The Target-site Resistance Mechanism And Cross-resistance Of Eclipta Prostrata In Paddy Fields To Acetohydroxyacid Synthase Inhibitors

With successive and wide use of chemical herbicides,weed resistance develops rapidly worldwide.Eclipta prostrata?L.?L.,is a common annual malignant broadleaf weed belonging to the Asteraceae family,which can infect several crops in many countries.AHAS inhibitors widely employed in agriculture production since their first commercialization,with their benefits of highly efficiency at a low rate,safety to mammals,and benignity to the environment.However,farmers have complained that the AHAS inhibitors failed to control E.prostrata under field rate in partial paddy fields in China.The aims of this study were to?1?detect the resistance of E.prostrata populations from the main occurrence areas in Shandong,Hubei,Jiangsu and Anhui paddy fields,?2?determine the resistance mechanism in biochemical level and sequencing the target-site gene,?3?characterize the cross-resistance levels to four chemical families?SUs,IMIs,TPs and PTBs?of AHAS inhibitors in resistant population.The main results are outlined below:?1?The results of single dose pyrazosulfuron-ethyl to 31 E.prostrata populations:one suspected resistant population?LC12-25?could survive at 30 g a.i.ha^-1 of pyrazosulfuron-ethyl,and others were susceptible and killed effectively.?2?The results of in vitro AHAS activity assays:the AHAS isolated from the resistant population?LC12-25?was much less susceptible than that from susceptible population?LC12-24?.Compared with susceptible population?LC12-24?,the RI values to pyrazosulfuron-ethyl,bensulfuron-methyl,tribenuron-methyl?SUs?are 116.8,177.6,77.3;the RI values to pyroxsulam,penoxsulam?TPs?are293.3,27.8;the RI value to bispyribac-sodium?PTB?is 196.5;the RI values to imazethapyr,imazapic?IMIs?are 11.8,18.3 in the resistant population?LC12-25?,respectively.?3?The results of target-site gene detection:compared with the AHAS in susceptible population?LC12-24?,one point mutation was detected in resistant population?LC12-25?.CCC was replaced by TCC at position 197[the amino acid numbers standardized to the Arabidopsis thaliana?L.?Heynh.]within AHAS,causing the substitution of Pro to Ser.?4?The results of cross-resistance bioassays:the resistant population?LC12-25?was highly resistant to SUs,TPs,PTBs,and moderately resistant to IMIs.Compared with the susceptible population?LC12-24?,the resistance index?RI?values to pyrazosulfuron-ethyl,bensulfuron-methyl,tribenuron-methyl?SUs?are 133.6,172.1,195.1;the RI values to pyroxsulam,penoxsulam?TPs?are97.6,30.4;the RI value to bispyribac-sodium?PTBs?is 165.8;and the RI values to imazethapyr and imazapic?IMIs?are 10.2,19.1 in the resistant population?LC12-25?,respectively.In summary,this study detects one AHAS-R E.prostrata population in Jiangsu,determines the resistance mechanism by measuring in vitro AHAS activity and sequencing the AHAS,and confirms the cross-resistance patterns in whole-plant bioassays.Therefore,the resistanct population?LC12-25?was broad cross-resistance to SUs,TPs,PTBs,and IMIs conferring by Pro-197-Ser mutation within AHAS.