Growth Characterization of Kochia (Kochia scoparia) with Substitutions at Pro197 or Trp574 Conferring Resistance to Acetolactate Synthase–Inhibiting Herbicides

Abstract Over 90% of Canadian kochia populations are resistant to acetolactate synthase (ALS)– inhibiting herbicides. We questioned whether the target site–based resistance could affect plant growth and competitiveness. Homozygous F2 herbicide-resistant (HR) kochia plants with an amino acid substitution at Trp574 (sources: Alberta [AB], Saskatchewan [SK], and Manitoba [MB]), or Pro197 (MB, AB with two populations) were grown in replacement series with homozygous F2 herbicide-susceptible (HS) plants from the corresponding heterogeneous population (total: six populations). In pure stands, growth of HR plants from AB and SK was similar to that of HS plants, regardless of mutation; conversely, MB2-HR plants (Trp574Leu) developed more slowly and were taller than MB2-HS plants. Final dry weight of HR plants in pure stands was similar across all six populations, whereas that for HS plants in pure stands and HR–HS plants in mixed stands (50–50%) varied with population. Results for AB and SK populations suggest li...