Published online by Cambridge University Press: 20 January 2017
Henbit is a facultative broadleaf winter annual in the Lamiaceae family.Acetolactate synthase (ALS) inhibitors are primarily used to control a broadspectrum of weeds, including henbit. During 2012 to 2013, field applicationsof ALS-inhibiting herbicides were ineffective in controlling a henbitpopulation from Marion County, KS (MCK). To confirm field-evolved resistanceto ALS inhibitors, response of MCK henbit and a known susceptible henbitpopulation from Kansas (DPS) to varying doses of three different ALSinhibitors were examined: chlorsulfuron, imazamox, and propoxycarbazone.Results of the dose–response experiments suggest that the MCK population ishighly resistant to chlorsulfuron (resistance index [R/S] > 1,000) andpropoxycarbazone (R/S = 331) but is susceptible to imazamox. A full-length ALS gene sequence obtained using the 5′- and 3′- rapidamplification of complementary DNA ends approach revealed a Pro197 to Arg point mutation (a common mutation that confersresistance to sulfonylurea herbicides, e.g., chlorsulfuron) in the MCKhenbit. No other known resistance-conferring mutations were found in thestudy. Evolved resistance to major classes of ALS inhibitors in the MCKhenbit will reduce herbicide options for its control. To our knowledge, thisis the first case of evolution of herbicide resistance in henbit.
Associate editor for this paper: Patrick J. Tranel, University of Illinois.