A pH-responsive fludioxonil pesticide microcapsule with high sustained-release performance, a preparation method and application thereof

Abstract

This invention discloses a pH-responsive fludioxonil pesticide microcapsule suspension with high sustained-release performance, its preparation method, and its applications. The preparation method involves adding diphenylmethane diisocyanate, fludioxonil technical, and dibutyltin dilaurate to ethyl acetate, stirring at room temperature, and ultrasonically treating until completely dissolved to obtain a homogeneous oil phase. Then, OP-10 emulsifier is added to a chitosan aqueous solution and stirred until completely dissolved to obtain a continuous aqueous phase. The oil phase is then added dropwise to the aqueous phase. After the addition is complete, a high-speed shearing machine is used for shearing and emulsification to form a stable oil-in-water emulsion. The reaction is then stirred at 60±5℃ for 3±0.5 h to allow the diphenylmethane diisocyanate and chitosan molecules to undergo in-situ interfacial polymerization at the oil-water interface, resulting in the microcapsule suspension. The microcapsules obtained by this invention are uniform, smooth, and non-adhesive; they can effectively promote sorghum seed germination while inhibiting seed-borne pathogens; they can also be used for foliar spraying of sorghum to control anthracnose in seedlings; and they enable continuous, intelligent, and controllable pesticide release.

Description

Technical Field

[0001] This invention relates to a pH-responsive fludioxonil pesticide microcapsule suspension with high sustained-release performance, its preparation method and its uses, belonging to the field of high-performance microcapsule technology. Background Technology

[0002] Sorghum (Sorghum bicolor (L.) Moench) is a core raw material crop for my country's liquor industry, possessing excellent resistance characteristics such as drought and salt tolerance. With the continuous development of the domestic liquor industry, the scale of sorghum planting has expanded year by year. However, sorghum seeds have a relatively small grain size and weak emergence ability, and seed-borne diseases are severe in producing areas. Among them, sorghum anthracnose, caused by *Colletotrichum sublineola*, is a global fungal disease that has broken out widely in major producing areas of Northeast, North, and Southwest my country. This pathogen mainly overwinters on seeds and diseased plant debris in the field. Infected seeds are the main carriers for long-distance disease transmission. Under high temperature and humidity conditions, it can undergo multiple reinfections through airflow and rainwater, infecting multiple organs of sorghum, including leaves, leaf sheaths, rachis, and grains. After infection, it easily causes leaf death, rachis breakage, and grain shriveling. In severe cases, field yield losses can reach 20% to 50%. Due to the combined effects of seed characteristics and seed-borne diseases, the natural emergence rate of sorghum direct seeding in the field is only 25% to 30%. To ensure yield, farmers generally increase seeding rates and repeatedly apply pesticides, which not only wastes seed resources and increases labor costs for thinning in the field, but also further exacerbates the spread of seed-borne diseases, hindering the healthy development of the sorghum industry. Currently, chemical control is the main method for preventing and controlling anthracnose and seed-borne diseases in sorghum, mainly divided into seed pretreatment (seed soaking, seed dressing, conventional coating) and foliar spraying during the seedling stage. Fludioxonil, as a low-toxicity, broad-spectrum contact phenylpyrrole fungicide, can inhibit the transfer of fungal glucose phosphorylation and block the energy metabolism of pathogens, showing outstanding efficacy against various seed-borne and soil-borne fungal diseases. It is currently the mainstream agent for sorghum seed treatment and seedling disease control.

[0003] Currently, the formulation systems relied upon for the control of sorghum diseases, pests, and seed-borne diseases are mainly divided into three categories: traditional pesticide formulations, conventional seed coating agents, and existing pesticide microcapsule formulations. Their development status, preparation processes, application methods, and process conditions are detailed below: Traditional pesticide formulations are currently the most widely used types in agricultural production, mainly including emulsifiable concentrates (ECs), wettable powders, powders, and early ordinary suspension concentrates. Emulsifiable concentrates use volatile organic solvents such as toluene and xylene as dispersion media, and their production and application processes are simple; they only need to be diluted with water according to a specified ratio before use for seed soaking or foliar spraying. Wettable powders and powders are solid powder formulations that rely on inert fillers to carry the active ingredient. In the field, they are mostly applied by dry seed coating, water-based spraying, or direct application, and the entire process does not require complex temperature or rate control. Ordinary suspension concentrates are water-based modified formulations, where the active ingredient is dispersed in water through mechanical grinding, and can be directly used for seed coating or foliar application. These traditional formulations have low production barriers and are convenient to use, and have long dominated the pesticide application market.

[0004] Seed coating technology is a mainstream standardized seed treatment technology. This technology has been developed for many years both domestically and internationally. my country began related research in the 1970s. Currently, commercially available conventional seed coating agents are mainly prepared by simple physical mixing and grinding of fungicides, film-forming agents, and nutrient adjuvants. The coating process involves uniformly spraying or coating the compounded preparation onto the seed surface, which then cures under natural conditions at room temperature to form a physical coating film. The process is mild and relatively simple, relying solely on a simple film-forming structure to achieve agent adhesion, and is currently the standard technical solution for sorghum seed treatment.

[0005] Pesticide microcapsules are a key green slow-release pesticide formulation supported by national policies in recent years, and a core development direction for replacing traditional formulations. Originating in the 1930s, this technology was first industrialized abroad. Since the launch of my country's first commercial pesticide microcapsule product in 1982, related research has gradually progressed, and a mature material system and preparation process have been established. Its application in crop seed coating is being explored. Based on the wall material raw materials, existing microcapsule wall materials are mainly divided into three categories: natural polymers, semi-synthetic polymers, and synthetic polymers. Natural polymers are represented by chitosan, sodium alginate, gelatin, and starch, and are natural, non-toxic, and biodegradable. Semi-synthetic polymers are mainly modified cellulose materials, exhibiting excellent film-forming properties. Synthetic polymers include polyurethane, polyurea, and polylactic acid, which possess outstanding mechanical strength and chemical stability. Based on the preparation principle, the mainstream preparation methods in the industry include four categories: spray drying, interfacial polymerization, complex coagulation, and self-assembly. The operation steps and process conditions differ for each type: First, spray drying involves uniformly dispersing the pesticide core material in a wall material solution to prepare a stable emulsion. Then, high-pressure equipment is used to atomize the emulsion, and a high-temperature hot air stream is used to rapidly evaporate the solvent. After the wall material solidifies, powdered microcapsules are obtained. This process requires specialized high-pressure atomization and high-temperature drying equipment. Second, interfacial polymerization involves dissolving the reactive monomer and pesticide active ingredient in the oil phase, followed by high-speed shear emulsification to form an oil-in-water emulsion. The reaction temperature is controlled... The first method involves adjusting the temperature, stirring speed, and reaction time to induce polymerization at the interface between oil and water monomers, forming a capsule shell. This is a common process for preparing microcapsules for bactericides. The second method involves complex coagulation, where two polymer wall materials with opposite charges are dissolved in water. After dispersing the core material, the pH value, wall material concentration, and ratio of the system are precisely controlled. Phase separation and coagulation are initiated by electrostatic interaction, followed by cross-linking and solidification to obtain microcapsules. This process is highly sensitive to environmental parameters. The third method involves self-assembly, which relies on non-covalent bonds such as hydrogen bonds and electrostatic interactions to drive molecules to spontaneously form ordered micro-nano structures. This process requires no high temperature, strong mechanical force, or toxic cross-linking agents, and the reaction conditions are the mildest.

[0006] Although existing technologies have formed a complete system for the prevention and control of sorghum diseases and seed treatment, an analysis of the process principles, material characteristics, and actual application scenarios reveals that all existing technologies have obvious defects and shortcomings. The specific problems and their causes are as follows: First, traditional pesticide formulations have poor overall performance and cannot meet the requirements of green agriculture. Emulsifiable concentrate (EC) formulations rely on large amounts of toxic organic solvents, posing problems such as flammability, strong irritation, and health hazards to operators during production and application. Furthermore, the volatilization of these organic solvents causes air and soil pollution; this deficiency is inherent in the solvent system design of ECs themselves. Wettable powders and other powder formulations, being in powder form, lack adhesion and film-forming structures, easily generating dust during production and application that drifts with the wind, threatening surrounding non-target organisms and the ecological environment. Simultaneously, traditional formulations do not encapsulate and protect the active ingredients, leaving them directly exposed to the natural environment. These active ingredients are severely degraded by sunlight, leached by rainwater, and eroded by soil microorganisms, resulting in short-lasting effects and low utilization rates. To ensure efficacy, farmers are forced to continuously increase the dosage and frequency of application, leading to secondary problems such as excessive pesticide residues and increasing pathogen resistance. Furthermore, traditional formulations are simply physical mixtures of the components, lacking targeted delivery and controllable release structures. They cannot adjust the drug release rate according to changes in the target microenvironment such as pathogen infection and seed germination, resulting in completely uncontrolled drug release.

[0007] Secondly, existing conventional seed coating agents have limited functionality and insufficient long-term control capabilities. Commercially available conventional seed coating agents rely solely on ordinary film-forming materials to form a simple physical film layer on the seed surface, lacking a slow-release coating structure. The agent is rapidly released and lost within a short period, making it difficult to sustainably inhibit anthracnose pathogens lurking on the seed surface and inside. This results in poor long-term control of seed-borne diseases. The root cause of this problem lies in the fact that the formulation structure is merely a physical compound, without incorporating a controlled-release functional system. Furthermore, existing seed coating agent formulations focus solely on disease control, without adding bioactive or growth-promoting functional materials, failing to address the inherent weaknesses of sorghum seeds, such as weak emergence ability and low germination rates. Moreover, conventional film-forming materials have limited surface activity and adhesion properties, resulting in weak resistance to rain erosion. When used for foliar spraying, their wettability is poor, making them unsuitable for both seed coating and foliar spraying applications.

[0008] Third, existing pesticide microcapsule technology faces technical bottlenecks in three aspects: wall materials, preparation processes, and functional design. Regarding wall materials, each of the three mainstream types has its shortcomings: natural polymer wall materials, while green, safe, and biocompatible, have weak intermolecular forces, resulting in low mechanical strength and poor structural stability, making it impossible to achieve precise and controllable release of pesticide components; semi-synthetic polymer-modified cellulose wall materials have excellent film-forming properties, but insufficient molecular structural stability, making them prone to hydrolysis under complex acidic, alkaline, and high-temperature environments in the field, thus destroying the overall structure of the microcapsules; pure synthetic polymer wall materials have high mechanical strength and stable chemical properties, but are mostly petroleum-based materials, with poor biocompatibility and difficulty in natural degradation, easily causing secondary pollution through long-term accumulation in agricultural environments. In terms of preparation technology, various mainstream processes have limitations: spray drying relies on expensive specialized equipment, resulting in high preparation costs and making large-scale field application difficult; complex coagulation relies on electrostatic interactions for molding, and even small fluctuations in the system's pH and wall material ratio can disrupt phase equilibrium, leading to poor encapsulation stability and extremely low process tolerance; pure self-assembly methods have weak binding forces, resulting in low drug loading capacity in the prepared micro / nano carriers and making industrial mass production difficult; conventional interfacial polymerization methods mostly use single synthetic monomers to prepare the capsule wall without combining natural functional materials for modification, resulting in single-function capsule walls and some formulations having high ecotoxicity. In terms of functional design, most pesticide microcapsules currently only achieve basic sustained-release effects, and the capsule walls do not have environmentally responsive structures such as pH, enzymes, and temperature, making it impossible to intelligently release drugs on demand in specific scenarios such as pathogen infection and seed germination; at the same time, most existing microcapsules only focus on disease control and do not integrate seed growth promotion functions, failing to simultaneously solve the industry problem of low sorghum emergence rates, and most formulations are only suitable for single scenarios such as seed coating or foliar spraying, resulting in poor scenario adaptability.

[0009] In summary, the current field of sorghum anthracnose control and seed treatment faces multiple challenges: traditional pesticide formulations cause serious pollution and have low efficacy; conventional seed coating agents lack long-lasting effects and have limited functions; existing pesticide microcapsules are constrained by wall material defects, process limitations, and insufficient functional design, making it difficult to simultaneously meet the comprehensive needs of green environmental protection, intelligent controlled release, disease control, seed growth promotion, and multi-scenario application. Therefore, developing a dedicated microcapsule seed coating agent that adapts to the needs of sorghum production and combines intelligent responsive release, high-efficiency antibacterial activity, seed growth promotion, and multi-scenario application has become an urgent technical challenge to be solved in this field. Summary of the Invention

[0010] This invention provides a pH-responsive fludioxonil pesticide microcapsule suspension with high sustained-release performance, its preparation method, and its uses. The obtained microcapsules are uniform, smooth, non-adhesive, and have good stability. They can effectively promote sorghum seed germination while inhibiting seed-borne pathogens. They can also be used for foliar spraying of sorghum to control anthracnose in seedlings. They can adapt to pH fluctuations in the microenvironment of crop leaves and rhizosphere, thereby achieving continuous, intelligent, and controllable pesticide release at the target site.

[0011] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a highly sustained-release, pH-responsive fludioxonil microcapsule suspension with chitosan-polyurethane copolymer as the wall material, comprising the following steps: S1 Oil phase preparation: Diphenylmethane diisocyanate (MDI), fludioxonil technical and dibutyltin dilaurate (DBTDL) were added to ethyl acetate, stirred at room temperature and sonicated until completely dissolved to obtain a homogeneous oil phase; S2 Aqueous Phase Preparation: The emulsifier is added to the chitosan aqueous solution and stirred until completely dissolved to obtain a continuous aqueous phase; the emulsifier is OP-10, or the emulsifier is a mixture of AEO-9 and Span-80 in a mass ratio of (2.5~3.5):1, or the emulsifier is a mixture of OP-10, AEO-9 and Span-80 in a mass ratio of 1:(1.5~2.5):(0.8~1.2); S3 Emulsification and In-situ Polymerization: The oil phase obtained in step S1 is added dropwise to the aqueous phase obtained in step S2. After the addition is complete, a high-speed shear machine is used for shearing and emulsification to form a stable oil-in-water (O / W) emulsion. Then, the mixture is stirred at 60±5℃ for 3±0.5h to allow diphenylmethane diisocyanate and chitosan molecules to undergo in-situ interfacial polymerization at the oil-water interface, thereby generating a highly slow-release pH-responsive fludioxonil microcapsule suspension with chitosan-polyurethane copolymer as the wall material in one step.

[0012] The above-mentioned oil-in-water microcapsule suspension, prepared by interfacial polymerization using fludioxonil as the bactericidal active core material and a polyurethane-polyurea composite system formed by crosslinking chitosan and diphenylmethane diisocyanate as the capsule wall, exhibits uniform particle size distribution and excellent thermal stability.

[0013] All raw materials used in this application are commercially available conventional industrial products, requiring no additional purification.

[0014] In S2 above, preferably, the emulsifier is a mixture of AEO-9 and Span-80 in a mass ratio of (2.5~3.5):1, or the emulsifier is a mixture of OP-10, AEO-9 and Span-80 in a mass ratio of 1:(1.5~2.5):(0.8~1.2). More preferably, the emulsifier is a mixture of OP-10, AEO-9 and Span-80 in a mass ratio of 1:(1.5~2.5):(0.8~1.2).

[0015] In S1 above, the mass ratio of fludioxonil to diphenylmethane diisocyanate is (0.5~2):2; the mass amount of dibutyltin dilaurate is 1~5% of the mass of diphenylmethane diisocyanate. To improve the performance of the resulting suspension, in S2, the mass ratio of diphenylmethane diisocyanate to chitosan is 1:(4±0.5); the mass of the emulsifier is 4±0.5% of the mass of the chitosan aqueous solution; and the mass concentration of the chitosan aqueous solution is 1±0.2%.

[0016] The volume ratio of the above ethyl acetate to chitosan aqueous solution is (15~20):80.

[0017] In S2 above, the chitosan aqueous solution has a chitosan mass concentration of 1 ± 0.1%, and is prepared using an acetic acid aqueous solution with an acetic acid volume fraction of 1 ± 0.1%; the degree of deacetylation of chitosan (CTS) is ≥ 90%.

[0018] To further improve the stability and performance of the resulting suspension, in S2, the shear emulsification speed was 15000±1000 rpm and the time was 180±30 s; in S2, the stirring speed was 500±100 rpm during the stirring reaction.

[0019] A highly sustained-release, pH-responsive fludioxonil microcapsule suspension with chitosan-polyurethane copolymer as the wall material is prepared by the above-mentioned preparation method. The composite microcapsules have a regular spherical core-shell structure with fludioxonil as the core and chitosan-polyurethane covalent copolymer as the shell. The microcapsules have a uniform morphology, and the outer shell is dense, intact, smooth, undamaged, without dents or deformities, and without adhesion or agglomeration. The particle size distribution index (PDI) is ≤0.13, the fludioxonil encapsulation efficiency is ≥87%, and can reach up to 91.16%. The zeta potential is ≥51mV, and can reach 68.28mV.

[0020] The aforementioned shell layer is an interpenetrating network structure formed by the covalent bonding of chitosan and polyurethane through amino-isocyanate bonds, rather than a physical blend or stepwise coating structure; the core layer is high-purity fludioxonil technical grade, without any other additives.

[0021] The above-mentioned high-slow-release pH-responsive fludioxonil microcapsule suspension with chitosan-polyurethane copolymer as the wall material is used to promote sorghum seed germination; and / or to prevent and control sorghum anthracnose.

[0022] The aforementioned high-slow-release, pH-responsive fludioxonil microcapsule suspension with chitosan-polyurethane copolymer as the wall material is used as a seed coating agent to promote sorghum seed germination while inhibiting seed-borne pathogens; and / or can be used for foliar spraying of sorghum to control anthracnose in seedlings; it can adapt to pH fluctuations in the microenvironment of crop leaves and rhizosphere, thereby achieving continuous, intelligent, and controllable pesticide release at the target site, with the release accelerating as the pH increases.

[0023] The pH of the apoplastic spores (intercellular spaces) in healthy sorghum leaves is typically 4.5-5.5, indicating a slightly acidic pH. Anthracnose outbreaks cause a gradual increase in pH, with the increase becoming more pronounced as the disease progresses. This application's pH response perfectly matches the pH changes observed during an anthracnose outbreak. It also features intelligent controlled-release, long-lasting antibacterial action, seedling growth promotion, and environmental friendliness.

[0024] When using chitosan-polyurethane copolymer as the wall material, the high-release pH-responsive fludioxonil microcapsule suspension is used as a seed coating agent. The ratio of agent volume to seed mass (v / m) is 1:100 to 1:25, with a preferred ratio of 1:50. The microcapsule suspension is added to the seed coating machine along with the seeds. The machine is started and rotated at a constant speed until the agent is evenly coated on the seed surface, forming a complete coating layer. After coating, the seeds are placed in an electric heating drying oven and dried at a constant temperature of 20-30℃ (preferably 25℃) until the moisture content is ≤13.5%. After drying, the seeds can be stored at room temperature or refrigerated at 4℃. The germination rate of sorghum seeds is as high as 91.33%. When using a high-release, pH-responsive fludioxonil microcapsule suspension with chitosan-polyurethane copolymer as the wall material for foliar spraying, dilute the microcapsule suspension with deionized water according to the severity of disease in the field, controlling the concentration of the active ingredient (fludioxonil) to 100–200 μg / mL, and spray evenly on both sides of the sorghum leaves. The formulation exhibits excellent wetting properties and resistance to rain washout, requiring no additional treatment after spraying. At an active ingredient concentration of 100 μg / mL, the inhibition rate against sorghum anthracnose reaches 97.52%, significantly higher than that of fludioxonil technical and commercial fludioxonil seed dressing agents.

[0025] The microcapsule suspension of this application has excellent leaf surface wettability and hydrophilicity, with a contact angle of 34.2° and a surface tension of 36.48±0.30 mN / m. It forms a film structure on the surface of sorghum leaves, spreads evenly on the leaves, and has a sustained-release effect of more than 30 days.

[0026] Patent application number 202510910927.7 discloses a fludioxonil microcapsule with an ethyl cellulose-polydopamine double-shell structure. While the improved double-shell structure enhances surface smoothness, it also introduces... Figure 1 It is clearly visible that a large amount of deposits still adhere to the surface, with numerous pores, an uneven surface, poor shell integrity, and a tendency for core material leakage. Especially... Figure 3 It can be seen that when the time reaches 300 hours, its release tends to level off, and the maximum release amount is limited. Furthermore, its... Figure 4 It can be seen that there is basically no difference in release at pH 7 and 10, and the release only increases under acidic conditions at pH 5.

[0027] Patent application number 202511006698.2 discloses a microcapsule prepared using raw materials such as sodium lignosulfonate and colloidal protective agent. Although it also exhibits pH responsiveness, its... Figure 1 It is clearly visible that the two capsules are fused together, with their necks adhered together, resulting in agglomeration and adhesion, and there are also small particles of byproducts in the background. This conjoined structure is a fatal flaw, leading to difficulty in dispersion within the system, easy sedimentation, localized agglomeration, and resulting in either excessively high or insufficient levels of active ingredients in the finished product. Especially... Figure 3 It can be seen that when the time reaches 96 hours, its release has become relatively slow, and the maximum release amount is limited.

[0028] And as in this application Figure 3 As shown in section c, the particles are regular and spherical, without deformities or depressions, demonstrating excellent microcapsule spheroidization. Furthermore, the outer shell of this application is dense and smooth, without obvious pores or damage, with intact capsule walls and good encapsulation effect. All particles are independent and complete single spheres, without adhesion or aggregation, with dense and smooth capsule walls, narrow particle size distribution, and excellent dispersibility. This application... Figure 11 As can be seen from c, the release rate of this product still shows a significant increase after 720 hours, indicating that it is still in the release state, which significantly prolongs the release period and improves the effective utilization rate of fludioxonil. Furthermore, the release changes are significant at pH 5.4, 7.4, and 9.4, demonstrating an effective spontaneous intelligent pH response. The release is slow under acidic conditions and accelerates under neutral and alkaline conditions.

[0029] For the preparation of solid microcapsule powder, a portion of the suspension can be centrifuged at 8000-12000 rpm (preferably 10000 rpm) for 8-12 min (preferably 10 min). After collecting the precipitate, it can be freeze-dried to obtain FLU@CTS-PUMC microcapsule powder, which can be used for physicochemical detection, powder compounding and other applications.

[0030] To address the current production challenges in the sorghum industry, such as the high incidence of seed-borne anthracnose and low seed germination rates, as well as the numerous technical shortcomings of traditional pesticide formulations, conventional seed coating agents, and existing pesticide microencapsulation technologies, including severe environmental pollution, low efficacy utilization, limited functionality, poor process stability, insufficient adaptability to various scenarios, and lack of intelligent controlled release, this invention overcomes the following technical problems: Traditional formulations lack encapsulation protection for pesticide active ingredients, making them susceptible to decomposition by sunlight and leaching by rainwater. This results in short-lasting effects and significant field losses. Farmers are forced to increase pesticide dosage and application frequency to maintain efficacy, further exacerbating secondary problems such as excessive pesticide residues and increased pathogen resistance. This invention utilizes a microcapsule suspension system, completely eliminating highly polluting solvents and dust-based formulations. By encapsulating and protecting pesticides through the capsule wall, it significantly improves pesticide utilization, extends the duration of efficacy, and reduces environmental and safety risks associated with pesticide use from the source.

[0031] Sorghum anthracnose primarily spreads and initially infects via seeds. Conventional treatments such as seed soaking, seed coating, and foliar spraying only provide short-term inhibition and cannot effectively eliminate latent pathogens inside and on the seed surface. Under high temperature and humidity, the disease is prone to recurrence. Furthermore, sorghum seeds have weak emergence ability, and due to seed-borne diseases, direct seeding germination rates in the field are only 25%–30%. Simple fungicides cannot improve seed vigor or germination rate. This invention utilizes core-shell microcapsules to achieve slow release of the agent, providing long-term inhibition of seed-borne pathogens and completely cutting off the source of initial infection. Simultaneously, the bioactivity of the cell wall material activates the antioxidant defense system of sorghum seeds, enhancing seed germination vigor and addressing the two major production problems of recurrent anthracnose and low germination rates.

[0032] Existing commercial sorghum seed coating agents are mostly simple physical mixtures of fungicides and adjuvants, relying solely on ordinary film-forming materials to form a single-layer physical coating on the seed surface. The agents are rapidly released and lost within a short time, resulting in weak long-term disease prevention capabilities. Furthermore, the formulations and film-forming structures of these seed coating agents are only suitable for the single application of seed coating. When used for foliar spraying, they suffer from poor wetting properties, weak adhesion, and insufficient resistance to rain washout, failing to meet the needs of both seed coating and seedling foliar spraying—two mainstream application scenarios. This invention constructs a core-shell microcapsule structure based on interfacial polymerization, possessing stable sustained-release properties. Simultaneously, it optimizes the surface characteristics of the formulation, enabling it to form a uniform and dense coating layer on the seed surface while also spreading well on the sorghum leaf surface and resisting rain washout, achieving a single formulation suitable for both application scenarios.

[0033] Existing pesticide microcapsule wall materials, categorized into three main types, all have significant shortcomings: natural polymer materials offer good biocompatibility and biodegradability, but suffer from low mechanical strength and poor structural stability, making precise controlled release of pesticides difficult; semi-synthetic polymer materials exhibit excellent film-forming properties, but have weak resistance to acids, alkalis, and high temperatures, and are prone to hydrolysis and damage in complex field environments; synthetic polymer materials demonstrate outstanding mechanical strength and chemical stability, but are mostly difficult to biodegrade naturally and have poor biocompatibility, easily causing secondary pollution if accumulated in farmland over a long period. This invention utilizes a polyurethane-polyurea composite wall material formed by crosslinking chitosan and diphenylmethane diisocyanate. This material leverages a three-dimensional covalent crosslinking network to enhance the mechanical strength and structural stability of the capsule wall, while chitosan imparts excellent biocompatibility, biodegradability, and pH sensitivity, achieving a synergistic balance between the wall material's mechanical properties, controlled release performance, and environmental friendliness.

[0034] Current mainstream pesticide microcapsule preparation processes have many limitations: spray drying requires expensive specialized equipment, resulting in high production costs and hindering large-scale adoption; complex coagulation is extremely sensitive to parameters such as pH and wall material ratio, leading to low process tolerance and difficulty in stabilizing microcapsule encapsulation efficiency and particle size uniformity; conventional interfacial polymerization methods lack systematic optimization of emulsifiers, shear conditions, and polymerization parameters, easily resulting in problems such as emulsion stratification, uneven microcapsule size, and low encapsulation efficiency, failing to meet the requirements of industrial production. This invention, through long-term creative work, systematically screened the optimal emulsifier type and dosage, simultaneously optimizing the entire process parameters of high-speed shearing and isothermal polymerization. The resulting microcapsules exhibit uniform particle size, excellent encapsulation efficiency, and high pesticide loading. The entire process is simple to operate, uses only conventional industrial products as raw materials, is cost-controllable, highly replicable, and suitable for large-scale production and field promotion.

[0035] Conventional sustained-release microcapsules can only achieve passive, uniform release, failing to adjust the release rate according to changes in the field microenvironment. In target areas where anthracnose pathogens are active, the release amount is insufficient, limiting the disease control effect; in non-target areas, the pesticide is released ineffectively, resulting in pesticide waste. This invention fully utilizes the pH-sensitive properties of chitosan to construct a pH-responsive intelligent release system. In the alkaline microenvironment where anthracnose is prevalent, the capsule wall structure is loose, accelerating pesticide release; in acidic and neutral environments, the cross-linked structure is dense, slowing the release rate, achieving "on-demand" pesticide release. This significantly improves the precision of disease control and further reduces ineffective pesticide waste.

[0036] Currently, sorghum disease control agents generally have limited functions, focusing only on inhibiting pathogen growth and failing to improve seed physiological activity or activate the plant's own defense system, thus failing to address the dual needs of disease prevention and seedling strengthening. This invention organically combines the bactericidal active ingredient fludioxonil with biostimulating chitosan. Microencapsulation activates the glutathione metabolic pathway in sorghum, enhancing the activity of antioxidant enzymes such as SOD, POD, and CAT, thereby strengthening the stress resistance of seeds and seedlings. While effectively inhibiting anthracnose, it also promotes seed germination, root growth, and seedling dry matter accumulation, achieving a breakthrough in integrated disease control, seedling growth promotion, and stress resistance enhancement.

[0037] Traditional pesticide formulations and some synthetic polymer-based microcapsules, when applied to crops, result in excessively high instantaneous pesticide concentrations, easily causing phytotoxicity to sorghum seeds and seedlings. Simultaneously, some adjuvants and wall materials exhibit high biotoxicity and are difficult to degrade, threatening non-target organisms in the field and disrupting the ecological balance of farmland. This invention, on the one hand, relies on the slow-release properties of microcapsules to effectively reduce the instantaneous pesticide concentration on the crop surface and within the crop, completely avoiding the risk of phytotoxicity; on the other hand, the composite wall material has good biocompatibility and is biodegradable, resulting in low overall toxicity of the formulation, making it friendly to sorghum plants, soil, and the surrounding ecological environment, meeting the requirements of green agricultural development.

[0038] Unless otherwise specified or agreed upon in this application, all percentages in this application refer to percentages by mass.

[0039] Explanation of abbreviations in this application:

[0040] Any techniques not mentioned in this invention are based on existing technologies.

[0041] This invention uses chitosan (CTS) and diphenyl diisocyanate (MDI) as wall materials and fludioxonil (FLU) as the active ingredient to prepare FLU@CTS-PUMC polyurea-polyurethane microcapsule formulations via interfacial polymerization. Compared to existing products and conventional preparation processes such as fludioxonil technical (FLU-TC), commercially available fludioxonil suspension concentrate (FLU-SC), and unloaded CTS-PUMC matrix, this invention possesses significant innovative advantages in four core dimensions: microstructure, pH-responsive controlled-release capability, long-lasting sustained-release performance, and application scenario compatibility. Furthermore, it comprehensively improves overall performance in terms of drug loading efficiency, thermal stability, leaf adhesion, antibacterial activity, biosafety, environmental friendliness, and ease of operation. All advantages have been verified through systematic experiments and supported by quantitative data, as detailed below: I. The microstructure is regular and uniform, and the particle structure and colloidal stability are greatly optimized. The existing CTS-PUMC matrix particles have an average particle size of 2538.87 nm, with a rough surface and obvious agglomeration, resulting in poor particle uniformity and easy formation of stratification and sedimentation. This invention optimizes the fludioxonil feed ratio and interfacial polymerization conditions to obtain FLU@CTS-PUMC 1.0 as the optimal sample, achieving a qualitative improvement in its microstructure and particle properties: the sample has an average particle size of only 1608.00 nm, a polydispersity index (PDI) as low as 0.125, a particle size distribution conforming to a standard normal distribution, and highly uniform particle size; the particles are generally regular spherical with a smooth, impurity-free surface. Under electron microscopy, a clear and complete core-shell structure can be observed, with the shell being a polyurea-polyurethane structure formed by the polymerization of chitosan amino and hydroxyl groups and MDI isocyanate groups, and the fludioxonil active ingredient stably encapsulated within the core.

[0042] Regarding colloidal stability, the Zeta potential of fludioxonil technical grade is -55.13 mV, that of the CTS-PUMC matrix is ​​69.40 mV, and that of FLU@CTS-PUMC 1.0 is 51.29 mV. These higher potential values ​​give the microcapsule dispersion system excellent anti-agglomeration ability, effectively solving the problems of particle aggregation and uneven efficacy during storage of traditional formulations. Combined characterization results from Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) confirm that fludioxonil is fixed inside the microcapsules only through hydrogen bonds, van der Waals forces, and interfacial covalent interactions, without molecular structure degradation. The structural stability of the composite system is far superior to that of traditional pesticide formulations that simply physically mix the active ingredient and the carrier.

[0043] II. Possesses significant pH-responsive release characteristics, enabling intelligent and controllable pesticide release.

[0044] Traditional fludioxonil technical and commercially available suspension concentrates are passive release systems, meaning their release rate is not regulated by environmental pH and cannot adapt to the acid-base differences in crop rhizosphere and leaf surface environments, easily leading to problems such as excessively rapid or insufficient release. This invention leverages the natural pH-sensitive properties of chitosan and the polyurea-polyurethane cross-linked shell structure to give FLU@CTS-PUMC excellent pH-responsive release performance.

[0045] A 720-hour long-acting release test revealed that under three typical conditions—pH 5.4 (acidic), pH 7.4 (neutral), and pH 9.4 (alkaline)—the cumulative release rates of fludioxonil from the microcapsules were 40.73%, 62.93%, and 75.49%, respectively, with the release rate increasing sequentially with increasing pH. The mechanism of action is as follows: in acidic environments, the amino and hydroxyl groups of chitosan undergo high protonation, resulting in a denser cross-linked network in the capsule shell, effectively inhibiting the diffusion of the active ingredient. In neutral and alkaline environments, the degree of amino protonation decreases, the capsule shell structure gradually loosens, and the drug release rate increases synchronously. Release kinetic fitting results show that the drug release process of this invention optimally conforms to the Ritger-Peppas model (0.45 < n < 0.89), synergistically regulated by molecular diffusion and slow erosion of the capsule wall. This is a non-Fick diffusion mechanism, exhibiting strong controllability of the release rhythm. It can precisely match the microenvironmental characteristics of different crop growth zones, achieving targeted intelligent drug release and overcoming the technical shortcomings of uncontrollable drug release behavior in existing pesticide formulations.

[0046] III. The sustained-release period is significantly extended, and the pesticide's efficacy is greatly enhanced.

[0047] Existing conventional formulations have poor sustained-release performance and short duration of action: fludioxonil technical FLU-TC has a maximum cumulative release rate of 69.20% within 72 hours under different pH conditions; the commercially available suspension concentrate FLU-SC has a maximum cumulative release rate of 67.02% within 168 hours. Both are immediate-release formulations, which require frequent reapplication of pesticides in agricultural applications, resulting in high labor costs and easy waste of pesticides.

[0048] This invention, FLU@CTS-PUMC, overcomes the limitations of traditional formulations in drug release, exhibiting significant advantages in long-acting sustained release: During a 720-hour (30-day) testing period, the formulation consistently and stably releases the active ingredient without any sudden drug release, with a sustained-release period exceeding 30 days, far longer than existing commercial formulations. Simultaneously, the microencapsulated structure significantly improves the thermal stability of fludioxonil: pure fludioxonil technical grade experiences a mass loss exceeding 95% at 327℃, with a maximum weight loss rate of -1.5% / ℃; FLU@CTS-PUMC's thermal decomposition peak shifts to 384℃, and the maximum weight loss rate decreases to -0.58% / ℃. The encapsulation effectively delays the thermal decomposition of the active ingredient, broadening the applicable temperature range for formulation storage, transportation, and field application, further ensuring stable efficacy. This long-acting sustained-release characteristic not only reduces the frequency of pesticide spraying and labor input but also avoids the risk of phytotoxicity caused by excessively high drug concentrations in a short period, significantly improving pesticide utilization efficiency.

[0049] IV. It can be used for both seed coating and foliar spraying, with a wide range of applications and strong adaptability.

[0050] Traditional pesticide formulations are often limited to single functions, mostly suitable only for foliar spraying and unable to address seed treatment needs. This invention, FLU@CTS-PUMC, is a multifunctional integrated formulation that can simultaneously meet the needs of both sorghum seed coating and foliar spraying without requiring formula adjustments. It offers dual functionality and exceptional versatility.

[0051] 1. Advantages of Foliar Spray Application: Sorghum leaves have a hydrophobic surface with a deionized water contact angle of 95.7° and a surface tension of 72.86±0.16 mN / m. Traditional fludioxonil technical grade has a droplet contact angle of 77.82°, resulting in droplets that easily bounce and roll off, leading to low adhesion to the leaf surface. The formulation of this invention can reduce the droplet contact angle to 34.2° and the surface tension to as low as 36.48±0.30 mN / m. The droplets exhibit no bounce on the sorghum leaf surface, demonstrating excellent spreadability and adhesion. The microcapsules can be uniformly deposited on the leaf surface to form a functional film, adhering to the crop surface for a long time. This synergistic effect with the slow-release properties provides sustained disease prevention.

[0052] 2. Advantages of Seed Coating Application: Scanning electron microscopy confirmed that FLU@CTS-PUMC can form a uniform and complete coating layer on the surface of sorghum seed coat, with clear boundaries between the coating layer, seed coat layer, and endosperm layer, without damaging the internal seed tissue. When seeds were coated with 1% FLU@CTS-PUMC (1:50 ratio of drug to seed), the germination rate of sorghum seeds reached 91.33%, far exceeding the 64.67% of the blank control group, and the seed pathogen infection rate was reduced to 0%. After treatment, the aboveground dry weight of seedlings reached 0.1007 g, and the underground dry weight reached 0.0516 g. While effectively controlling seed-borne diseases, it can significantly promote seed germination and seedling growth.

[0053] V. Other Comprehensive Technological Advantages

[0054] In addition to the four core advantages mentioned above, this invention also has several additional advantages compared to existing processes and products, including high drug loading efficiency, excellent antibacterial effect, biosafety, simple process, and environmental friendliness. 1. Flexible and controllable drug loading and encapsulation performance: The drug loading rate and encapsulation rate of the formulation can be precisely adjusted by controlling the amount of fludioxonil added. Among them, the encapsulation rate of FLU@CTS-PUMC 0.5 is up to 91.16%, and the drug loading rate of FLU@CTS-PUMC 2.0 can reach 24.76%. The preferred sample FLU@CTS-PUMC 1.0 has an encapsulation rate of 87.26%, with high active ingredient encapsulation efficiency and effective reduction of raw material loss.

[0055] 2. Outstanding antibacterial and disease-preventing effects: Against the main pathogenic bacterium of sorghum, *Colletotrichum sublineola*, the formulation of this invention achieves a half-maximal effective concentration (EC50) of [missing value]. 50 The concentration was 6.64 μg / mL, lower than that of fludioxonil technical (12.00 μg / mL) and commercially available suspension concentrate (7.76 μg / mL); the mycelial inhibition rate was as high as 97.52% at a concentration of 100 μg / mL. Field seedling trials showed that at a concentration of 200 μg / mL, the formulation had a protective activity of 86.38% and a curative activity of 87.97%, with significantly better disease treatment effects than existing commercial agents. It could also destroy the mycelial morphology of pathogenic fungi, block their energy metabolism, and had a stable and long-lasting antibacterial effect.

[0056] 3. Excellent biocompatibility and no phytotoxicity: At conventional application concentrations of 100 μg / mL and 200 μg / mL, sorghum seedlings treated with the formulation of this invention showed normal growth without wilting, yellowing, or other phytotoxic symptoms; the seed coating treatment had no toxic side effects on seeds and seedlings throughout the entire process, and at the same time promoted the accumulation of dry matter in seedlings, making it a safe agricultural formulation.

[0057] 4. Simple process, low energy consumption, and environmentally friendly: This invention uses interfacial polymerization to prepare microcapsules. The reaction conditions are mild and the process is simplified. Compared with traditional microcapsule preparation processes involving multi-layer coating and composite modification, it is easier to operate, consumes less energy, and is suitable for industrial production. The chitosan used is a natural biodegradable polymer material. The formulation can be naturally degraded after use, with no pesticide residue pollution, which meets the requirements of green agricultural development.

[0058] In summary, the FLU@CTS-PUMC microcapsule formulation prepared by this invention comprehensively overcomes the shortcomings of existing fludioxonil formulations, such as uneven morphology, uncontrollable drug release, short duration of effect, and single function. It also has four core highlights: excellent particle morphology, intelligent pH response, ultra-long sustained release, and dual use for seed coating and spraying. At the same time, it has high drug loading efficiency, strong antibacterial ability, biosafety, green environmental protection, and convenient production and use. It has extremely high industrialization value and promotion prospects in the field of green control of seed-borne diseases and seedling diseases in crops such as sorghum. Attached Figure Description

[0059] Figure 1 Stability of microcapsule emulsions prepared with different emulsifiers; Figure 2 OM and SEM morphology analysis of microcapsules prepared for different emulsifiers; Figure 3 SEM morphology analysis of microcapsules prepared with different amounts of OP-10 emulsifier; Figure 4 SEM morphology analysis of microcapsules prepared under different emulsification shear rates and shear times; Figure 5 SEM morphology analysis of microcapsules prepared under different stirring rates, reaction temperatures and reaction times; Figure 6 Preparation process and chemical reaction mechanism of FLU@CTS-PUMC (A, B); typical agricultural applications of this material in foliar spraying and seed coating (C, D); antibacterial and disease-resistant mechanism of FLU@CTS-PUMC-coated sorghum seeds against C. s. (E); Figure 7SEM images of (A, A1)CTS-PUMC, (B, B1)FLU@CTS-PUMC 0.5, (C, C1)FLU@CTS-PUMC 1.0 and (D, D1)FLU@CTS-PUMC 2.0; TEM images of (E)CTS-PUMC, (F)FLU@CTS-PUMC 0.5, (G)FLU@CTS-PUMC 1.0 and (H)FLU@CTS-PUMC 2.0; polydispersity index (PDI) of different concentrations of FLU@CTS-PUMC (I); particle size distribution of different concentrations of FLU@CTS-PUMC (J); encapsulation efficiency and drug loading rate of different concentrations of FLU@CTS-PUMC (K); Zeta potential (L); TG curves (M) and DTG curves (N) of FLU, CTS-PUMC and FLU@CTS-PUMC. Figure 8 The TG curves (A) and DTG curves (B) for FLU, CTS-PUMC, and FLU@CTS-PUMC are shown. Figure 9 FTIR spectra of MDI, FLU, CTS-PUMC, and FLU@CTS-PUMC (A); XRD patterns of FLU, CTS-PUMC, and FLU@CTS-PUMC (B); XPS scan spectra of FLU, CTS-PUMC, and FLU@CTS-PUMC (C); High-resolution XPS spectra of FLU, CTS-PUMC, and FLU@CTS-PUMC (DN); High-resolution XPS spectra of FLU surface elements (C1s, O1s, N1s, F1s) (D, E, F, G); High-resolution spectra of CTS-PUMC surface elements (C1s, O1s, N1s) (H, I, J); High-resolution spectra of FLU@CTS-PUMC surface elements (C1s, O1s, N1s, F1s) (K, L, M, N); Figure 10 Three-dimensional conformational dynamics (A) of fludioxonil (FLU)-loaded CTS-MDI microcapsules in 100 nanosecond molecular dynamics (MD) simulations; quantitative conformational parameters include: (B) root mean square deviation (RMSD), (C) solvent accessible surface area (SASA), (D) number of hydrogen bonds (H-bonds) and (E) radius of gyration (RG). Figure 11 The FLU accumulation and release kinetics of FLU-TC, FLU-SC, and FLU@CTS-PUMC at different pH values; Figure 12Static contact angle, surface tension, bouncing behavior, droplet spreading performance, and post-deposition scanning electron microscopy images of CTS, FLU-TC (FT), FLU-SC (FS), CTS-PUMC (CP), and FLU@CTS-PUMC (FCP) on sorghum leaves at the same concentration; Figure 13 Treatment with CTS, FLU-TC, FLU-SC, CTS-PUMC, and FLU@CTS-PUMC was used to target the anti-anthrax bacteria (Colletotrichum gloeosporioides). C. g. ), tea tree anthracnose ( C. f. ) and *Colletotrichum sorghum* anthracnose ( C. s. Preliminary screening inhibition rate heatmap (concentrations of 25 and 50 μg / mL, A); *Colletotrichum sorghum* anthracnose was treated for 5 days with different concentrations of CTS, FLU-TC (FT), FLU-SC (FS), CTS-PUMC (CP), and FLU@CTS-PUMC (FCP). C. s. Image of fungal community (B); *Colletotrichum sorghum* anthracnose after treatment with different concentrations of test reagents. C. s. The inhibition rate of ) was analyzed by significant difference analysis at the same concentration (C); Figure 14 Anthracnose of *Colletotrichum sorghum* after treatment with different concentrations of test reagents ( C. s. SEM images of hyphal morphology: CK (A); CTS at concentrations of 50 and 100 μg / mL (B, C); FLU-TC at concentrations of 50 and 100 μg / mL (D, E); FLU-SC at concentrations of 50 and 100 μg / mL (F, G); CTS-PUMC at concentrations of 50 and 100 μg / mL (H, I); FLU@CTS-PUMC at concentrations of 50 and 100 μg / mL (J, K); Figure 15 CTS, FLU-TC (FT), FLU-SC (FS), CTS-PUMC (CP), and FLU@CTS-PUMC (FCP) were used to inhibit the activity of *Colletotrichum sorghum* anthracnose (…). Cs The protective effect of ) on disease symptoms (A); Figure 16 CTS, FLU-TC (FT), FLU-SC (FS), CTS-PUMC (CP), and FLU@CTS-PUMC (FCP) were used to inhibit the activity of *Colletotrichum sorghum* anthracnose (…). Cs The protective effect of lesion length (B) and its effect on Cs The protective activity (C) was determined. Sorghum treated with 1% DMSO (dissolved in PDA medium) and sterile water was used as a control (CK). Figure 17CTS, FLU-TC (FT), FLU-SC (FS), CTS-PUMC (CP), and FLU@CTS-PUMC (FCP) were used to inhibit the activity of *Colletotrichum sorghum* anthracnose (…). Cs The therapeutic effect of the disease: symptoms (A); Figure 18 CTS, FLU-TC (FT), FLU-SC (FS), CTS-PUMC (CP), and FLU@CTS-PUMC (FCP) were used to inhibit the activity of *Colletotrichum sorghum* anthracnose (…). Cs The therapeutic effect of lesion length (B) and its effect on Cs The therapeutic effect (C). Sorghum treated with 1% DMSO (dissolved in PDA medium) and sterile water was used as a control (CK). Figure 19 SEM images of the surface of untreated sorghum seeds (A, B); SEM images of the cross-section of untreated sorghum seeds (C, D); SEM images of the surface of FLU@CTS-PUMC coated sorghum seeds (E, F); SEM images of the cross-section of FLU@CTS-PUMC coated sorghum seeds (G, H). Figure 20 Germination rate (A) and infection rate (B) of sorghum seeds under different coating treatments; Photograph of germination boxes of sorghum seeds (C); Figure 21 Image showing the shoot length (A), root length (B), aboveground dry weight (C), and underground dry weight (D) of sorghum seedlings under different coating treatments; image (E) showing the shoot and root length of sorghum seedlings under different coating treatments after 7 days of growth. Figure 22 The activities of SOD, POD, and CAT and the content of GSH in microencapsulated sorghum seeds (A); Principal component analysis (PCA) diagram of differential gene expression (DEGs) in microencapsulated sorghum seeds (B); Upset diagram of DEGs (C); Signaling pathways enriched by differentially expressed genes (D). Figure 23The phenylpropane biosynthesis pathway includes: C4H, trans-cinnamic acid 4-monooxygenase; Phe, phenylalanine; COMT, caffeic acid 3-O-methyltransferase; 4CL, 4-coumarate-CoA ligase; CCR, cinnamyl-CoA reductase; CAD, cinnamyl alcohol dehydrogenase; POD, peroxidase; and CALDH, coniferaldehyde dehydrogenase. The glutathione metabolism pathway includes: GGCT, gamma-glutamyl cyclotransferase; GGT, gamma-glutamyl transpeptidase; LAP, leucine acylaminopeptidase; and G6PD, glucose-6-phosphate 1-dehydrogenase. Starch and sucrose metabolic pathways: α-AMY, α-amylase; β-AMY, β-amylase; GBE, 1,4-α-glucan branching enzyme; SS, starch synthase; UGPase, UTP-glucose-1-phosphate uridine transferase; SPS, sucrose phosphate synthase; SuSy, sucrose synthase; INV, β-fructofuranosidase; FRK, fructokinase; EGLC5 / 6, glucose-1-phosphate adenosine transferase; BG, β-glucosidase; AGPase, glucose-1-phosphate adenosine transferase; SPP, sucrose-6-phosphatase; GBSS, granule-bound starch synthase; EG, endoglucanase. The relative expression levels of differentially expressed genes (DEGs) are displayed using a heatmap. The color gradient represents the expression value after Z-score normalization, with red indicating high expression and cyan indicating low expression. Figure 24 The phytotoxic effects of FLU@CTS-PUMC on sorghum seedlings at a concentration of 100 μg / mL were investigated. Figure 25 The phytotoxic effects of FLU@CTS-PUMC on sorghum seedlings at a concentration of 200 μg / mL were investigated. Figure 26 SEM morphology analysis of microcapsules prepared in Examples 4-7 (A corresponds to Example 4, B corresponds to Example 5, C corresponds to Example 6, and D corresponds to Example 7). Detailed Implementation

[0060] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0061] In all cases, unless otherwise specified, the temperature was at room temperature (15~25℃); unless otherwise specified, the stirring speed was 300 rpm.

[0062] Fludioxonil technical grade (FLU-TC, 98% purity) was purchased from Zhejiang Yulong Pharmaceutical Co., Ltd. (Zhejiang, China); chitosan (CTS, 90% deacetylation, molecular weight 200,000) was purchased from Shanghai Maclean Biochemical Co., Ltd. (Shanghai, China); diphenylmethane diisocyanate (MDI, 99% purity) was purchased from Shandong Wanhua Chemical Group Co., Ltd. (Shandong, China); dibutyltin dilaurate (DBTDL, 95% purity) was purchased from Aladdin Reagent Co., Ltd. (Shanghai, China); dialysis bags (Viskase / Combined Carbonization, MWCO=1000Da); nonionic surfactants. OP-10, NP-10, AEO-9, Span-80, Tween-80 (AR), acetic acid (AR), ethanol (AR), and ethyl acetate (AR) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Beijing, China); methanol (HPLC grade) was purchased from Anhui Energy and Chemical Co., Ltd.; fludioxonil suspension seed coating agent (25 g / L) was purchased from Syngenta Nantong Crop Protection Co., Ltd. (Jiangsu, China); "Hongyingzi 1619" sorghum seeds were provided by Guizhou Maotai Group Hongyingzi Agricultural Technology Development Co., Ltd.; all chemicals were used directly without further purification; deionized water was used throughout the experiment.

[0063] Main equipment: High-speed shearing machine (Fluko FA25D, Germany); Magnetic stirrer (IKARCTbasic, Germany); Dynamic light scattering (DLS) analyzer (NanoBrookOmni, USA); Freeze dryer (CTFD-10S-U) Ningbo Xinzhi Biotechnology Co., Ltd.; Optical microscope (CX40 series, Ningbo Sunny Instruments Co., Ltd.); Scanning electron microscope (FESEM, NovaNanoSEM™450, FEI, USA); Transmission electron microscope (TEM, TalosF200C, FEI, USA); Thermogravimetric analyzer (Netzsch STA449F3, Germany); Fourier transform infrared (FTIR) spectroscopy (Thermo Fisher Scientific Nicole). TiS20 (USA); X-ray diffraction (XRD) pattern (Rigaku Ultima IV, Japan); X-ray photoelectron (XPS) energy dispersive spectroscopy (Thermo Scientific K-Alpha, USA); UV spectrophotometer (TU-1901) Shanghai Spectrum Instruments Co., Ltd.; High performance liquid chromatograph (1260 Infinity II, Agilent, USA); Contact angle meter (OCA15EC, Data Physics Instruments GmbH, Germany); Seed coating machine (5TYBY-300, China); Electric drying oven (DGT-G250S) Hefei Dascate Biotechnology Co., Ltd.; Fully automated microplate reader (Sunrise™, Tecan Group Ltd, Switzerland).

[0064] Encapsulation efficiency and loading rate of FLU@CTS-PUMC: 1 mL of 1% FLU@CTS-PUMC emulsion peak was dispersed in 10 mL of methanol, placed in a centrifuge tube, and centrifuged at 10000 rpm / min for 10 min. The supernatant was collected using a 1.5 mL syringe, filtered through a 0.22 μm organic membrane, and transferred to a mass spectrometry analysis bottle. The FLU content in the supernatant was determined by HPLC. (HPLC conditions: Infinity LabPoroshell 120EC-C18 (4.6 mm × 100 mm, 4 µm), methanol:water (70:30), 1.0 mL / min, 297 nm, 35℃, injection volume 20 μL). The content of free FLU in the supernatant was quantified using a calibration curve of peak area versus FLU concentration (y = 4.2255x - 16.927, R² = 0.9995) (Figure S2). The encapsulation efficiency (EE) and drug loading (LC) of FLU were calculated according to formulas (1) and (2), respectively: (1) (2) (Where, m total FLU represents the total mass of FLU in the system, m free FLU refers to the content of free FLU in the supernatant after centrifugation, and m FLU@CTS-PUMC represents the total mass of the drug-loaded microcapsules.) Preparation method of 1% chitosan aqueous solution: Add 1 g of chitosan powder (w / v) to 100 mL of 1% (v / v) acetic acid aqueous solution, stir thoroughly at 500 rpm and 50℃ until the chitosan is completely swollen and dissolved to obtain 1% chitosan aqueous solution.

[0065] In the performance evaluation, unless otherwise specified, FLU@CTS-PUMC refers to 1% FLU@CTS-PUMC prepared in Example 1.

[0066] Example 1

[0067] The 1% FLU@CTS-PUMC was prepared from the following raw materials: 1g fludioxonil, 10g ethyl acetate, 2g diphenylmethane diisocyanate, 0.1g dibutyltin dilaurate, 3.2g OP-10 emulsifier, and 80 mL 1% chitosan aqueous solution.

[0068] Step S1: 2.0 g of diphenylmethane diisocyanate (MDI), 1.0 g of fludioxonil (FLU) technical powder and 0.1 g of dibutyltin dilaurate (DBTDL) were added to 10 g of ethyl acetate liquid, stirred at room temperature for 5 min, and then sonicated (225W, on for 2 s, off for 3 s, the same for all other cases) for 5 min to fully dissolve and obtain the oil phase.

[0069] In step S2, 3.2 g of OP-10 emulsifier and 80 mL of 1% chitosan aqueous solution (CTS) were added to a beaker and stirred at room temperature for 4 min to obtain an aqueous phase. The oil phase was then slowly added dropwise (60 drops / min) to the aqueous phase while stirring at 200 rpm. After the addition was complete, the mixture was emulsified for 180 s using a high-speed shear press (Fluko FA25D, Germany) at 15000 rpm to form a stable oil-in-water (O / W) emulsion. The stable O / W emulsion was transferred to a beaker and reacted at 60 °C with magnetic stirring at 500 rpm for 3 h. After cooling, the mixture was diluted to a constant volume of 100 mL and stirred until homogeneous to obtain a 1% FLU@CTS-PUMC suspension.

[0070] Comparative Example 1

[0071] The OP-10 emulsifier in Example 1 was replaced with NP-10, AEO-9, Span-80, and Tween-80 respectively, and all other procedures were the same as in Example 1.

[0072] The prepared microcapsule suspension was allowed to stand at room temperature for 24 h, and the results were as follows: Figure 1 As shown in Table 1, the microcapsule emulsions prepared using NP-10, AEO-9, Span-80, and Tween-80 as emulsifiers exhibited obvious stratification and demulsification, indicating that these emulsifiers resulted in poor oil-water phase stability after emulsification. However, the microcapsule emulsion prepared using OP-10 as an emulsifier did not show stratification after standing for 24 hours, nor after an extended period of 30 days. Further testing of the thermal stability (54℃) and low-temperature stability (4℃) of the microcapsule emulsion prepared using OP-10 as an emulsifier, after standing for 30 days, showed no precipitation or stratification.

[0073] Table 1 Evaluation of emulsification results with different emulsifiers

[0074] In the table, the emulsifier dosage is the mass content of the emulsifier relative to the chitosan aqueous solution.

[0075] The morphology of the microcapsules was observed under an optical microscope and a scanning electron microscope, and the particle size and PDI value of the microcapsules were determined by DLS. The results are as follows: Figure 2As shown in Table 2, the microcapsules prepared using NP-10, AEO-9, and Tween-80 as emulsifiers exhibited significant agglomeration, with average particle sizes (D50) of 2474.52, 3030.63, and 2794.87 nm, and PDI values ​​of 0.249, 0.295, and 0.341, respectively. The microcapsules prepared with these emulsifiers showed poor stability, with larger average particle sizes and PDI values, resulting in lower encapsulation efficiency. However, the microcapsules exhibited good formability, all displaying a regular spherical shape. This indicates that the emulsifier has a significant impact on the morphology, average particle size, and dispersion stability of the microcapsules. The microcapsules prepared using Span-80 as an emulsifier had an average particle size (D50) of only 861.17 nm and a PDI value of 0.470. The microcapsules were not uniform in size, and an uneven surface was observed, resulting in poor formability and a low encapsulation efficiency of only 73.22%. The microcapsules prepared using OP-10 as an emulsifier had an average particle size of 1608.00 nm, a PDI value of 0.125, and uniform morphology, smooth and defect-free surface, and spherical shape, with an encapsulation efficiency as high as 87.97%.

[0076] Table 2. Particle size distribution and encapsulation efficiency of microcapsules prepared with different emulsifiers.

[0077] Comparative Example 2

[0078] The amount of OP-10 emulsifier in Example 1 was replaced with 0.8g, 1.6g, 3.2g and 6.4g respectively, and the rest were the same as in Example 1.

[0079] The results are as follows Figure 3 As shown in Table 3, with the increase of OP-10 emulsifier dosage, the average particle size of the microcapsules gradually decreased, and the encapsulation efficiency showed an initial increase followed by a decrease. When the OP-10 emulsifier dosage was 1% and 2%, the average particle size of the microcapsules was relatively large. Due to the low emulsifier dosage, the oil and water droplets were not mixed sufficiently and were unstable, making the core material prone to leakage, resulting in a low encapsulation efficiency. Among them, the microcapsules prepared with 4% OP-10 emulsifier had an average particle size of 1608.00 nm, a PDI value of 0.125, and the microcapsules had uniform morphology, smooth and defect-free surfaces, and were spherical, with an encapsulation efficiency as high as 87.97%. As the emulsifier dosage increased to 6% and 8%, the PDI value and encapsulation efficiency decreased significantly.

[0080] Table 3. Particle size distribution and encapsulation efficiency of microcapsules prepared with different amounts of OP-10 emulsifier

[0081] Comparative Example 3

[0082] Replace the shearing time of 180s in Example 1 with 120s and 300s (seconds) respectively, and refer to Example 1 for all other aspects. Figure 4 As shown in Table 4, the average particle size of the microcapsules decreased from 1788.87 nm to 1142.11 nm, with the encapsulation size initially increasing and then decreasing. The average particle size was smallest at a shearing time of 300 s, but this time exhibited microcapsule adhesion and aggregation. Furthermore, an excessively long shearing time of 300 s subjected the oil-water interface film to continuous and excessive mechanical action, easily leading to the rupture, coalescence, or deformation of already formed droplets, thus reducing the stability of the emulsion system. Simultaneously, prolonged shearing generates localized heat, raising the system temperature and potentially causing premature cross-linking of the wall material, incomplete polymerization, or structural inhomogeneity. Ultimately, this results in irregular microcapsule morphology, a wider particle size distribution, reduced encapsulation efficiency, and affects subsequent sphericity and structural integrity. Therefore, an appropriate shearing time is crucial for microcapsules.

[0083] The shear rate of 15000 rpm in Example 1 was replaced with 10000, 13000, and 18000 rpm respectively, with all other parameters remaining the same as in Example 1. Figure 4 As shown in Table 4, as the shear rate increased from 10,000 to 15,000 rpm, the average microcapsule size decreased from 2,637.99 nm to 1608.00 nm. However, at 18,000 rpm, the excessively high shear rate caused excessive shearing at the oil-water interface. This led to excessive fragmentation of the emulsion droplets, resulting in smaller and unevenly distributed droplets, reducing emulsion stability. Furthermore, the excessive shear force damaged the formed interfacial film, causing separation between the wall material and the core material, resulting in irregular microcapsule morphology, loose structure, and decreased encapsulation efficiency. Simultaneously, intense shearing generated localized high temperatures, potentially causing premature polymerization or excessive cross-linking of the wall material, ultimately affecting the sphericity and sustained-release performance of the microcapsules. At 15,000 rpm, the average microcapsule size was 1608.00 nm, the PDI value was 0.125, the microcapsules had uniform morphology, smooth and defect-free surfaces, and were spherical, with an encapsulation efficiency as high as 87.97%.

[0084] Table 4. Particle size distribution and encapsulation efficiency of microcapsules prepared under different emulsification shear rates and shear times.

[0085] Comparative Example 4

[0086] The stirring time of 3 hours in Example 1 was replaced with 2 hours and 4 hours respectively, while all other steps remained the same as in Example 1. Figure 5 As shown in Table 5, the microcapsules with reaction times of 2 h and 4 h had larger PDI values ​​and uneven morphology. The microcapsules with a reaction time of 3 h had the highest encapsulation rate (87.97%) and the smallest PDI value (0.125), and the microcapsules had uniform morphology.

[0087] The stirring temperature of 60℃ in Example 1 was replaced with 40℃ and 70℃ respectively, while all other conditions remained the same as in Example 1. Figure 5 As shown in Table 5, it was found that under excessively low and high temperatures of 40℃ and 70℃, the lower temperature led to incomplete polymerization, loose wall material, low encapsulation efficiency, and excessively rapid release; while the higher temperature easily caused explosive polymerization, agglomeration, or core material loss, resulting in a decrease in encapsulation efficiency and stability. Only at suitable temperatures can microcapsules with uniform particle size, smooth surface, dense structure, high encapsulation efficiency, and excellent sustained-release performance be obtained. The microcapsules prepared at 60℃ had an average particle size of 1608.00 nm, a PDI value of 0.125, uniform morphology, smooth and defect-free surface, spherical shape, and an encapsulation efficiency as high as 87.97%.

[0088] The stirring speed of 500 rpm in Example 1 was replaced with 300 rpm and 700 rpm respectively, with all other parameters remaining the same as in Example 1. Figure 5 As shown in Table 5, a low rotation speed of 300 rpm leads to uneven oil droplet dispersion, poor emulsion stability, a larger microcapsule particle size of 2010.33 nm, and a reduced encapsulation efficiency of 84.32%. At a rotation speed of 500 rpm, the oil droplets are evenly dispersed, the average microcapsule particle size is 1608.00 nm, the PDI value is 0.125, the microcapsules have uniform morphology, smooth and defect-free surfaces, and are spherical, with an encapsulation efficiency as high as 87.97%. A high rotation speed of 700 rpm, on the other hand, easily causes excessive droplet breakage and damage to the oil-water interface film, leading to aggregation and core material leakage, which in turn reduces the encapsulation efficiency and stability.

[0089] Table 5. Particle size distribution and encapsulation efficiency of microcapsules prepared under different stirring rates, reaction temperatures, and reaction times.

[0090] Comparative Example 5

[0091] The preparation of CTS-PUMC includes the following raw materials: 10g ethyl acetate, 2g diphenylmethane diisocyanate, 0.1g dibutyltin dilaurate, 3.2g OP-10 emulsifier, and 80 mL 1% chitosan aqueous solution.

[0092] In step S1, 2.0 g of diphenylmethane diisocyanate (MDI) polymer liquid and 0.1 g of dibutyltin dilaurate (DBTDL) were added to 10 g of ethyl acetate liquid, stirred at room temperature and sonicated for 10 min to fully dissolve them to obtain the oil phase.

[0093] In step S2, 3.2 g of OP-10 emulsifier and 80 mL of 1% chitosan aqueous solution (CTS) were added to a beaker to obtain the aqueous phase. The oil phase was then slowly added dropwise (60 drops / min) to the aqueous phase and mixed evenly. The mixture was emulsified for 180 s using a high-speed shear mixer (Fluko FA25D, Germany) at 15000 rpm to form a stable oil-in-water (O / W) emulsion. The stable oil-in-water (O / W) emulsion was transferred to a beaker and reacted with magnetic stirring at 500 rpm at 60 °C for 3 h. After cooling, the mixture was diluted to a constant volume of 100 mL to obtain a CTS-PUMC suspension.

[0094] Example 2

[0095] 0.5% FLU@CTS-PUMC was prepared from the following raw materials: 0.5 g fludioxonil, 10 g ethyl acetate, 2 g diphenylmethane diisocyanate, 0.1 g dibutyltin dilaurate, 3.2 g OP-10 emulsifier, and 80 mL 1% chitosan aqueous solution.

[0096] Step S1: 2.0 g of diphenylmethane diisocyanate (MDI), 0.5 g of fludioxonil (FLU) technical powder and 0.1 g of dibutyltin dilaurate (DBTDL) were added to 10 g of ethyl acetate liquid, stirred at room temperature for 5 min, and then sonicated (225W, on for 2 s, off for 3 s, the same for all other cases) for 5 min to fully dissolve and obtain the oil phase.

[0097] In step S2, 3.2 g of OP-10 emulsifier and 80 mL of 1% chitosan aqueous solution (CTS) were added to a beaker to obtain the aqueous phase. The oil phase was then slowly added dropwise (60 drops / min) to the aqueous phase and mixed evenly. The mixture was emulsified for 180 s using a high-speed shear mixer (Fluko FA25D, Germany) at 15000 rpm to form a stable oil-in-water (O / W) emulsion. The stable oil-in-water (O / W) emulsion was transferred to a beaker and reacted with magnetic stirring at 500 rpm at 60°C for 3 h. After cooling, the mixture was diluted to a constant volume of 100 mL and stirred evenly to obtain a 0.5% FLU@CTS-PUMC suspension.

[0098] Example 3

[0099] 2% FLU@CTS-PUMC was prepared from raw materials comprising: 2.0 g fludioxonil, 10 g ethyl acetate, 2.0 g diphenylmethane diisocyanate, 0.1 g dibutyltin dilaurate, 3.2 g OP-10 emulsifier, and 80 mL 1% chitosan aqueous solution.

[0100] Step S1: Add 2.0 g of diphenylmethane diisocyanate (MDI), 2.0 g of fludioxonil (FLU) technical powder and 0.1 g of dibutyltin dilaurate (DBTDL) to 10 g of ethyl acetate liquid, stir at room temperature for 5 min, and then sonicate (225W, on for 2 s, off for 3 s, the same for all other cases) for 5 min to fully dissolve it to obtain the oil phase.

[0101] In step S2, 3.2 g of OP-10 emulsifier and 80 mL of 1% chitosan aqueous solution (CTS) were added to a beaker to obtain the aqueous phase. The oil phase was then slowly added dropwise (60 drops / min) to the aqueous phase and mixed evenly. The mixture was emulsified for 180 s using a high-speed shear mixer (Fluko FA25D, Germany) at 15000 rpm to form a stable oil-in-water (O / W) emulsion. The stable oil-in-water (O / W) emulsion was transferred to a beaker and reacted with magnetic stirring at 500 rpm at 60°C for 3 h. After cooling, the mixture was diluted to a constant volume of 100 mL and stirred evenly to obtain a 2% FLU@CTS-PUMC suspension.

[0102] Microcapsule morphology characterization

[0103] (1) Learning to use a microscope (OM)

[0104] After diluting the microcapsule emulsion, place it on a glass slide, adjust the optimal magnification of the objective and eyepiece, and observe the morphology of the microcapsules using an optical microscope and record the images.

[0105] (2) Scanning electron microscope (SEM)

[0106] After the microcapsule emulsion sample was dropped onto the silicon wafer and dried, it was evenly adhered onto the conductive adhesive. The sample was then sputtered with gold using an ion sputtering instrument (30 s). High-acceleration electrons at a voltage of 5 kW were directed at the sample, and images were obtained and recorded based on the electron beams returning from the sample.

[0107] (3) Transmission electron microscopy (TEM)

[0108] The microcapsule emulsion sample was dropped onto an electron microscope copper grid covered with a support membrane. After drying (or being blotted dry with filter paper), the morphology, particle size, and core-shell structure of the sample were observed and recorded by photography.

[0109] (4) Microcapsule particle size determination

[0110] The particle size, particle size distribution, polydispersity index (PDI), and zeta potential of the microcapsules were determined using a dynamic light scattering particle size analyzer (DLS). The particle size distribution was expressed as D10, D50, and D90, with D50 being the average particle size of the microcapsules.

[0111] Figure 7SEM and TEM images of FLU@CTS-PUMC 0.5 (0.5% FLU@CTS-PUMC suspension), FLU@CTS-PUMC 1.0 (1% FLU@CTS-PUMC suspension), and FLU@CTS-PUMC 2.0 (2% FLU@CTS-PUMC suspension) are shown. Specifically, FLU@CTS-PUMC 1.0 exhibits uniform particle size and morphology, with a smooth and impurity-free surface. The TEM images of FLU@CTS-PUMC 1.0 and FLU@CTS-PUMC 2.0 clearly show a distinct core-shell structure, which is a polyurea-polyurethane microcapsule shell formed by the polymerization reaction of amino (-NH2) and hydroxyl (-OH) groups in MDI and CTS, with the fludioxonil pesticide encapsulated at the center. Compared to CTS-PUMC, the particle size of FLU@CTS-PUMC decreases with increasing fludioxonil (FLU) content, and the microcapsule surface initially becomes smoother and then rougher. This phenomenon can be attributed to the fact that during interfacial polymerization, as the FLU concentration increases, due to the low solubility of FLU, some undissolved FLU precipitates from the oil phase, acting as small nuclei for microcapsule formation, thus reducing the average particle size of the microcapsules. Figure 7 As shown in Figures I, J, and K, the polydispersity index (PDI), particle size distribution, and pesticide loading characteristics of the microcapsules changed with pesticide concentration. The PDI of FLU@CTS-PUMC 1.0 was 0.125, with an average particle size of 1608.00 nm. The particle size distribution curves of both CTS-PUMC and FLU@CTS-PUMC conformed to a normal distribution. The pesticide loading (LC) of FLU@CTS-PUMC increased with increasing FLU concentration, with FLU@CTS-PUMC 2.0 achieving the highest loading of 24.76%. Conversely, the encapsulation efficiency (EE) gradually decreased with increasing FLU concentration, with FLU@CTS-PUMC 0.5 achieving an encapsulation efficiency of 91.16%. The zeta potentials of FLU technical and chitosan were -55.13 mV and 108.62 mV, respectively. Figure 1The positive zeta potential of chitosan originates from the abundant amino groups in its molecular structure. The zeta potential of CTS-PUMC is 69.40 mV, lower than that of chitosan, which is attributed to the consumption of a large number of amino groups during interfacial polymerization (chitosan amino groups react with MDI isocyanate groups to form microcapsules). The zeta potentials of FLU@CTS-PUMC 0.5, FLU@CTS-PUMC 1.0, and FLU@CTS-PUMC 2.0 are 60.28 mV, 51.29 mV, and 31.90 mV, respectively. The higher zeta potential values ​​indicate that the microcapsules have excellent colloidal stability, while the gradual decrease in zeta potential is related to the decrease in microcapsule encapsulation efficiency, leading to an increase in free FLU content. Based on the above characterization results, FLU@CTS-PUMC 1.0 exhibits uniform particle size and morphology, a smooth and impurity-free surface, a low PDI value (0.125), an average particle size (1608.00 nm), and a standard normal particle size distribution. FLU@CTS-PUMC 1.0 also exhibited excellent encapsulation efficiency (87.26%) and release efficiency (22.44%), as well as a stable zeta potential of 51.29 mV.

[0112] Microcapsule thermal stability

[0113] Thermogravimetric analysis (TGA) was performed to study the thermal properties of the microcapsules. The test samples were freeze-dried, and approximately 10 mg of pesticide technical (FLU-TC), empty microcapsules (CTS-PUMC), and fludioxonil microcapsules (FLU@CTS-PUMC) were weighed and placed in the thermogravimetric analyzer. Argon was used as the protective gas, and the temperature was gradually increased from room temperature to 800°C at a rate of 10°C / min. Data were recorded and plotted for analysis.

[0114] The thermal stability of FLU (fludioxonil), CTS-PUMC, and FLU@CTS-PUMC was studied using a combined TG-DTG analysis. Figure 8As shown, FLU exhibits significant weight loss in the 200-327℃ range, with a mass loss exceeding 95% at 327℃, while the residual mass of FLU is only 3.1% at 800℃. Its DTG curve shows a sharp and strong peak at 302℃, with a maximum weight loss rate of -1.5%℃⁻¹, indicating a rapid and uncontrolled thermal decomposition process in FLU. Both CTS-PUMC and FLU@CTS-PUMC exhibit three-stage thermal decomposition behavior. The initial weight loss of 2.1% in the first stage (0-254℃) of CTS-PUMC is attributed to the evaporation of physically adsorbed water and residual solvents from the environment. The second stage (241-431℃) results in a 65.2% mass loss, originating from the decomposition of chitosan (CTS), urea bonds (-NH-CO-NH-), and urethane groups (-NHCOO-) within the polyurethane-polyurea microcapsules. The third stage (431-563℃) further results in a 17.7% mass loss, corresponding to the degradation of residual carbon. The DTG curve of CTS-PUMC showed a moderate intensity peak at 390℃, with a weight loss rate of -0.7%℃⁻¹, reflecting a relatively slow and uniform decomposition process. The 1.9% weight loss of FLU@CTS-PUMC in the first stage (0-221℃) can be attributed to the removal of adsorbed water and residual solvent. The second stage (231-426℃) saw a mass loss of 70.4%, originating from the co-decomposition of chitosan (CTS), urea bonds (-NH-CO-NH-), urethane groups (-NHCOO-), and FLU within the polyurea-polyurethane microcapsules. The third stage (426-534℃) resulted in an additional 15.7% mass loss due to further degradation of residual carbon. Notably, the DTG curve of FLU@CTS-PUMC (1%FLU@CTS-PUMC) showed a shift in the decomposition peak at 384℃, with the maximum weight loss rate decreasing to approximately -0.58%℃. -1 This confirms that microencapsulation technology effectively delays the thermal decomposition of FLU. The combined results demonstrate that FLU@CTS-PUMC enhances the thermal stability of FLU and further validates the successful encapsulation of FLU in CTS-PUMC microcapsules.

[0115] Microcapsule characterization

[0116] FTIR spectroscopy was used to monitor the formation of key chemical bonds during microcapsule assembly, while XRD analysis was used to elucidate changes in crystallinity and interfacial interactions. Figure 9 As shown, all samples (FLU, MDI, CTS-PUMC, FLU@CTS-PUMC (1% FLU@CTS-PUMC)) were at approximately 1600 cm⁻¹. -1The presence of overlapping C=C stretching vibrations in the aromatic rings confirms the shared benzene ring structural unit. MDI exhibits a distinct isocyanate absorption peak at 2240 cm⁻¹, while this peak is not detected in CTS-PUMC. In contrast, CTS-PUMC and FLU@CTS-PUMC show peaks at 1723 cm⁻¹, respectively. -1 and 1728cm -1 The characteristic peak of the urethane group (-NHCOO-) was observed at 1538 cm⁻¹; the urea bond (-NH-CO-NH-) was observed at 1538 cm⁻¹ in both CTS-PUMC and FLU@CTS-PUMC. -1 and 1531cm -1 FLU was detected at 2221 cm⁻¹. These results confirm that the amino and hydroxyl groups on chitosan react with the functional groups of MDI to form a polyurea-polyurethane shell, consistent with previous observations regarding the synthesis of chitosan-MDI polyurethane. Notably, FLU was detected at 2221 cm⁻¹. -1 The characteristic C≡N stretching vibration at 1235cm -1 and 1096cm -1 The CF and CO stretching peaks at 2228 cm⁻¹ were retained in FLU@CTS-PUMC (slightly shifted to 2228 cm⁻¹). -1 1237cm -1 and 1102cm -1 These subtle peak shifts indicate that FLU was successfully encapsulated without chemical degradation, maintaining its structural integrity. XRD analysis ( Figure 9 B) confirmed the high crystallinity of FLU, which is 14-29 cm⁻¹. -1 The diffraction peaks at 20.1° and 20.4° are sharp and consistent with previously reported solid-state structures. In contrast, CTS-PUMC and FLU@CTS-PUMC exhibit broad amorphous peaks at 20.1° and 20.4°, respectively. After loading FLU, these peaks show a slight 2θ shift, reduced intensity, and a decreased full width at half maximum (FWHM). The slight 2θ shift indicates physical interactions (such as hydrogen bonding and van der Waals forces) between FLU and CTS-PUMC, altering the original interlayer spacing of CTS-PUMC and confirming the formation of a composite material rather than a simple physical mixture. The reduced diffraction intensity and FWHM change indicate that FLU molecules are embedded between the crystalline regions and molecular chains of CTS-PUMC, disrupting its ordered structure and reducing crystallinity—an effect similar to that observed in pesticide-chitosan composites. These results collectively validate that FLU is successfully immobilized within CTS-PUMC through encapsulation by a polyurea-polyurethane shell and physical interfacial interactions.

[0117] XPS further elucidated the interaction mechanism of FLU, CTS-PUMC, and the FLU@CTS-PUMC complex. For example... Figure 9As shown in C, G, and N, characteristic peaks of FLU were observed in both the FLU and FLU@CTS-PUMC complexes, confirming the successful loading of FLU into the microcapsules. For the C1s spectrum of CTS-PUMC (…),… Figure 9 Deconvolution analysis of the D, H, and K groups decomposed them into two peaks at 530.5 eV (CO) and 532.1 eV (C=O), corresponding to the hydroxyl and amide groups of chitosan, respectively. These polar sites on CTS-PUMC enable FLU to form hydrogen bonds and electrostatic interactions, thereby achieving stable immobilization of FLU on CTS-PUMC. Figure 9 As shown in F, J, and M, the characteristic binding energy of N1s in CTS-PUMC is 400.85 eV, while this value shifts slightly upward to 401.22 eV in FLU@CTS-PUMC. This shift confirms the covalent cross-linking between the amino and hydroxyl groups of chitosan and the isocyanate groups of MDI, and further indicates an electron cloud interaction between the electron-withdrawing F groups of FLU and the N atoms of CTS-PUMC. In summary, these results verify that FLU was not only successfully loaded onto CTS-PUMC, but also formed a stable composite microcapsule structure through covalent bonds.

[0118] Molecular Dynamics

[0119] Figure 10 Example A visually illustrates the evolution of the three-dimensional conformation of the FLU-loaded CTS-MDI composite microcapsules during molecular dynamics (MD) simulations (obtained in Example 1). Initially, the red region (representing MDI crosslinking nodes / FLU molecules) and the blue region (chitosan fragments) exhibit significant spatial separation, indicating a dense, heterogeneous, non-equilibrium conformation. Subsequently, the overall conformation gradually transforms from the initial dense state to a moderately expanded three-dimensional network structure. In the later stages of the simulation, the spatial distribution of the red and blue regions stabilizes, without significant conformational shifts or component separation, maintaining a uniform and dense three-dimensional structure. This stability perfectly matches the convergence behavior of subsequent RMSD, RG, SASA, and hydrogen bond quantity indices. RMSD is a key indicator of structural stability; a lower value indicates less conformational fluctuation and higher stability. Figure 10 As shown in Figure B, the RMSD of the CTS-MDI composite microcapsules fluctuated significantly in the 0-40 ns period, rapidly decreasing from approximately 5.8 nm, followed by a significant reduction in fluctuation after 40-100 ns, eventually stabilizing in the 5.0-5.2 nm range. This indicates that the three-dimensional cross-linked network of the microcapsules has reached dynamic equilibrium, confirming structural stability. SASA was used to characterize the densification degree of the microcapsule cross-linked network. In the initial stage, the SASA value rapidly and continuously decreased from approximately 500 nm² to 320 nm², subsequently stabilizing and converging to approximately 300 nm². Figure 10C). This indicates the formation of a dense and stable CTS-MDI microcapsule network. The number of hydrogen bonds decreased sharply from approximately 290 to 230, mainly driven by two mechanisms: (1) the densification of the cross-linked network significantly reduced solvent-carrier hydrogen bonds; (2) the carrier-drug hydrogen bonds formed by FLU molecules and chitosan polar groups (hydroxyl and amino groups) only partially offset this reduction, reflecting the dynamic adaptation of drug loading. The number of hydrogen bonds fluctuated in the range of 210-230, indicating that the hydrogen bond interactions between carrier-carrier, carrier-drug, and solvent-carrier systems were in a dynamic equilibrium. Figure 10 D). The RG value, as a measure of structural compactness, continuously increased from approximately 3.2 nm to 4.2 nm in the initial stage, revealing the dynamic conformational rearrangement mechanism of chitosan chains after MDI crosslinking: the formation of covalent crosslinking sites disrupted the initial compact folded conformation of chitosan, and the polymer segments gradually extended outward under the synergistic rearrangement driven by solvent penetration and secondary interactions (such as hydrogen bonding and hydrophobic interactions). The continuous increase in the RG value indicates that the crosslinked network transformed from an initial compact stacked state to a more extended three-dimensional spatial configuration. Subsequently, the RG value converged and stabilized in the range of 4.2–4.4 nm. Figure 10 (E) This confirms that the three-dimensional cross-linked network has formed a thermodynamically stable three-dimensional spatial conformation, in which the elongation trend of polymer segments is dynamically balanced by the spatial constraints of covalent cross-linking. Overall, the molecular dynamics simulation results are consistent with the experimental characterization analysis results, providing molecular-level evidence for the structural stability and drug loading performance of CTS-MDI microcapsules.

[0120] pH-responsive sustained-release kinetics of FLU@CTS-PUMC

[0121] The release behavior of FLU-TC, FLU-SC, and FLU@CTS-PUMC in phosphate-buffered saline (PBS) at different pH values ​​(5.4, 7.4, and 9.4) was evaluated using the dialysis bag method. Specifically, 10 mL of FLU@CTS-PUMC suspension (10 mg / mL) was transferred to a dialysis bag with a molecular weight cutoff (MWCO) of 1000 Da. The sealed dialysis bag was then immersed in a beaker containing 100 mL of PBS buffer at the target pH. The beaker was placed on a magnetic stirrer and incubated at 25 °C with stirring at 200 rpm / min to ensure uniform dispersion of FLU. At predetermined time intervals, 0.5 mL of release medium was withdrawn from the beaker and immediately replenished with an equal volume of fresh PBS buffer at the same pH to maintain a constant system volume. The concentration of released FLU was determined by high-performance liquid chromatography (HPLC). The cumulative release rate (Cr) was calculated based on the standard curve (y=4.1585x-15.119, R²=0.9997) and formula (3) as shown in Figure S3:

[0122] (Where, Cr represents the cumulative release rate of FLU (%); V1 represents the volume of PBS buffer drawn within a preset time interval, which is fixed at 0.5 mL; V0 refers to the total volume of the release medium, which is 100 mL in this study; Cn (mg / mL) represents the concentration of FLU in the buffer at time n; mFLU (mg) represents the total amount of FLU added to the dialysis bag.)

[0123] The development of intelligent sustained-release / controlled-release pesticide microcapsules is an important research direction in the current field of pesticide formulation. For example... Figure 11 As shown, within 720 h (30 days), the cumulative release rates of FLU in FLU@CTS-PUMC (prepared in Example 1) at pH 5.4, 7.4, and 9.4 reached 40.73%, 62.93%, and 75.49%, respectively; within 72 h (3 days), the cumulative release rates of FLU in FLU-TC (fludioxonil technical) at pH 5.4, 7.4, and 9.4 reached 46.75%, 58.53%, and 69.20%, respectively; 168 Within 7 days, the cumulative release rates of FLU in FLU-SC (fludioxonil seed coating agent (commercial drug)) reached 42.62%, 55.79%, and 67.02% at pH 5.4, 7.4, and 9.4, respectively. Under different pH conditions, the release of FLU in FLU@CTS-PUMC continuously increased over time, with its slow-release performance significantly superior to the immediate-release FLU-TC and FLU-SC. Furthermore, the sustained-release performance of the commercial drug FLU-SC was superior to the rapid-release drug FLU-TC. The release of FLU@CTS-PUMC indicated that its release rate was fastest in alkaline environments, exhibiting a clear pH-responsive release characteristic. This pH-responsive microcapsule formulation can adapt to pH fluctuations in the leaf and rhizosphere microenvironment of crops, thereby achieving continuous and controllable pesticide release at the target site. Therefore, it provides a sustainable material strategy for the development of intelligent pesticide delivery.

[0124] Microcapsule leaf surface wettability

[0125] To investigate the leaf wetting properties of FLU@CTS-PUMC, we measured the static contact angle, surface tension, droplet bounce behavior, leaf diffusion performance after spraying, and pesticide microcapsule adhesion to different solutions. The static contact angle was measured using an OCA15EC contact angle meter via the pendant drop method: sorghum leaves were fixed on a glass slide, and solution droplets were added to the leaf surface using a microsyringe. Images were immediately captured, and the contact angle was calculated. Three replicates were set for each solution. Surface tension was measured using the pendant drop method: after a pendant drop formed at the injection needle tip, the surface tension value was calculated through droplet profile analysis. Three replicates were set for each solution. The droplet bounce behavior test was conducted using an OCA15EC contact angle meter in conjunction with a high-speed camera: the microsyringe was raised to the optimal height, and droplets were vertically added to a horizontally placed sorghum leaf. The dynamic process of droplet impact on the leaf surface was recorded. Three replicates were set for each treatment. Wetting performance was assessed based on morphological changes after droplet impact. The prepared solution was then sprayed onto sorghum leaves, and the diffusion behavior of different solutions on fresh sorghum leaves was recorded by photography, noting whether they formed droplets on the leaf surface. After the solution on the leaf surface had completely evaporated, the leaf samples were freeze-dried and subjected to gold sputtering. The adhesion state of the pesticide microcapsules on the leaf surface was observed using scanning electron microscopy (SEM) to comprehensively evaluate the leaf wettability of the pesticide microcapsules.

[0126] To evaluate the leaf surface wettability and hydrophilicity of FLU@CTS-PUMC (obtained in Example 1) on sorghum leaves, deionized water was used as a control in the experiment. Figure 12The deionized water treatment showed the largest contact angle (95.7°) and surface tension (72.86±0.16 mN / m), indicating that the sorghum leaf surface is hydrophobic. The high surface tension of deionized water (72.86±0.16 mN / m) indicates strong cohesive forces within water molecules. Water on the leaves was difficult to spread and easily formed droplets that rolled off. The high surface tension combined with the hydrophobic surface resulted in spherical / hemispherical water droplets with poor wettability. FLU-TC exhibited the same pattern. Since fludioxonil (FLU) is a hydrophobic pesticide, to improve its effective utilization, FLU was dissolved in dimethyl sulfoxide (DMSO) before being mixed with water. The results showed that compared to water, FLU-TC had a lower contact angle (77.82°) and surface tension (59.94±0.32 mN / m), but still higher than other treatments, and also exhibited droplet formation on the sorghum leaves. Chitosan aqueous solution, rich in amino (-NH2) and hydroxyl (-OH) groups, exhibits excellent hydrophilicity, with a contact angle of 57.2° and surface tension of 48.39±0.03 mN / m. Both the commercial pharmaceutical formulation and the microcapsule formulation prepared in this study showed significant decreases in contact angle and surface tension, indicating good hydrophilicity and leaf wettability. The FLU@CTS-PUMC formulation exhibited even lower contact angles (34.2°) and surface tensions (36.48±0.30 mN / m). Subsequent bouncing tests on six droplets showed significant bouncing in the water treatment and FLU-TC treatment, while the other droplets (CTS, FLU-SC, CTS-PUMC, and FLU@CTS-PUMC) did not exhibit droplet bounce on sorghum leaves, indicating that FLU@CTS-PUMC possesses excellent adhesion and hydrophilicity. During pesticide spraying, FLU@CTS-PUMC spreads evenly on the leaf surface and adheres well. Scanning electron microscopy confirmed the uniform deposition of FLU@CTS-PUMC on sorghum leaves, revealing numerous microcapsule spheres forming a membrane structure on the leaf surface. These results collectively demonstrate that FLU@CTS-PUMC possesses excellent leaf wettability and hydrophilicity, enabling stable adhesion to leaves and improving pesticide utilization. Furthermore, FLU@CTS-PUMC exhibits slow-release properties (with an effective duration of over 30 days), significantly inhibiting the spread and infection of seed-borne diseases and seedling diseases in sorghum. This demonstrates its significant industrial value in ensuring normal seed germination and seedling growth.

[0127] In vitro antifungal activity

[0128] (1) The inhibition rate of fludioxonil microcapsules against multiple pathogens was evaluated using the mycelial growth rate inhibition method. The three anthrax pathogens used in this study were: Colletotrichumgloeosporioides ( Cg ), Colletotrichumfructicola ( Cf ), Colletotrichumsublineola ( Cs) Three strains were isolated and identified from the seeds of the sorghum variety “Hongyingzi 1619”, which are seed-borne pathogens of sorghum, and preserved in our laboratory. CTS, FLU-TC, FLU-SC, CTS-PUMC, and FLU@CTS-PUMC were selected at concentrations of 25 μg / mL and 50 μg / mL (where μg / mL refers to the content of the active ingredient; unless otherwise specified, the meaning is similar) as treatment groups. FLU-TC, as a hydrophobic pesticide, was dissolved in 1% DMSO to prepare the desired fludioxonil solution. 1% DMSO (in PDA) and sterile water served as control groups (CK). All drug-treated petri dishes were incubated on potato dextrose agar (PDA medium) at 28±1℃ for 5 days. The in vitro antifungal activity of different pesticide formulations and their corresponding control groups against these three anthrax pathogens was preliminarily evaluated.

[0129] (2) Seven concentrations of fludioxonil, namely 1.5625 μg / mL, 3.125 μg / mL, 6.25 μg / mL, 12.5 μg / mL, 25 μg / mL, 50 μg / mL and 100 μg / mL, were selected as treatment groups. Since FLU-TC is a hydrophobic pesticide, it needs to be dissolved in 1% DMSO to prepare the fludioxonil solution of the required concentration. Therefore, 1% DMSO (in PDA) and sterile water were used as control groups (CK) and EC was calculated. 50 Values ​​were evaluated for different pesticide formulations and their corresponding control groups. Colletotrichum sublineola ( Cs The researchers used a sterile punch to precisely cut 5 mm diameter pores from a 5-day-old culture dish to observe the in vitro antifungal activity of the fungus. Colletotrichum sublineola ( Cs Mycelial cakes were then placed in the center of petri dishes containing different pesticide supplements. After culturing the fungi at 28±1℃ for 5 days, when the fungal colonies in the blank control group reached a diameter exceeding 5 cm in the petri dish, the colony diameter was measured using a ruler in a cross-sectional manner, and the average value was calculated to determine the colony size. The growth inhibition rate was calculated using the following formula: Inhibition rate (%) = (Control colony diameter - Treated colony diameter) / (Control colony diameter - 5 mm mycelial disc diameter) × 100%. The inhibition rate was determined by linear regression analysis. Colletotrichum sublineola ( Cs The median effective concentration (EC50) of compounds with significant inhibitory activity 50 This analysis correlates the observed growth inhibition probability with the logarithmic scale of the concentration.

[0130] First, the in vitro antifungal activity of FLU@CTS-PUMC (obtained in Example 1) was evaluated, with FLU-TC and FLU-SC used as controls for different pesticide formulations, CTS used as a microcapsule wall material control, and CTS-PUMC used as an empty microcapsule control. Figure 13 A). At initial screening concentrations of 25 μg / mL and 50 μg / mL, FLU-TC, FLU-SC, and FLU@CTS-PUMC all showed resistance to three sorghum anthracnose pathogens. Colletotrichum gloeosporioides ( C. g. ), Colletotrichum fructicola ( C. f. ) and Colletotrichum sublineola ( C. s. FLU@CTS-PUMC exhibited antifungal activity. In contrast, chitosan (CTS, microcapsule wall material) and pesticide-free CTS-PUMC did not show significant antifungal activity against these three pathogens. Specifically, FLU@CTS-PUMC showed antifungal activity against these pathogens at concentrations of 25 μg / mL and 50 μg / mL. Cg The antifungal activity (inhibition rates of 67.31% and 72.49%, respectively) was comparable to that of FLU-SC, but superior to that of FLU-TC. (Targeting...) Cf FLU@CTS-PUMC exhibited lower antifungal activity at the same concentration (inhibition rates: 68.62% and 71.26%), slightly lower than FLU-SC but still superior to FLU-TC. (Targeting...) Cs FLU@CTS-PUMC achieved inhibition rates of 85.40% and 92.84% at concentrations of 25 μg / mL and 50 μg / mL, respectively, which were higher than those of FLU-TC (76.16% and 75.83%) and FLU-SC (84.57% and 84.02%). It is noteworthy that FLU-TC, FLU-SC, and FLU@CTS-PUMC all inhibited the inhibition of PUMC. Cs It exhibits excellent antifungal activity, and Colletotrichum sublineola ( Cs This pathogen has been identified as the main causative agent of sorghum anthracnose. Therefore, we will... CsThe selected anthrax strain was chosen as the target strain for subsequent experiments. Subsequently, the mycelial growth rate method was used to determine the effects of different concentrations of pesticide formulations on... Cs Antifungal activity ( Figure 13 B). The antifungal activity of FLU@CTS-PUMC was positively correlated with concentration. Compared with FLU-TC and FLU-SC, FLU@CTS-PUMC exhibited a stronger antifungal effect. At all tested concentrations, FLU@CTS-PUMC showed the best antifungal activity against [the fungi]. Cs The inhibition rates of these inhibitors were significantly higher than those of FLU-TC and FLU-SC, while CTS and CTS-PUMC still showed no significant antifungal activity. Figure 13 C). Specifically, the inhibition rates of FLU@CTS-PUMC at concentrations of 1.5625, 3.125, 6.25, 12.5, 25, 50, and 100 μg / mL were significantly higher than those of FLU-TC and FLU-SC, with the maximum inhibition rate reaching 97.52% at 100 μg / mL. The half-maximal effective concentration (EC50) was further calculated based on the mycelial growth inhibition rate. 50 Values ​​(Table S1). EC of FLU@CTS-PUMC 50 The concentration was 6.64 μg / mL, lower than FLU-TC (12.00 μg / mL) and FLU-SC (7.76 μg / mL). These results further confirm the efficacy of FLU@CTS-PUMC for [the following purposes]. Cs Its excellent antifungal activity indicates its great potential as a promising fungicide formulation. Furthermore, the above results demonstrate that different formulations of the same pesticide have varying effects on... Cs Antifungal effects and EC 50 Significant differences exist.

[0131] FLU@CTS-PUMC Cs Influence of mycelial morphology (SEM)

[0132] Given FLU@CTS-PUMC for Colletotrichum sublineola ( C. s. FLU@CTS-PUMC exhibited excellent in vitro antifungal activity (up to 97.52% at 100 μg / mL). We further investigated the effects of FLU@CTS-PUMC on... Cs The influence of hyphal morphology.

[0133] Method: [The text abruptly ends here, likely due to an incomplete sentence or a formatting error.] Colletotrichum sublineola ( CsThree 5 mm diameter mycelial cakes were cut from the edge of the colony and transferred to potato dextrose broth (PDB). After incubation at 28 ± 1 °C for 48 h, the broth cultures were supplemented with 100 μg / mL and 200 μg / mL concentrations of CTS, FLU-TC, FLU-SC, CTS-PUMC, and FLU@CTS-PUMC (prepared in Example 1). FLU-TC, as a hydrophobic pesticide, was dissolved in 1% DMSO to prepare the required concentration of fludioxonil solution; sterile water was used as a control (CK). The mixture was thoroughly homogenized and incubated for another 24 h. Subsequently, the samples were washed three times with 10 mM phosphate-buffered saline (PBS, pH 7.4), fixed with 2.5% glutaraldehyde at 4 °C for 12 h, and then washed three times with the same 10 mM PBS (pH 7.4). The fixed samples underwent two rounds of gradient ethanol dehydration (30%, 50%, 70%, and 90%), with each concentration treated for 10 min, followed by two washes with 100% ethanol (10 min each). After freeze-drying for 2 h, the hyphal morphology was observed by scanning electron microscopy (SEM).

[0134] The results showed that untreated hyphae (CK) exhibited robust growth, a smooth surface, and a slender, rod-shaped morphology. Figure 14 A). Similarly, mycelia treated with chitosan (CTS) at concentrations of 50 μg / mL and 100 μg / mL also maintained good growth performance, smooth surface, and slender rod-shaped morphology. Figure 14 B and C). However, after treatment with FLU-TC, FLU-SC, and FLU@CTS-PUMC at concentrations of 50 μg / mL and 100 μg / mL, the hyphal morphology changed significantly, with obvious twisting and wrinkling observed on the surface. The morphological changes became more pronounced with increasing fludioxonil concentration. Furthermore, hyphae treated with high concentrations (50 μg / mL and 100 μg / mL) of CTS-PUMC also showed some morphological changes (B and C). Figure 14 H and I). These findings indicate that FLU-TC, FLU-SC, and FLU@CTS-PUMC can all disrupt [the system / system]. Cs The hyphal morphology. According to multiple studies, the changes in hyphal morphology induced by FLU@CTS-PUMC may be related to... Cs This is related to energy metabolism, thus inhibiting mycelial growth in a concentration-dependent manner, with a more significant effect at higher concentrations. In summary, the results of this study confirm that FLU@CTS-PUMC significantly alters... Cs The morphology, through inhibition Cs The energy metabolism pathway is disrupted, cutting off the energy supply for hyphal growth and thus inhibiting hyphal growth, damaging hyphal physiological functions, and ultimately leading to... Cs die.

[0135] Antifungal activity in sorghum seedlings

[0136] Based on the above in vitro antifungal activity results, we further investigated the effects of FLU@CTS-PUMC on... Colletotrichum sublineola ( Cs To assess the protective and therapeutic activities of FLU@CTS-PUMC, this study used a pot experiment to evaluate its effects. Cs The control effect was investigated. In the activity protection test, sorghum seeds of the "Hongyingzi 1619" variety were sown in the soil and cultured at a constant temperature of 28±1℃ for 40 days. Sorghum plants with vigorous leaf growth were selected for in vivo antifungal activity determination. First, sorghum leaves were sprayed with CTS, FLU-TC, FLU-SC, CTS-PUMC, and FLU@CTS-PUMC (prepared in Example 1) at concentrations of 100 μg / mL and 200 μg / mL, respectively. FLU-TC, as a hydrophobic pesticide, was dissolved in 1% DMSO to prepare the required concentration of fludioxonil solution; 1% DMSO (in PDA) and sterile water were used as controls (CK). 24 hours after spraying, a wound less than 5 mm was created on the sorghum leaf using a sterile syringe, and a 5 mm diameter puncture was cut from the culture dish after 5 days of culture using a sterile punch. Cs Fungal cakes were placed on the scratches on sorghum leaves. Sorghum seedlings were then cultured in darkness for 48 h in a greenhouse at 28±1℃ and 95% humidity. After observing anthracnose infection on the sorghum leaves, the seedlings were cultured under constant humidity conditions for 7 days with a 12 h light / 12 h dark cycle. When symptoms appeared, the seedlings were photographed and the length of the lesions on the sorghum leaves was measured. This was also to evaluate the effects of the compounds on... Cs To assess the therapeutic activity, fungal inoculation was performed as described above. The strain was first inoculated onto sorghum leaves and allowed to grow for one day. When disease symptoms appeared, the sorghum leaves were sprayed with CTS, FLU-TC, FLU-SC, CTS-PUMC, and FLU@CTS-PUMC at concentrations of 100 μg / mL and 200 μg / mL. FLU-TC, being a hydrophobic pesticide, was dissolved in 1% DMSO to prepare the required concentration of fludioxonil solution. 1% DMSO (in PDA) and sterile water were used as controls (CK). Subsequently, seedlings were cultured for 7 days under a 12-hour light / 12-hour dark cycle and constant humidity until symptoms appeared. At this time, the seedlings were photographed and the length of lesions was measured. Protective and therapeutic activities were calculated using the following formula: Protective activity and therapeutic activity (%) = (Leg length in control group - Leg length in treatment group) / (Leg length in control group) × 100%.

[0137] like Figure 15-18As shown, at a concentration of 200 μg / mL, FLU@CTS-PUMC... Cs The protective and therapeutic activities of FLU@CTS-PUMC were 86.38% and 87.97%, respectively, while those of FLU-SC were 86.72% and 81.02%, respectively. No significant difference was found in the protective activity between FLU@CTS-PUMC and FLU-SC, but the therapeutic activity of FLU@CTS-PUMC was significantly higher than that of FLU-SC. Furthermore, FLU@CTS-PUMC and FLU-SC exhibited significantly better protective and therapeutic activities than CTS (6.25%, 10.15%), CTS-PUMC (27.68%, 13.69%), and FLU-TC (81.03%, 75.06%). This indicates that the efficacy of fludioxonil (FLU technical grade) is lower than that of microcapsule formulations and commercial suspensions. Therefore, formulation and microencapsulation of pesticide technical grade are particularly important and have significant implications for addressing the pesticide industry's adaptation issues. At a lower concentration of 100 μg / mL, FLU@CTS-PUMC still showed good protective (81.36%) and therapeutic (81.79%) activities in vivo. Similarly, its protective activity was comparable to FLU-SC, but its therapeutic activity was significantly higher; both activities were significantly higher than CTS (4.46%, 3.42%), FLU-TC (72.32%, 70.31%), and CTS-PUMC (0.89%, 1.32%).

[0138] Seed coating

[0139] 1% CTS aqueous solution, 2.5% fludioxonil suspension seed coating agent, CTS-PUMC, 0.5% FLU@CTS-PUMC, 1.0% FLU@CTS-PUMC, and 2.0% FLU@CTS-PUMC were mixed in a seed coating machine at different pesticide volume-to-seed mass ratios (v / m). The coating machine was continuously rotated until the liquid formulation was evenly adhered to the seed surface. After coating, the seeds were removed and dried in a 25°C oven until the moisture content was approximately 12%, and then refrigerated at 4°C for later use. Untreated sorghum seeds served as the control group (CK).

[0140] Table 2-1 Seed Coating Treatment

[0141] Untreated and coated seeds were sliced ​​using a cryostat. The slices were placed on conductive adhesive, freeze-dried for 6 h, sputter-coated with gold for 60 s, and the structure of the coating layer, coating surface, and embryo of microencapsulated sorghum seeds was observed by scanning electron microscopy.

[0142] like Figure 19As shown, the seed coat surface of untreated sorghum seeds exhibits a rough, velvety morphology (AB). Cross-sectional observation reveals a clear seed coat and germ layer, with starch granules visible in the germ layer (CD). For coated sorghum seeds, numerous FLU@CTS-PUMC microcapsule particles (EF) were observed on the seed coat surface; these pesticide microcapsules are uniformly adhered to the seed coat surface, achieving a slow-release effect and thus improving pesticide utilization. Cross-sections of coated seeds show distinct structures of the coating layer, seed coat, and germ layer, with a large number of starch granules still retained in the germ layer (GH). Combined microscopic observation results confirm that FLU@CTS-PUM successfully forms a uniformly adhered coating layer structure on the surface of sorghum seeds.

[0143] The effect of FLU@CTS-PUMC coating treatment on sorghum seed germination

[0144] Germination experiments were conducted in an artificial climate chamber. Following the seed germination experiment procedure of the research group, the cultivation conditions were set at 25℃, 70% relative humidity, and a photoperiod of 12 h light / 12 h dark. For the sorghum seed germination experiment, in accordance with national standards, the pre-treated coated sorghum seeds were sown in a square culture box lined with three layers of filter paper, and water was sprayed evenly. Each treatment was repeated in triplicate, with 100 seeds per group. The measured indicators included germination rate, susceptibility rate, shoot length, root length, aboveground dry weight, and underground dry weight. Specific measurement indicators and methods are described below: Germination rate (%) = (Number of germinated seeds on day 7 / Total number of seeds tested) × 100%.

[0145] Infection rate (%) = (Number of infected seeds on day 7 / Total number of seeds tested) × 100%.

[0146] Bud length (cm) was measured using a ruler from the base of the coleoptile to the tip of the longest leaf. Root length (cm) was determined using a ruler from the rootstock junction to the tip of the longest taproot. Ten germinating seeds were randomly selected from each replicate, and the average of the replicates was taken as the final bud and root lengths.

[0147] The dry weight (g) of the aboveground and underground parts was determined. The stems and roots of the seedlings were separated, and surface moisture was absorbed with filter paper. Three replicates were set up, with stems and roots from five seedlings collected as one sample per replicate. The samples were first blanched in an oven at 105℃ for 2 h, then dried at a constant temperature of 80℃ to constant weight. Finally, the samples were weighed, and the average dry weight of each replicate was calculated.

[0148] Studies have shown that chitosan can serve as a nutrient, effectively promoting seed germination and seedling growth, as well as root and shoot development. It also acts as an excellent coating material for pesticides and for microcapsules. Therefore, we investigated the effects of optimal pesticide coating concentration and pesticide-to-seed ratio (v / m) on various indicators during sorghum seed germination to explore the function and role of chitosan in seed germination. The experimental results are as follows: Figure 20 As shown in A and C, the germination rate of sorghum seeds coated with 1% FLU@CTS-PUMC (1:50) reached 91.33%, significantly higher than that of the control group (CK), 1% CTS (1:50), 2.5% FLU-SC (1:50), CTS-PUMC (1:50), 0.5% FLU@CTS-PUMC (1:50), and 2.0% FLU@CTS-PUMC (1:50) treatment groups. Combined with... Figure 20 Data B and C show that the seed infection rate in group CK reached 51%, and pathogens were clearly observed on the germination boxes, corresponding to a germination rate of only 64.67%, indicating that seed infection significantly affected seed germination. In contrast, the pathogen infection rates of seeds treated with 2.5% FLU-SC and 1% FLU@CTS-PUMC at different pesticide-to-seed ratios (v / m) were significantly lower than those in group CK. The 2.5% FLU-SC (1:50) and 1% FLU@CTS-PUMC (1:50) treatments had the lowest pathogen infection rates (0%), indicating that the pesticide microgels we prepared had the same inhibitory effect on seed-borne pathogens as commercial pesticides, with equally significant results. The results show that the 1% FLU@CTS-PUMC (1:50) coating treatment can both promote seed germination and inhibit seed-borne pathogens, and also demonstrates that FLU@CTS-PUMC has no toxic effect on sorghum seeds. Furthermore, seedling growth indicators were measured, such as... Figure 21 As shown in A, B, and E, the sorghum plant height and root length treated with 1% FLU@CTS-PUMC (1:100) and (1:50) were significantly higher than those of the CK group, 1% CTS group, 2.5% FLU-SC group, CTS-PUMC group, 0.5% FLU@CTS-PUMC group, and 2.0% FLU@CTS-PUMC group. The experimental results indicate that 1% FLU@CTS-PUMC at lower concentrations has a more significant promoting effect on sorghum plant height and root length, and its effect is superior to 2.5% FLU-SC. This may be attributed to the microencapsulation treatment of the pesticide, which reduces the concentration of active ingredients, improves utilization efficiency, and reduces phytotoxicity. Regarding the dry weight of sorghum seedlings, the aboveground and underground dry weights of the 1% FLU@CTS-PUMC (1:50) treatment group reached 0.1007 g and 0.0516 g, respectively, significantly higher than other treatment groups and the control group. Figure 21(C and D). These results all demonstrate that FLU@CTS-PUMC has no toxic effect on sorghum leaves and seeds, and that FLU@CTS-PUMC coating treatment significantly promotes dry matter accumulation in sorghum during the early germination stage, confirming its biosafety. During seed coating, the resulting uniform coating layer continuously releases pesticides, controlling seed-borne and seedling diseases, combining disease control, seed growth promotion, and biosafety characteristics, highly aligning with the green and intelligent development direction of pesticide formulations. This provides a novel multifunctional formulation solution for the green control of seed-borne diseases. Therefore, FLU@CTS-PUMC is a promising slow-release pesticide formulation.

[0149] The antibacterial mechanism of FLU@CTS-PUMC coating on sorghum seeds

[0150] To investigate the effects of microencapsulation coating on the activity of antioxidant enzymes and anti-anthrax properties of sorghum seeds, the activities of SOD, POD, and CAT, as well as the content of GSH, were measured, and transcriptome analysis was performed. Figure 22 As shown in Figure A, the SOD, POD, and CAT activities in the FCP group were 1752.60 U / g, 75.03 ΔOD, and 1752.60 U / g, respectively. 470 The levels of FCP (169.12 μmol / min / g) and GSH were significantly higher in the FCP group than in the CK and CP groups, while there was no significant difference between the CK and CP groups. This indicates that FCP coating can enhance the resistance of seeds to seed-borne anthracnose in the early stage of seed germination by increasing antioxidant enzyme activity and GSH content. In transcriptome analysis, principal component analysis (PCA) showed that PC1 and PC2 explained 89.72% and 4.91% of the total variance, respectively, totaling 94.63%. The three groups of samples were significantly separated along the PC1 axis, and the repetitive samples within each group were tightly clustered, indicating that FCP coating is the main reason for the differences in gene expression patterns, and the experimental data are reliable. Figure 22 B). For example... Figure 22 As shown in Figure C, in the FCP vs CK, CP vs CK, and FCP vs CP comparison groups, the upregulated DEGs were 2238, 810, and 551, respectively, while the downregulated DEGs were 1077, 361, and 331, respectively. UPSET plot analysis showed that the FCP vs CK group had the highest total number of DEGs, of which 1251 were upregulated genes specific to this group and 608 were downregulated genes specific to this group, indicating that FCP coating mainly exerts its regulatory role by activating gene expression. To investigate the biological function and molecular pathways of sorghum seeds responding to microcapsule coating, KEGG enrichment analysis was performed on the DEGs of the three comparison groups (FCP vs CK, CP vs CK, FCP vs CP), as shown below. Figure 22As shown in Figure D, the DEGs of all three comparison groups were significantly enriched in the three core pathways of phenylpropanoid biosynthesis, glutathione metabolism, and starch and sucrose metabolism. In-depth analysis of the FCP vsCK group revealed differential expression of genes related to plant hormone signal transduction pathways, in addition to the core pathways. This indicates that FCP coating can coordinate seed germination and disease resistance processes by regulating hormone signals such as auxin and abscisic acid. In summary, FCP coating significantly enhances the stress resistance and physiological activity of sorghum seeds through multi-pathway synergistic regulation, activating antioxidant and disease resistance-related pathways and optimizing energy metabolism, providing a molecular theoretical basis for its control of sorghum anthracnose and its application in seed treatment to promote growth. Analysis of the DEGs of FCP vs CK, CP vs CK, and FCP vs CP, which were significantly enriched in the phenylpropanoid biosynthesis, glutathione metabolism, and starch and sucrose metabolism pathways, showed... Figure 23 As shown in the heatmap, the phenylpropane biosynthesis pathway exhibits significantly high expression of key enzyme genes such as C4H, COMT, 4CL, CCR, CAD, CALDH, and POD in the FCP coating. These genes drive lignin synthesis and polymerization, strengthen the mechanical strength of the seed cell wall, form a physical barrier, and directly inhibit anthracnose infection. Furthermore, they produce antibacterial and antioxidant substances such as flavonoids and phenolic acids.

[110] Meanwhile, the high expression of the POD gene and the increased enzyme activity were consistent, effectively scavenging reactive oxygen species (ROS), reducing oxidative damage, and enhancing seed stress and disease resistance. In the glutathione metabolic pathway, key enzyme genes such as GGCT, GGT, LAP, and G6PD were significantly highly expressed in the FCP group in the heatmap, promoting glutathione (GSH) recycling. Combined with the increased GSH content in the FCP group, this strengthened cellular antioxidant defense and cleared ROS generated by pathogen stress. High G6PD expression provided sufficient NADPH, ensuring the reduced state of GSH, and synergistically with antioxidant enzymes such as SOD and CAT to maintain cellular functional stability, providing protection for seed germination. The starch and sucrose metabolic pathway ensured energy supply and coordinated growth and disease resistance. In the heatmap, key enzyme genes such as α-AMY, β-AMY, GBE, SS, UGPase, SPS, SuSy, INV, and FRK were significantly overexpressed in FCP coating. This accelerated starch degradation and sugar metabolism, providing sufficient ATP and carbon skeleton for seed germination; and optimized energy allocation, providing material support for defense pathways such as phenylpropanoid and glutathione metabolism. FCP coating synergistically regulates three pathways: activating phenylpropanoid biosynthesis and glutathione metabolism to enhance physical / chemical antibacterial defense and antioxidant capacity; and simultaneously optimizing starch and sucrose metabolism to ensure energy supply. This systematic regulation is consistent with physiological indicators and transcriptome enrichment results, elucidating the molecular physiological mechanism by which FCP treatment enhances the anthracnose resistance of sorghum seeds.

[0151] Phytotoxic effects of FLU@CTS-PUMC on sorghum

[0152] Given the efficacy of FLU@CTS-PUMC in vitro and during the seedling stage... Cs All three formulations showed significant efficacy. We evaluated their phytotoxicity in sorghum seedlings to investigate the toxic effects of this microcapsule formulation. Sorghum leaves were sprayed with CTS, FLU-TC, FLU-SC, CTS-PUMC, and FLU@CTS-PUMC at concentrations of 100 μg / mL and 200 μg / mL, respectively. FLU-TC, as a hydrophobic pesticide, was dissolved in 1% DMSO to prepare the required concentration of fludioxonil solution. 1% DMSO (dissolved in PDA) and sterile water were used as control groups. The wilting status of sorghum leaves was assessed after 7 days to demonstrate the biocompatibility of the microcapsules.

[0153] like Figure 24-25 As shown, sorghum plants treated with 100 and 200 μg / mL FLU@CTS-PUMC maintained normal growth, with well-developed leaves and no wilting symptoms. The same growth performance was observed in the CTS, FLU-TC, FLU-SC, and CTS-PUMC treatment groups. These results collectively indicate that FLU@CTS-PUMC is not phytotoxic to sorghum.

[0154] Example 4

[0155] The 1% FLU@CTS-PUMC was prepared from the following raw materials: 1.0 g of fludioxonil, 10 g of ethyl acetate, 2.0 g of diphenylmethane diisocyanate, 0.1 g of dibutyltin dilaurate, 3.2 g of a mixture of OP-10 emulsifier and AEO-9 emulsifier in a mass ratio of 1:3, and 80 mL of 1% chitosan aqueous solution.

[0156] Step S1: 2.0 g of diphenylmethane diisocyanate (MDI), 1.0 g of fludioxonil (FLU) technical powder and 0.1 g of dibutyltin dilaurate (DBTDL) were added to 10 g of ethyl acetate liquid, stirred at room temperature for 5 min, and then sonicated (225W, on for 2 s, off for 3 s, the same for all other cases) for 5 min to fully dissolve and obtain the oil phase.

[0157] Step S2: A mixture of OP-10 emulsifier and AEO-9 emulsifier at a mass ratio of 1:3 and 80 mL of 1% chitosan aqueous solution (CTS) were added to a beaker to obtain an aqueous phase. The oil phase was then slowly added dropwise (60 drops / min) to the aqueous phase and mixed thoroughly. The mixture was emulsified for 180 s using a high-speed shear press (Fluko FA25D, Germany) at 15000 rpm to form a stable oil-in-water (O / W) emulsion. The stable O / W emulsion was transferred to a beaker and reacted with magnetic stirring at 500 rpm at 60°C for 3 h. After cooling, the mixture was diluted to a constant volume of 100 mL and stirred thoroughly to obtain a 1% FLU@CTS-PUMC suspension.

[0158] Example 5

[0159] The 1% FLU@CTS-PUMC was prepared from the following raw materials: 1.0 g of fludioxonil, 10 g of ethyl acetate, 2.0 g of diphenylmethane diisocyanate, 0.1 g of dibutyltin dilaurate, 3.2 g of a mixture of OP-10 emulsifier and Span-80 emulsifier in a mass ratio of 1:3, and 80 mL of 1% chitosan aqueous solution.

[0160] Step S1: 2.0 g of diphenylmethane diisocyanate (MDI), 1.0 g of fludioxonil (FLU) technical powder and 0.1 g of dibutyltin dilaurate (DBTDL) were added to 10 g of ethyl acetate liquid, stirred at room temperature for 5 min, and then sonicated (225W, on for 2 s, off for 3 s, the same for all other cases) for 5 min to fully dissolve and obtain the oil phase.

[0161] Step S2: A mixture of OP-10 emulsifier and Span-80 emulsifier at a mass ratio of 1:3 and 80 mL of 1% chitosan aqueous solution (CTS) were added to a beaker to obtain an aqueous phase. The oil phase was then slowly added dropwise (60 drops / min) to the aqueous phase and mixed thoroughly. The mixture was emulsified for 180 s using a high-speed shear press (Fluko FA25D, Germany) at 15000 rpm to form a stable oil-in-water (O / W) emulsion. The stable O / W emulsion was transferred to a beaker and reacted with magnetic stirring at 500 rpm at 60°C for 3 h. After cooling, the mixture was diluted to a constant volume of 100 mL and stirred thoroughly to obtain a 1% FLU@CTS-PUMC suspension.

[0162] Example 6

[0163] The 1% FLU@CTS-PUMC was prepared from the following raw materials: 1.0 g of fludioxonil, 10 g of ethyl acetate, 2.0 g of diphenylmethane diisocyanate, 0.1 g of dibutyltin dilaurate, 3.2 g of a mixture of Span-80 emulsifier and AEO-9 emulsifier in a mass ratio of 3:1, and 80 mL of 1% chitosan aqueous solution.

[0164] Step S1: 2.0 g of diphenylmethane diisocyanate (MDI), 1.0 g of fludioxonil (FLU) technical powder and 0.1 g of dibutyltin dilaurate (DBTDL) were added to 10 g of ethyl acetate liquid, stirred at room temperature for 5 min, and then sonicated (225W, on for 2 s, off for 3 s, the same for all other cases) for 5 min to fully dissolve and obtain the oil phase.

[0165] In step S2, a mixture of Span-80 emulsifier and AEO-9 emulsifier at a mass ratio of 3:1 and 80 mL of 1% chitosan aqueous solution (CTS) were added to a beaker to obtain an aqueous phase. The oil phase was then slowly added dropwise (60 drops / min) to the aqueous phase and mixed thoroughly. The mixture was emulsified for 180 s using a high-speed shear press (Fluko FA25D, Germany) at 15000 rpm to form a stable oil-in-water (O / W) emulsion. The stable O / W emulsion was transferred to a beaker and reacted with magnetic stirring at 500 rpm at 60°C for 3 h. After cooling, the mixture was diluted to a constant volume of 100 mL and stirred thoroughly to obtain a 1% FLU@CTS-PUMC suspension.

[0166] Example 7

[0167] The 1% FLU@CTS-PUMC was prepared from the following raw materials: 1.0 g of fludioxonil, 10 g of ethyl acetate, 2.0 g of diphenylmethane diisocyanate, 0.1 g of dibutyltin dilaurate, 3.2 g of a mixture of OP-10 emulsifier, AEO-9 emulsifier and Span-80 emulsifier in a mass ratio of 1:2:1, and 80 mL of 1% chitosan aqueous solution.

[0168] Step S1: 2.0 g of diphenylmethane diisocyanate (MDI), 1.0 g of fludioxonil (FLU) technical powder and 0.1 g of dibutyltin dilaurate (DBTDL) were added to 10 g of ethyl acetate liquid, stirred at room temperature for 5 min, and then sonicated (225W, on for 2 s, off for 3 s, the same for all other cases) for 5 min to fully dissolve and obtain the oil phase.

[0169] In step S2, a mixture of OP-10 emulsifier, AEO-9 emulsifier, and Span-80 emulsifier in a mass ratio of 1:2:1, and 80 mL of 1% chitosan aqueous solution (CTS) were added to a beaker to obtain an aqueous phase. The oil phase was then slowly added dropwise (60 drops / min) to the aqueous phase and mixed thoroughly. The mixture was emulsified for 180 s using a high-speed shear press (Fluko FA25D, Germany) at 15000 rpm to form a stable oil-in-water (O / W) emulsion. The stable O / W emulsion was transferred to a beaker and reacted with magnetic stirring at 500 rpm at 60°C for 3 h. After cooling, the mixture was diluted to a constant volume of 100 mL and stirred thoroughly to obtain a 1% FLU@CTS-PUMC suspension.

[0170]

Claims

1. A method for preparing a highly sustained-release, pH-responsive fludioxonil microcapsule suspension using chitosan-polyurethane copolymer as the wall material, characterized in that: The preparation of a microcapsule suspension with fludioxonil as the core material and chitosan-polyurethane copolymer as the capsule wall specifically includes the following steps: S1 Oil phase preparation: Diphenylmethane diisocyanate, fludioxonil technical and dibutyltin dilaurate were added to ethyl acetate, stirred at room temperature and sonicated until completely dissolved to obtain a homogeneous oil phase; S2 Aqueous Phase Preparation: The emulsifier is added to the chitosan aqueous solution and stirred until completely dissolved to obtain a continuous aqueous phase; the emulsifier is OP-10, or the emulsifier is a mixture of AEO-9 and Span-80 in a mass ratio of (2.5~3.5):1, or the emulsifier is a mixture of OP-10, AEO-9 and Span-80 in a mass ratio of 1:(1.5~2.5):(0.8~1.2); S3 Emulsification and In-situ Polymerization: The oil phase obtained in step S1 is added dropwise to the aqueous phase obtained in step S2. After the addition is complete, a high-speed shear machine is used for shearing and emulsification to form a stable oil-in-water emulsion. Then, the mixture is stirred at 60±5℃ for 3±0.5h to allow diphenylmethane diisocyanate and chitosan molecules to undergo in-situ interfacial polymerization at the oil-water interface, thereby generating a highly slow-release pH-responsive fludioxonil microcapsule suspension with chitosan-polyurethane copolymer as the wall material in one step.

2. The preparation method according to claim 1, characterized in that: In S1, the mass ratio of fludioxonil to diphenylmethane diisocyanate is (0.5~2):2; the mass of dibutyltin dilaurate is 1~5% of the mass of diphenylmethane diisocyanate.

3. The preparation method according to claim 1 or 2, characterized in that: In S2, the mass ratio of diphenylmethane diisocyanate to chitosan is 1:(4±0.5); the mass of the emulsifier is 4±0.5% of the mass of the chitosan aqueous solution.

4. The preparation method according to claim 1 or 2, characterized in that: The volume ratio of ethyl acetate to chitosan aqueous solution is (15~20):80; in S2, the mass concentration of chitosan in the chitosan aqueous solution is 1±0.1%, and it is prepared using an acetic acid aqueous solution with a volume fraction of 1±0.1%; the degree of deacetylation of chitosan (CTS) is ≥90%.

5. The preparation method according to claim 1 or 2, characterized in that: In S2, the shear emulsification speed is 15000±1000 rpm and the time is 180±30 s; And / or, in S2, the stirring speed is 500±100 rpm during the stirring reaction.

6. A highly sustained-release, pH-responsive fludioxonil microcapsule suspension with chitosan-polyurethane copolymer as the wall material, characterized in that, The composite microcapsules are prepared by the preparation method according to any one of claims 1-5; the composite microcapsules are regular spherical core-shell structures with fludioxonil as the core and chitosan-polyurethane covalent copolymer as the shell, with uniform morphology, dense, intact, smooth outer shell, no damage, no unevenness, no deformity, no adhesion, no agglomeration, particle size distribution index ≤0.13, fludioxonil encapsulation rate ≥87%, and zeta potential ≥51mV.

7. The use of the highly sustained-release pH-responsive fludioxonil microcapsule suspension with chitosan-polyurethane copolymer as the wall material as described in claim 6, characterized in that: Used to promote sorghum seed germination; and / or, used to prevent and control sorghum anthracnose.

8. The use according to claim 7, characterized in that: As a seed dressing agent, it promotes sorghum seed germination while inhibiting seed-borne pathogens; and / or can be used for foliar spraying of sorghum to control anthracnose in seedlings; it can adapt to pH fluctuations in the microenvironment of crop leaves and rhizosphere, thereby achieving continuous, intelligent, and controllable pesticide release at the target site, with the release accelerating as the pH increases.

9. The use according to claim 8, characterized in that: When used as a seed coating agent, the volume ratio of the agent to the seed mass (v / m) is 1:100 to 1:25; the germination rate of sorghum seeds is as high as 91.33%. The microcapsule suspension is added to the seed coating machine along with the seeds. The machine is started and rotated at a constant speed until the agent is evenly coated on the seed surface, forming a complete coating layer. After coating, the seeds are placed in an electric heating drying oven and dried at a constant temperature of 20-30℃ (preferably 25℃) until the moisture content is ≤13.5%. When used for foliar spraying, dilute the microcapsule suspension with deionized water and control the fludioxonil concentration to 100-200 μg / mL. Spray evenly on both sides of sorghum leaves. The formulation has excellent wettability and resistance to rain washout. No additional treatment is required after spraying. The inhibition rate of sorghum anthracnose is ≥97.52%.

10. The use according to claim 8 or 9, characterized in that: The microcapsule suspension has excellent leaf wettability and hydrophilicity, with a contact angle of 34.2° and a surface tension of 36.48±0.30 mN / m. It forms a film structure on the surface of sorghum leaves, spreads evenly on the leaves, and has a sustained-release effect of more than 30 days.

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