Study On Resistance Of Cyhalofop-butyl In Leptochloa Chinensis (L) Nees

Leptochloa chinensis（L）Nees is an annual gramineous weed.It has strong tillering ability,high plant rate and good adaptability to adverse environment（e.g.,waterlogging and drought）.L.chinensis is a severe weed in the rice field of Hubei,Hunan,Jiangxi,Guangdong and Zhejiang provinces in China.Cyhalofop-butyl is an acetyl-CoA carboxylase（ACCase）inhibitor herbicide which has been widely used to control the annual grass weeds in the rice field.In this study,the resistance levels of 13 field populations of L.chinensis from Jingmen,Jingzhou,Wuxue,Xianning,Xiangyang,Nanchang and Changsha cities of Hubei province to cyhalofop-butyl were assayed by whole plant bioassay method.A cyhalofop-butyl resistance population TCGD16 was been found,and the cross-resistance and multi-resistance of TCGD16 to other herbicides were determined.Additionally,the metabolic and target resistance mechanisms of TCGD16 to cyhalofop-butyl were studied.This research is significant for the scientific and reasonable use of cyhalofop-butyl and resistant management of L.chinensis.（1）The bioassay results showed that 13 field populations of Leptochloa chinensis have developed different levels of resistance to cyhalofop-butyl.TCGD16 population showed the highest resistance to cyhalofop-butyl with the LD₅₀0 of 58.64 g a.i.ha^-1（RI=6.58）.The LD₅₀0 values of other populations varied from 8.94 to 52.92 g a.i.ha^-1（RI=1.01-5.93）.Among 13 field population,two field populations（WX15,NC16）showed sensitive levels（RI<2）,ten field populations（CB17,GA16,GA15,CS16,WX16,GA17,TC16,JM17,XY14,WX14）showed low level of resistance（2<RI<6）and one field population（TCGD16）showed moderate level of resistance（RI>6）.The cross-resistance and multi-resistance of TCGD16 population were determined.The results showed that the TCGD16 population exhibits cross-resistance with metamifop,penoxsulam,bispyribac and quinclorac.（2）The ACCase CT functional domain genes of the resistance population（TCGD16）and the sensitive population（NC16）were amplified and sequenced.Point mutations of the plant CT domain gene of chloroplastic ACCase have not been found in these seven amino acid sites（Ile 1781,Trp 1999,Trp 2027,Ile 2041,Asp 2078,Cys 2088,Gly 2096）,which were associated with ACCase resistance.The results indicated that the resistance of TCGD16 population to cyhalofop-butyl were likely endowed by non-target site resistance.（3）The synergistic effects of four enzyme inhibitors（PBO,NBD-Cl,malathion,cyanuric chloride）on cyhalofop-butyl were determined.The GST inhibitor（NBD-Cl）was found to significantly reverse the resistance of the resistant population.The LD₅₀ value of TCGD16 to cyhalofop-butyl plus NDB-CL was 13.38 g a.i.ha^-1,compered with 38.77 g a.i.ha^-1 without NDB-Cl.The result showed that NDB-Cl can significantly revere the resistance of TCGD16.The activity of GST enzyme was measured in L.chinensis resistant and sensitive population.It was found that the GST activity was significantly higher in the resistant population than in the sensitive population.Therefore,the resistance of TCGD16 population to cyhalofop-butyl is attributed mainly to the enhanced GST activity.（4）The effect of the combined action of enzyme inhibitor NDB-CL and cyhalofop-butyl on the growth of rice was determined.No significant difference was found between the addition and non-addition of NDB-CL(270 g a.i.ha^-1)in the same dose treatment of cyhalofop-butyl on the plant height and dry weight of rice.However,the plant height and dry weight of rice were affected if the treated dose of cyhalofop-butyl was higher than the recommended dose(90 g a.i.ha^-1).