Kiwifruit root exudates, and preparation method and application thereof

Abstract

The present application belongs to the technical field of biological agents, and relates to a kiwi root exudate as well as a preparation method and application thereof. The kiwi root exudate is prepared by water-cultivating kiwi tissue culture seedlings, collecting root exudate solution, filtering and freeze-drying. The exudate powder can be added to a xanthomonas fermenting liquid to prevent and treat kiwi bacterial canker disease. When the final concentration of the exudate is not less than 50 mg / L, the growth, movement and antagonistic pathogenic bacteria ability of the xanthomonas can be significantly enhanced, and the ex situ control efficiency is increased from 62.3% to 85.1%. The preparation method is simple, the exudate and the biocontrol agent have significant synergistic effect, and more ways are provided for green prevention and control of kiwi canker disease.

Description

Technical Field

[0001] This invention belongs to the field of biopharmaceutical technology and relates to a kiwifruit root exudate, its preparation method and application. Background Technology

[0002] Kiwifruit (Actinidia chinensis) is an important economic fruit tree. However, pathogenic kiwifruit varieties caused by *Pseudomonas syringae* (…) Pseudomonas syringae pv. actinidiae Bacterial canker (Psa) of kiwifruit has become a common disease threatening kiwifruit cultivation. After infecting branches, leaves, and flowers, this disease causes bark rot, gumming, and even the death of the entire plant, and is extremely difficult to control once it breaks out. Therefore, developing efficient and environmentally friendly canker control technologies has become an urgent need for the industry.

[0003] Currently, the control of bacterial canker in kiwifruit still relies primarily on chemical methods, with the widespread use of copper-based agents (such as Bordeaux mixture and copper hydroxide) and antibiotics like streptomycin. However, these methods have several drawbacks: long-term, high-frequency application leads to the development of resistant pathogens, resulting in a gradual decrease in efficacy; copper accumulation in the soil poses ecological risks; and antibiotic residues threaten fruit safety. Biological control, as an alternative technology, has gained attention in recent years, with researchers isolating and screening rhizosphere antagonistic strains to suppress the disease. However, single antagonistic bacteria generally suffer from weak colonization and unstable efficacy in the complex field environment, making sustained disease control difficult. Therefore, there is an urgent need in this field for a kiwifruit canker control strategy that can overcome the shortcomings of existing control technologies. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the shortcomings of existing kiwifruit canker control technologies, such as the easy generation of resistance and environmental problems by chemical agents and the unstable efficacy of single biocontrol bacteria. This invention provides a kiwifruit root exudate that can significantly enhance the control effect of biocontrol bacteria, as well as its simple and controllable preparation method, and its application in enhancing the control of bacterial canker in kiwifruit by Flavobacterium.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for preparing kiwifruit root exudates includes the following steps: selecting kiwifruit tissue culture seedlings, disinfecting and rinsing them, and then placing them in sterile water for hydroponic culture under alternating light and dark conditions; collecting the aqueous solution after hydroponic culture to obtain a root exudate solution; filtering, concentrating and drying the root exudate solution to obtain the kiwifruit root exudate powder.

[0007] Furthermore, the kiwifruit variety is Hayward. Hayward is a known disease-resistant variety, and its root exudates contain substances that specifically promote the growth of beneficial bacteria.

[0008] Furthermore, the surface disinfection involves immersing the roots of the tissue culture seedlings in a solution with an effective chlorine concentration of 0.5-1% for at least 10 minutes, followed by rinsing with sterile water. This treatment effectively removes epiphytic microorganisms from the root surface, ensuring that the subsequently collected exudates are produced in situ from the roots.

[0009] Furthermore, the hydroponic culture conditions are a temperature of 26±1°C, 16 hours of light and 8 hours of darkness per day, for at least 3 days. Under these conditions, the tissue culture seedlings exhibit active root secretion, sufficient secretion accumulation, and a short operation cycle.

[0010] As a further limitation of the above preparation method, the filtration is carried out using a 0.22μm filter membrane to remove particles and microorganisms from the solution; the concentration and drying is carried out by freeze drying, which can quickly remove moisture at low temperature and retain heat-sensitive or easily oxidized active components in the secretions to the greatest extent.

[0011] Furthermore, the present invention also provides a kiwifruit root exudate, which is prepared by any of the above-described preparation methods. The exudate thus obtained is a powdery solid, which is convenient for long-term storage and quantitative use.

[0012] This invention also provides the above-mentioned kiwifruit root exudate in enhancing Flavobacterium Flavobacterium Prevention and treatment of bacterial canker in kiwifruit and / or promotion of Flavobacterium Flavobacterium Applications during growth.

[0013] Furthermore, the *Flavobacterium* mentioned is *Flavobacterium* F-55, with accession number CGMCC No. 26998. This strain was deposited on March 31, 2023, at the China General Microbiological Culture Collection Center (CGMCC), located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing. See the published document number CN116286558B for details. Experimental verification has shown that *Flavobacterium* F-55 has good antagonistic ability against *Actinidia chinensis*, the pathogen causing bacterial canker in kiwifruit.

[0014] Furthermore, the kiwifruit root exudate was added to the fermentation broth of Flavobacterium F-55, and the final concentration of the kiwifruit root exudate in the fermentation broth was not less than 50 mg / L. Experiments showed that at a final concentration of 100 mg / L, the growth rate, motility, and antagonistic activity of Flavobacterium F-55 were significantly enhanced. Selectable concentrations were 50 mg / L, 100 mg / L, 150 mg / L, 200 mg / L, 50 mg / L~100 mg / L, 50 mg / L~150 mg / L, 50 mg / L~200 mg / L, 100 mg / L~150 mg / L, 100 mg / L~200 mg / L, and 150 mg / L~200 mg / L.

[0015] Furthermore, the pathogen of the bacterial canker disease of kiwifruit is *Pseudomonas syringae* kiwifruit pathogenic strain (…). Pseudomonas syringae pv. actinidiae Pretreatment of detached kiwifruit leaves with fermentation broth containing the above-mentioned concentration of root exudates by flavobacterium F-55 can significantly reduce pathogen infection, and its detached control efficacy against bacterial canker of kiwifruit can be increased from 62.3% when flavobacterium F-55 is used alone to more than 85.1%.

[0016] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages: The preparation method provided by this invention is simple and controllable. The hydroponic collection and freeze-drying process is straightforward, requiring no complex equipment, and is easy to scale up and standardize. The resulting secretion powder is stable and easy to store and transport. Experiments have shown that Hayward root exudates significantly promote the growth and motility of Flavobacterium F-55 and enhance its antagonistic effect against pathogenic kiwifruit strains of *Pseudomonas syringae*, increasing the in vitro control efficacy from 62.3% to 85.1%, achieving a synergistic disease control effect. Root exudates are natural substances produced by the plant itself, and Flavobacterium F-55 is a native beneficial bacterium isolated from the rhizosphere. The combined application of these two does not introduce chemical pesticides, meeting the requirements of green agriculture. The precise combination of exudates and specific biocontrol strains achieves a shift from broad-spectrum inhibition to targeted regulation, providing a new, highly efficient bacterial agent prototype for the biological control of bacterial canker in kiwifruit. Activating biocontrol bacteria using root exudates from disease-resistant varieties holds promise for developing practical products in seedling treatment and root irrigation, demonstrating significant industrialization potential. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a photograph of the appearance of the kiwifruit root exudate powder prepared in Example 1.

[0019] Figure 2 This is a colony morphology diagram of the activated Flavobacterium F-55 strain in Example 2 on a PDA plate.

[0020] Figure 3 This image shows the inhibitory effect of Flavobacterium F-55 fermentation broth alone on detached kiwifruit leaf canker in Example 7. Treatment a (positive control) was inoculated with GFP-M228 solution permeated into the leaf disc. Treatment b (negative control) involved permeating the leaf disc with sterile water only; treatment c was the F-55-only treatment group (without the addition of root exudates), in which the leaf disc was first permeated with F-55 bacterial solution under vacuum, and then permeated with GFP-M228 bacterial solution.

[0021] Figure 4 This is a growth curve diagram showing the effect of different concentrations of kiwifruit root exudates on the growth of Flavobacterium F-55 in Example 3.

[0022] Figure 5 This is a growth curve diagram showing the effect of the optimal concentration of kiwifruit root exudate on the growth promotion of Flavobacterium F-55 in Example 4.

[0023] Figure 6 This is a comparative graph showing the effect of the optimal concentration of kiwifruit root exudate on the motility of Flavobacterium F-55 in Example 5.

[0024] Figure 7 Photographs of the inhibition zones in Example 6 show the effect of the optimal concentration of kiwifruit root exudate on the antagonistic ability of Flavobacterium F-55 fermentation broth against ulcer pathogens. In the figure, a is a photograph of the plate inhibition zone; b is a statistical bar chart.

[0025] Figure 8 The image shows the inhibitory effect of the optimal concentration of kiwifruit root exudate combined with Flavobacterium F-55 in 8 on detached kiwifruit leaves against bacterial canker. Treatment a (positive control) involved leaf discs being infiltrated only with GFP-M228 inoculum; treatment b (negative control) involved leaf discs being infiltrated only with sterile water; and treatment d (F-55 combination treatment group) involved first vacuum-permeating the leaf discs with F-55 combination bacterial solution, and then infiltrating them with GFP-M228 bacterial solution. Detailed Implementation

[0026] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental and detection methods described in each embodiment are conventional methods; the reagents and materials described are commercially available unless otherwise specified. Unless otherwise specified, all percentages in the following embodiments refer to mass percentages. Unless otherwise specified, all proportions in the following embodiments refer to mass ratios.

[0027] Flavobacterium ( Flavobacterium F-55 was deposited on March 31, 2023, at the China General Microbiological Culture Collection Center (CGMCC, address: No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing), with accession number CGMCC No. 26998. Pathogenic strain: *Pseudomonas syringae* kiwifruit pathogenic strain ( Pseudomonas syringae pv. actinidiae M228 is a green fluorescent protein (GFP)-tagged strain, hereinafter referred to as GFP-M228. Its pathogenicity is consistent with that of the wild type and it is used to evaluate the control effect.

[0028] The preparation method of the culture medium used in the following examples is briefly described below: PDA solid culture medium: Take 200g of peeled potatoes, cut them into pieces, add 1L of distilled water and boil for 30min. Filter through four layers of gauze, add 20g of glucose and 15g of agar to the filtrate, add water to 1L, and autoclave at 121℃ for 15min.

[0029] PDB liquid culture medium: except for the absence of agar, it is the same as PDA. After sterilization, it is ready for use.

[0030] LB solid medium: 10g tryptone, 5g yeast extract, 10g NaCl, 15g agar, 1L distilled water, sterilized at 121℃ for 20min.

[0031] LB liquid medium: LB without agar, sterilized for later use.

[0032] KB semi-solid medium: 10g peptone, 15mL glycerol, 1.963g K2HPO4·3H2O, 1.232g MgSO4, 1L distilled water, adjust pH to 7.0~7.2; if preparing swarming medium with a 0.4% agar concentration, add 4g agar powder; if preparing swimming medium with a 0.25% agar concentration, add 2.5g agar powder; sterilize at 121℃ for 20min, cool to about 60℃ and pour into plates, 10mL per 60mm dish, let solidify and use.

[0033] 0.8% water agar medium: 8g agar powder, 1L distilled water, sterilize at 121℃ for 20min.

[0034] Example 1: Preparation of Kiwi Root Exudates Hayward kiwifruit tissue culture seedlings with uniform growth (5-6 true leaves) that have undergone rooting culture for approximately 2.5-3 months (70-90 days) were selected. The root culture medium was carefully removed, and the root surface was gently rinsed with running tap water. Subsequently, the roots of the tissue culture seedlings were surface disinfected by immersing them in a 0.6% NaClO solution for 10 minutes. After removal, they were rinsed three times with sterile water for 30 seconds each time. The disinfected seedlings were placed in Erlenmeyer flasks containing 100 mL of sterile water and cultured in a plant incubator under the following conditions: temperature 26±1°C, photoperiod 16 hours light / 8 hours dark. After 3 days of culture, the plants were discarded, and the liquid in the Erlenmeyer flasks was collected; this is the crude root exudate extract. The collected root exudate solution was filtered through a 0.22 μm microporous membrane for sterilization, and the filtrate was collected. The filtrate was pre-frozen at -80°C, then transferred to a freeze dryer for freeze drying [vacuum freezer parameters: cold trap temperature -100°C, compressor: 7 / 8HP, vacuum pump speed 162L / min, vacuum degree 0.1 ~ 1 Torr (approximately 13 ~ 133 Pa), drying time 60-70h]. A pale yellow powdery solid was obtained, which is Hayward root exudate powder. It was sealed and stored at -80°C for later use. Its appearance is as follows... Figure 1 As shown.

[0035] Example 2: Preparation of Flavobacterium F-55 fermentation broth Using an inoculation loop, pick up Flavobacterium F-55 from the CGMCC No. 26998 preservation tube, streak it onto a PDA agar plate, and incubate it upside down at 28°C for 48 hours to activate it. Pick a single activated colony and streak it onto a fresh PDA plate, incubate at 28°C for 24-48 hours to obtain purified colonies. The colony morphology is as follows: Figure 2 As shown. Using a sterile toothpick, a suitable amount of bacterial cells was inoculated into a test tube containing 5 mL of PDB liquid medium. The tube was then incubated at 28°C and 180 rpm for 24 hours using a shaker to obtain the seed culture. The OD600 value of the seed culture was adjusted to approximately 0.1 using PDB medium to obtain the standardized F-55 bacterial culture for subsequent experiments.

[0036] Example 3: Screening for the optimal growth-promoting concentration Weigh the root exudate powder obtained in Example 1, dissolve and dilute it with sterile water to prepare stock solutions of different concentrations [all stock solutions were filtered through a 0.22 μm microporous membrane for sterilization]. Add the F-55 bacterial suspension (OD600≈0.1) from Example 2 to 50 mL of PDB liquid medium at an inoculation rate of 1% (v / v), and add the corresponding volume of exudate stock solution to make the final concentrations of root exudate in the medium 50 mg / L, 100 mg / L, 150 mg / L, and 200 mg / L, respectively. A control group without added exudate was also set up. The culture was carried out at 28℃ with shaking at 180 rpm, and OD600 values ​​were measured at 0, 3, 6, 9, 12, 15, 18, 21, and 24 h. Growth curves were plotted, and the results are shown below. Figure 4 As shown.

[0037] Depend on Figure 4 It can be seen that adding root exudates of different concentrations can promote the growth of F-55. Among them, the concentration of 100 mg / L showed the fastest increase in OD600 value and the highest final biomass, indicating that 100 mg / L is the optimal concentration for promoting the growth of F-55.

[0038] Example 4: The promoting effect of the optimal concentration on the growth of Flavobacterium F-55 F-55 bacterial suspension (1%, v / v) and root exudate solution were added to 50 mL of PDB liquid medium to bring the final concentration of exudate to 100 mg / L; the control group was treated with an equal volume of sterile water instead of the exudate solution. The culture conditions and growth curve determination methods were the same as in Example 3. Results are as follows: Figure 5 As shown, compared with the control, the F-55 bacterial culture with 100 mg / L root exudate showed a higher OD600 value throughout the logarithmic growth phase and the stationary phase, demonstrating a significant growth advantage.

[0039] Example 5: Effect of optimal concentration on the motility of Flavobacterium F-55 (1) Swarming test: F-55 cells prepared in Example 2 were picked up with a toothpick and inoculated into PDB liquid medium containing 100 mg / L root exudate. The medium was then cultured at 28°C and 180 rpm for 24 hours with shaking. The resulting bacterial solution was adjusted to OD600≈0.1 with sterile water [Specific implementation method: 2 mL of the above F-55 bacterial solution was taken into a 2 mL sterile EP tube, centrifuged at 12000 rpm for 2 min, the supernatant was discarded, and the solution was resuspended with sterile water; then centrifuged at 12000 rpm for 2 min, the medium was washed away, the supernatant was discarded, and finally the solution was resuspended with 2 mL of sterile water. 200 μL of the resuspended bacterial solution was taken and its OD600 was measured. The amount of resuspended bacterial solution required to adjust the final bacterial solution to OD600≈0.1 was (1000 / OD600 of the resuspended bacterial solution) μL, and the amount of sterile water required was 1000-(1000 / OD600 of the resuspended bacterial solution) μL]. Take 2.5 μL of the bacterial culture and spot it in the center of a KB semi-solid medium plate containing 0.4% agar. Incubate at 16°C for 24 hours and measure the diameter of the bacterial diffusion zone.

[0040] (2) Swimming test: The prepared bacterial solution was punctured with a sterile toothpick and inoculated into a KB semi-solid medium plate containing 0.25% agar. The plate was incubated at 16°C for 24 hours. The spread of bacteria from the puncture point was observed and recorded.

[0041] A control group was set up, consisting of F-55 bacterial culture without the addition of root exudates. The results are as follows: Figure 6 As shown, the diffusion circle diameter of F-55 bacterial solution with added 100 mg / L root exudate was significantly larger than that of the control, indicating that root exudate significantly enhanced the swarming and swimming ability of F-55.

[0042] Example 6: Effect of optimal concentration on the antagonistic ability of Flavobacterium F-55 First, prepare GFP-M228 bacterial plates: Activate the GFP-M228 strain on LB agar plates, pick a single colony and inoculate it into LB liquid medium, incubate at 28°C and 220 rpm with shaking until OD600 = 1.0. Take this bacterial suspension and add it at a ratio of 5% (v / v) to sterilized PDA solid medium (containing 1.5% agar) cooled to approximately 40°C, mix quickly, pour into 90 mm diameter petri dishes, and allow to solidify completely to obtain the bacterial plates.

[0043] Fermentation broth treatment: As described in Example 5, F-55 was cultured in PDB containing 100 mg / L root exudates to obtain the treatment group bacterial broth; simultaneously, F-55 was cultured in PDB without exudates as the control group bacterial broth. The obtained culture broth was centrifuged at 4°C and 12,000 rpm for 10 minutes, and the supernatant was collected and filtered through a 0.22 μm filter membrane for sterilization to obtain the sterile fermentation supernatant of F-55.

[0044] Perforated agar plates were made using a sterile punch (5 mm diameter). 20 μL of either the treatment group's or the control group's sterile fermentation filtrate was added to each well. Three replicates were prepared for each group. The plates were incubated upright at 28°C for 24 hours. The diameter of the inhibition zone was measured using the cross-sectional method, and the average value was recorded. Results are as follows: Figure 7 As shown, the diameter of the inhibition zone in the treatment group was between 17-20 mm, while the diameter of the inhibition zone in the control group was about 8-9 mm. The treatment group was significantly larger than the control group, indicating that adding 100 mg / L of root exudate can greatly enhance the inhibitory effect of the antagonistic substances produced by F-55 on ulcer bacteria.

[0045] Example 7: In vitro efficacy of Flavobacterium F-55 alone Take healthy kiwi leaves, wash off surface dust with sterile water, then soak them in a 6‰ sodium hypochlorite solution for 5 minutes to disinfect the surface. Rinse thoroughly with sterile water until there is no pungent odor, then remove and air dry. Use a 1.6cm inner diameter punch to create leaf discs, avoiding the midrib.

[0046] Preparation of GFP-M228 inoculum: Activated GFP-M228 was inoculated into LB liquid medium and cultured at 28°C with shaking until OD600 = 1.0. The culture was then diluted with sterile water to OD600 = 0.1, and this diluted solution was further diluted 500 times with sterile water. The final inoculum concentration was approximately 2 × 10⁻⁶. 5 CFU / mL.

[0047] Preparation of Flavobacterium F-55 fermentation broth: F-55 bacterial culture (OD600≈0.1, concentration approximately 1.0 ≈ 1×10⁻⁶) was obtained according to the method in Example 2. 9 Take 80 μL of this bacterial culture (CFU / mL) and add it to 40 mL of sterile water. Mix well to prepare the F-55 treatment solution.

[0048] Process according to the following groups: Treatment a (positive control): The leaf disc was placed in the GFP-M228 inoculum prepared above and inoculated under vacuum at 0.1 MPa for 30 seconds.

[0049] Treatment b (negative control): The leaf disc was placed in sterile water and vacuum permeated under the same conditions.

[0050] Treatment c (F-55 single treatment group): Place the leaf disc into the above F-55 treatment solution, vacuum permeate for 30 seconds, remove it and place it on sterile filter paper to slightly absorb the surface moisture, place it at 16℃ for 24 hours, and then permeate it with GFP-M228 bacterial solution according to the method of treatment a.

[0051] After the infiltration of each treatment group was completed, the leaf discs were rinsed three times with sterile water. Then, the leaf discs were placed on 0.8% water agar plates and incubated at 16°C for 3 days. The occurrence of lesions was observed and recorded. The experimental results are as follows: Figure 3 As shown in the figure. Statistical analysis showed that the lesion area in treatment c was significantly smaller than that in treatment a, and the in vitro control efficacy of F-55 fermentation broth alone against peptic ulcer was 62.3%.

[0052] Example 8: In vitro control efficacy of the optimal concentration of root exudate combined with Flavobacterium F-55 The preparation of leaf discs, the preparation of GFP-M228 permeation bacterial solution, and the vacuum permeation method are all the same as in Example 7.

[0053] Preparation of F-55 fermentation broth containing exudates: F-55 bacterial culture (1%, v / v) and root exudate stock solution were added to PDB liquid medium to achieve a final exudate concentration of 100 mg / L. The medium was then incubated at 28℃ with shaking at 180 rpm for 48 hours to obtain the F-55-treated bacterial culture (OD600≈0.1, concentration approximately 1×10⁻⁶). 9 Take 80 μL of the bacterial culture and add it to 40 mL of sterile water. Mix well to obtain the combined treatment permeate.

[0054] Process according to the following settings: Treatment a: Same as the positive control in Example 7.

[0055] Treatment b: The negative control of the same as in Example 7.

[0056] Treatment d (combined treatment group): The leaf disc was placed in the above combined treatment permeate solution, vacuum permeated for 30 seconds, placed at 16℃ for 24 hours, and then permeated with GFP-M228 bacterial solution according to the method of treatment a.

[0057] The methods for infiltration, washing, and culture observation were the same as in Example 7. The results are as follows: Figure 8 As shown. With Figure 3 Compared to treatment c, treatment d showed smaller lesion areas and extremely mild symptoms, with its in vitro control efficacy against kiwifruit canker increasing to 85.1%. Therefore, in the presence of 100 mg / L Hayward root exudate, Flavobacterium F-55 significantly improved its in vitro control efficacy against kiwifruit canker.

[0058] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate preferred embodiments. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A method for preparing kiwifruit root exudate, characterized in that, include: Kiwi fruit tissue culture seedlings were selected, and after surface disinfection and rinsing, they were placed in sterile water for hydroponic culture under alternating light and dark conditions. Collect the aqueous solution after hydroponic culture to obtain a root exudate solution; The root exudate solution was filtered, concentrated, and dried to obtain the kiwifruit root exudate powder.

2. The method for preparing kiwifruit root exudate according to claim 1, characterized in that, The kiwifruit variety mentioned is Hayward.

3. The method for preparing kiwifruit root exudates according to claim 1, characterized in that, The surface disinfection involves immersing the roots of the tissue culture seedlings in a solution with an effective chlorine concentration of 0.5-1% for at least 10 minutes, followed by rinsing with sterile water.

4. The method for preparing kiwifruit root exudate according to claim 1, characterized in that, The hydroponic culture conditions are a temperature of 26±1°C, 16 hours of light and 8 hours of darkness per day, for at least 3 days.

5. The method for preparing kiwifruit root exudate according to claim 1, characterized in that, Filtration is performed using a 0.22μm filter membrane; The concentration and drying process is freeze drying.

6. A kiwifruit root exudate, characterized in that, It is prepared by the method for preparing kiwi root exudate according to any one of claims 1 to 5.

7. The kiwifruit root exudate according to claim 6 enhances the effect of Flavobacterium... Flavobacterium Prevention and treatment of bacterial canker in kiwifruit and / or promotion of Flavobacterium Flavobacterium Applications during growth.

8. The application according to claim 7, characterized in that, The Flavobacterium mentioned is Flavobacterium F-55, with accession number CGMCC No. 26998.

9. The application according to claim 7, characterized in that, The kiwifruit root exudate was added to the fermentation broth of Flavobacterium F-55, and the final concentration of the kiwifruit root exudate in the fermentation broth was not less than 50 mg / L.

10. The application according to claim 7, characterized in that, The pathogen causing bacterial canker in kiwifruit is *Pseudomonas syringae* var. *sinensis*. Pseudomonas syringae pv. actinidiae .

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