A composite natural plant essential oil chitosan nanomicrocapsule, its preparation method and application

Abstract

The present invention relates to a composite natural plant essential oil chitosan nanomicrocapsule, a preparation method and an application thereof. The nanomicrocapsule is used for preventing and controlling melon fusarium wilt, with the composite natural plant essential oil as the core material and chitosan as the wall material; the composite natural plant essential oil includes myrrh essential oil, chamomile essential oil and cnidium monnieri essential oil. The present invention utilizes the nanomicrocapsule technology to embed the liquid essential oil into the chitosan wall material to form a solid state, which has high stability and is easy to store and transport. Among them, through the adjustment of the preparation process, the obtained nanomicrocapsules can encapsulate more plant essential oils to obtain the optimal embedding rate. At the same time, when the obtained nanomicrocapsules are applied to prevent and control melon fusarium wilt, the antibacterial rate can reach more than 85%. The raw materials for preparing the nanomicrocapsules of the present invention are green and can be completely decomposed, which can reduce pollution and chemical residues, and has great application prospects in the prevention and control of crop diseases.

Description

Technical Field

[0001] The present invention relates to the technical field of pesticide formulations. Specifically, it is a composite natural plant essential oil chitosan nanomicrocapsule and its preparation method and application. Background Art

[0002] Plant diseases caused by pathogenic bacteria seriously affect the yield and quality of food crops. For example, melon fusarium 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, zucchinis, etc. are more severely affected. Using chemical pesticides is currently the main solution to control melon fusarium wilt, but the use of chemical pesticides is often accompanied by problems such as the generation of drug resistance by pathogenic bacteria, excessive residues of harmful pesticides, and environmental pollution. Natural plant essential oils are secondary metabolites in plants, and their chemical compositions are relatively complex. Due to containing main antibacterial components such as phenolic substances, terpene aldehyde substances, and monohydric alcohols, they are often used as natural broad-spectrum bactericides. In the field of pest and disease control, plant essential oils can effectively inhibit the growth and reproduction of pathogenic bacteria, have high biological activity against pests, good antibacterial ability, long-lasting effect, are not prone to generate drug resistance, and have low toxicity to humans and animals and do not pollute the environment, etc. They are being applied more and more widely and are expected to become natural substitutes for chemical pesticides.

[0003] However, plant essential oils have a strong odor, high volatility, and poor solubility, and are easily affected by environmental factors such as light and heat, making their use and storage difficult, which greatly limits their application. The nanomicrocapsule technology uses polymer materials as carriers to encapsulate the core materials to be protected into tiny particles with a diameter of micrometers or nanometers, so as to achieve the functions of fixing, protecting, and controlled release of the core materials within a certain period of time. Using the nanomicrocapsule 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 disadvantages of essential oils, enhancing 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 disease resistance.

[0004] However, at present, pesticides are still mainly used in the field of controlling melon fusarium wilt. Based on improving the utilization rate, stability, and control efficiency of essential oils, it is still necessary to further study the method of encapsulating plant essential oils by combining the nanomicrocapsule technology and the compounding problem of plant essential oils for plant essential oil nanomicrocapsules that can effectively control melon fusarium wilt. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a composite natural plant essential oil chitosan nanomicrocapsule and its preparation method and application on the basis of improving the control efficiency of melon fusarium wilt, further enhancing the stability of plant essential oils and prolonging the drug effect.

[0006] To solve the above technical problems, the present invention provides the following technical solutions:

[0007] With the development of the protected cultivation area, the accumulation of soil bacteria in greenhouses and plastic greenhouses has increased year by year, making the occurrence of melon fusarium wilt increasingly serious. The symptoms can occur throughout the growth period, and the disease is most severe from flowering to fruiting stage. If the disease occurs before emergence after sowing, it can cause seed rot. When seedlings are diseased, the fibrous roots decrease and the leaves are wrinkled. They wither and turn yellow, lodge and die, and the stem base is light yellow. When adult plants are diseased, the diseased plants grow slowly, and the leaves gradually wilt from bottom to top, especially obvious at noon. In the early stage, they wilt during the day and recover at night. As the disease progresses, the plants cannot recover in the morning and evening and soon die. Therefore, it is urgent to improve the control efficiency of melon fusarium 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 control melon fusarium wilt is the main technical problem to be solved in 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, wherein the composite natural plant essential oil chitosan nano-microcapsule uses the composite natural plant essential oil as the core material and chitosan as the 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 control of melon fusarium wilt.

[0009] Among them, chitosan is a natural polymer material with good biocompatibility and biodegradability, and is friendly to the environment. While wall materials such as gelatin and cyclodextrin have poor stability to acids, alkalis and light and are easily damaged by external environmental factors. Cyclodextrin and gelatin have their specific applications in the drug delivery system. Therefore, the present invention selects chitosan as the wall material of the nano-microcapsule.

[0010] Preferably, the purity of the myrrh essential oil ≥ 95%, the purity of the chamomile essential oil ≥ 95%, and the purity of the cnidium monnieri essential oil ≥ 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 preparation method of the composite natural plant essential oil chitosan nano-microcapsule, comprising the following steps:

[0014] (1) Chitosan is added to an acetic acid solution and stirred until dissolved to obtain a chitosan acetate solution; an alkaline solution is added to adjust the pH of the chitosan acetate solution and set aside.

[0015] (2) After adjusting the pH, Tween 80 is added to the chitosan acetate solution. After stirring evenly, a compound natural plant essential oil is added and stirring is continued until evenly mixed to obtain an oil-in-water emulsion.

[0016] (3) Sodium tripolyphosphate is added dropwise to the oil-in-water emulsion while stirring. After dropping, stirring is continued for...

[0017] (4) After the cross-linking reaction, centrifugation is carried out, the lower layer precipitate is washed, ultrasonically dispersed, and then freeze-dried to obtain the product.

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

[0019] Preferably, in step (1), the mass fraction of the acetic acid solution is 1%; the mass ratio of chitosan to the volume of the 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 acetate solution is adjusted to 4.8.

[0020] Preferably, in step (2), the mass ratio of chitosan to the volume of Tween 80 is 5-6 g: 5 mL; the mass ratio of chitosan to the compound 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 compound natural plant essential oil is 1-2 h.

[0021] Preferably, in step (2), the mass ratio of chitosan to the volume of Tween 80 is 5.7 g: 5 mL; the mass ratio of chitosan to the compound 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 dropping rate of sodium tripolyphosphate is 20 drops / s; the cross-linking reaction time is 2-3 h.

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

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

[0025] Preferably, in step (4), the centrifugation speed is 10,000 r / min and the centrifugation time is 20 min; the ultrasonic dispersion power is 50 w and the ultrasonic dispersion time is 10 min.

[0026] The present invention also provides an application of the composite natural plant essential oil chitosan nanomicrocapsule in preventing and controlling melon fusarium wilt.

[0027] Preferably, during the whole growth period of the melon, the composite natural plant essential oil chitosan nanomicrocapsule is buried around the plants.

[0028] Preferably, when fusarium oxysporum is found to infect during the seedling stage of the melon, 0.01 g of the composite natural plant essential oil chitosan nanomicrocapsule is buried around the roots of the plants at a depth of 2-3 cm.

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

[0030] For the composite plant essential oil of the present invention, myrrh, chamomile, and cnidium monnieri essential oils are selected. When the three are mixed, the antibacterial effect on the pathogen of melon fusarium wilt is good. Most studies on the antibacterial effect of essential oils focus on the antibacterial effect of single essential oils. Compared with single essential oils, the antibacterial effect of the composite essential oil obtained after mixing essential oils is better. Similar plant essential oils are used in combination to play a synergistic role and enhance the antibacterial effect. In the present invention, the antibacterial rate of cnidium monnieri essential oil used alone 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 uses the nanomicrocapsule technology to embed the liquid essential oil into the chitosan wall material to form a solid state, which has high stability and is easy to store and transport. Among them, through the adjustment of the preparation process, such as the mass relationship of chitosan, composite essential oil, and sodium tripolyphosphate, the obtained nanomicrocapsules can encapsulate more plant essential oils and obtain the optimal embedding rate. At the same time, when the obtained nanomicrocapsules are applied to the prevention and control of melon fusarium wilt, the antibacterial rate can reach more than 85%.

[0032] The raw materials for preparing the nanomicrocapsules of the present invention are green, can be completely decomposed, can reduce pollution and chemical residues, and have great application prospects in the prevention and control of crop diseases. Description of the Drawings

[0033] Figure 1 Antibacterial experiment results of different plant essential oils in Example 1 of the present invention;

[0034] Figure 2 Antibacterial experiment 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, it can be seen that the antibacterial effect of the compound essential oil of myrrh, chamomile, and cnidium fruit is the best. Among them, the antibacterial rate of myrrh essential oil + chamomile essential oil + cnidium fruit essential oil (volume ratio 2:1:1) is the highest, reaching 96.67%. The antibacterial rate of myrrh essential oil + chamomile essential oil + cnidium fruit essential oil (volume ratio 1:2:1) is 93.25%, and the antibacterial rate of myrrh essential oil + chamomile essential oil + cnidium fruit essential oil (volume ratio 1:1:2) is 90.31%. The antibacterial rate of myrrh essential oil + chamomile essential oil + cnidium fruit essential oil (volume ratio 1:1:1) is 91.54%. Since the antibacterial mechanisms of different essential oils are not exactly the same, the antibacterial effects are also different for different volume ratios of essential oils.

[0047] (2) Preparation method of the composite natural plant essential oil chitosan nanomicrocapsule, including the following steps:

[0048] 1) Add 5.7 g of chitosan to 100 mL of glacial acetic acid solution with a mass fraction of 1%, stir overnight at room temperature, and after complete dissolution, obtain a chitosan acetic acid solution; add 2 mol / L sodium hydroxide solution to adjust the pH of the chitosan acetic acid solution to 4.8 for standby;

[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, add 5 mL of Tween 80 to the chitosan acetic acid solution, stir at room temperature for 1 h, then add 2.28 g of composite natural plant essential oil (the mixed volume ratio of myrrh essential oil, chamomile essential oil, and cnidium fruit essential oil in the composite natural plant essential oil is 1:2:1), and continue to stir at room temperature for 1 h to obtain an oil-in-water emulsion;

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

[0052] 3) While stirring, add 1.425 g of sodium tripolyphosphate dropwise to the oil-in-water emulsion (the dropping speed is 20 drops / s), and continue to stir after dropping for 2 h of cross-linking reaction;

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

[0054] 4) After the cross-linking reaction, centrifuge at a speed of 10000 r / min for 20 min, remove the supernatant, wash the lower precipitate 3 times, disperse it in deionized water, ultrasonically disperse it at a power of 50 w for 10 min, and then freeze-dry at -20°C for 48 h to obtain it.

[0055] Example 2

[0056] This example provides a method for preparing composite natural plant essential oil chitosan nanomicrocapsules. The difference from Example 1 is that in step 3), the mass ratio of chitosan to sodium tripolyphosphate is 4:1 (i.e., 7.6 g of chitosan and 1.9 g of sodium tripolyphosphate are added in the experiment); and in step 2), the mass ratios of chitosan to the composite natural plant essential oil are 1:0, 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1.0, 1:1.2, 1:1.4 respectively; 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 into a 10 mL volumetric flask, dilute it to the mark with absolute ethanol, and shake well; respectively transfer 0, 0.2, 0.4, 0.6, 0.8, 1.0 mL of the essential oil ethanol solution, dilute it to 10 mL with absolute ethanol, and shake well for standby. Use a UV-visible spectrophotometer to measure its absorbance at 282 nm, and plot a standard curve with the concentration of the essential oil and the corresponding absorbance value.

[0058] Determination of the encapsulation efficiency of the nanomicrocapsules obtained in this example. Encapsulation efficiency determination method: Disperse 50 mg of nanomicrocapsules in 5 mL of HCl solution (2 mol / L). The concentration of the obtained nanomicrocapsule hydrochloric acid solution (i.e., the initial essential oil concentration) is 10 mg / mL. Heat it at 95 °C for 30 min, add 1 mL of absolute ethanol to the cooled mixture, mix well, and centrifuge. Measure the absorbance value of the free essential oil in the supernatant at 282 nm, and substitute it into the standard curve to calculate the concentration of the essential oil. The results are shown in Table 2.

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

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

[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 Entrapment efficiency 30.34％ 33.33％ 51.25％ 45.56％ 35.92％ 33.33％ 26.67％ 20.28％

[0062] The encapsulation efficiency is the key for the composite essential oil core material to play its role and is also a key indicator for evaluating the utilization rate of essential oil. It can be seen from Table 2 that as the mass ratio of chitosan to the composite natural plant essential oil increases, the encapsulation efficiency shows a trend of first increasing and then decreasing. The reason for this result may be that when the amount of essential oil added is relatively small, the amount of essential oil encapsulated when forming the capsule wall by crosslinking is less. As the amount of essential oil increases, although the amount of essential oil loaded in the microcapsules is increasing, the proportion relative to the total added amount is gradually decreasing. Therefore, when the mass ratio of chitosan to the composite natural plant essential oil is 1:0.4, after reaching the maximum encapsulation efficiency of 51.25%, it starts to show a downward trend.

[0063] Example 3

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

[0065] The encapsulation efficiency of the nanomicrocapsules obtained in this embodiment and Example 1 was measured. The measurement method was the same as that in Example 2, and the results are shown in Table 3. As the amount of sodium tripolyphosphate added decreased, the encapsulation efficiency showed a trend of first increasing and then decreasing, and the maximum encapsulation efficiency was reached under the condition of a mass ratio of chitosan to sodium tripolyphosphate of 4:1.

[0066] Table 3 Encapsulation efficiency of nanomicrocapsules obtained with different mass ratios of chitosan to sodium tripolyphosphate

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

[0068] Application Example

[0069] Antibacterial effect of nanomicrocapsules: The nanomicrocapsules obtained in Example 1 were placed in the melon disease field, in melon potted plants inoculated with Fusarium wilt pathogen, and in Petri dishes of Fusarium wilt pathogen of melons, respectively, and the antibacterial rate of the nanomicrocapsules was counted. And it was compared with the commercially available pesticide, Duo Ling, and the specific method was as follows.

[0070] On a PDA plate, half was used to culture the Fusarium wilt pathogen of melons (a bacterial cake with a diameter of 0.5 cm), and half was used to place 0.01 g of the prepared nanomicrocapsules. After culturing at 28 °C for 3 days, the antibacterial rate was measured. Antibacterial rate =

[0071] (Colony diameter of the control group - Colony diameter of the treatment group) / Colony diameter of the control group × 100%.

[0072] Place 0.01 g of the prepared nanomicrocapsules in a seedling tray inoculated with Fusarium wilt of melons, bury them at a depth of 1 cm around the roots, and measure the antibacterial rate after 7 days; the total number of inoculated plants in this experiment was 90. Antibacterial rate =

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

[0074] In a greenhouse with diseased Fusarium wilt of melons, place 0.01 g of the prepared nanomicrocapsules at a depth of 2 - 3 cm around the diseased plants, and measure the antibacterial rate 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 rates of each experimental group are better than that of the commercially available pesticide, Duofuling, and are all greater than 85%, indicating that the nano-microcapsules of the present invention have good antibacterial effect on melon fusarium wilt.

[0076] Table 4 Antibacterial rates of nano-microcapsules and commercially available pesticide, Duofuling

[0077]

[0078] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill 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 manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the claims of this patent application.

Claims

1. A composite natural plant essential oil chitosan nanomicrocapsule, characterized in that The composite natural plant essential oil chitosan nano-microcapsule uses composite natural plant essential oil as the core material and chitosan as the 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 control of melon fusarium wilt; 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).

2. The composite natural plant essential oil chitosan nanomicrocapsule according to claim 1, characterized in that, The mass ratio of the chitosan to the composite natural plant essential oil is 1:(0.2 - 1.4).

3. The composite natural plant essential oil chitosan nanomicrocapsule according to claim 2, wherein, 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 the chitosan to the composite natural plant essential oil is 1:0.4; The purity of the myrrh essential oil ≥ 95%, the purity of the chamomile essential oil ≥ 95%, and the purity of the cnidium monnieri essential oil ≥ 95%.

4. A preparation method of a composite natural plant essential oil chitosan nanomicrocapsule, characterized in that, Using the composite natural plant essential oil chitosan nano-microcapsule according to any one of claims 1 - 3, comprising the following steps: (1) Add chitosan to an acetic acid solution, stir to dissolve to obtain a chitosan acetic acid solution; add an alkali solution to adjust the pH of the chitosan acetic acid solution, and set aside; After adjusting the pH, add Tween 80 to the chitosan acetic acid solution, stir evenly, then add the composite natural plant essential oil and continue 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; While stirring, dropwise add sodium tripolyphosphate to the oil-in-water emulsion, and continue to stir after dropping to carry out a cross-linking reaction; After the cross-linking reaction, centrifuge, wash the lower precipitate, disperse it by ultrasonic wave, and then freeze-dry to obtain it.

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

6. The preparation method according to claim 4, characterized in that In the step (2), the mass ratio of chitosan to the volume of 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 - 2 h; the stirring time after adding the composite natural plant essential oil is 1 - 2 h.

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 dropping rate of sodium tripolyphosphate is 20 drops / s; the cross-linking reaction time is 2 - 3 h.

9. The preparation method according to claim 4, wherein In the step (4), the centrifugation speed is 9000 - 11000 r / min, the centrifugation time is 10 - 30 min; the ultrasonic dispersion power is 40 - 60 w, the ultrasonic dispersion time is 10 - 20 min; freeze-dry at -20°C for 48 h.

10. Application of a composite natural plant essential oil chitosan nano-microcapsule in preventing and controlling melon fusarium wilt, characterized in that, Using the composite natural plant essential oil chitosan nano-microcapsule according to any one of claims 1 - 3.

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