| With the long-term and large-scale use of chemical herbicides,the problem of resistance to cultivated field weeds has become more severe.Amaranthus retroflexus L.is a common annual broadleaf weed in soybean fields.It is widely distributed in China and seriously harms the yield of soybeans.It is classified as a vicious weed in many parts of the world.Imazethapyr is an acetolactate synthase(ALS)inhibitor herbicide.It used to play an important role in the control of broadleaf weeds in soybean fields.However,due to long-term and excessive use of imazethapyr,the population of Amaranthus retroflexus in some areas of Heilongjiang Province has developed different degrees of resistance to imazethapyr.Amaranthus retroflexus is still difficult to effectively control at 3-times the recommended field rate,and with the increase in the number of years of use,the resistance of Amaranthus retroflexus has also continuously increased.In order to further clarify the resistance mechanism of Amaranthus retroflexus to imazethapyr and provide a theoretical basis for the research and management of resistant weeds,the resistant population(R)of Amaranthus retroflexus in soybean field of Nenjiang County,Heihe City,Heilongjiang Province and the sensitive population(S)of Amaranthus retroflexus in Dongning County,Mudanjiang City,Heilongjiang Province were used as the research object in this study.Physiological mechanism,metabolic mechanism,target enzyme activity changes and target gene mutations of the resistant population(R)of Amaranthus retroflexus were studied.The main experimental results are as follows:(1)Physiological mechanism of Amaranthus retroflexus resistant to imazethapyr1)After imazethapyr treatment,the chlorophyll content of the R and S populations of Amaranthus retroflexus decreased with time,the chlorophyll content began to rise after 7 days.After 14 days of application,the chlorophyll content returned to the highest level and then continued to decline.After 28-day of application,the chlorophyll content of R population was reduced by 11.2% compared with the control group of R population without imazethapyr,and S population was reduced by 63.1% compared with the control group of S population without imazethapyr.The chlorophyll content of R population was always higher than that of S population throughout the experiment.2)After imazethapyr treatment,the photosynthetic rate of the R and S populations of Amaranthus retroflexus decreased with time,the photosynthetic rate began to rise after 7 days.After 14 days of application,the photosynthetic rate returned to the highest level and then continued to decline.After 28-day of application,the photosynthetic rate of R population was reduced by 13.9% compared with the control group of R population without imazethapyr,and S population was reduced by 56.6% compared with the control group of S population without imazethapyr.The photosynthetic rate of R population was always higher than that of S population throughout the experiment.3)After imazethapyr treatment,the pore conductance of the R and S populations of Amaranthus retroflexus decreased with time,the pore conductance began to rise after 7 days.After 14 days of application,the pore conductance returned to the highest level and then continued to decline.After 28-day of application,the pore conductance of R population was reduced by 10.8% compared with the control group of R population without imazethapyr,and S population was reduced by 78.4% compared with the control group of S population without imazethapyr.The pore conductance of R population was always higher than that of S population throughout the experiment.4)After imazethapyr treatment,the SOD activity of the R and S populations of Amaranthus retroflexus decreased with time,the SOD activity began to rise after 7 days.After 14 days of application,the SOD activity returned to the highest level and then continued to decline.After 21-day of application,the SOD activity of R population was reduced by 8.0% compared with the control group of R population without imazethapyr,and S population was reduced by 23.0% compared with the control group of S population without imazethapyr.The SOD activity of R population was always higher than that of S population throughout the experiment.5)After imazethapyr treatment,the POD activity of the R and S populations of Amaranthus retroflexus decreased with time,the POD activity began to rise after 7 days.After 14 days of application,the POD activity returned to the highest level and then continued to decline.After 21-day of application,the POD activity of R population was increased by 30.0% compared with the control group of R population without imazethapyr,and S population was increased by 15.0% compared with the control group of S population without imazethapyr.The POD activity of R population was always higher than that of S population throughout the experiment.6)After imazethapyr treatment,the CAT activity of the R and S populations of Amaranthus retroflexus decreased with time,the CAT activity began to rise after 7 days.After 14 days of application,the CAT activity returned to the highest level and then continued to decline.After 21-day of application,the CAT activity of R population was increased by 17.0% compared with the control group of R population without imazethapyr,and S population was increased by 5.0% compared with the control group of S population without imazethapyr.The CAT activity of R population was always higher than that of S population throughout the experiment.(2)Mechanism of metabolic resistance of Amaranthus retroflexus to imazethapyr1)Combined treatment of P450 inhibitors such as malathion,prochloraz and piperonyl bromide with imazethapyr all decreased the resistance of the Amaranthus retroflexus resistant population(R)to imazethapyr.Among them,malathion and imazethapyr were the most effective treatments.Compared with the application of imazethapyr alone,the fresh weight inhibition rate of R population increased by 27.7%.2)After imazethapyr treatment,the GSTs activity of the R and S populations of Amaranthus retroflexus decreased with time,the GSTs activity began to rise after 7 days.After 14 days of application,the GSTs activity returned to the highest level and then continued to decline.The GSTs activity of R population and S population increased 1.05 times and 0.55 times respectively compared with the untreated group.The GSTs activity value of R population was higher than that of S population throughout the experiment period.The GSTs activity of R population is less inhibited than that of S population,it can always be maintained at a high level.(3)Changes in target enzyme ALS activityAfter imazethapyr treatment,the ALS activity of the R and S populations of Amaranthus retroflexus decreased with time,the ALS activity began to rise after 7 days.After 14 days of application,the ALS activity returned to the highest level.Compared with the untreated group,the ALS activity of R population increased by 4.91% and that of S population decreased by 0.3%.The ALS activity value of R population was higher than that of S population throughout the experiment period.The ALS activity of R population is less inhibited than that of S population,it can always be maintained at a high level,with stronger self-repairing ability.(4)Mechanism of resistance of Amaranthus retroflexus to imazethapyr and fomesafenR population had mutations at different positions in the conserved region of the ALS gene sequence,and three mutation sites were founded in the Amaranthus retroflexus R population of the same collection place.A single nucleotide change of GCT to GTT at 205,resulted in the substitution of Ala by Val.TGG was changed to TTG,resulting in a substitution of Trp-574-Leu.AGC was replaced by ACC,leading to a Ser-653-Thr mutation.AGG was changed to GGG at 128 and GAT was replaced by AAT at 476 in all resistant plants,resulting in PPO gene(PPX2L)Arg-128-Gly and Asp-476-Asn mutations,respectively. |
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