Mechanisms of Resistance to Diclofop of Two Wild Oat (Avena fatua) Biotypes from the Willamette Valley of Oregon

Abstract

Laboratory experiments were conducted to determine the mechanism of resistance to diclofop in two wild oat biotypes (designated ‘B’ and ‘C’ biotypes) from the Willamette Valley of Oregon. Resistance could not be attributed to differential absorption, translocation, or metabolism of diclofop. Resistance was not correlated with membrane plasmalemma repolarization following diclofop acid treatment. Compared to a susceptible (’S') wild oat biotype, acetyl CoA carboxylase from the B and C biotypes showed a 10.3 and 4.5 fold increase in the level of resistance, respectively, to diclofop acid. Cross-resistance to fenoxaprop acid was 5.5 and 7.3 times higher in the B and C biotypes, respectively than the S biotype. Correlation between resistance at the whole plant level and at the ACCase level was good for diclofop and fenoxaprop in the B biotype. For the C biotype, this correlation was not as good. Possible reasons for the discrepancy are given.