Plant materials
Seeds were collected from kochia individuals from locations in the western US and western Canada between 2010 and 2015 (Table 1). Crops grown at the sampled locations included winter wheat, no-till fallow, and sugar beet. A total of 44 kochia locations from eight different states in the USA and one province in Canada were used for the analyses (Table 1). A population is defined as the seed from kochia individuals isolated from a single field at a geographically distinct location. The number of individuals sampled per population varied from five to 20, with at least 100 seeds sampled per plant and collecting from plants across at least 0.5 ha. GS populations were collected from several locations in Kansas, Colorado, and Oregon. Populations suspected to contain GR individuals were collected throughout Kansas, Colorado, Oregon, Idaho, Oklahoma, Texas, Montana, and Alberta (Table 1). Populations from Colorado (Westra, Nissen, Getts, Westra, & Gaines, 2019), Oregon and Idaho (Kumar et al., 2018), and Montana (Kumar, Jha, & Reichard, 2014) were previously screened for glyphosate resistance.