Fenoxaprop-P resistance in Phalaris minor conferred by an insensitive acetyl-coenzyme A carboxylase.
A population of Phalaris minor, putatively resistant to fenoxaprop-P and identified in a wheat field in Israel during 1993, showed 20-fold resistance in the laboratory when compared to a susceptible biotype. The resistant biotype also had enhanced resistance (1.1- to 3.0-fold) to acetyl-coenzyme A carboxylase (ACCase) inhibitors such as diclofop, clodinafop, sethoxydim and tralkoxydim, but was equally susceptible to propanil, isoproturon and methabenzthiazuron, which did not inhibit this enzyme. Resistant and susceptible biotypes had similar rates of absorption, translocation and metabolism based on studies using [14C]fenoxaprop-P, suggesting resistance was due to another mechanism. ACCase from the resistant biotype was 19-fold less sensitive to fenoxaprop-P than that obtained from the susceptible biotype, and 1.5- to 5-fold less sensitive to clodinafop, tralkoxydim and cycloxydim. As there was a close association between the concentration-response at the whole plant level and ACCase sensitivity to fenoxaprop-P and other ACCase-inhibiting herbicides, resistance to fenoxaprop-P conferred by a modified ACCase was suggested.