Preparation method of microalgae nano-selenium and application of biotransformed nano-selenium in prevention and treatment of plant late blight

Abstract

The invention discloses a preparation method of microalgae nano-selenium and application of biotransformed nano-selenium in prevention and treatment of plant late blight. The novel preparation method of the microalgae nano-selenium comprises the following steps: firstly, extracting an intracellular extract of chlorella pyrenoidosa, and then adding sodium selenite into the intracellular extract to carry out nano-selenium conversion; compared with an existing reported method that after sodium selenite is added into a microalgae living body culture solution to be converted into nano-selenium, algae is taken to break cells, and the nano-selenium is collected, the method has the advantages that the microalgae living body does not need to be used when the nano-selenium is biologically converted, and the subsequent complicated nano-selenium separation and purification steps can be avoided; the nano-selenium obtained by converting the intracellular extract can be directly applied. Experiments prove that the effect of the nano-selenium obtained through biotransformation on inhibiting phytophthora infestans of potato late blight pathogenic bacteria is obviously better than that of chemically synthesized nano-selenium, and the nano-selenium obtained through biotransformation has an obvious effect on preventing and treating potato late blight and has an obvious effect on promoting plant growth.

Description

Technical Field

[0001] The invention relates to the technical field of plant disease prevention and control and green new pesticides, and in particular to a method for preparing microalgae nano-selenium and application of biotransformed nano-selenium in preventing and controlling plant late blight. Background Art

[0002] Potato late blight is the world's largest crop disease and can be called the "cancer" of potatoes. The pathogen of potato late blight is Phytophthora infestans, which belongs to the genus Phytophthora in the order Peronosporales, family Pythiaceae, class Oomycetes. It is the pathogen of potato and tomato late blight. In potato late blight, the pathogen population is mainly spread to other Solanaceae crops by wind or water through potato seed potatoes and fallen leaves, causing a devastating disease cycle.

[0003] Chemical control is still the main means of preventing and controlling late blight. However, because the climatic conditions in most potato-producing areas in my country are suitable for the spread of late blight, it is difficult to reduce the number of chemical pesticide applications, which poses serious environmental risks and pesticide residue problems. Therefore, the development and promotion of new, efficient, and eco-friendly disease control drugs and technologies is an important demand for food production in my country and even the world. In recent years, the rapid development of nanotechnology has provided new methods for modern agriculture, and nanopesticides have become a frontier in the research and development of green pesticide formulations due to their advantages such as large specific surface area, high permeability, and high prevention efficiency. How to develop and promote new, efficient, and eco-friendly nanopesticide products and green control technologies is an important demand for potato production in my country and even the world.

[0004] Selenium (Se) is an essential trace element for humans and animals. It has been widely used to treat more than 40 diseases, including tumors, osteoarthritis (Keshan disease), diabetes, cardiovascular and cerebrovascular diseases, etc. Selenium has the functions of promoting plant growth, increasing crop yield and quality, antagonizing heavy metals, resisting stress, and resisting diseases and insect pests. In the environment, selenium is present in the form of Se 2+ 、Se 6+ 、Se 0 and Se 2-There are four chemical valences, each of which can be converted into each other and show different active functions. Among them, nano-selenium is widely used in medical and agricultural fields such as anti-cancer, antibacterial, and antiviral due to its high biological activity, high biocompatibility, and high specific surface area. Selenium in nature mainly exists in the form of inorganic selenium and organic selenium. Inorganic selenium is mainly selenite and selenate, which are obtained from by-products of metal mines. Organic selenium includes natural organic selenium, such as selenoproteins in animals and plants; artificial biological transformation of organic selenium, such as selenium-enriched yeast, selenium-enriched edible fungi, etc.; and artificially synthesized organic selenium, such as selenized carrageenan. With the widespread application of nanotechnology, people have developed a new type of selenium preparation-nanoselenium by combining different types of new nanotechnology methods with selenium; nano-selenium is a red elemental selenium in powder form, which is the least toxic form of many selenium elements that have been discovered. However, due to the difficulty in extracting and purifying nano-selenium, chemical and physical synthesis are the main ways to synthesize nano-selenium, but there are defects such as large environmental pollution, high cost, and unstable activity. How to biosynthesize high-quality nano-selenium resources is an urgent problem to be solved. Microalgae are excellent selenium carriers and have the unique advantage of efficiently converting inorganic selenium into the fourth generation of stable nano-selenium. Using microalgae extracts to synthesize nano-selenium not only avoids complex extraction processes, but also has higher stability and purity, and can be directly applied to the research and development of new medicines, new pesticides, and new veterinary drugs.

[0005] At present, there are few reports on the application of biological nano-selenium in the prevention and control of potato late blight. The development of biological pesticides for potato late blight based on nano-selenium is of great significance for potato production and environmental protection. Summary of the invention

[0006] The purpose of the present invention is to solve the above problems and provide a method for preparing microalgae nano-selenium and the application of biotransformed nano-selenium in preventing and controlling plant late blight.

[0007] In order to achieve its purpose, the present invention adopts the following technical solution:

[0008] The first aspect of the present invention provides a method for preparing microalgae nano-selenium, comprising the following steps:

[0009] S1. Extraction of intracellular extracts of microalgae

[0010] The microalgae species are cultured in a culture medium until the growth retardation period to the stable period. After the culture is completed, the culture solution is centrifuged to collect the algae, and the algae are resuspended with a suspending agent to form an algae slurry suspension. The suspension is taken to break the algae cells, and the supernatant is collected after centrifugation (the contents in the cells after the cell breakage are dissolved in the suspending agent and collected by centrifugation) to obtain the microalgae intracellular extract;

[0011] S2. Synthesis of Nano-Selenium from Microalgae Intracellular Extracts

[0012] Take the intracellular extract of microalgae, add sodium selenite thereto, and shake and culture the reaction until the solution turns red to obtain the nano-selenium solution.

[0013] Preferably, in step S1, the algae suspension is resuspended with a suspending agent and diluted to a concentration of OD 600 =8-12; the suspending agent is selected from PBS buffer, MOPS buffer, HEPES buffer and Tris buffer;

[0014] The method for disrupting cells is ultrasonic disruption, preferably: the suspension is subjected to constant temperature ultrasonic disruption in an ice bath, the ultrasonic frequency is 20-30 kHz, the working interval is 4-6s / 2-4s, the ultrasonic power is 800-1200w, and the ultrasonic time is 25-35min;

[0015] The suspension is taken to break the algal cells and the obtained precipitate is also resuspended with a suspending agent and then centrifuged to collect the supernatant to extract the cell contents as much as possible. The supernatants obtained multiple times are combined into one portion and then fixed to the volume of the original culture solution with a suspending agent before being used in step S2;

[0016] In step S2, the obtained red solution is prepared as a lyophilized powder: a solution sample is collected and directly used for freeze drying to obtain a lyophilized powder;

[0017] Preferably, the microalgae is Chlorella vulgaris; in step S1, the microalgae species are cultured in a culture medium at 25-30° C. to a growth retardation phase to a stable phase; and in step S2, the shaking culture conditions are shaking culture at 25-30° C. and 3000-30000 lux illumination conditions.

[0018] The prepared red nano-selenium solution can be directly used in plant disease prevention and control to reduce costs; after further purification, it can be used in food additives, medical materials and other fields; it can be prepared as freeze-dried powder for easy storage and application.

[0019] The second aspect of the present invention provides the use of biotransformed nano-selenium in any of the following:

[0020] (1) Application in inhibiting Phytophthora infestans;

[0021] (2) Application in the preparation of products for inhibiting Phytophthora infestans;

[0022] (3) Application in the prevention and treatment of plant late blight;

[0023] (4) Application in the preparation of products for preventing and controlling plant late blight;

[0024] (5) Application in promoting plant growth;

[0025] (6) Application in the preparation of plant growth promoters.

[0026] In the above-mentioned application technology solution, the nano-selenium is nano-selenium obtained by biotransformation of microalgae; preferably, the microalgae is Chlorella pyrenoidosa.

[0027] In the above-mentioned application technology solution, the plant late blight includes potato late blight and tomato late blight.

[0028] In the above application technology scheme, the application concentration of nano-selenium is 4-30 mg / L, preferably 4-25 mg / L or 4-10 mg / L or 9-23 mg / L.

[0029] In the above application technology scheme, in the application of preventing and controlling plant late blight, the application method of nano-selenium is: preparing nano-selenium into a solution and then using it for seed soaking, seed mixing, root irrigation or plant leaf spraying.

[0030] The third aspect of the present invention provides a product for inhibiting Phytophthora infestans or for preventing and controlling late blight of plants, wherein the active ingredient of the product is nano-selenium obtained by biotransformation.

[0031] In the above-mentioned product technical solution, the nano-selenium is obtained by biotransformation of microalgae, and preferably the microalgae is Chlorella pyrenoidosa.

[0032] The working concentration of nano-selenium in the product is 4-30 mg / L, preferably 4-25 mg / L or 4-10 mg / L or 9-23 mg / L.

[0033] The beneficial effects of the present invention are:

[0034] On the one hand, the present invention provides a new method for preparing microalgae nano-selenium. Compared with the previously reported method of adding sodium selenite to the culture medium of living microalgae to convert it into nano-selenium and then taking the algae and crushing the cells to collect the nano-selenium, the method of the present invention does not require the use of living microalgae in the biotransformation of nano-selenium, and can avoid the subsequent complex nano-selenium separation and purification steps. The nano-selenium obtained by the conversion of intracellular extracts can be directly used.

[0035] On the other hand, the present invention provides the application of biotransformed nano-selenium in preventing and controlling plant late blight. Experiments of the present invention have confirmed that the effect of nano-selenium obtained by biotransformation in inhibiting the pathogenic bacteria of potato late blight, Phytophthora infestans, is significantly better than that of chemically synthesized nano-selenium. The biotransformed nano-selenium is significantly effective in preventing and controlling potato late blight and has a significant effect in promoting plant growth. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1The synthesis and characterization of nano-selenium from RLXCh3 intracellular extract are shown: (A) Nano-selenium solutions formed after adding 0, 50, 100, 150, and 200 mg / L to the intracellular extract, respectively; (B) Transmission electron microscopy image of nano-selenium synthesized from the intracellular extract; (C) Energy spectrum scanning image of nano-selenium synthesized from the intracellular extract, indicating that the synthesized nanoparticles are nano-selenium; (D) Particle size scanning image of nano-selenium synthesized from the intracellular extract, indicating that the average particle size of the synthesized nano-selenium particles is 200 nm.

[0037] Figure 2 The antibacterial activity of RLXCh3 biosynthesized nano-selenium against Phytophthora infestans is shown: (A) The effect of microalgae nano-selenium on the colony growth of Phytophthora infestans; (B) SEM scanning electron microscopy showed that treatment with lethal concentrations of nano-selenium caused severe shrinkage, shriveling and cell death of Phytophthora infestans hyphae and sporangiospores.

[0038] Figure 3 The half-inhibitory concentration of microalgae nanoselenium against Phytophthora infestans is shown.

[0039] Figure 4 The antibacterial activity and half-inhibitory concentration of chemically synthesized nano-selenium against Phytophthora infestans are shown: (A and C): The effect of chemically synthesized nano-selenium on the colony growth of Phytophthora infestans; (B and D): The half-inhibitory concentration of chemically synthesized nano-selenium against Phytophthora infestans.

[0040] Figure 5 The results show the inhibition of microalgae nano-selenium on the pathogenicity of pathogens: (A) Microalgae nano-selenium at different concentrations has a significant inhibitory effect on Phytophthora infestans, and completely inhibits its pathogenicity at a concentration of 23 mg / L: (B) The necrosis area of ​​tubers caused by Phytophthora infestans after treatment with microalgae nano-selenium at different concentrations. *: P < 0.05; ***: P < 0.001.

[0041] Figure 6 The results show the promoting effect of microalgae nano-selenium on potato disease resistance and growth: (A) Potato pot experiment with microalgae nano-selenium mixed with soil; (B and C) The effect of microalgae nano-selenium on potato growth with (B) and without (C) inoculation at the time of sowing; ***: P<0.001. DETAILED DESCRIPTION

[0042] The present invention will be further described below in conjunction with embodiments, but the present invention is not limited thereto.

[0043] The experimental methods in the following examples are conventional methods unless otherwise specified.

[0044] The microalgae used in the embodiment of the present invention is Chlorella pyrenoidosa RLXCh3 isolated independently by this laboratory, and its preservation information is as follows: the algae species RLXCh3 was sent to the China Center for Type Culture Collection (CCTCC) for preservation in May 2022, the address is Wuhan University, No. 299, Bayi Road, Wuchang District, Wuhan City, Hubei Province, preservation date: May 16, 2022; preservation number: CCTCC NO: M 2022648; classification name: Chlorella pyrenoidosa RLXCh3. RLXCh3 has been disclosed in Chinese patent ZL 202210984422.1 (patent name: A high-protein protein-producing pyrenoid algae and its cultivation method and application).

[0045] Example 1

[0046] 1. Preparation of intracellular extracts of Chlorella pyrenoidosa

[0047] The RLXCh3 algae were cultured in BG11 + 20 g / L glucose medium until the stable phase. The culture conditions were: 28°C, 150 rpm, and light intensity of 1000 lux. After the culture was completed, the culture medium was centrifuged at 8000 × g for 10 min, and the algae were collected and resuspended in PBS (pH = 7.2) to form an algae slurry and diluted to the appropriate concentration (OD 600 =10). The suspension was subjected to constant temperature ultrasonic crushing in an ice bath, with an ultrasonic frequency of 25 kHz, a working interval of 5s / 3s, an ultrasonic power of 1000w, and an ultrasonic time of 30min. The supernatant was then collected after centrifugation at 12,000×g for 10min, and the precipitate was resuspended with PBS and centrifuged again to collect the supernatant. Finally, the collected supernatants were combined and fixed to the volume of the original culture medium with PBS to obtain the RLXCh3 intracellular extract for later use. 2. Synthesis and characterization of nano-selenium in RLXCh3 intracellular extract

[0048] The RLXCh3 intracellular extract was divided into 5 parts, and sodium selenite was added to the final concentration of 0, 50 mg / L, 100 mg / L, 150 mg / L, and 200 mg / L, respectively, and reacted at 28°C, 150 rpm, and then at a light intensity of 30,000 lux. After the solution turns completely red (about 5-7 days), the solution sample is collected and directly used for freeze drying, and the obtained freeze-dried powder is used for subsequent nano-selenium transmission electron microscopy detection, energy spectrum scanning, DLS particle size analysis and other characterizations. Freeze drying is performed using a ChristAlpha2-4LSC basic vacuum freeze dryer, and the specific operation is as follows: Take 30 mL of red liquid and place it in a 50 mL centrifuge tube, and freeze it in liquid nitrogen until it is completely frozen. Put the processed sample in, turn on the instrument, preheat for 15 minutes and then prefreeze for 20 minutes. When the temperature of the cold trap drops to about 89°C, turn on the vacuum pump to evacuate the sample until the vacuum degree stabilizes to about 0.2 Pa, indicating that the main drying has begun. Determine the drying time based on the sample state and quality, which is generally 2 to 3 days.

[0049] like Figure 1 As shown, the synthesized nanoparticles have regular morphology, and the energy spectrum scan shows that the synthesized nanoparticles are indeed nano-selenium, and the weight percentage of selenium in the entire nanoparticles is 61.57% (in the nanoparticles, the single element selenium is in the center, and the periphery is wrapped with organic substances such as proteins, sugars, and lipids through covalent bonding or chelation to form nanoparticles). DLS particle size analysis shows that the average particle size of nano-selenium is 200nm.

[0050] This embodiment provides a new method for synthesizing microalgae nano-selenium: first extract the intracellular extract of Chlorella pyrenoidosa, and then add sodium selenite to the intracellular extract to convert it into nano-selenium. Compared with the previously reported method of adding sodium selenite to the living culture fluid of microalgae to convert it into nano-selenium and then taking the algae to break the cells to collect the nano-selenium, the method of this embodiment does not require the use of living microalgae in the bioconversion of nano-selenium, and can avoid the subsequent complex nano-selenium separation and purification steps. The nano-selenium obtained by the conversion of the intracellular extract can be used directly or after freeze-drying.

[0051] Example 2: Detection of the antibacterial activity of nano-selenium against potato late blight

[0052] 1. Plate antibacterial test

[0053] Preparation of rye culture medium: Weigh 60g rye flour, add 500mL sterile water and soak for 36 hours. Filter to obtain filtrate 1, and save for later use; filter the residue in a 55℃ water bath for 3 hours to obtain filtrate 2; mix filtrate 1 and filtrate 2, sterilize at 121℃ for 10 minutes, and filter to obtain filtrate 3; add 20g sucrose and 12g agar to filtrate 3, dissolve and mix, dilute to 1L with sterile water, and sterilize at 121℃ for 20 minutes to obtain rye culture medium.

[0054] ICP-MS detected that the average selenium content in the nano-selenium freeze-dried powder prepared by adding 200 mg / L sodium selenite in Example 1 was 184 mg / g), and the nano-selenium freeze-dried powder was prepared into a 46 mg / mL nano-selenium aqueous solution mother liquor, which was then added to a 65°C rye solid culture medium in proportion to a nano-selenium working concentration (the concentration of selenium in the culture medium) of 0, 2, 9, 16, and 23 mg / L, respectively. After being shaken thoroughly to mix, the plate was poured. At the same time, the purchased chemically synthesized nano-selenium was added to the rye solid culture medium in the same way until the nano-selenium working concentration was 0.1, 0.5, 1, 5, 10, 20, and 30 mg / L, respectively. Because the concentrations of the nano-selenium mother liquors synthesized in the two methods are different, there are differences in the setting of the concentration used, but it does not affect the plate antibacterial test effect and IC 50 Calculation. After the plate solidifies, a 0.6 cm diameter block of Phytophthora infestans (strains T30-4 and 88069) of potato late blight pathogen was inoculated to the middle of the culture dish and placed in an inverted culture in a 20°C mold incubator. Experiments on RLXCh3 biotransformation of nano-selenium and chemically synthesized nano-selenium were carried out simultaneously. Chemically synthesized nano-selenium is a nano-selenium sol purchased from Yantai Jialong Nano Industry Co., Ltd., 3000 ppm, item number: 20220523, with a particle size of 80 nm. After 7 days, the colony diameter, inhibition rate and half inhibition concentration were determined.

[0055] Inhibition rate % = [(control colony diameter - treated colony diameter) / (control colony diameter - 0.6)] * 100%.

[0056] The results showed that compared with the control group, the nano-selenium biotransformed by RLXCh3 significantly inhibited the colony growth of potato late blight pathogens T30-4 and 88069 ( Figure 2 ), and their half inhibition concentrations were 4.67mg / L and 4.32mg / L ( Figure 3 The vertical axis represents cell viability, and the horizontal axis represents the Log10 value of nano-selenium concentration). The antibacterial rate was higher than 92% when treated with 9 mg / L, and the inhibition rate was 100% when treated with 16 mg / L. Scanning electron microscopy ( Figure 2B) shows that the mycelium and cyst spores of pathogens treated with 16 mg / L microalgae nano-selenium showed severe shrinkage, shriveling and cell death. The half-inhibitory concentrations of commercially synthesized nano-selenium against Phytophthora infestans T30-4 and 88069 were 5.59 mg / L and 4.94 mg / L, respectively. Figure 4 ). The antibacterial experimental results of microalgae nano-selenium and chemically synthesized nano-selenium are shown in Tables 1 and 2. Under the same antibacterial rate, the required concentration of microalgae nano-selenium is significantly lower than that of chemically synthesized nano-selenium. The inhibitory effect of RLXCh3 biotransformed nano-selenium is more significant than that of chemically synthesized nano-selenium. The reason may be that the particle sizes of the two nano-seleniums are different, and the nano-selenium particles obtained by biosynthesis are wrapped with proteins, sugars, lipids and other organic substances in the form of covalent binding or chelation. These substances may also play an auxiliary role in inhibiting pathogenic fungi.

[0057] Table 1 Antibacterial results of microalgae nanoselenium

[0058]

[0059] Table 2 Antibacterial results of chemically synthesized nano-selenium

[0060]

[0061] 2. Potato Tuber Experiment

[0062] In order to further clarify the inhibitory effect of microalgae nano-selenium on the pathogenicity of pathogens, the T30-4 bacterial block grown for 5 days was placed in IC 50 The tubers were immersed in microalgae nano-selenium aqueous solution with a concentration of 4.67 mg / L and high concentration of 9 mg / L and 23 mg / L (all refer to the effective concentration of selenium) for 24 hours and then inoculated on the Faureta potato tubers. The potato tubers inoculated with the fungus blocks treated with sterile water for 24 hours were used as controls. All tubers were cultured in the dark at 20°C and the relative humidity was maintained above 90%. The size of the necrotic spots on the tubers was measured 7 days after inoculation. The results showed that ( Figure 5 ), the pathogenicity of the fungus after nano-selenium treatment was significantly reduced. The necrosis area of ​​potato tubers caused by Phytophthora infestans was 17.27 cm 2 The necrotic spot area caused by Phytophthora infestans treated with 4.67 mg / L microalgae nano-selenium was 8.94 cm 2 The area of ​​necrotic spots caused by Phytophthora infestans treated with 9 mg / L microalgae nano-selenium was only 1.78 cm 2 , the infestation of Phytophthora treated with 23 mg / L microalgae nano-selenium lost its pathogenicity.

[0063] 3. Potato Potted Plant Experiment

[0064] The T30-4 plate cultured for 15 days was washed with sterile water to obtain the sporangium suspension and the concentration was adjusted to 105 Sporangium / mL for later use. Add microalgae nano-selenium to the sporangium suspension. Cut the seed potato into pieces according to individual buds and soak them in the sporangium suspension with microalgae nano-selenium solution for 1 hour. Then plant them in pots with nutrient soil, and pour an equal volume of the remaining soaking liquid into the planting pots. The water treatment was used as the negative control of this experiment, and the sporangium suspension treatment without microalgae nano-selenium was used as the positive control of this experiment. Each treatment had 8 plants and was repeated 3 times. The treated plants were placed in a light greenhouse, and the growth of the plants was investigated after culturing at 25°C for 4 weeks, and the average plant height and disease rate of potatoes were determined. This experiment was divided into two major groups, namely the inoculation of pathogenic Phytophthora infestans ( Figure 6 inoculated group) and uninoculated group with Phytophthora infestans ( Figure 6 inoculated group).

[0065] Among them, the inoculated group of Phytophthora infestans was divided into three experimental groups: CK group (i.e., a mixture of Phytophthora infestans spore suspension and water), 4.67 mg / L microalgae nanoselenium group (i.e., IC 50 group, adding microalgae nano-selenium with a final concentration of 4.67 mg / L to the spore suspension of Phytophthora infestans), and 9 mg / L microalgae nano-selenium group (i.e., adding microalgae nano-selenium with a final concentration of 9 mg / L to the spore suspension of Phytophthora infestans).

[0066] The group not inoculated with Phytophthora infestans was divided into three experimental groups: CK group (i.e., clean water group), microalgae nano-selenium aqueous solution with a concentration of 4.67 mg / L (without Phytophthora infestans), and microalgae nano-selenium aqueous solution with a concentration of 9 mg / L (without Phytophthora infestans).

[0067] The statistical results are as follows Figure 6 As shown, microalgae nano-selenium has a significant promoting effect on potato growth and can reduce the occurrence of late blight. In the absence of inoculation, the average height of the plants in the CK group was 23.13 cm, the average height of the plants treated with 4.67 mg / L microalgae nano-selenium was 29.00 cm, and the average height of the plants treated with 9 mg / L microalgae nano-selenium was 29.50 cm. In the case of inoculation, the disease rate of the CK group was 100%, and the average height of the plants was 4.50 cm; the disease rate of the group treated with 4.67 mg / L microalgae nano-selenium was 62.50%, and the average height of the plants was 6.38 cm; the disease rate of the group treated with 9 mg / L microalgae nano-selenium was 25.00%, and the average height of the plants was 6.75 cm. Microalgae nano-selenium can significantly reduce the incidence of late blight and promote growth.

Claims

1. A method for preparing microalgae nano-selenium, characterized in that: The steps include: S1. Extraction of intracellular extracts of microalgae The microalgae species are cultured in a culture medium until the growth retardation period to the stable period. After the culture is completed, the culture solution is centrifuged to collect the algae, and the algae are resuspended with a suspending agent to form an algae slurry suspension. The suspension is taken to break the algae cells, and the supernatant is collected after centrifugation to obtain the microalgae intracellular extract; S2. Synthesis of Nano-Selenium from Microalgae Intracellular Extracts Take the intracellular extract of microalgae, add sodium selenite thereto, and shake and culture the reaction until the solution turns red to obtain a nano-selenium solution.

2. The preparation method according to claim 1, characterized in that: In step S1, Resuspend into algal slurry suspension with suspending agent and dilute to a concentration of OD 600 =8-12; the suspending agent is selected from PBS buffer, MOPS buffer, HEPES buffer and Tris buffer; The method for disrupting cells is ultrasonic disruption, preferably: the suspension is subjected to constant temperature ultrasonic disruption in an ice bath, the ultrasonic frequency is 20-30 kHz, the working interval is 4-6s / 2-4s, the ultrasonic power is 800-1200w, and the ultrasonic time is 25-35min; The suspension is taken to break the algal cells and the obtained precipitate is also resuspended with a suspending agent and then centrifuged to collect the supernatant to extract the cell contents as much as possible. The supernatants obtained multiple times are combined into one portion and then fixed to the volume of the original culture solution with a suspending agent before being used in step S2; In step S2, the obtained red solution is prepared as a lyophilized powder: a solution sample is collected and directly used for freeze drying to obtain a lyophilized powder; Preferably, the microalgae is Chlorella vulgaris; in step S1, the microalgae species are cultured in a culture medium at 25-30° C. to a growth retardation phase to a stable phase; and in step S2, the shaking culture conditions are shaking culture at 25-30° C. and 3000-30000 lux illumination conditions.

3. Application of biotransformed nano-selenium in any of the following: (1) Application in inhibiting Phytophthora infestans; (2) Application in the preparation of products for inhibiting Phytophthora infestans; (3) Application in the prevention and treatment of plant late blight; (4) Application in the preparation of products for preventing and controlling plant late blight; (5) Application in promoting plant growth; (6) Application in the preparation of plant growth promoters.

4. The use according to claim 3, characterized in that: The nano-selenium is nano-selenium obtained by biotransformation of microalgae; preferably, the microalgae is Chlorella pyrenoidosa.

5. The use according to claim 3, characterized in that: The plant late blight includes potato late blight and tomato late blight.

6. The use according to any one of claims 3 to 5, characterized in that: The application concentration of nano-selenium is 4-30 mg / L, preferably 4-25 mg / L or 4-10 mg / L or 9-23 mg / L.

7. The use according to claim 3, characterized in that: In the application of preventing and controlling plant late blight, the application method of nano-selenium is: the nano-selenium is prepared into a solution and then used for seed soaking, seed mixing, root irrigation or plant leaf spraying.

8. A product for inhibiting Phytophthora infestans or for preventing and controlling late blight of plants, characterized in that: The active ingredient of the product is nano-selenium obtained by biotransformation.

9. The product according to claim 8, characterized in that: The nano-selenium is obtained by bioconversion of microalgae, and preferably the microalgae is Chlorella pyrenoidosa.

10. The product according to claim 9, characterized in that: The working concentration of nano-selenium in the product is 4-30 mg / L, preferably 4-25 mg / L or 4-10 mg / L or 9-23 mg / L.

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