%D 2006 %0 ARTICLE %T The role of altered acetyl-CoA carboxylase in conferring resistance to fenoxaprop-P-ethyl in Chinese sprangletop ( Leptochloa chinensis ( L ) Nees ) . %J Pest Manag . Sci . %V 62 ( 11 ) %P 1109-15 %A Pornprom T %A Mahatamnuchoke P %A Usui K %M pub16964592 %X From paddy field observations in 2002 and 2004 , fenoxaprop-P-ethyl resistance in Chinese sprangletop ( Leptochloa chinensis ( L ) Nees ) has been studied using information collected from 11 sites in the Saphan-Sung district of Bangkok , Thailand . The resistant Chinese sprangletop was found in nine rice fields , whereas the susceptible Chinese sprangletop was found in only two rice fields . In greenhouse experiments , both fenoxaprop-P-ethyl-resistant and susceptible Chinese sprangletop from the same location were investigated for 50% growth reduction based on phytotoxicity , plant height and fresh and dry weight . The resistant Chinese sprangletop showed apparent resistance at 14-21 days after herbicide application at a rate of 21 . 1-337 . 6 g AI ha ( -1 ) . The resistance index of resistant Chinese sprangletop was 10-25 times higher than that of the susceptible Chinese sprangletop . In addition , Chinese sprangletop did not exhibit multiple resistance to oxadiazon , propanil and quinclorac . According to acetyl-CoA carboxylase ( ACCase ) assays , the level of ACCase specific activity in the resistant Chinese sprangletop was significantly higher than that in the susceptible Chinese sprangletop . Similarly , the ACCase activity of the resistant Chinese sprangletop was 10 times less sensitive to fenoxaprop-P-ethyl than that of the susceptible Chinese sprangletop , based on the I50 values . The present study of the mechanism responsible for resistance in the biotypes investigated indicated that there was a close association between the concentration-response at the whole-plant level and ACCase sensitivity to fenoxaprop-P-ethyl , and resistance to fenoxaprop-P-ethyl was conferred by a modified ACCase at the target site , as suggested by higher specific activity and less sensitivity to the herbicide .