, rapid detection measures are necessary. Soil-based resistance assays are limited by edaphic factors, application timing, variable seeding depth and rainfall amount. Therefore, cost-effective techniques mitigating effects of edaphic factors that are appropriate for small- to large-scale assays are needed. Our research goal was to identify and quantify resistance to the VLCFA-inhibiting herbicides, S-metolachlor and pyroxasulfone, using a soilless greenhouse assay. Dose-response experiments were conducted under greenhouse conditions with pre-germinated waterhemp seeds planted on the vermiculite surface, which had been saturated with S-metolachlor (0.015-15 μM), pyroxasulfone (0.0005-1.5 μM), or S-metolachlor plus the cytochrome P450 (P450) inhibitor, malathion. Lethal dose estimates of 50% (LD50) and growth reduction of 50% (GR50) were calculated for S-metolachlor and pyroxasulfone PRE and used to determine resistance indices (RI) for resistant populations (CHR and SIR) relative to sensitive populations, SEN and ACR. RI values for S-metolachlor using LD50 values calculated relative to SEN and ACR were 17.2 and 15.2 (CHR) or 11.5 and 10.1 (SIR), while RI values for pyroxasulfone using LD50 values calculated relative to SEN and ACR were 3.8 and 3.1 (CHR) or 4.8 and 3.8 (SIR). Malathion decreased the GR50 of S-metolachlor to a greater degree in CHR compared to ACR, consistent with P450 involvement in S-metolachlor resistance in CHR. Results from these soilless assays are in accord with previous findings in soil-based systems that demonstrate CHR and SIR are resistant to S-metolachlor and pyroxasulfone. This method provides an effective, reproducible alternative to soil-based systems for studying suspected PRE herbicide-resistant populations and will potentially assist in identifying non-target-site resistance mechanisms.
抗预萌发（PRE）土壤施药除草剂的现象，如超长链脂肪酸（VLCFA）延伸酶抑制剂，已在来自美国伊利诺伊州的两个水苋菜（Amaranthus tuberculatus（Moq.）J.D. Sauer）种群（SIR 和 CHR）中得到证实。为了限制抗草种群的传播，需要快速检测措施。基于土壤的抗性测定受到土壤因素、施药时间、可变播种深度和降雨量的限制。因此，需要具有成本效益的技术来减轻适用于小至大规模测定的土壤因素的影响。我们的研究目标是使用无土温室测定法来鉴定和量化对 VLCFA 抑制性除草剂 S-甲草氯和吡唑草酮的抗性。在温室条件下进行了剂量反应实验，将预发芽的水苋菜种子种植在蛭石表面上，该表面已用 S-甲草氯（0.015-15 μM）、吡唑草酮（0.0005-1.5 μM）或 S-甲草氯加细胞色素 P450（P450）抑制剂马拉硫磷饱和。计算了 S-甲草氯和吡唑草酮 PRE 的致死剂量 50%（LD50）和生长抑制 50%（GR50），并用于确定相对于敏感种群 SEN 和 ACR 的抗性指数（RI）。使用相对于 SEN 和 ACR 计算的 LD50 值计算的 S-甲草氯的 RI 值分别为 17.2 和 15.2（CHR）或 11.5 和 10.1（SIR），而使用相对于 SEN 和 ACR 计算的 LD50 值计算的吡唑草酮的 RI 值分别为 3.8 和 3.1（CHR）或 4.8 和 3.8（SIR）。马拉硫磷在 CHR 中比在 ACR 中更能降低 S-甲草氯的 GR50，这与 CHR 中 P450 参与 S-甲草氯抗性一致。无土测定的结果与土壤系统中先前的发现一致，表明 CHR 和 SIR 对 S-甲草氯和吡唑草酮具有抗性。这种方法为研究疑似 PRE 除草剂抗性种群提供了一种有效、可重复的替代土壤系统方法，并有可能有助于鉴定非靶标位点抗性机制。
