Study On Glyphosate Resistance Of Conyza Canadensis(L.)Conq

On the basis of collecting horseweed populations in Hunan Province,glyphosate resistance level of horseweed were detected with different methods.Then,preliminary study on resistance mechanism and chemical control of glyphosate-resistant horseweed were conducted,which would provide scientific basis for field control of glyphosate resistant horseweed.The results were as follows:(1) When petri dish dose-response bioassay was applied to determine glyphosate resistance of horseweed,horseweed populations from YuanJiang and Hunau was found with highest resistance level,whose IR value reached separately5.79and4.26.GR50value of YuanJiang population reached4113.78g/hm2,which was notablely higher than the recommendation dose of glyphosate(900-1200g/g/hm2).(2) When fresh weight inhibition ratio and symptom index were separately applied to determine glyphosate resistance level of horseweed,there was some difference existed. When applying weight inhibition ratio,the IR value of YuanJiang and Hunau were separately5.46and4.01,with GR50value of3879.67g/hm2and2845.83g/hm2;While applying symptom index,the IR value of YuanJiang and Hunau were separately4.71and3.46,and the GR50value were separately3344.54g/hm2and2453.30g/hm2,which were lower than that determined by fresh weight inhibition ratio.For other nine horseweed populations that with relatively lower IR value,the results obtained was also similar to populations from YuanJiang and Hunau.(3) When resitant and sensitive horseweed were treated with1800g/hm2glyphosate,EPSPS activity of resistant horseweed population almost remained unchanged,while EPSPS activity in sensitive horseweed population was inhibited and presented a trend of continuous falling,which illustrated that glyphosate inhibited EPSPS activity of sensitive horseweed,while had little effect on EPSPS activity of resistant horseweed population. When resitant and sensitive horseweed were treated with1800g/hm2glyphosate,there was obvious difference between accumulation of shikimic acid. Shikimic acid in sensitive horseweed presented a trend of continuous rising and reached a highest level of647ug/g9days after treatment.While shikimic acid in resistant horseweed almost remained unchanged with treatment time and kept lower level,which was significantly lower that that of sensitive horseweed population.For resistant and sensitive horseweed population with no glyphosate treatment,shikimic acid both kept very low and remained almost unchanged.(4) There was little difference between GST activity of resistant and sensitive horseweed population.From the first to fifth day after glyphosate treatment,GST activity of sensitive horseweed was higher that that of resistant population. While on the seventh day,GST activity of resistant horseweed presented a peek value and was higher than sensitive population.Thereafter,GST activity of resistant horseweed began to fall and became lower than that of sensitive population again.(5) Distribution of glyphosate in leaf and stem of resistant and sensitive horseweed was different. Glyphosate was transferred from leaf to stem along with treatment time in sensitive horseweed.Nine days after treatment,distribution of glyphosate reached balance and the glyphosate concentration in leaf and stem were almost equal,concentration ratio between leaf and stem fell to1.2from3.9.While in resistant horseweed, concentration ratio between leaf and stem rised from3.8to5.3,which illustrated glyphosate accumulated in horseweed leaf and the amount transfered to stem was relatively less.(6) Among selected herbicides and herbicide combinations used to control glyphosate resistant horseweed,combination of glyphosate+paraquat,glyphosate+saflufenacil and glyphosate+fomesafen had preferable control effect on resistant horseweed,control effect7days after treatment reached separately93.3%、95.4%and89.2%.When applying single herbicide to control horseweed,hericides with preferable effect were paraquat, saflufenacil,glyphysate.MCPa and MCPa.control effect reached separately89.7%、92%、91.5%and89.1%.Control effect15days after treatment of all herbicides presented a little rise or fall,but with no big change.Herbicides and herbicide combination with preferable fresh weight control effect15days after treatment were glyphosate+paraquat, glyphosate+saflufenacil,glyphosate+fomesafen, paraqual, saflufenacil and glyphysate. MCPa,fresh weight control effect of which all reached90%or higher than90%.The best time for controlling glyphosate resistant horseweed was at10-leaf-stage of horseweed,and the control effect was obviously better than4-leaf-stage and15-leaf-stage.When glyphosate resistant horseweed was treated at10-leaf stage,control effect of all herbicides and herbicide combinations reached87%or higher.