Horseweed [Conyza canadensis (L.) Cronquist] is a facultative winter annual weed that can emerge from March to November in Michigan. Fall-emerging C. canadensis overwinters as a rosette, while spring-emerging C. canadensis skips the rosette stage and immediately grows upright upon emergence. In Michigan, primary emergence recently shifted from fall to spring/summer and therefore from a rosette to an upright growth type. Growth chamber experiments were conducted to determine (1) whether both C. canadensis growth types could originate from a single parent and (2) whether common environmental cues can influence growth type. Variations in temperature, photoperiod, competition, shading, and soil moisture only resulted in the rosette growth type in four C. canadensis populations originating from seed collected from a single parent of the upright growth type. However, a vernalization period of 4 wk following water imbibition, but before germination, resulted in the upright growth type. Dose–response experiments were conducted to determine whether glyphosate sensitivity differed between C. canadensis growth types generated from a single parent of the upright growth type. Upright-type C. canadensis from known glyphosate-resistant populations ISB-18 and MSU-18 were 4- and 3-fold less sensitive to glyphosate than their rosette siblings, respectively. Interestingly, differences in glyphosate sensitivity were not observed between growth types from the susceptible population. These results suggest that while C. canadensis populations shift from winter to summer annual life cycles, concurrent increases in glyphosate resistance could occur.

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影响马草 (Conyza canadensis) 生长类型及其对草甘膦敏感性的环境因素

马草 [加拿大白粉虱(L.) Cronquist] 是一种兼性冬季一年生杂草，可以在密歇根州的 3 月至 11 月出现。秋季出现C.canadensis像玫瑰花一样越冬，而春天出现C.canadensis跳过玫瑰花结阶段并在出现后立即直立。在密歇根州，主要出苗最近从秋季转变为春季/夏季，因此从莲座型转变为直立生长型。进行生长室实验以确定（1）两者是否C.canadensis生长类型可能来自单亲和（2）常见的环境线索是否会影响生长类型。温度、光周期、竞争、遮荫和土壤水分的变化仅导致 4 个中的莲座丛生长类型C.canadensis源自从直立生长类型的单亲收集的种子的种群。然而，吸水后4周的春化期，但在发芽前，导致了直立生长类型。进行剂量反应实验以确定草甘膦敏感性是否在C.canadensis由直立生长类型的单亲产生的生长类型。立式C.canadensis来自已知抗草甘膦种群的 ISB-18 和 MSU-18 对草甘膦的敏感性分别比它们的玫瑰花结同胞低 4 倍和 3 倍。有趣的是，在易感人群的生长类型之间没有观察到草甘膦敏感性的差异。这些结果表明，虽然C.canadensis种群从冬季转向夏季的年度生命周期，草甘膦抗性可能同时增加。