Mechanism of Resistance to ACCase-Inhibiting Herbicides in Wild Oat (Avena fatua) from Latin America

Whole-plant response of two suspected resistant Avena fatua biotypes from Chile and Mexico to ACCase-inhibiting herbicides [aryloxyphenoxypropionate (APP), cyclohexanedione (CHD), and pinoxaden (PPZ)] and the mechanism behind their resistance were studied. Both dose-response and ACCase enzyme activity assays revealed cross-resistance to the three herbicide families in the biotype from Chile. On the other hand, the wild oat biotype from Mexico exhibited resistance to the APP herbicides and cross resistance to the CHD herbicides, but no resistance to PPZ. Differences in susceptibility between the two biotypes were unrelated to absorption, translocation, and metabolism of the herbicides. PCR generated fragments of the ACCase CT domain spanning the potential mutations sited in the resistant and susceptible biotypes were sequenced and compared. A point mutation was detected in the aspartic acid triplet at the amino acid position 2078 in the Chilean biotype and in isoleucine at the amino acid position 2041 in the Mexican wild oat biotype, which resulted in a glycine triplet and an asparagine triplet, respectively. On the basis of in vitro assays, the target enzyme (ACCase) in these resistant biotypes contains a herbicide-insensitive form. This is the first reported evidence of resistance to pinoxaden in A. fatua.