Study On Resistance Of Alopecurus Aequalis To Mesosulfuron-methyl And Its Target-site Resistant Mechanism

Wheat is one of the major crops in China.Alopecurus aequalis,a predominant weed species in wheat fields,can no longer be controlled by mesosulfuron-methyl application after continuous use over several years.The susceptibility of A.aequalis to mesosulfuron-methyl was investigated by the seed and whole-plant bioassay experiments.The whole-plant bioassay assays were conducted to determine the cross-resistance and multiple resistance profiles of the mesosulfuron-methyl-resistant populations.We studied effects of mesosulfuron-methyl on target enzyme acetolactate synthase at the biochemical levels.Furthermore,at the molecular level,the difference of the acetolactate synthase(ALS)gene sequence and ALS expression level was studied.In addition,available techniques used for chemical control of mesosulfuron-methyl-resistant A.aequalis were studied.The results are as follows:Based on dose-response studies,JNXW-1 was defined as susceptible population with the lowest ED50.JTJY-1 and JHHZ-1 populations were found to be resistant to mesosulfuron-methyl,with resistance index(RI)values of 19.1 and 28.6 by seed bioassay,12.4 and 5,4 by whole-plant bioassay,respectively.JTJY-1 population displayed resistance to the SU(Sulfonylurea)herbicides rimsulfuron,nicosulfuron,metsulfuron-methyl,SCT(Sulfonylaminocarbonyltriazolinone)herbicide flucarbazone,the TP(Triazolopyrimidine)herbicides pyroxsulam and penoxsulam.The RIs were 4.3,4.2,3.1,6.8,4.3,3.1,respectively.This population showed low resistance to IMI(midazolinone)herbicides imazamox and imazapic,with the RIs less than 2.However,the JHHZ-1 population exhibited resistance to rimsulfuron,nicosulfuron,metsulfuron-methyl,flucarbazone,pyroxsulam,penoxsulam,imazamox and imazapic,with RI values of 14.9,3.4,5.9,16.6,16.3,3.2,10.6 and 6.3,respectively.High resistance was recorded in the JTJY-1 population to the ACCase(Acetyl Coenzyme A Carboxylase)inhibitors,fenoxaprop-P-ethyl,clodinafop-propargyl and pinoxaden,which had RI values of 224.6,55.3 and 4.9,respectively.The reduced sensitivity of ALS was one reason for two populations highly resistant to mesosulfuron-methyl.The results of ALS activity in vitro:the ALS enzyme of the resistant population express lower sensitivity to mesosulfuron-methyl than that of the susceptible population.The IC50 of JTJY-1 and JHHZ-1 populations to mesosulfuron-methyl were 14.04 and 14.90 ?M and the resistance index was 22.6 and 22.0,respectively.Amplified 1809 bp of the ALS gene without any intron and derived 603 amino acid sequences.The amplified areas encompass eight previously identified resistance mutations.The sequences were deposited in the GenBank database(Accession No.KJ872549,KJ872550 and KJ872551 for JNXW-1,JTJY-1 and JHHZ-1,respectively.)ALS gene sequence obtained from JTJY-1 population contained a single nucleotide substitution(C/A),which resulted in a substitution of Pro 197 to Thr.A substitution of Leu to Trp at amino acid position 574 in each plant of the JHHZ-1 population was observed,The expression levels of ALS gene between resistant and sensitive populations have no significant difference.So the expression of ALS gene might not be the reason for the high resistance.In order to find out effective herbicides which could be used to control A.aequalis resistant to mesosulfuron-methyl in wheat fields,the suspectibility of A.aequalis resistant populations to 13 herbicides were evaluated by pot-spraying method.In order to expand kill-weeding spectrum,reduce the cost and increase effect,a optimum formulation was screened out to control mesosulfuron-methyl-resistant A.aequalis by Gowing's method and isoble method,which was pinoxaden to fluroxypyr and the ratio was 1:2.The pot-spraying experiments showed that the mixture of pinoxaden and fluroxypyr got the good effect against main principal weed in summer-harvested fields.