LOCALIZED ORIGINS OF HERBICIDE RESISTANCE IN ALOPECURUS-MYOSUROIDES

The process of evolution of resistance to acetyl-coenzyme A carboxylas e (ACCase)-inhibiting herbicides was investigated in four distinct pat ches Alopecurus myosuroides Huds. (blackgrass) that occur within adjac ent fields on a cereal farm in Nottinghamshire, UK. In one field, ther e was a 'main' patch containing 96% resistant plants and two 'satellit e' patches containing approximate to 2.9% and 4.4% resistant plants, a nd in an adjacent field another patch contained 25% resistant plants. Genome fingerprinting by simple sequence repeat (SSR)-anchored polymer ase chain reaction (PCR) was used to analyse variation at 30 genetic l oci in at least 20 resistant and 20 sensitive individual plants from e ach patch, from additional resistant populations from Essex and Lincol nshire, and from a sensitive reference population. Banding patterns we re found to be highly repeatable. Each patch contained a high level of genetic diversity, regardless of its resistance status, and there was evidence for genetic differences between the patches (Gst = 0.14, Nei 's distances up to 0.26). There was no evidence that resistance had sp read from the 'main' patch to the others, as resistant and sensitive p lants in the same patch were more closely related on average than were resistant plants from neighbouring patches. The most likely explanati ons of this distribution, and their implications, are discussed.