Preparation Of CuONPs Composite Nanogel And Its Application In Prevention And Control Of Two Tobacco Leaf Diseases

Plant disease prevention and control is an important link in agricultural production.At present,the plant diseases are still mainly controlled by chemical pesticides.However,excessive use of chemical pesticides in the field is likely to lead to pesticide residues exceeding the standard and cause environmental pollution,so it is urgent to develop new pesticides with good efficacy and degradability to meet the needs of green agriculture.In recent years,nano-pesticides prepared from cellulose,chitosan,alginate,and other bio-based materials have gradually attracted the attention of plant protection researchers due to their advantages of good control effect,non-pollution,and biodegradability.Unlike small-molecular pesticides,these bio-based nanomaterials are mostly bio-derived extracts,which have the advantages of biodegradability,low toxicity,and high biocompatibility.Among them,alginate,as a highly functional bio-based polymer,has number of carboxyl groups on its surface,which can be cross-linked with divalent ions(such as Ca²⁺,Cu²⁺,Zn²⁺,etc.)to prepare nanogel.At present,bio-based nanogels had been deeply studied in the fields of medicine,materials,industry,etc.,but in agricultural plant protection,there were few reports on the prevention and control of diseases by nanogel.Therefore,in this study,alginate was used as the main raw material to synthesize nanogel using phase transition temperature method,and a series of composite nanogels with excellent antibacterial and disease resistance were synthesize by in-situ reduction,surface modification and other strategies.The different nanogels were characterized,and the control effects of different plant diseases were evaluated to explore their antibacterial and synergistic mechanisms.The results showed that the composite nanogels had better antibacterial and disease resistance effects than commercial bactericides,and could promote plant growth,which had good application prospects for agricultural disease control.For tobacco wildfire disease,in this paper,two different copper oxide nanoparticles（Cu ONPs）nanogels were prepared useing two different reducing agents,and the cetyltrimethylammonium chloride（CTAC）was coated on the surface of the nanogel to increase the stability of the nanogel.The effects of different reducing agents on the morphology,ion release,bacteriostasis and disease control of the nanogel were compared.The results showed that compared with the addition of sodium borohydride（SBH）in the nanogel,the reducing agent polydopamine（PDA）could significantly increase the release rate of Cu²⁺of Cu ONPs composite nanogel.By increasing the release rate of Cu²⁺,nanogel could more effectively destroy the bacterial cell membrane,leading to the breakdown and invagination of the bacterial cell membrane.The indoor prevention experiment also proved that the composite nanogel containing PDA had better prevention and treatment effects on tobacco wildfire disease.At the same time,the increase of Cu²⁺release rate also improves the immune response of plants and helped them to better resist disease.In addition,the addition of PDA in the nanogel enhanced the adhesion and erosion resistance of nanogel on the leaf surface,indicating that the nanogel had a longer impact on plants.Further research found that the increase of Cu²⁺release rate in Cu ONPs composite nanogel not only had no negative impact on plant growth,but also promoted plant growth.Aimed at the fungal disease tobacco brown spot disease,a new composite alginate nanogel that containing Cu ONPs andε-PL was fabricated via in situ reduction of Cu ONPs in nanogel andε-PL surface coating.Based on the chelation of amide bond ofε-PL and Cu²⁺released by Cu ONPs,the synergy effect between Cu²⁺andε-PL layer of the nanogel made the nanogel（Cu ONP@ALGNP@PL）performed high bacteriostatic and disease control effect under low Cu²⁺andε-PL concentration（Cu concentration was 40.09μg/m L,ε-PL concentration was 11.90μg/m L）.Study showed that the nanogel could more significantly destroy the fungal cell membrane than Cu ONP@ALGNP and ALGNP@PL,also better than commercial fungicide Cu Ca SO₄（Cu concentration was 120μg/m L）.Furthermore,Cu ONP@ALGNP@PL could seriously affect the spore production,spore germination rate and bud tube elongation length of Alternaria alternate.Moreover,at the same Cu concentration,Cu ONP@ALGNP@PL was safer for seed germination than Cu Ca SO₄.The antibacterial effect of the above three nanogels was compared in laboratory experiment,and the best antibacterial nanogel（Cu ONP@ALGNP@PL）was selected,and the field disease control effect of the nanogel was further evaluated.The results showed that the nanogel still had good disease control effect in the field,and could significantly reduce the incidence rate and disease index of tobacco wildfire disease and tobacco brown spot disease,and the disease control effect was significantly better than the commercial bactericide thiodiazole copper.At the same time,Cu ONP@ALGNP@PL could significantly promote the increase of leaf length,leaf width and leaf area of tobacco in the field,which had a positive impact on tobacco plants.And the results of transcriptome showed that Cu ONP@ALGNP@PL could induce resistance to Yunyan 87 and enrich number of differential genes in plant hormone signal transduction,plant MAPK signal pathway,plant pathogen interaction pathway and other disease-resistant pathways.Analysis of the expression quantity of the differential genes of the disease resistance pathway found that the ethylene and jasmonic acid related differential genes were all up-regulated,indicating that Cu ONP@ALGNP@PL may be resistant through the hormone pathway.To summary,in this study,alginate was used as raw material to synthesize nanogel,and small size Cu ONPs were combined inside the nanogel by in-situ reduction technology.For different diseases,nanogel was modified internally and externally to synthesize composite nanogel with excellent antibacterial and disease control effects.On the one hand,the nanogel could damage pathogen,on the other hand,it could induce resistance to plants.At the same time,the addition of PDA could further enhance the leaf adhesion of the nanogel,so that the composite nanogel had better leaf adhesion behavior than the commercial fungicides,indicating that the application of the nanogel can improve crop protection,which was less affected by climate factors.And this improvement could reduce the number of applications during crop production,reduce the cost of disease prevention and control in the field,and reduce environmental pollution caused by disease control,which had good application prospects.