Application method and application of lemongrass volatile oil in plant growth promotion

Abstract

The invention belongs to the technical field of plant growth regulators, and discloses an application method and application of lemongrass volatile oil in promoting plant growth, and the application method of the lemongrass volatile oil in promoting plant growth comprises the following steps: step 1, preparing a lemongrass volatile oil solution; the method comprises the following steps: putting 1kg of dried lemon grass and distilled water into a 10L round-bottom flask according to a ratio of 1: 8, soaking for 10 hours, and distilling for 6-9 hours by adopting a steam distillation method; and 2, removing moisture from the collected lemon grass volatile oil by using anhydrous sodium sulfate, storing the lemon grass volatile oil in a brown bottle, and placing the brown bottle in a refrigerator at-20 DEG C for later use. The lemon grass volatile oil is found to be used as a non-hormone small molecule and can promote plant growth; the lemon grass volatile oil is found to promote the increase of the auxin content; after the lemon grass volatile oil is prepared into the nano-emulsion, plant growth can be promoted through leaf spraying and root irrigation.

Description

Technical Field

[0001] The invention belongs to the technical field of plant growth regulators, and in particular relates to an application method and use of lemongrass volatile oil in promoting plant growth. Background Art

[0002] The root system is the main organ for plants to absorb water and nutrients. A good root system architecture directly affects rhizosphere processes and interactions, and is essential for plant growth, development, yield, quality, economic value, and coping with different stress conditions. The growth and development of the root system and changes in the root system architecture are regulated by complex endogenous signal pathways and are affected by many biological and abiotic factors. Regulating the root system architecture and promoting the development of lateral roots and root hairs can enhance plant growth and rhizosphere nutrient absorption and improve fertilizer utilization.

[0003] Plant secondary metabolites play a vital "ecological role", but their potential in the green development of agriculture has not been fully utilized. Lemongrass (Cymbopogon citratus (DC.) Stapf) volatile oil is widely available and inexpensive, and its main components include citronellal, geraniol and citronellol. Some studies have studied the chemical composition of lemongrass volatile oil from other perspectives such as the development and manufacture of flavors and fragrances, antioxidants, bioherbicides, and fungicides, but there has been no research on the effect of lemongrass volatile oil on plant growth.

[0004] Through the above analysis, the problems and defects of the prior art are as follows:

[0005] There is no research on the effects of lemongrass essential oil on plant growth. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides an application method and use of lemongrass volatile oil in promoting plant growth.

[0007] The present invention is achieved in that a method for applying lemongrass volatile oil in promoting plant growth comprises:

[0008] Step 1: put 1 kg of dried lemongrass and distilled water in a 10L round-bottom flask at a ratio of 1:8, soak for 10 hours, and then distill for 6-9 hours using steam distillation;

[0009] Step 2: After removing moisture from the collected lemongrass volatile oil with anhydrous sodium sulfate, the oil is stored in a brown bottle and placed in a -20°C refrigerator for later use.

[0010] Furthermore, the volatile oil is used in promoting plant growth, wherein the plants include the model plant Arabidopsis thaliana and the crops pepper and rice, and the volatile oil is prepared by steam distillation.

[0011] Furthermore, the volatile oil acts on the plant in the form of gas volatilization, and the volatile oil is adsorbed by filter paper in the laboratory and placed in a culture dish.

[0012] Furthermore, the volatile oil is applied in the field using a lemongrass volatile oil nanoemulsion, and the volatile oil surfactant Tween 80 and the co-surfactant anhydrous ethanol are used as solvent and dispersant.

[0013] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0014] First, the present invention discovered that lemongrass volatile oil, as a non-hormone small molecule, can promote plant growth;

[0015] It was found that lemongrass volatile oil promotes the increase of plant auxin content; after the lemongrass volatile oil is prepared into a nanoemulsion, it can promote plant growth through leaf spraying and root irrigation.

[0016] The invention introduces a novel plant growth promotion method, i.e., using lemongrass volatile oil to promote plant growth. The method firstly mixes dried lemongrass with distilled water in a ratio of 1:8, soaks the mixture in a round-bottom flask for 10 hours, and then uses a steam distillation method to distill the mixture for 6-9 hours to extract the volatile oil. The extraction method can fully retain the active ingredients in the lemongrass volatile oil, and provides high-quality raw materials for subsequent plant growth promotion applications.

[0017] The extracted lemongrass volatile oil was dehydrated with anhydrous sodium sulfate, stored in a brown bottle, and placed in a refrigerator at -20°C for future use. This storage method effectively extends the shelf life of the volatile oil while maintaining its biological activity and stability. More importantly, this volatile oil is suitable for promoting the growth of a variety of plants, including the model plant Arabidopsis thaliana and important crops such as peppers and rice, showing its wide applicability and application potential.

[0018] Under laboratory conditions, we used gas volatilization to make lemongrass volatile oil act on plants. Specifically, we adsorbed the volatile oil on filter paper and placed it in a petri dish, so that the volatile oil was released in the form of gas and acted on the plants. This method is simple and easy to use, and it is easy to control the concentration and action time of the volatile oil, providing a powerful tool for studying the promotion of volatile oil on plant growth.

[0019] In order to apply this method to field practice, we further developed lemongrass volatile oil nanoemulsion as a carrier for field application. This nanoemulsion uses Tween 80 as a surfactant and anhydrous ethanol as a cosurfactant, which can effectively disperse the volatile oil in water to form a stable emulsion. This nanoemulsion not only improves the adhesion and permeability of the volatile oil on plant leaves, but also enhances its biological activity, thereby significantly improving the effect of the volatile oil on plant growth. This technology further provides important technical support for the widespread application of lemongrass volatile oil in agricultural production.

[0020] Third, as auxiliary evidence of the inventiveness of the claims of the present invention, it is also reflected in the following important aspects:

[0021] (1) The expected benefits and commercial value of the technical solution of the present invention after transformation are:

[0022] Improve crop yields: As a plant growth regulator, the use of lemongrass essential oil can effectively improve the growth conditions of plants, thereby expected to increase crop yields.

[0023] Reduce environmental pollution: Since lemongrass volatile oil, as a plant growth regulator, can reduce the use of fertilizers and pesticides, it can be expected to reduce environmental pollution in the agricultural production process, which is beneficial to the protection and sustainable development of the ecological environment.

[0024] Market potential: As people's awareness of food safety and environmental protection increases, the demand for natural and environmentally friendly plant growth regulators is gradually increasing. As a natural and pollution-free plant growth regulator, lemongrass essential oil has broad market prospects and potential.

[0025] Industrial chain extension: The use of lemongrass volatile oil as a plant growth regulator can drive the development of related industrial chains, such as lemongrass planting, processing, and sales, forming a complete industrial chain.

[0026] Technological innovation: The transformation of lemongrass essential oil as a plant growth regulator is an important direction of agricultural technological innovation. The successful application of this technology will help improve agricultural production efficiency and quality and promote the upgrading and development of the agricultural industry.

[0027] (2) The technical solution of the present invention fills the technical gap in the industry at home and abroad:

[0028] Development of natural plant growth regulators: Currently, most of the plant growth regulators on the market are artificially synthesized. However, lemongrass volatile oil, as a plant growth regulator from a natural source, its development and application fills the technical gap of plant growth regulators from natural sources.

[0029] Multifunctional application of lemongrass essential oil in agriculture: Although lemongrass essential oil has certain applications in traditional medicine, cosmetics and other fields, its use as a plant growth regulator in the agricultural field is relatively rare. The proposal of this technical solution fills the gap in the application of lemongrass essential oil in promoting plant growth, increasing yield, and improving quality.

[0030] Innovation of environmentally friendly agricultural inputs: With the improvement of environmental awareness, agricultural production has higher and higher requirements for the environmental friendliness of inputs. As a natural and pollution-free agricultural input, the development and application of lemongrass essential oil meets the innovative needs of environmentally friendly agricultural inputs and fills the technical gap in this field.

[0031] (3) The technical solution of the present invention solves a technical problem that people have been eager to solve but have never been able to solve successfully: in the Chinese medicinal material planting industry, some Chinese medicinal materials such as Paris polyphylla and Panax notoginseng grow slowly and take a long time to grow. If they can be applied to Chinese medicinal material planting, the growth rate of medicinal materials can be accelerated and the planting period of medicinal materials can be shortened, which will promote the innovative development of the Chinese medicinal material industry. In crop planting, the use of hormone pesticides can be reduced or avoided, pesticide residues can be reduced, and crop quality can be improved.

[0032] (4) The technical solution of the present invention overcomes technical prejudice:

[0033] As a volatile substance of plants, plant essential oils are unstable and volatile, which limits their use. However, the technology of making essential oils into nanoemulsions overcomes the technical prejudice of low utilization rate of essential oils, greatly reduces their volatility, improves their stability, and facilitates storage and transportation. At the same time, it further improves the adhesion, dispersion and permeability of essential oils on plant leaves, and can also be used through root irrigation. Various methods of use can promote plant growth.

[0034] Fourthly, the method for applying lemongrass volatile oil in promoting plant growth provided by the embodiment of the present invention finally obtains high-purity lemongrass volatile oil through a series of precise steps and treatments, thereby ensuring its effectiveness and stability in promoting plant growth.

[0035] Step S101: Extracting lemongrass essential oil

[0036] 1. Raw materials preparation:

[0037] Choose 1kg of fresh dried lemongrass to ensure its quality and purity of ingredients to ensure the effectiveness of the extracted volatile oil.

[0038] 2. Soak:

[0039] Put the dried lemongrass and distilled water in a 10L round-bottom flask at a ratio of 1:8 (1kg dried lemongrass with 8L distilled water). Soak for 10 hours to fully dissolve and extract the active ingredients in the lemongrass, preparing for the subsequent distillation extraction.

[0040] 3. Steam distillation:

[0041] After the soaking is completed, the steam distillation device is started and the distillation process is carried out for 6-9 hours. During the distillation process, the water vapor is heated to volatilize the volatile components in the lemongrass. The steam carrying these components is cooled through the condenser and condensed into liquid, which contains volatile oil and a small amount of water.

[0042] Step S102: Processing and storage

[0043] 4. Volatile oil collection and dehydration:

[0044] The collected distillate is placed in a separatory funnel for separation to obtain preliminary lemongrass volatile oil.

[0045] The initially obtained volatile oil is dehydrated with anhydrous sodium sulfate. As a desiccant, anhydrous sodium sulfate can absorb the water in the volatile oil and make the volatile oil more pure.

[0046] 5. Storage of volatile oil:

[0047] Transfer the dehydrated lemongrass essential oil to a brown bottle. The brown bottle can prevent the essential oil from being affected by light and oxidized or degraded, maintaining its stability and the activity of the active ingredients.

[0048] Finally, place the brown bottle in a refrigerator at -20°C. The low temperature environment can further prevent the oxidation and volatilization of the volatile oil, ensuring its quality in subsequent use.

[0049] Application effect:

[0050] 1. Promotes Plant Growth:

[0051] The extracted and processed lemongrass volatile oil contains a variety of effective ingredients that promote plant growth, such as citronellol, geraniol, etc. These ingredients can improve the disease resistance and growth rate of plants by regulating the physiological activities of plants.

[0052] In practical applications, diluting lemongrass volatile oil in a certain proportion and spraying it on the surface of plants or applying it to the soil can effectively promote the growth and health of plants.

[0053] Through precise soaking, distillation, dehydration and preservation steps, the application method of lemongrass volatile oil in promoting plant growth provided by the embodiment of the present invention can effectively extract and preserve the effective ingredients in lemongrass, ensuring its high efficiency and stability in application. This method not only improves the growth rate and health of plants, but also provides a natural and environmentally friendly plant growth promoter. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 The present invention is a flowchart of a method for applying lemongrass volatile oil in promoting plant growth provided by an embodiment of the present invention.

[0055] Figure 2 This is a graph showing the effect of lemongrass volatile oil provided by an embodiment of the present invention on the growth of Arabidopsis thaliana.

[0056] Figure 3 This is a graph showing the effect of lemongrass volatile oil on the auxin content of Arabidopsis thaliana provided by an embodiment of the present invention.

[0057] Figure 4 It is the KEGG enrichment analysis of the common differential genes between the low concentration lemongrass volatile oil (LC) and the high concentration lemongrass volatile oil (HC) provided in the embodiment of the present invention, showing the enriched top 9 pathway maps.

[0058] Figure 5 This is a graph showing the effect of root irrigation with the lemongrass volatile oil nanoemulsion provided by an embodiment of the present invention on the growth of peppers.

[0059] Figure 6 This is a diagram showing the effect of spraying the lemongrass volatile oil nanoemulsion on the growth of pepper and rice provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0060] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0061] like Figure 1 As shown, a method for applying lemongrass volatile oil in promoting plant growth provided by an embodiment of the present invention comprises the following steps:

[0062] S101, placing 1 kg of dried lemongrass and distilled water in a ratio of 1:8 into a 10 L round-bottom flask, soaking for 10 hours, and then distilling for 6-9 hours using a steam distillation method;

[0063] S102, removing moisture from the collected lemongrass volatile oil with anhydrous sodium sulfate, storing the oil in a brown bottle, and placing the bottle in a -20°C refrigerator for later use.

[0064] The embodiment of the present invention provides an application of volatile oil in promoting plant growth, wherein the plants include the model plant Arabidopsis thaliana and the crops pepper and rice, and the volatile oil is prepared by steam distillation.

[0065] The volatile oil provided in the embodiment of the present invention acts on the plant in the form of gas volatilization. The volatile oil is adsorbed by filter paper in the laboratory and placed in a culture dish.

[0066] The volatile oil provided in the embodiment of the present invention is applied in the field using a lemongrass volatile oil nanoemulsion, wherein the volatile oil surfactant Tween 80 and the co-surfactant anhydrous ethanol are used as solvent and dispersant.

[0067] Example 1: Extraction of lemongrass essential oil

[0068] 1 kg of dried lemongrass was mixed with distilled water in a ratio of 1:8 into a 10 L round-bottom flask. After soaking for 10 hours, the mixture was distilled by steam distillation for 6-9 hours. The collected lemongrass volatile oil was dehydrated with anhydrous sodium sulfate and stored in a brown bottle. The oil was then placed in a -20°C refrigerator for later use.

[0069] Example 2: Treatment of Arabidopsis thaliana with lemongrass essential oil

[0070] Lemongrass essential oil emulsions with concentrations of 0.5 mg mL-1 and 1 mg mL-1 were prepared with 2-DMSO-T aqueous solution (1 / 1000 Tween 80 and 20 / 1000 DMSO (dimethyl sulfoxide)), and then filtered with a 0.22 μm microporous filter membrane. The 2-DMSO-T aqueous solution was used as the control solution.

[0071] Arabidopsis seeds were placed in a 4°C refrigerator for 3 days for vernalization, and then placed in a 1.5 mL EP tube for surface sterilization. The sterilized seeds were placed on 1 / 8 MS basal medium (Murashige and Skoog basal salt mixture, catalog number: M5524) for germination and growth. The plate was placed vertically at 90°C to allow the roots to grow downward along the agar surface, 22°C, and the light intensity was 150 μmol·m -2 ·s -1 The Arabidopsis thaliana was grown for 4 days under the conditions of 16 h of light and 8 h of darkness. After germination, filter paper pieces with a diameter of 5 mm were placed on the lid of the dish at equal distances. 7 μL of volatile oil and control solution were added to each filter paper piece. Each treatment was repeated 5-7 times. The Arabidopsis thaliana biomass was measured after 20 days of cultivation under the conditions of 16 h of light and 8 h of darkness at 22°C.

[0072] Example 3: Preparation of lemongrass volatile oil nanoemulsion

[0073] Step 1: Weigh 80 g of Tween 80 and 40 g of anhydrous ethanol into a 250 mL conical flask, place it on a magnetic stirrer and stir for 5 min, then ultrasonicate it in an ice bath for 20 min.

[0074] Step 2: Prepare emulsion (taking 18g and concentration of 111mg / mL as an example)

[0075] Weigh 8g of the above mixed surfactant with Km=2 (Km is the ratio of Tween 80 to anhydrous ethanol) in a 50mL conical flask, add 2g of volatile oil, seal with plastic wrap, place on a magnetic stirrer and stir for 5min, then place in an ultrasonic machine for ice bath ultrasonication for 20min, then let stand for 15min, place the conical flask on a magnetic stirrer while adding water and stirring, slowly add, add 8g of water in total. After adding water, continue stirring for 5min, then place in an ultrasonic machine for ice bath ultrasonication for 20min, and prepare a nanoemulsion.

[0076] Example 4: Root irrigation of lemongrass essential oil nanoemulsion on peppers

[0077] Pepper seedlings of uniform size were selected for transplanting. Five days later, roots were irrigated with 0.5 mg / mL lemongrass volatile oil nanoemulsion once every 10 days, for a total of two times. Plant height, stem diameter, biomass, and root weight of the peppers were counted.

[0078] Example 5: Spraying lemongrass volatile oil nanoemulsion on rice

[0079] Rice seedlings of uniform size were selected for transplanting. Five days later, 0.5 mg / mL lemongrass volatile oil nanoemulsion was sprayed on the leaves until water dripped from the leaves. The plant height, stem diameter, biomass, and root weight of the rice were counted.

[0080] Figure 2 Effects of lemongrass essential oil on the growth of Arabidopsis. (A) Growth of Arabidopsis under different concentrations of essential oil. Arabidopsis seedlings were grown on vertically oriented 1 / 8MS agar plates for 20 days under different concentrations of lemongrass essential oil. The three treatments were: CK-0, LC-0.5mg / mL and HC-1mg / mL. (B) Comparison of leaf size between CK, LC and HC. (C) Effects of lemongrass essential oil on Arabidopsis biomass, in order of main root length, lateral root number, lateral root length, lateral root density, fresh weight and dry weight.

[0081] Figure 1The results showed that 0.5mg / mL and 1mg / mL concentrations of lemongrass essential oil significantly promoted the root growth and leaf area of ​​Arabidopsis. The taproot length, number of lateral roots, lateral root length, lateral root density, fresh weight, and dry weight of Arabidopsis seedlings treated with 0.5mg / mL lemongrass essential oil were significantly higher than those of the control group, especially the taproot length and number of lateral roots. The taproot length increased by 1.57 times, while the number of lateral roots increased by 2.05 times. Compared with the control group, there was no significant difference in the fresh weight and dry weight of Arabidopsis after treatment with 1mg / mL lemongrass essential oil, but the taproot length and lateral root length increased by 1.6 times and 1.61 times, respectively. In addition to the significant difference in the underground part, the leaves of Arabidopsis treated with the two concentrations were also significantly larger than those of the control group. The results show that lemongrass essential oil can promote the growth of Arabidopsis.

[0082] Figure 3 Effect of lemongrass essential oil on the auxin content of Arabidopsis thaliana. (A) After 7 days of LC and HC treatment, transgenic seedlings were stained with DR5∷GUS for 12 h. Twenty seedlings were treated in each experimental group, and the experiment was repeated three times. (B) Effect of lemongrass essential oil on the auxin level of Arabidopsis thaliana. Experimental data are expressed as the mean ± standard error of 5 biological replicates, *, 0.01 <P<0.05;,P<0.01;*,P<0.001。

[0083] from Figure 3 A shows that compared with seedlings not treated with volatile oil, increased GUS expression can be detected in the root tips of DR5::GUS seedlings after applying lemongrass volatile oil. After treatment with LC concentration of lemongrass volatile oil, the staining in the root tip is deeper than that in the control group and has a tendency to spread. After treatment with HC concentration of lemongrass volatile oil, GUS staining is not only darker in the root tip, but also partially in the elongation zone and mature zone. Figure 3 B shows that the auxin concentration increased significantly after treatment with lemongrass essential oil, especially the LC concentration of lemongrass essential oil. This result shows that lemongrass essential oil can promote the increase of plant auxin content.

[0084] Figure 4 KEGG enrichment analysis of differentially expressed genes between low-concentration lemongrass essential oil (LC) and high-concentration lemongrass essential oil (HC) shows the top 9 enriched pathways. The y-axis represents the pathway category, the x-axis represents the degree of enrichment of the pathway, the size of the shape represents the number of differentially expressed genes, and the color represents the degree of enrichment. The redder the color, the more significant the enrichment.

[0085] The KEGG database was used to annotate the DEGs co-enriched in LC and HC, such as Figure 4As shown in the figure, the enriched pathways include: cysteine ​​and methionine metabolism, glycine, serine and threonine metabolism, protein processing in the endoplasmic reticulum, biosynthesis of cofactors, MAPK signaling pathway-plant, plant hormone signal transduction pathway, etc. This shows that lemongrass essential oil may promote the growth of Arabidopsis by affecting amino acid metabolism, energy metabolism and protein synthesis in Arabidopsis. Among these nine pathways, the plant hormone signal transduction pathway is the most significant, which can regulate the synthesis and conduction of plant hormones such as auxin, cytokinin, abscisic acid and gibberellin, and plays an important role in the growth of plant stems, leaves, roots, etc. As a defense mechanism for biotic or abiotic stress, the MAPK cascade signaling pathway will induce its activation to produce resistance or tolerance when pathogens invade plants or reactive oxygen species accumulate excessively. Therefore, lemongrass essential oil not only regulates Arabidopsis growth-related genes to promote growth, but also may regulate the expression of defense-related genes.

[0086] Figure 5 Effect of lemongrass essential oil nanoemulsion root irrigation on pepper growth. The blank group was irrigated with the same amount of water, and the treatment group was irrigated with 0.5 mg / mL lemongrass essential oil nanoemulsion.

[0087] Figure 6 Effects of spraying lemongrass volatile oil nanoemulsion on the growth of pepper and rice. A: Effects of spraying lemongrass volatile oil nanoemulsion on the growth of pepper. B: Effects of spraying lemongrass volatile oil nanoemulsion on the growth of rice. The blank was sprayed with an equal amount of water, and the treatment group was sprayed with 0.5 mg / mL lemongrass volatile oil nanoemulsion.

[0088] In order to further verify the potential of nanoemulsions for wide application in agricultural production, a pot experiment was conducted. Figure 5 As shown in A, the growth of pepper after nanoemulsion irrigation was significantly better than that of the blank group. Nanoemulsion treatment increased the height of pepper by 1.34 times, the stem diameter by 1.43 times, and the root weight and biomass were significantly increased. In addition, the effect of nanoemulsion on the growth of pepper and rice was studied by foliar spraying. The results showed that nanoemulsion can effectively promote the growth of pepper and rice. Among them, the height of pepper increased by 1.15 times, and the root weight increased by 1.56 times; the root weight, stem weight, and leaf weight of rice increased by 1.31, 1.16, and 1.59 times, respectively, and the number of shoots increased by 1.36 times ( Figure 6 ). In summary, lemongrass volatile oil nanoemulsion has significant advantages in promoting crop growth, increasing yield and quality.

[0089] Plant-derived volatile oils (EOs) are secondary metabolites of plants, widely found in various aromatic plants. As a typical small molecule compound, they have an inherent advantage in penetrating plant cell walls and play a vital "ecological role". Currently, EOs are mostly used in the medical field, food, cosmetics and perfume industries, and their potential in the green development of agriculture has not yet been fully explored.

[0090] Phytohormones are key regulators of plant growth and development, and their multifaceted roles in promoting plant growth and enhancing crop resistance to environmental stress are increasingly recognized. This study can promote the transformation of agricultural practices and promote the sustainability and resilience of the agricultural environment by preparing plant volatiles into preparations that can be directly sprayed on leaves or irrigated into roots to increase the content and stress resistance of plant hormones.

[0091] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for applying lemongrass volatile oil in promoting plant growth, characterized in that: The method for applying the lemongrass volatile oil in promoting plant growth comprises the following steps: Step 1: put 1 kg of dried lemongrass and distilled water in a 10L round-bottom flask at a ratio of 1:8, soak for 10 hours, and then distill for 6-9 hours using steam distillation; Step 2: After removing moisture from the collected lemongrass volatile oil with anhydrous sodium sulfate, the oil is stored in a brown bottle and placed in a -20°C refrigerator for later use.

2. The method for applying lemongrass volatile oil in promoting plant growth as claimed in claim 1, characterized in that: The invention discloses an application of volatile oil in promoting plant growth. The plants include the model plant Arabidopsis thaliana and the crops pepper and rice. The volatile oil is prepared by steam distillation.

3. The method for applying lemongrass volatile oil in promoting plant growth as claimed in claim 2, characterized in that: The volatile oil acts on the plant in the form of gas volatilization. In the laboratory, a filter paper is used to absorb the volatile oil and placed in a culture dish.

4. The method for applying lemongrass volatile oil in promoting plant growth as claimed in claim 2, characterized in that: The volatile oil is applied in the field using a lemongrass volatile oil nanoemulsion, and the volatile oil surfactant Tween 80 and the co-surfactant anhydrous ethanol are used as solvent and dispersant.

5. A method for extracting lemongrass volatile oil based on the method according to claim 1, characterized in that: The method includes: Dried lemongrass was mixed with distilled water in a ratio of 1:8 and placed in a 10L round-bottom flask and soaked for 10 hours; The soaked mixture is distilled by steam distillation, and the distillation time is 6 to 9 hours; The obtained lemongrass volatile oil was collected and dehydrated with anhydrous sodium sulfate; The lemongrass volatile oil after removing moisture was stored in a brown bottle and placed in a refrigerator at -20°C for later use.

6. A method for treating Arabidopsis thaliana using lemongrass essential oil based on the method of claim 1, characterized in that: The method includes: Lemongrass essential oil emulsions with concentrations of 0.5 mg mL^-1 and 1 mg mL^-1 were prepared with 2-DMSO-T aqueous solution containing Tween-80 and DMSO; Arabidopsis seeds were vernalized at 4°C for 3 days; The vernalized seeds were surface sterilized and placed on 1 / 8MS basal medium for germination and growth; Filter paper sheets containing lemongrass essential oil emulsion were placed on the germinated Arabidopsis plants and cultured under specific light and temperature conditions, and then the biomass of Arabidopsis plants was measured.

7. A method for preparing a lemongrass volatile oil nanoemulsion based on the method of claim 1, characterized in that: The method includes: Tween 80 and anhydrous ethanol were mixed in a certain proportion, stirred on a magnetic stirrer and ultrasonicated in an ice bath; When preparing the emulsion, the mixed surfactant and lemongrass essential oil were mixed, stirred on a magnetic stirrer, and then ultrasonicated in an ice bath; Water was added while stirring, and the ice bath ultrasonic treatment was continued to prepare the lemongrass volatile oil nanoemulsion.

8. A method for promoting pepper growth using lemongrass volatile oil nanoemulsion based on the method of claim 1, characterized in that: The method includes: Select pepper seedlings of uniform size for transplanting; On the fifth day after transplanting, the pepper seedlings were root-irrigated with lemongrass volatile oil nanoemulsion at a concentration of 0.5 mg / mL, once every 10 days, for a total of two treatments; The plant height, stem diameter, biomass and root weight of pepper after treatment were counted and compared.

9. A method for promoting rice growth using lemongrass volatile oil nanoemulsion based on the method of claim 1, characterized in that: The method includes: Select rice seedlings of uniform size for transplanting; On the fifth day after transplanting, the rice seedlings were foliarly sprayed with lemongrass volatile oil nanoemulsion at a concentration of 0.5 mg / mL until water dripped from the leaves; The plant height, stem diameter, biomass and root weight of rice after treatment were counted and compared.

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