Multiple mechanisms of resistance to fenoxaprop-P-ethyl in United Kingdom and other European populations of herbicide-resistant Alopecurus myosuroides (Black-Grass)

This study investigated the biochemical mechanisms that bestow resistance t o fenoxaprop-P-ethyl in a range of European field populations of the grass weed black-grass (Alopecurus myosuroides). Eleven populations were assessed for resistance to fenoxaprop-P-ethyl in a glasshouse experiment. Results c onfirmed that two populations (Roth and Lars) were susceptible and that the remaining nine populations showed different degrees of resistance to fenox aprop-P-ethyl. Biochemical analysis of fenoxaprop-P-ethyl metabolism and ta rget sire sensitivity showed that, although enhanced metabolism played an i mportant role in herbicide resistance in black-grass, it could not account for resistance in all of the populations. Resistance at the whole-plant lev el correlated well with reduced acetyl Go-enzyme A carboxylase sensitivity (target site resistance) in two of the populations (one from the United Kin gdom and one from Germany) but enhanced metabolism appeared to be the prima ry mechanism of resistance in the majority of the other populations. The gr eatest level of enhanced metabolism occurred in the population from Belgium . We suggest that resistance in Lines El may be explained by multiple resis tance mechanisms-the expression of both insensitive acetyl Go-enzyme A carb oxylase and an increased rate of detoxification. However, resistance in the population Clay from the United Kingdom could be explained neither by targ et site insensitivity nor by an enhanced rate of metabolism. These results provide conclusive evidence that a single resistance mechanism alone cannot explain insensitivity to fenoxaprop-P-ethyl in European resistant black-gr ass populations and that additional, as yet uncharacterized, mechanisms mus t also be present. (C) 1999 Academic Press.