James Lee

Comparison of acetolactate synthase enzyme inhibition among resistant and susceptible Xanthium strumarium biotypes

Abstract Failure to control Xanthium strumarium with acetolactate synthase (ALS) inhibitor herbicides has been reported in Iowa and surrounding states. Single-seed descent techniques were used to isolate three X. strumarium biotypes: CAM-10 from near Cambridge, Iowa; Colo-25 from near Colo, Iowa; and Ohio-1 from Fulton County, Ohio. Ohio-1 and Colo-25 were selected because of apparent resistance to imazethapyr, whereas CAM-10 was selected for observed sensitivity to imazethapyr. The biotypes were assayed in vitro with three different ALS inhibitor herbicides, and ALS activity was measured. The 50% inhibition values (I50) of ALS for imazethapyr were determined to be ninefold or higher for the Ohio-1 and Colo-25 biotypes compared to the CAM-10 biotype. The I50 for imazaquin was determined to be about ninefold higher for the Colo-25 biotype and sixfold higher for the Ohio-1 biotype when compared to the CAM-10 biotype. All biotypes were equally sensitive to chlorimuron ethyl. The resistance was due to a single dominant nuclear gene. Nomenclature:Chlorimuron; imazethapyr; Xanthium strumarium L. XANST, common cocklebur.

Dry matter yield differences of five common cocklebur (Xanthium strumarium) biotypes grown at a common site

Abstract Five common cocklebur biotypes from southern Minnesota, central Iowa, southern Iowa, and Ohio were grown at the Iowa State University Curtiss Research Farm in 1995 and 1996 to examine intraspecific variations. Maximum plant heights were measured, and anthesis dates and day of bur set were recorded. At the end of the growing season, all plants were excised at the soil surface and weighed. Common cocklebur biotypes did not differ significantly in height. Flowering date was associated strongly with photoperiod and varied little between years within a biotype. But flowering date and bur set date differed among biotypes. The highest dry matter yields occurred in later flowering biotypes. Nomenclature: Common cocklebur, Xanthium strumarium L. XANST.