Department of Evolution, Ecology, and Organismal Biology, Ohio State University, Columbus, OH, 43210, USA.
Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA, 50011, USA.
Sci Rep. 2018 Jul 11;8(1):10483. doi: 10.1038/s41598-018-28163-w.
Glyphosate is an important herbicide worldwide, but its efficacy has been compromised where weed species have evolved glyphosate resistance. To better understand evolutionary outcomes of continued and strong selection from glyphosate exposure, we characterized variation in resistance in self-pollinating Conyza canadensis (horseweed) in Ohio and Iowa, where glyphosate resistance was first reported in 2002 and 2011, respectively. In 2015, we collected seeds from a total of 74 maternal plants (biotypes) from no-till soybean fields vs. non-agricultural sites in each state, using one representative plant per site. Young plants from each biotype were sprayed with glyphosate rates of 0x, 1x (840 g ae ha), 8x, 20x, or 40x. Resistant biotypes with at least 80% survival at each dosage were designated as R1 (1x), R2 (8x), R3 (20x), or R4 (40x). Nearly all Ohio agricultural biotypes were R4, as were 62% of biotypes from the non-agricultural sites. In Iowa, R4 biotypes were clustered in the southeastern soybean fields, where no-till agriculture is more common, and 45% of non-agricultural biotypes were R1-R4. Our results show that resistance levels to glyphosate can be very high (at least 40x) in both states, and that non-agricultural sites likely serve as a refuge for glyphosate-resistant biotypes.
草甘膦是一种全球范围内重要的除草剂，但当杂草物种进化出对草甘膦的抗性时，其功效就会受到影响。为了更好地理解在持续和强烈的草甘膦暴露选择下的进化结果，我们对俄亥俄州和爱荷华州自花授粉的加拿大豚草（马唐）中的抗性变异进行了特征描述，2002 年和 2011 年分别首次报道了这两个州的草甘膦抗性。2015 年，我们从每个州的免耕大豆田和非农业地点共采集了 74 株母株（生物型）的种子，每个地点使用一株代表植物。来自每个生物型的幼苗都被喷洒了 0x、1x（840 g ae ha）、8x、20x 或 40x 的草甘膦剂量。在每个剂量下存活率至少为 80%的抗性生物型被指定为 R1（1x）、R2（8x）、R3（20x）或 R4（40x）。几乎所有来自俄亥俄州农业地区的生物型都是 R4，而非农业地区的生物型中有 62%是 R4。在爱荷华州，R4 生物型聚集在东南部的大豆田中，那里免耕农业更为普遍，而 45%的非农业生物型是 R1-R4。我们的结果表明，在这两个州，草甘膦的抗性水平可能非常高（至少 40x），并且非农业地区可能是对草甘膦具有抗性的生物型的避难所。
