Authors: J P RuizSantaella A Heredia R De Prado
Publish Date: 2005/09/14
Volume: 223, Issue: 2, Pages: 191-199
Abstract
Cyhalofopbutyl CB 244cyano2fluorophenoxyphenoxypropanoic acid butyl ester R is an aryloxyphenoxypropionate AOPP herbicide for postemergence use in rice to control grasses mainly Echinochloa spp Similar to other AOPP and cyclohexanedione herbicides the site of action of CB is acetylcoenzyme A carboxylase ACCase an enzyme in fatty acid biosynthesis The mechanisms involved in the selectivity of CB in rice Oryza sativa L—absorption translocation metabolism and ACCase susceptibility—were studied Studies of in vitro inhibition of ACCase in E oryzoides and O sativa L species discounted any differential active site sensitivity as the basis of tolerance to CB The O sativa L cuticle was uniformly covered by waxes with predominantly unshaped large waxes randomly distributed obtaining absorption values of under 30 24 h after application HAA The E oryzoides cuticle formed a nonuniform covered reticule with less wax density and areas lacking in waxes reaching maximum values of absorption rising to 73 24 HAA Translocation studies revealed no significant differences either between species or between times remaining in the treated leaf There was a good correlation between the rate of metabolism and plant tolerance Plant metabolism studies demonstrated that tolerant rice inactivated the esterases producing a lack of functionality thus reducing the conversion of CB to cyhalofop acid which is the active form of the herbicide Moreover it increased the metabolism of the herbicide forming non toxic metabolites much faster than E oryzoides It was concluded that the basis of rice tolerance to CB was a lack of esterase functionality a reduced absorption through the cuticle and an increase in cyhalofop acid metabolism
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