GRAMINICIDE RESISTANCE OF ACETYL-COA CARBOXYLASE FROM ORNAMENTAL GRASSES

Blue fescues [Festuca ovina var. glauca (Lam.) Koch, and F. amethystina L.] are resistant to graminicides, whereas fountain grass [Pennisetum alopecuroides (L.) Spreng.] and most other grasses are sensitive. Evidence suggests that selective control of grasses by the graminicides fluazifop (an aryloxyphenoxypropionate) and sethoxydim (a cyclohexanedione) is often due to differential resistance at the primary site of action, acetyl-CoA carboxylase (ACCase). ACCase activity was obtained from fountain grass and four cultivars of blue fescue to determine whether resistance at the whole plant level correlated with ACCase resistance in vitro. ACCase activity was represented by in vitro incorporation of radioactive bicarbonate into an acid- and heat-stable product. Enzyme activity was dependent on acetyl-CoA and ATP and was inhibited in the presence of avidin, suggesting that activity was due to ACCase. Compared to ACCase from fountain grass, ACCase from fescues was 70 to 88 times more resistant to fluazifop and 216 to 422 times more resistant to sethoxydim. Differences of this magnitude at the enzyme level may be sufficient to explain differential response between blue fescues (resistant) and fountain grass (sensitive) at the whole plant level. © 1993 by Academic Press, Inc.