Preparation Of Azoxystrobin Nanoparticles Based On Iron Based Mesoporous Materials And Their Prevention And Control Of Rice Sheath Blight

Rice is one of the most widely planted crops in the world,which provides an important guarantee for the survival of the global population.However,the infection of rice sheath blight leads to a sharp decline in the yield and quality of rice,which will have a significant impact on the food supply.Azoxystrobin is a widely used fungicide,which can inhibit most fungal diseases,such as sheath blight,rice blast,powdery mildew and downy mildew.However,the azoxystrobin pesticide formulations sold on the market have some problems,such as low utilization rate of pesticides,and serious loss of effective components in the environment,so it is necessary to prepare a new dosage form that is green and environmentally friendly and improve the utilization rate of pesticides.Nano-carriers can promote the release of pesticides in the target,and reduce the loss and degradation of pesticides in the environment.In addition,nano-carriers can promote plant growth and regulate plant stress resistance.Therefore,the rational use of nano-carriers can reduce the loss of pesticides after application,and provide a new green solution for the control of rice sheath blight.In this study,iron-based silica nanocarriers were constructed,and the utilization rate of azoxystrobin and the ability to prevent rice sheath blight were improved by carrier loading.At the same time,the prepared nanoparticles could promote the growth and disease resistance of rice.The main research contents are as follows:(1)Firstly,Fe3O4 nanoparticles were prepared by the chemical coprecipitation method and then ferro-based mesoporous silica nanoparticles were coated with mesoporous silica.Enzyme-responsive drug delivery carriers(AZOX@AFS-Pec)were prepared by loading pyrimethanil esters into the prepared nanoparticles by solvent volatilization and coating pectin on the surface of drug-carrying nanoparticles.AZOX@AFS-Pec has a load rate of up to 28.6%on pyrimethanil.Subsequently,the nanoparticles were characterized by transmission electron microscopy(TEM),scanning electron microscopy(SEM),Fourier infrared spectrometer,and specific surface area analyzer.The results showed that the nanoparticles were spherical,uniform in morphology and particle size(40 nm),with a specific surface area of 951 m2/g and pore volume of 1.09 cm3/g.The aperture is 3.71 nm.The specific surface area and pore volume decreased to 144 m2/g and 0.260 cm3/g respectively after loading pyrimethanil and pectin encapsulation.The pore size did not change,indicating that pyrimethanil and pectin had successfully loaded on the surface of nanoparticles.The release behavior of AZOX@AFS-Pec is consistent with the Ritger-Peppas model,and the n value is greater than 0.450 in the presence of pectinase,indicating that the release of pyrimethanil is a combination of dissolution release and Fick diffusion.(2)The inhibitory effect of AZOX@AFS-Pec nanoparticles on rice sheath wilt was determined in vitro and in vivo.The results showed that the EC50 of AZOX@AFS-Pec nanoparticles on rice sheath wilt was 1.93 mg/L,and the EC50 of pyrimethanil suspension was 2.60 mg/L.In vivo,the disease indices of 30 mg/L AZOX@AFS-Pec nanoparticles and pyrimethanil suspension against rice grain blight were 80.7%and 86.4%,respectively.The disease indices in the prevention tests were 11.1%and 18.9%(inoculation after 2 h),29.4%and 58.3%(inoculation after 3d),80.1%and 100%(inoculation after 7d),respectively.Therefore,the inhibition effect of AZOX@AFS-Pec nanoparticles on rice sheath wilt was higher than that of commercial azoxystrobin suspensions in vitro,and the control ability of rice sheath wilt was similar to that of azoxystrobin suspensions in vivo,but the prevention effect of AZOX@AFS-Pec nanoparticles on rice sheath wilt was better than that of azoxystrobin suspensions.Subsequently,the wettability of AZOX@AFS-Pec nanoparticle suspension on rice leaves and its resistance to rainwater erosion were tested.It was found that the nanoparticle suspension had similar wettability to that of pyrimethanil suspension,and that AZOX@AFS-Pec nanoparticle had stronger resistance to rainwater erosion.In addition,the LC50 values of AZOX@AFS-Pec nanoparticles and pyrimethanil suspension were 5.40 μg/cm2 and 2.39 μg/cm2,respectively.The results showed that AZOX@AFS-Pec nanoparticles significantly reduced the acute toxicity of pyrimethanil to Pyrimethanil.(3)The effect of AZOX@AFS-Pec nanoparticle suspension spraying on rice resistance was determined.Using AZOX@AFS-Pec nanoparticles to control rice sheath blight,it was found that AZOX@AFS-Pec could promote the growth of rice,and regulate the content of chlorophyll a and the level of auxin in rice leaves.Similarly,in the prevention test,it can be found that compared with pyrimethanil suspension,AZOX@AFS-Pec nanoparticles have more significant effects on the growth of rice,can promote the increase of chlorophyll a and total chlorophyll content in rice leaves,reduce the level of auxin,and increase the content of salicylic acid.In addition,it was found that AZOX@AFS-Pec nanoparticles can induce the increase of antioxidant enzyme content in rice and enhance the resistance of plants.