Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, AK, USA.
Food & Natural Resources, Fisher Delta Research Center, University of Missouri College of Agriculture, Portageville, MO, USA.
Pest Manag Sci. 2021 Feb;77(2):1001-1012. doi: 10.1002/ps.6111. Epub 2020 Oct 28.
Protoporphyrinogen IX oxidase 2 (PPO2) inhibitors are important for the management of glyphosate- and acetolactate synthase-resistant Palmer amaranth [Amaranthus palmeri (S.) Wats.]. The evolving resistance to PPO inhibitors is of great concern. We surveyed the evolution of resistance to fomesafen in the US Mid-south and determined its correlation with the known functional PPO2 target-site mutations (TSM).
The 167 accessions analyzed were grouped into five categories, four resistant (147) and one susceptible (20). Arkansas accessions constituted 100% of the susceptible group while the Missouri accessions comprised 60% of the most resistant category. The majority of Mississippi accessions (88%) clustered in the high-survival-high-injury category, manifesting an early-stage resistance evolution. One hundred and fifteen accessions were genotyped for four known TSMs; 74% of accessions carried at least one TSM. The most common single TSM was ΔG210 (18% of accessions) and the predominant double mutation was ΔG210 + G399A (17%). Other mutations are likely less favorable, hence are rare. All TSMs were detected in three accessions. Further examination revealed that 9 and two individuals carried G399A + G210 and G399A + R128G TSM in the same allele, respectively. The existence of these combinations is supported by molecular modeling.
Resistance to PPO inhibitors is widespread across the Mid-southern USA. Highly resistant field populations have plants with multiple mutations. G399A is the most prone to co-occur with other ppo2 mutations in the same allele. Mutation at R128 in the configuration of the PPO2 catalytic domain restrains the co-occurrence of R128G with ΔG210, making ΔG210 + G399A the most plausible, tolerable functional mutation combination to co-occur in the same ppo2 allele.
原卟啉原氧化酶 2（PPO2）抑制剂对于管理草甘膦和乙酰乳酸合酶抗性的 Palmer 苋菜[Amaranthus palmeri（S.）Wats.]非常重要。对 PPO 抑制剂的抗药性不断发展令人担忧。我们调查了美国中南部对氟磺胺草醚的抗药性演变，并确定了其与已知的功能性 PPO2 靶标突变（TSM）的相关性。
分析的 167 个品系分为五类，其中四类为抗性（147），一类为敏感性（20）。阿肯色州的品系构成了敏感组的 100%，而密苏里州的品系构成了最抗药性组的 60%。密西西比州的大多数品系（88%）聚类在高存活率高损伤类，表现出早期抗药性演变。115 个品系进行了四个已知 TSM 的基因型分析；74%的品系至少携带一个 TSM。最常见的单一 TSM 是ΔG210（18%的品系），主要的双突变是ΔG210+G399A（17%）。其他突变可能不太有利，因此很少见。所有 TSM 都在三个品系中检测到。进一步检查显示，9 个和 2 个个体分别在同一等位基因中携带 G399A+G210 和 G399A+R128G TSM。这些组合的存在得到了分子建模的支持。
PPO 抑制剂在整个美国中南部地区广泛存在抗性。高度抗性的田间种群植物具有多种突变。G399A 最有可能与同一等位基因中的其他 ppo2 突变同时发生。在 PPO2 催化结构域中 R128 的突变限制了 R128G 与ΔG210 的同时发生，使得ΔG210+G399A 成为最合理、可耐受的功能性突变组合，可在同一 ppo2 等位基因中同时发生。
