MECHANISMS OF RESISTANCE TO DICLOFOP OF 2 WILD OAT (AVENA-FATUA) BIOTYPES FROM THE WILLAMETTE VALLEY OF OREGON

Laboratory experiments were conducted to determine the mechanism of re sistance to diclofop in two wild oat biotypes (designated 'B' and 'C' biotypes) from the Willamette Valley of Oregon. Resistance could not b e attributed to differential absorption, translocation, or metabolism of diclofop, Resistance was not correlated with membrane plasmalemma r epolarization following diclofop acid treatment. Compared to a suscept ible ('S') wild oat biotype, acetyl CoA carboxylase from the B and C b iotypes 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 tha n the S biotype. Correlation between resistance at the whole plant lev el 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. Possi ble reasons for the discrepancy are given.