TARGET ENZYME-BASED RESISTANCE TO ACETYL-COENZYME-A CARBOXYLASE INHIBITORS IN ELEUSINE-INDICA

A biotype of Eleusine indica L. Gaertn. from Malaysia, which had a field history of two or three applications of fluazifop-p-butyl per year over 4-5 years, was previously found to show 100-fold resistance to the herbicide under field conditions compared with a susceptible population. This biotype is cross-resistant to other aryloxyphenoxypropanoate and cyclohexanedione herbicides. Previous research has shown no evidence for differential uptake, translocation, or metabolism of fluazifop-butyl between the R and S biotypes. Fluazifop acid reduced [C-14]acetate incorporation into the lipid fraction of leaf disks of the S biotype but not of the R biotype. Acetyl coenzyme A carboxylase (ACCase) from the S biotype was sensitive to fluazifop, fenoxaprop, sethoxydim, and clethodim, with I-50 values ranging from 1.0 to 5.6 mu M. In contrast, ACCase from the R biotype was much less sensitive to fluazifop, fenoxaprop, and sethoxydim, with I-50 values of >500, 25, and 77 mu M, respectively. ACCase from the R biotype showed only a low level of resistance to clethodim, with an I-50 of 6.6 mu M. The close correlation between the whole plant and ACCase sensitivities to various ACCase inhibitors suggests that herbicide resistance in this biotype is conferred by a mutation to the herbicide target site, ACCase. (C) 1995 Academic Press, Inc.