Enhanced metabolism of fluazifop acid in a biotype of Digitaria sanguinalis resistant to the herbicide fluazifop-P-butyl

A population of Digitaria sanguinalis has evolved resistance to the herbicide fluazifop-P-butyl following selection with six applications of this herbicide over 4 years. The resistant population is also resistant to the chemically similar aryloxyphenoxypropanoate (APP) herbicides haloxyfop-methyl and quizalofop-P-ethyl, shows a lower level of resistance to the cyclohexanedione (CHD) herbicide sethoxydim, but is not resistant to clethodim. Acetyl-coenzyme A carboxylase isolated from plants of both resistant and susceptible populations was equally sensitive to APP and CHD herbicides. Absorption of [C-14]fluazifop-butyl and translocation of C-14 from [C-14]fluazifop-butyl were similar in plants from both populations. Plants of both resistant and susceptible populations rapidly hydrolyzed [C-14]fluazifop-butyl to [C-14]fluazifop acid in leaves; however, [C-14]fluazifop acid was metabolised to other compounds at a more rapid rate in the resistant plants. Enhanced metabolism of the toxophore fluazifop acid is a likely mechanism of resistance in this population. (C) 1997 Academic Press.