| Wheat is the second largest food crop after rice in China.Therefore,it is important for sticking to the strategic bottom line of "Grain is basically self-sufficient and rations are absolutely safe" to ensure the high yield and good harvest of wheat in China.In recent years,Aegilops tauschii,which is a kind of vicious weeds in wheat field,has seriously threatened the safety of wheat production because of the ever-expanding scope of harm and the ever-increasing degree of harm.Under current production conditions,mesosulfuron-methyl is the only herbicide that can selectively control wheat.However,there are problems such as unsatisfactory drug effect and high risk of pesticide harm.Therefore,it is of great significance for wheat production to research on the application technology of the safety agent mefenpyr-diethyl and mesosulfuron-methyl,and to further improve the safety of wheat and the control effect of A.tauschii.Based on the study of the occurrence and damage law of A.tauschii,this study proposed the use of mefenpyr-diethyl for seed dressing synergistic with mesosulfuron-methyl for spraying to prevent and control A.tauschii in the field,and has initially proved its necessity and feasibility.At the same time,the mechanism of action of mefenpyr-diethyl was systematically studied.The main results obtained are as follows:1.Vicious weed A.tauschii in wheat field has been widespread in the main wheat producing area of Hebei Province.The area of occurrence in 2019 was about 1.5 million hectares.The average density of different plots was 8.89 stems/m2,the average was 26.80%,and the frequency was 63.54%.From 2018 to 2020,the density and frequency of A.tauschii continued to rise in Baoding area.Compared with 2018,the average density of A.tauschii in 2019 and 2020 increased by 40.59%and 94.37%,and the frequency increased by 8.07 and 5.15 percent,respectively.It is clear that the most important way to spread A.tauschii is the commercial wheat.When A.tauschii spreads to a new area,its colonization ability is very strong:one plant/m2 can establish a population,and the population grows fast after planting.And the harm of A.tauschii has a certain concealment.The harm is small in the early stage but rapidly increases in the later stage.The model of wheat yield loss for A.tauschii is Y=2.6589+0.8011X,where X is the logarithm of A.tauschii(basic seedling)density and Y is the probability value of yield loss rate.The optimal sowing depth of A.tauschii is 1-3 cm,the optimal germination temperature is 15℃-20℃,the optimal budding temperature is 20℃,and the most suitable pH for germination and budding is 8.0.When the osmotic potential is in the range of-0.4--0.1 MPa,it will promote seed germination and budding,and when the osmotic potential reaches-0.6 MPa,it will inhibit germination;In addition,it is sensitive to NaCl and Na2SO4.The natural evolution direction of A.tauschii and different weed mixed communities is different,and the effect of the same herbicide treatment on the evolution direction of different communities is also diversified.2.The traditional method of using mefenpyr-diethyl(mixed with mesosulfuron-methyl and sprayed with stem and leaves)could increase the degradation rate of mesosulfuron-methyl in A.tauschii by 24%,and increase the resistance of A.tauschii to mesosulfuron-methyl by 7.93 times.In order to solve this problem,this study put forward the idea of using mefenpyr-diethyl for seed dressing.Laboratory test results shown that the seed dressing of mefenpyr-diethyl could increase the resistance of wheat to mesosulfuron-methyl by 21.82 times,which was better than the traditional spray method(7.02 times).It was further proved that under indoor conditions,50-200 g of mefenpyr-diethyl per 100 kg of seeds is used for seed dressing,which was safe for wheat and lasts for more than 40 days.After different varieties of wheat were treated with mefenpyr-diethyl,their resistance to mesosulfuron-methyl increased by 10.57%-52.57%.So,it is necessary and feasible to use mefenpyr-diethyl for seed dressing.3.Developed a special dosage form suitable for seed dressing-15%mefenpyr-diethyl seed treatment liquid.It has good physical and chemical properties,meets the requirements of the seed treatment liquid agent,and can be applied to actual production.And it has laid a foundation for further research on the use of mefenpyr-diethyl for seed dressing technology.It was preliminarily clear that the field dosage of 15%mefenpyr-diethyl seed treatment liquid was 12.5-50 g a.i./100kg,which was safe for wheat and could effectively protect wheat from mesosulfuron-methyl.4.The mechanism of mefenpyr-diethyl to increase the resistance of wheat to mesosulfuron-methyl included the following:(1)Accelerating the degradation rate of mesosulfuron-methyl in wheat;(2)Inducing the up-regulation of wheat stress-related transcription factors and protein kinases,and significantly up-regulating the expression of herbicide metabolic enzyme genes,while significantly down-regulating the effect of mesosulfuron-methyl stress on wheat transcriptome;(3)Improving the ALS activity of wheat and reducing the degree of inhibition of mesosulfuron-methyl on wheat ALS activity;At the molecular level,it had no significant effect on the expression of ALS gene ALS1 and ALS2;but under mesosulfuron-methyl stress,it could reduce the impact on the expression of ALS1 and ALS2;(4)The direct effect on the CYP450s content was small,but it cauld maintain the high CYP450s content of wheat under mesosulfuron-methyl stress;at the molecular level,it could reduce the expression of CYP450s gene CYP1,and could also maintain high expression of CYP1 under mesosulfuron-methyl stress;(5)The direct effect on GSTs content was small,but it could make wheat obtain higher GSTs content under mesosulfuron-methyl stress;at the molecular level,it could increase the expression level of GSTs gene GST1.At the same time,wheat could obtain higher GST1 expression under the stress of mesosulfuron-methyl.The main innovations of this study are as follows:(1)It was found that mefenpyr-diethyl could significantly increase the resistance of Aegilops tauschii to mesosulfuron-methyl.To solve this problem,the idea of using mefenpyr-diethyl for seed dressing was proposed and proved its feasibility;(2)Developed a special dosage form suitable for seed dressing-15%mefenpyr-diethyl seed treatment liquid agent,and preliminary clarified its use technology;(3)Combined with transcriptome analysis,the mechanism of action of mefenpyr-diethyl was revealed systematically from the aspects of degradation rate of mesosulfuron-methyl,target enzyme activity and expression,detoxification enzyme content and expression.The research on the application technology of mefenpyr-diethyl for seed dressing provides new ideas for the scientific control of Aegilops tauschii in the wheat field and lays a material foundation,which has certain application value in production;The research on the mechanism of action of mefenpyr-diethyl has important role in the development of new safeners and the rational use of safeners.At the same time,it has reference significance and academic value for the research on the selective mechanism of herbicides and the mechanism of weed resistance. |
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