Composite natural plant essential oil chitosan nano microcapsule as well as preparation method and application thereof

Abstract

The invention relates to a composite natural plant essential oil chitosan nano microcapsule and a preparation method and application thereof, the nano microcapsule is used for preventing and treating muskmelon fusarium wilt, the composite natural plant essential oil is used as a core material, and chitosan is used as a wall material; the composite natural plant essential oil comprises myrrh essential oil, chamomile essential oil and fructus cnidii essential oil. The essential oil in a liquid state is embedded into the chitosan wall material by utilizing a nano microcapsule technology to form a solid state, so that the stability is high, and the essential oil is easy to store and transport. According to the present invention, the preparation process is adjusted, such that the obtained nanometer microcapsule can wrap more plant essential oil so as to obtain the optimal embedding rate; meanwhile, when the obtained nano microcapsule is applied to prevention and treatment of muskmelon fusarium wilt, the bacteriostasis rate can reach 85% or above. The raw materials for preparing the nano microcapsule are green and can be completely decomposed, pollution and chemical residues can be reduced, and the nano microcapsule has a huge application prospect in the aspect of crop disease control.

Description

Technical Field

[0001] The present invention relates to the technical field of pesticide preparations, in particular to a composite natural plant essential oil chitosan nano-microcapsule and a preparation method and application thereof. Background Art

[0002] Plant diseases caused by pathogens seriously affect the yield and quality of grain crops. For example, melon wilt, commonly known as dead seedlings, dead vines, wilt disease, and vine cutting disease, is a worldwide soil-borne disease that invades from the roots, and melons, zucchini, etc. are more seriously affected. The use of chemical pesticides is currently the main solution for the prevention and control of melon wilt, but the use of chemical pesticides is often accompanied by problems such as pathogenic bacteria developing drug resistance, excessive residues of harmful pesticides, and environmental pollution. Natural plant essential oils are secondary metabolites in plants with a relatively complex chemical composition. Because they contain phenolic substances, terpenoids, monohydric alcohols and other main antibacterial components, they are often used as natural broad-spectrum fungicides. In the field of pest control, plant essential oils can effectively inhibit the growth and reproduction of pathogens. They have the advantages of high biological activity against pests, good antibacterial ability, long effectiveness, not easy to develop drug resistance, low toxicity to humans and animals, and no environmental pollution. They are increasingly widely used and are expected to become a natural substitute for chemical pesticides.

[0003] However, plant essential oils have strong odors, strong volatility, and poor solubility. They are easily affected by environmental factors such as light and heat, and are difficult to use and store, which greatly limits their application. Nano-microcapsule technology uses polymer materials as carriers to encapsulate the core material that needs to be protected into tiny particles with a diameter of micrometers or nanometers, thereby achieving the effect of fixing, protecting, and controlling the release of the core material within a certain period of time. Using nano-microcapsule technology, liquid plant essential oils can be embedded in wall materials such as cyclodextrin, gelatin, and chitosan to form a solid state, thereby improving the shortcomings of essential oils, improving the stability of essential oils, achieving the purpose of continuous and slow release, and expanding the application scope of plant essential oils in the field of antibacterial and anti-disease.

[0004] However, at present, pesticides are still the main method for the prevention and control of melon wilt. On the basis of improving the utilization rate, stability and prevention efficiency of essential oils, combined with the nano-microcapsule technology to encapsulate plant essential oils and the compounding of plant essential oils, further research is needed on plant essential oil nano-microcapsules that can effectively prevent and control melon wilt. Summary of the invention

[0005] To this end, the technical problem to be solved by the present invention is to provide a composite natural plant essential oil chitosan nano-microcapsule and a preparation method and application thereof on the basis of improving the control efficiency of melon wilt, so as to further improve the stability of the plant essential oil and prolong the efficacy.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] With the development of protected land cultivation area, the accumulation of soil bacteria in greenhouses and plastic greenhouses has increased year by year, making the occurrence of melon wilt more and more serious. Symptoms can occur throughout the growth period, and the disease is most serious from flowering to fruiting period. The disease can cause rotten seeds after sowing and before emergence. Seedlings are sick, fibrous roots are reduced, and leaves are wrinkled. Wither and yellow, lodging and dying, the stem base is light yellow. The disease occurs in the adult stage, the diseased plant grows slowly, and the leaves gradually wilt from bottom to top, which is particularly obvious at noon. The wilting during the day in the early stage recovers at night. As the disease progresses, the plant cannot recover sooner or later and dies soon. Therefore, it is urgent to improve the prevention and control efficiency of melon wilt. At the same time, based on the current application of plant essential oils in the field of antibacterial and disease resistance, and the development of plant essential oil nano-microcapsule technology, how to obtain a plant essential oil nano-microcapsule that can effectively prevent and treat melon wilt is the main technical problem solved by this application.

[0008] In view of the technical problems existing in the prior art, the present invention provides a composite natural plant essential oil chitosan nano microcapsule. The composite natural plant essential oil chitosan nano microcapsule uses the composite natural plant essential oil as a core material and chitosan as a wall material; the composite natural plant essential oil comprises myrrh essential oil, chamomile essential oil and cnidium monnieri essential oil; the composite natural plant essential oil chitosan nano microcapsule is used for the prevention and treatment of melon wilt disease.

[0009] Among them, chitosan is a natural polymer material with good biocompatibility and degradability, and is environmentally friendly. However, wall materials such as gelatin and cyclodextrin have poor stability to acid, alkali and light, and are easily destroyed by external environmental factors. Cyclodextrin and gelatin have specific applications in drug delivery systems. Therefore, the present invention selects chitosan as the wall material of nano microcapsules.

[0010] Preferably, the purity of the myrrh essential oil is ≥95%, the purity of the chamomile essential oil is ≥95%, and the purity of the cnidium monnieri essential oil is ≥95%;

[0011] Preferably, the mixing volume ratio of myrrh essential oil, chamomile essential oil and cnidium monnieri essential oil in the composite natural plant essential oil is (1-2):(1-2):(1-2); the mass ratio of chitosan to the composite natural plant essential oil is 1:0.2-1.4;

[0012] Preferably, the mixing volume ratio of myrrh essential oil, chamomile essential oil and cnidium monnieri essential oil in the composite natural plant essential oil is 2:1:1; the mass ratio of chitosan to the composite natural plant essential oil is 1:0.4;

[0013] The present invention also provides a method for preparing composite natural plant essential oil chitosan nano-microcapsules, comprising the following steps:

[0014] (1) adding chitosan to glacial acetic acid solution, stirring and dissolving, to obtain chitosan acetic acid solution; adding alkaline solution to adjust the pH of the chitosan acetic acid solution, and setting aside;

[0015] (2) After adjusting the pH, Tween 80 is added to the chitosan acetic acid solution, and after stirring evenly, the composite natural plant essential oil is added and continued to stir evenly to obtain an oil-in-water emulsion;

[0016] (3) adding sodium tripolyphosphate dropwise to the oil-in-water emulsion while stirring, and continuing to stir after the addition;

[0017] (4) After the cross-linking reaction, centrifuge, wash the lower precipitate, disperse it by ultrasonic, and freeze-dry it to obtain the product.

[0018] Preferably, in step (1), the mass fraction of the glacial acetic acid solution is 1-2%; the volume ratio of the mass of chitosan to the glacial acetic acid solution is 5-6g:100mL; the alkaline solution is a sodium hydroxide solution, and the concentration of the alkaline solution is 1-2mol / L; the pH of the chitosan acetic acid solution is adjusted to 4-5;

[0019] Preferably, in step (1), the mass fraction of the glacial acetic acid solution is 1%; the volume ratio of the mass of chitosan to the glacial acetic acid solution is 5.7 g:100 mL; the alkaline solution is a sodium hydroxide solution, and the concentration of the alkaline solution is 2 mol / L; the pH of the chitosan acetic acid solution is adjusted to 4.8;

[0020] Preferably, in step (2), the mass ratio of chitosan to Tween 80 is 5-6 g:5 mL; the mass ratio of chitosan to the composite natural plant essential oil is 1:0.2-1.4; the stirring time after adding Tween 80 is 1-2 h; the stirring time after adding the composite natural plant essential oil is 1-2 h;

[0021] Preferably, in step (2), the mass ratio of chitosan to Tween 80 is 5.7 g:5 mL; the mass ratio of chitosan to the composite natural plant essential oil is 1:0.4;

[0022] Preferably, in step (3), the mass ratio of chitosan to sodium tripolyphosphate is 1-6:1; the rate of adding sodium tripolyphosphate is 20 drops / s; and the time of the cross-linking reaction is 2-3 hours;

[0023] Preferably, in step (3), the mass ratio of chitosan to sodium tripolyphosphate is 4:1;

[0024] Preferably, in step (4), the centrifugal speed is 9000-11000 r / min, and the centrifugal time is 10-30 min; the ultrasonic dispersion power is 40-60 w, and the ultrasonic dispersion time is 10-20 min; freeze drying is performed at -20°C for 48 h;

[0025] Preferably, in step (4), the centrifugal speed is 10000 r / min, and the centrifugal time is 20 min; the ultrasonic dispersion power is 50 w, and the ultrasonic dispersion time is 10 min;

[0026] The invention also provides an application of composite natural plant essential oil chitosan nano microcapsules in preventing and treating melon wilt.

[0027] Preferably, during the entire growth period of the melon, the composite natural plant essential oil chitosan nano-microcapsules are buried around the plant.

[0028] Preferably, when the melon seedlings are found to be infected with wilt bacteria, 0.01 g of composite natural plant essential oil chitosan nano-microcapsules are buried around the roots of the plants at a depth of 2-3 cm.

[0029] The technical solution of the present invention achieves the following beneficial technical effects:

[0030] The composite plant essential oil of the present invention selects myrrh, chamomile and cnidium monnieri essential oils, and the three have good antibacterial effect on melon wilt pathogens when mixed. Most of the research on the antibacterial effect of essential oils focuses on the antibacterial effect of a single essential oil. Compared with a single essential oil, the antibacterial effect of the composite essential oil obtained after the essential oil is compounded will be better. Similar plant essential oils are used together to play a synergistic role and enhance the antibacterial effect. The antibacterial rate of cnidium monnieri essential oil used alone in the present invention is 56.62%, the antibacterial rate of myrrh essential oil is 64.59%, the antibacterial rate of cnidium monnieri essential oil+myrrh essential oil is 87.65%, the antibacterial rate of chamomile essential oil is 92.39%, and the antibacterial rate of chamomile essential oil+myrrh essential oil+cnidium monnieri essential oil is 96.67%.

[0031] The present invention utilizes nano-microcapsule technology to embed liquid essential oil into chitosan wall material to form a solid state with high stability and easy storage and transportation. The preparation process is adjusted, such as the mass relationship among chitosan, compound essential oil and sodium tripolyphosphate, so that the obtained nano-microcapsules can encapsulate more plant essential oils and obtain the optimal embedding rate. At the same time, when the obtained nano-microcapsules are used for the prevention and treatment of melon wilt, the antibacterial rate can reach more than 85%.

[0032] The raw materials for preparing the nano-microcapsules of the present invention are green and can be completely decomposed, thereby reducing pollution and chemical residues, and have great application prospects in the prevention and treatment of crop diseases. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The antibacterial test results of different plant essential oils in Example 1 of the present invention;

[0034] Figure 2 The antibacterial test results of myrrh essential oil + chamomile essential oil + cnidium monnieri essential oil in Example 1 of the present invention;

[0035] Among them, (a) myrrh essential oil + chamomile essential oil + cnidium monnieri essential oil (volume ratio is 1:2:1); (b) myrrh essential oil + chamomile essential oil + cnidium monnieri essential oil (volume ratio is 2:1:1); (c) myrrh essential oil + chamomile essential oil + cnidium monnieri essential oil (volume ratio is 1:1:2); (d) myrrh essential oil + chamomile essential oil + cnidium monnieri essential oil (volume ratio is 1:1:1);

[0036] Figure 3 The antibacterial rate of the nanocapsules obtained in Example 1 of the present invention against melon pathogens from different sources. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and technical effect of the invention of this application clearer, the technical scheme in the embodiment of this application will be clearly and completely described below in conjunction with the drawings in the embodiment of this application. Obviously, the described embodiment is a part of the embodiment of this application, not all the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0038] The following is a detailed description of a composite natural plant essential oil chitosan nano-microcapsule of the present invention and its preparation method and application through specific examples.

[0039] Example 1

[0040] This embodiment provides a method for preparing composite natural plant essential oil chitosan nano-microcapsules.

[0041] (1) Screening experiment of plant essential oils

[0042] The antibacterial experiment was carried out on the pathogen of melon wilt (Fusarium oxysporum melon-specific type) using natural plant essential oils such as myrrh, chamomile, cnidium monnieri, zedoaria, star anise, and lavender (all purchased from Ji'an Xusheng Spice Oil Co., Ltd., with an essential oil purity of 95%).

[0043] Antibacterial test method: half of the PDA plate was cultured with melon wilt pathogens (0.5 cm diameter bacterial cake), and the other half was dripped with 10 μL of plant essential oils of each experimental group (if it is a mixed essential oil combination, the total volume of the mixed essential oil is 10 μL) (see Table 1 for details), and the control was dripped with sterile water (10 μL), and cultured at 28°C for 3 days, and the antibacterial rate of each experimental group was determined. The results are shown in Table 1. Figure 1 , Figure 2 Wherein, the antibacterial rate = (the colony diameter of the control group - the colony diameter of the treatment group) / the colony diameter of the control group × 100%.

[0044] Table 1 Antibacterial rate of different plant essential oils

[0045]

[0046] According to the experimental results, the antibacterial effect of myrrh, chamomile and cnidium monnieri compound essential oil is the best, and the antibacterial rate of myrrh essential oil + chamomile essential oil + cnidium monnieri essential oil (volume ratio of 2:1:1) is the highest at 96.67%, the antibacterial rate of myrrh essential oil + chamomile essential oil + cnidium monnieri essential oil (volume ratio of 1:2:1) is 93.25%, the antibacterial rate of myrrh essential oil + chamomile essential oil + cnidium monnieri essential oil (volume ratio of 1:1:2) is 90.31%; the antibacterial rate of myrrh essential oil + chamomile essential oil + cnidium monnieri essential oil (volume ratio of 1:1:1) is 91.54%. Due to the different antibacterial mechanisms of different essential oils, the antibacterial effects of different essential oil volume ratios are also different.

[0047] (2) A method for preparing composite natural plant essential oil chitosan nano-microcapsules, comprising the following steps:

[0048] 1) Add 5.7 g of chitosan to 100 mL of 1% glacial acetic acid solution, stir at room temperature overnight, and obtain chitosan acetic acid solution after it is completely dissolved; add 2 mol / L sodium hydroxide solution to adjust the pH of the chitosan acetic acid solution to 4.8, and set aside;

[0049] That is, the mass ratio of chitosan to the volume of glacial acetic acid solution is 5.7 g:100 mL;

[0050] 2) After adjusting the pH, 5 mL of Tween 80 was added to the chitosan acetic acid solution, and after stirring at room temperature for 1 h, 2.28 g of composite natural plant essential oil (the mixed volume ratio of myrrh essential oil, chamomile essential oil, and cnidium monnieri essential oil in the composite natural plant essential oil was 1:2:1) was added, and stirring was continued at room temperature for 1 h to obtain an oil-in-water emulsion;

[0051] That is, the mass ratio of chitosan to Tween 80 is 5.7 g:5 mL; the mass ratio of chitosan to composite natural plant essential oil is 1:0.4;

[0052] 3) 1.425 g of sodium tripolyphosphate was added dropwise to the oil-in-water emulsion while stirring (the dropping speed was 20 drops / s), and stirring was continued after the addition to carry out the cross-linking reaction for 2 h;

[0053] That is, the mass ratio of chitosan to sodium tripolyphosphate is 4:1;

[0054] 4) After the cross-linking reaction, centrifuge at 10000r / min for 20min, remove the supernatant, wash the lower sediment three times, disperse it in deionized water, ultrasonically disperse it at a power of 50w for 10min, and then freeze-dry it at -20℃ for 48h.

[0055] Example 2

[0056] The present embodiment provides a method for preparing composite natural plant essential oil chitosan nano-microcapsules, which is different from that of Example 1 in that the mass ratio of chitosan to sodium tripolyphosphate in step 3) is 4:1 (i.e., 7.6 g chitosan and 1.9 g sodium tripolyphosphate are added in the experiment); and the mass ratios of chitosan to composite natural plant essential oil in step 2) are 1:0, 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1.0, 1:1.2, and 1:1.4, respectively; the other steps and parameters are the same as those in Example 1;

[0057] Standard curve determination: Use a pipette to transfer 10 μL of essential oil to a 10 mL volumetric flask, dilute to volume with anhydrous ethanol, and shake well; transfer 0, 0.2, 0.4, 0.6, 0.8, and 1.0 mL of essential oil ethanol solution to 10 mL with anhydrous ethanol, shake well for later use. Use a UV-visible spectrophotometer to measure its absorbance at 282 nm, and draw a standard curve based on the concentration of essential oil and the corresponding absorbance value.

[0058] The embedding rate of the nano-microcapsules obtained in this embodiment was determined by dispersing 50 mg of the nano-microcapsules in 5 mL of HCl solution (2 mol / L), the concentration of the resulting nano-microcapsule hydrochloric acid solution (i.e., the initial essential oil concentration) was 10 mg / mL, heated at 95°C for 30 min, and 1 mL of anhydrous ethanol was added to the cooled mixture to mix and centrifuge. The absorbance of the free essential oil in the supernatant was determined at 282 nm, and the concentration of the essential oil was calculated by substituting it into the standard curve. The results are shown in Table 2.

[0059] Encapsulation rate = free essential oil concentration in supernatant / initial essential oil concentration × 100%

[0060] Table 2 Encapsulation efficiency of nanocapsules obtained with different chitosan and composite natural plant essential oil mass ratios

[0061] Group (mass ratio) 1:0 1:0.2 1:0.4 1:0.6 1:0.8 1:1.0 1:1.2 1:1.4 Embedding rate 30.34％ 33.33％ 51.25％ 45.56％ 35.92％ 33.33％ 26.67％ 20.28％

[0062] The embedding rate is the key to the performance of the composite essential oil core material and is also a key indicator for evaluating the utilization rate of essential oil. It can be seen from Table 2 that with the increase in the mass ratio of chitosan to composite natural plant essential oil, the embedding rate shows a trend of first rising and then falling. The reason for this result may be that when the amount of essential oil added is relatively small, the amount of essential oil embedded during cross-linking to form the capsule wall is small. With the increase in the amount of essential oil, although the microcapsule loads more and more essential oil, the proportion relative to the total amount added gradually decreases. Therefore, when the mass ratio of chitosan to composite natural plant essential oil is 1:0.4, after reaching the maximum embedding rate of 51.25%, it begins to show a downward trend.

[0063] Example 3

[0064] This embodiment provides a method for preparing composite natural plant essential oil chitosan nano-microcapsules, which is different from that of Example 1 in that the mass ratio of chitosan to sodium tripolyphosphate in step 3) is different. In this embodiment, the mass ratio of chitosan to sodium tripolyphosphate is 1:1, 2:1, 3:1, 5:1, 6:1 (wherein 5.7 g chitosan is added in the experiment); the other steps and parameters are the same as those of Example 1;

[0065] The embedding rate of the nanocapsules obtained in this example and example 1 was measured in the same manner as in example 2, and the results are shown in Table 3. As the amount of sodium tripolyphosphate added decreased, the embedding rate showed a trend of first increasing and then decreasing, and reached the maximum embedding rate under the condition of a mass ratio of chitosan to sodium tripolyphosphate of 4:1.

[0066] Table 3 Embedding efficiency of nanocapsules obtained with different mass ratios of chitosan and sodium tripolyphosphate

[0067] Group (mass ratio) 1:1 2:1 3:1 4:1 5:1 6:1 Embedding rate 33.33％ 42.77％ 45.18％ 50.76％ 37.37％ 32.55％

[0068] Application Examples

[0069] Antibacterial effect of nanocapsules: The nanocapsules obtained in Example 1 were placed in a melon disease field, a melon potted plant inoculated with wilt pathogens, and a culture dish with melon wilt pathogens, and the antibacterial rate of the nanocapsules was calculated and compared with the commercial pesticide E-Drug, and the specific method is as follows.

[0070] On the PDA plate, half of the plate was cultured with melon wilt pathogens (0.5 cm diameter bacterial cake), and the other half was placed with 0.01 g of the prepared nanocapsules. The plates were cultured at 28°C for 3 days, and the inhibition rate was determined.

[0071] (Control group colony diameter - Treatment group colony diameter) / Control group colony diameter × 100%.

[0072] 0.01g of the prepared nanocapsules were placed in the seedling tray inoculated with melon wilt, buried around the roots to a depth of 1cm, and the antibacterial rate was measured after 7 days; the total number of inoculated plants in this experiment was 90.

[0073] (Total number of inoculated plants - number of diseased plants) / total number of inoculated plants × 100%.

[0074] In a greenhouse with melon wilt disease, 0.01g of the prepared nanocapsules were placed around the diseased plants at a depth of 2-3cm, and the antibacterial rate was measured after 10 days; the total number of diseased plants in this experiment was 30. Antibacterial rate = (total number of diseased plants - surviving plants) / total number of diseased plants × 100%.

[0075] The results showed (Table 4, Figure 3), the antibacterial rate of each experimental group was better than that of the commercially available pesticide, and was greater than 85%, indicating that the nano-microcapsules of the present invention had a good antibacterial effect on melon wilt.

[0076] Table 4 Antibacterial rate of nano-microcapsules and commercial pesticides

[0077]

[0078] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A composite natural plant essential oil chitosan nano microcapsule, characterized in that: The composite natural plant essential oil chitosan nano-microcapsule uses the composite natural plant essential oil as a core material and chitosan as a wall material; the composite natural plant essential oil includes myrrh essential oil, chamomile essential oil and cnidium monnieri essential oil; the composite natural plant essential oil chitosan nano-microcapsule is used for the prevention and treatment of melon wilt disease.

2. The composite natural plant essential oil chitosan nano microcapsule according to claim 1, characterized in that: The mixing volume ratio of myrrh essential oil, chamomile essential oil and cnidium monnieri essential oil in the composite natural plant essential oil is (1-2):(1-2):(1-2); the mass ratio of chitosan to the composite natural plant essential oil is 1:(0.2-1.4).

3. The composite natural plant essential oil chitosan nano microcapsule as claimed in claim 2, characterized in that: The mixing volume ratio of myrrh essential oil, chamomile essential oil and cnidium monnieri essential oil in the composite natural plant essential oil is 2:1:1; the mass ratio of chitosan to the composite natural plant essential oil is 1:0.4; The purity of the myrrh essential oil is ≥95%, the purity of the chamomile essential oil is ≥95%, and the purity of the cnidium monnieri essential oil is ≥95%.

4. A method for preparing composite natural plant essential oil chitosan nano-microcapsules, characterized in that: The method of using the composite natural plant essential oil chitosan nano-microcapsule as claimed in any one of claims 1 to 3 comprises the following steps: (1) adding chitosan to glacial acetic acid solution, stirring and dissolving, to obtain chitosan acetic acid solution; adding alkaline solution to adjust the pH of the chitosan acetic acid solution, and setting aside; (2) after adjusting the pH, adding Tween 80 to the chitosan acetic acid solution, stirring evenly, adding a composite natural plant essential oil and continuing to stir evenly to obtain an oil-in-water emulsion; the composite natural plant essential oil includes myrrh essential oil, chamomile essential oil and cnidium monnieri essential oil; (3) adding sodium tripolyphosphate dropwise to the oil-in-water emulsion while stirring, and continuing to stir after the addition to carry out a cross-linking reaction; (4) After the cross-linking reaction, centrifuge, wash the lower precipitate, disperse it by ultrasonic, and freeze-dry it to obtain the product.

5. The preparation method according to claim 4, characterized in that: In the step (1), the mass fraction of the glacial acetic acid solution is 1-2%; the volume ratio of the mass of chitosan to the glacial acetic acid solution is 5-6g:100mL; the alkaline solution is a sodium hydroxide solution, and the concentration of the alkaline solution is 1-2mol / L; the pH of the chitosan acetic acid solution is adjusted to 4-5.

6. The preparation method according to claim 4, characterized in that: In the step (2), the mass ratio of chitosan to Tween 80 is 5-6 g:5 mL; the mass ratio of chitosan to the composite natural plant essential oil is 1:(0.2-1.4).

7. The preparation method according to claim 4, characterized in that: In the step (2), the mixing volume ratio of myrrh essential oil, chamomile essential oil and cnidium monnieri essential oil in the composite natural plant essential oil is 2:1:1; the stirring time after adding Tween 80 is 1-2h; and the stirring time after adding the composite natural plant essential oil is 1-2h.

8. The preparation method according to claim 4, characterized in that: In the step (3), the mass ratio of chitosan to sodium tripolyphosphate is (1-6):1; the rate of adding sodium tripolyphosphate is 20 drops / s; and the time of the cross-linking reaction is 2-3 hours.

9. The preparation method according to claim 4, characterized in that: In the step (4), the centrifugal speed is 9000-11000 r / min, and the centrifugal time is 10-30 min; the ultrasonic dispersion power is 40-60 w, and the ultrasonic dispersion time is 10-20 min; and freeze drying is performed at -20°C for 48 h.

10. Application of composite natural plant essential oil chitosan nano-microcapsules in preventing and treating melon wilt, characterized in that: The composite natural plant essential oil chitosan nano-microcapsule as claimed in any one of claims 1 to 3 is used.

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