Preparation And Application Of Redox-Responsive Pesticides Controlled Release Agent

Pesticides are critical to the plant pest control and food security.However,some traditional pesticides formulations are inefficient,which not only leads to overuse and misuse of pesticides,but also causes environmental pollution.Compared with the traditional pesticides,stimuli-responsive pesticides controlled release agents can trigger the release with an intelligent response to stimuli.Apart from that,pesticides controlled release agents can effectively improve pesticides utilization and reduce the negative impact of pesticides on environment.However,the existing stimuli-responsive pesticide control releases are mostly in response to exogenous stimuli,leading to the mismatch between the released pesticides and the demand in practical applications.This research constructed a novel redox-responsive pesticides controlled release agent,and used reactive oxygen species（ROS）,an endogenous substance produced during the occurrence of pests and diseases,as an intelligent response stimulus to improve the accuracy and targeting of pesticide release.In addition,the synergistic application of pesticides and plant immunomodulator was conducted to prepare controlled release pesticides and plant immunomodulator in response to ROS release simultaneously.Furthermore,the dual-response pesticides and plant immunomodulator controlled-release formulations were prepared by introducing a second response stimulator,glutathione（GSH）,to improve the timeliness and efficiency of release.In this work,the characterization of the morphology,controlled release kinetics,redox responsiveness,fungus inhibitory activity and efficacy of three formulations（Vali@m PEG-TK-MTL,Vali@m PEG-TK-COS and Vali@m PEG-SS-TK-COS）were also investigated.This research used rice as the model plant,rice sheath blight disease caused by Rhizoctonia solani（R.solani）as the phytopathological model,and validamycin（Vali）,which has a good efficacy against rice sheath blight disease,as the model pesticides.Beyond that,the three formulations were applied in a simulated field environment and their efficacy was also studied.In this work,the following findings had been obtained from experimental studies.1 A ROS-responsive polymeric micelle m PEG-TK-MTL was synthesized from methoxy poly（ethylene glycol）（m PEG）,thioketal（TK）and 2-mercaptothiazoline（MTL）and loaded with Vali.The Vali@m PEG-TK-MTL was characterized by ¹H nuclear magnetic resonance（¹H NMR）and matrix-assisted laser desorption/ionization-time-of-flight mass（MALDI TOF）.The size of polymeric micelle was also measured by dynamic light scattering（DLS）,and the morphology of Vali@m PEG-TK-MTL was obtained by a transmission electron microscope（TEM）.The particle size of Vali@m PEG-TK-MTL were about 100-200 nm with dispersible measured by TEM.In vitro release experiments demonstrated that Vali@m PEG-TK-MTL was ROS-dependent,which also had good controlled release,and could rapidly release Vali under ROS production by plant stress.In the in vitro leaf experiment,the control effectiveness of Vali@m PEG-TK-MTL was decreased by 34.71%than that of Vali treatment group.2 In order to achieve ROS-responsive controlled release nanopesticides system with fungicidal and immunomodulatory bi-functions,COS was substituted for m PEG to synthesize m PEG-TK-COS and loaded with Vali.The size and morphology of Vali@m PEG-TK-COS were measured by DLS and TEM.The results showed that the average size of the Vali@m PEG-TK-COS were about 200 nm with good dispersion and spherical shape.In vitro release experiments it showed better ROS responsiveness,and Vali@m PEG-TK-COS could release both fungicide Vali and plant immunomodulator COS.In the in vitro leaf experiment,the control effectiveness of Vali@m PEG-TK-COS was decreased by 61.34%than Vali treatment group,so Vali@m PEG-TK-COS had better control effect than Vali.3 In order to make pesticides control release agents more timely and efficient,Vali@m PEG-TK-COS was optimized by introducing the GSH-responsive group 2,2’-dithiodioethanol（SS）to synthesize pesticides control agents with ROS,GSH dual response and immunomodulatory functions.The size and morphology of Vali@m PEG-SS-TK-COS was measured by DLS and TEM.The results showed that the average size of the Vali@m PEG-SS-TK-COS were about 200 nm with good dispersion and spherical shape.This controlled release nanopesticides achieved both ROS and GSH responsive functions,and could release both fungicide Vali and plant immunomodulator COS when H₂O₂ and GSH were added exogenously.In the in vitro leaf experiment,the control effectiveness of Vali@m PEG-SS-TK-COS treatment was decreased by 46.19%than Vali treatment group,so it had better control effect than Vali.4 For better application in practice,the efficacy of the three Vali controlled release agents（Vali@m PEG-TK-MTL,Vali@m PEG-TK-COS and Vali@m PEG-SS-TK-COS）were analyzed by simulating the actual agricultural production conditions and environment of the field.In the actual disease environment（air relative humidity 85-100%,temperature and light time 30℃,continuous 14 h light and the light intensity was 2.1×10⁴lx,26℃10 h darkness）,the rice was successfully infected with R.solani.Apart from that,the three medicinal effects and disease resistance mechanisms were preliminarily explored.As shown by the results,the disease control rates of Vali@m PEG-TK-MTL,Vali@m PEG-TK-COS and Vali@m PEG-SS-TK-COS were 71.10%,72.57%and 74.28%,respectively,which had good control effects on rice sheath blight.Meanwhile,compared with Vali,the control effects of COS were increased by 237.00%,241.90%and 247.60%,respectively,Vali@m PEG-SS-TK-COS had the beast control effectiveness.The same efficacy as Vali could reduce the use of pesticides by about65%.In addition,the contents of salicylic acid（SA）of d H₂O,Vali,Vali@m PEG-TK-MTL,Vali@m PEG-TK-COS and Vali@m PEG-SS-TK-COS treatment group were 60.20 ng.^-1,97.04ng.g^-1,106.20 ng.g^-1,686.91 ng.g^-1 and 425.08 ng.g^-1,respectively,proving that the COS released by Vali@m PEG-TK-COS and Vali@m PEG-SS-TK-COS could induce plants to produce SA and further trigger plant resistance.