Submitted to: Pest Management Science
Publication Type: Review Article
Publication Acceptance Date: 9/24/2004
Publication Date: 3/1/2005
Citation: Tan, S., Evans, R., Dahmer, M., Singh, B., Shaner, D.L. 2005. Imidazolinone-tolerant crops: history, current status, and future. Pest Management Science. Volume 61:pp246-257 Interpretive Summary:
Technical Abstract: Imidazolinone herbicides, which include imazapyr, imazapic, imazethapyr, imazamox, imazamethabenz, and imazaquin, control weeds by inhibiting the enzyme acetohydroxyacid synthase (AHAS) also called acetolactate synthase (ALS). AHAS is a critical enzyme for the biosynthesis of branched chain amino acids in plants. Several variant AHAS genes conferring imidazolinone tolerance were discovered in plants through mutagenesis and selection, and were used to create imidazolinone-tolerant maize (Zea mays L.), wheat (Triticum aestivum L.), rice (Oryza sativa L.), oilseed rape (Brassica napus L.), and sunflower (Helianthus annuus L.). These crops were developed using conventional breeding methods and commercialized as CLEARFIELD* crops from 1992 to the present. Imidazolinone herbicides control a broad spectrum of grass and broadleaf weeds in imidazolinone-tolerant crops including weeds that are closely-related to the crop itself and some key parasitic weeds. Imidazolinone-tolerant crops may also prevent rotational crop injury and injury caused by interaction between AHAS-inhibiting herbicides and insecticides. A single target-site mutation in the AHAS gene may confer tolerance to AHAS-inhibiting herbicides, thus it is technically possible to develop imidazolinone-tolerance trait in many crops. Activities are currently directed toward the continual improvement of imidazolinone tolerance and development of new CLEARFIELD* crops. Management of herbicide-resistant weeds and gene flow from crops to weeds are issues that must be considered with the development of any herbicide resistant crop. Thus extensive stewardship programs have been developed to address these issues for CLEARFIELD* crops.