Synthetic flora for breaking alfalfa seed dormancy and promoting seedling growth and application thereof

Abstract

The invention relates to the field of alfalfa planting, in particular to a synthetic flora for breaking dormancy of alfalfa seeds and promoting growth of seedlings and application of the synthetic flora. The invention provides a strain of sinorhizobium meliloti NFB5, the preservation number is CGMCC NO.33618, and the sinorhizobium meliloti NFB5 can break dormancy of alfalfa seeds and promote growth of alfalfa seedlings and root systems. According to the method, sinorhizobium meliloti NFB5 is compounded with one or two of screened salt-tolerant brevibacillus brevis EB3 and bacillus PS06 to obtain a synthetic flora, and alfalfa seeds are soaked in a bacterial solution containing the synthetic flora, so that the number of hard seeds can be remarkably reduced, the germination rate and germination potential of the seeds can be remarkably improved, and the germination rate of the seeds can be remarkably increased. Therefore, the synthetic flora can well break the dormancy of the alfalfa seeds, does not cause loss to the seeds, and does not reduce the quality of the seeds. In addition, the synthetic flora also has a significant growth promoting effect, and can significantly improve the plant height, root length, stem weight and root weight of seedlings.

Description

Technical Field

[0001] The invention relates to the field of alfalfa planting, and in particular to a synthetic bacterial community for breaking the dormancy of alfalfa seeds and promoting the growth of seedlings, and an application thereof. Background Art

[0002] Seed dormancy is a biological characteristic that species have developed during their long evolutionary development to resist adverse external environments. It is an important component of plant adaptability, which can prevent plant seeds from germinating under unsuitable conditions and ensure the survival and reproduction of species in harsh environments. Physical dormancy, also known as hardness, is common in leguminous plant seeds. Hardness is considered a necessary condition for the long-term survival of wild species. Many forage seeds with strong stress resistance generally have hard or impermeable seed coats as a mechanism to maintain the long-term viability of seeds. However, the hardness of seeds affects seed germination and seedling formation in the field, resulting in uneven seedling emergence, which seriously affects the rapid establishment of forage and has become an important issue that cannot be ignored in the artificial cultivation of leguminous forage.

[0003] Alfalfa is one of the important forage grasses. It has strong cold resistance and drought resistance. It can be promoted for planting in cold, arid and relatively barren areas. It has become a very valuable forage grass for the construction of artificial grasslands and the improvement of degraded grasslands in my country, and plays a key role in the healthy development of animal husbandry. However, the dormancy characteristics of its seeds hinder the utilization and variety improvement of alfalfa germplasm. At present, in actual production, seed dormancy can be relieved by mechanical wear, acid and alkali corrosion, high temperature soaking and other methods. Although it can break seed dormancy to a certain extent, these methods seriously affect the quality of seeds, resulting in an increase in the number of damaged seeds and abnormal seedlings, which greatly increases the amount of seeds used. Moreover, due to the decline in seed quality, it is difficult to form seedlings, which seriously affects the economic benefits of the forage planting industry. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a synthetic bacterial community for breaking alfalfa seed dormancy and promoting seedling growth and its application. Sinorhizobium alfalfa NFB5 and its synthetic bacterial community provided by the present invention can break alfalfa seed dormancy and promote alfalfa seedling and root growth.

[0005] In order to achieve the above object, the present invention provides the following technical solutions: The present invention provides a strain of Sinorhizobium alfalfa ( Sinorhizobium meliloti )NFB5, characterized in that the deposit number is CGMCC NO.33618.

[0006] The present invention provides a synthetic bacterial community, which is composed of the alfalfa sinensis NFB5 described in the above technical solution and other microorganisms; the other microorganisms include Bacillus ( Bacillus pratensis ) PS06 and / or Bacillus brevis halotolerant ( Brevibacillus halotolerans ) EB3; the preservation number of the salt-tolerant Bacillus brevis EB3 is CGMCC NO.33617.

[0007] The present invention provides a synthetic bacterial agent, which comprises the synthetic bacterial community described in the above technical solution; the OD of the synthetic bacterial community in the synthetic bacterial agent is 600 Value ≥ 0.2.

[0008] Preferably, the OD values ​​of the salt-tolerant Bacillus brevis EB3 and Bacillus PS06 are 600 The OD values ​​of the salt-tolerant Brevibacillus EB3 and the alfalfa Sinorhizobium NFB5 were the same as those of the 600 The OD values ​​of Bacillus PS06 and Sinorhizobium meliloti NFB5 were the same. 600 The values ​​are the same.

[0009] The present invention provides a method for preparing the synthetic bacterial agent described in the above technical solution, comprising the following steps: The strains in the synthetic bacterial community are cultured separately to obtain a bacterial suspension of each strain; the culture medium used in the culture includes LB culture medium; The bacterial suspensions of each strain are mixed to obtain the synthetic bacterial agent.

[0010] Preferably, the culture conditions include: temperature of 28-32° C. and pH of 6.8-7.2.

[0011] The present invention provides the use of the alfalfa Sinorhizobium NFB5 described in the above technical scheme, or the synthetic bacterial community described in the above technical scheme, or the synthetic bacterial agent described in the above technical scheme, or the synthetic bacterial agent prepared by the preparation method described in the above technical scheme in breaking the dormancy of alfalfa seeds and / or promoting the growth of alfalfa seedlings.

[0012] Preferably, the breaking of alfalfa seed dormancy includes: increasing the germination rate and / or germination potential of alfalfa seeds; and the promoting of alfalfa seedling growth includes: increasing one or more of the plant height, root length, stem weight and root weight of the alfalfa seedlings.

[0013] The present invention provides a method for breaking dormancy of alfalfa seeds, comprising the following steps: The sterilized alfalfa seeds are soaked in a microbial solution, and the soaked alfalfa seeds are germinated; the microbial solution includes the alfalfa Sinorhizobium NFB5 described in the above technical solution, or the synthetic bacterial community described in the above technical solution, or the synthetic bacterial agent described in the above technical solution, or the synthetic bacterial agent prepared by the preparation method described in the above technical solution.

[0014] The present invention provides a method for promoting the growth of alfalfa seedlings, comprising: applying a microbial liquid into soil where alfalfa seedlings are planted; the microbial liquid comprises the alfalfa Sinorhizobium NFB5 described in the above technical scheme or the synthetic bacterial community described in the above technical scheme or the synthetic bacterial agent described in the above technical scheme or the synthetic bacterial agent prepared by the preparation method described in the above technical scheme.

[0015] Beneficial effects: The present invention provides a Sinorhizobium meliloti NFB5, with a deposit number of CGMCC NO. 33618. The Sinorhizobium meliloti NFB5 provided by the present invention is a strain isolated from the roots of Stipa breviflora, and can break the dormancy of alfalfa seeds and promote the growth of alfalfa seedlings and roots.

[0016] Furthermore, the present invention compounded Sinorhizobium alfalfa NFB5 with one or two of the selected salt-tolerant Bacillus brevis EB3 and Bacillus PS06 to obtain a synthetic bacterial community, and by soaking alfalfa seeds in a bacterial solution containing the synthetic bacterial community, the growth of the alfalfa seeds can be significantly improved. P <0.05) reduced the number of hard seeds, significantly ( P <0.05) to improve the germination rate and germination potential of seeds, indicating that the synthetic bacterial community can effectively break the dormancy of alfalfa seeds without causing any loss to the seeds or reducing the seed quality, and the effect is better than that of a single strain. In addition, the synthetic bacterial community also has a significant growth-promoting effect, which can significantly ( P <0.05) increased seedling height, root length, stem weight and root weight, and its growth-promoting effect was better than that of a single strain. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the embodiments are briefly introduced below.

[0018] Figure 1 The colony morphology of EB3 strain and NFB5 strain; Figure 2 This is a picture of alfalfa seedlings treated with different test bacterial solutions in the test example; Figure 3 This is a real picture of alfalfa plants treated with different test bacterial solutions in the test example.

[0019] Biological Deposit Description Sinorhizobium meliloti NFB5, classified as Sinorhizobium meliloti , deposited in the General Microbiology Center of China Microorganism Culture Collection (CGMCC) on February 24, 2025, with the deposit address at Institute of Microbiology, Chinese Academy of Sciences, No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing, with the deposit number CGMCC NO.33618.

[0020] Halophilic Brevibacillus EB3, classified as Brevibacillus halotolerans , deposited in the General Microbiology Center of China Microorganism Culture Collection (CGMCC) on February 24, 2025, with the deposit address at Institute of Microbiology, Chinese Academy of Sciences, No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing, with the deposit number CGMCC NO.33617. DETAILED DESCRIPTION

[0021] The invention provides a Sinorhizobium meliloti NFB5, whose preservation number is CGMCC NO.33618.

[0022] The Sinorhizobium alfalfa NFB5 provided by the invention is a strain isolated from rhizosphere soil of yellow alfalfa, has a rod-shaped, oval, slightly yellowish colony morphology, a smooth surface, is aerobic, and egg white-like, and can break the dormancy of alfalfa seeds and promote the growth of alfalfa seedlings and root systems.

[0023] The present invention provides a synthetic bacterial community, which is composed of the alimentary sinensis NFB5 described in the above technical solution and other microorganisms; the other microorganisms include Bacillus PS06 and / or halophilic Bacillus brevis EB3; the preservation number of the halophilic Bacillus brevis EB3 is CGMCC NO.33617. The Bacillus PS06 described in the present invention is preserved in the China General Microbiological Culture Collection Center (CGMCC) with a preservation number of CGMCC 1.17355. T , and published in the paper [Shi Jiajia. Identification of a new strain of Bacillus PS06 isolated from the rhizosphere soil of Stipa breviflora and its growth-promoting effect [D]. Inner Mongolia: Inner Mongolia University, 2021.].

[0024] As an embodiment, the other microorganisms include Bacillus PS06 and Sinorhizobium meliloti NFB5.

[0025] The salt-tolerant brevis bacillus EB3 provided by the invention is a strain isolated from the roots of Stipa breviflora, has a rod-shaped, elliptical, slightly yellowish, opaque colony morphology, a rough surface, aerobic, and irregular edges, and can break the dormancy of alfalfa seeds and promote the growth of alfalfa seedlings and root systems.

[0026] The present invention combines Sinorhizobium alfalfa NFB5 with one or two of the selected salt-tolerant Bacillus brevis EB3 and Bacillus PS06 to obtain a synthetic bacterial flora, which can significantly ( P <0.05) reduced the number of hard seeds, significantly ( P<0.05) to improve the germination rate and germination potential of seeds, indicating that the synthetic bacterial community can effectively break the dormancy of alfalfa seeds without causing any loss to the seeds or reducing the seed quality, and the effect is better than that of a single strain. In addition, the synthetic bacterial community also has a significant growth-promoting effect, which can significantly ( P <0.05) increased seedling height, root length, stem weight and root weight, and its growth-promoting effect was better than that of a single strain.

[0027] Based on the above advantages, the present invention provides a synthetic bacterial agent, which includes the synthetic bacterial community described in the above technical solution; the OD of the synthetic bacterial community in the synthetic bacterial agent is 600 As an embodiment, the OD of the synthetic bacterial community in the synthetic bacterial agent is 600 The value is 0.2.

[0028] As an embodiment, the OD values ​​of the salt-tolerant Brevibacillus EB3 and Bacillus PS06 are 600 The OD values ​​of the salt-tolerant Brevibacillus EB3 and the alfalfa Sinorhizobium NFB5 were the same as those of the 600 The OD values ​​of Bacillus PS06 and Sinorhizobium meliloti NFB5 were the same. 600 The values ​​are the same.

[0029] The present invention provides a method for preparing the synthetic bacterial agent described in the above technical solution, comprising the following steps: The strains in the synthetic bacterial community are cultured separately to obtain a bacterial suspension of each strain; the culture medium used in the culture includes LB culture medium; Each bacterial suspension is mixed to obtain the synthetic bacterial agent.

[0030] As an embodiment, the culture conditions include: a temperature of 28-32° C. and a pH of 6.8-7.2.

[0031] As an embodiment, the OD of each bacterial suspension is 600 Value ≥ 0.2; As another embodiment, the OD of each bacterial suspension 600 As an embodiment, each bacterial suspension is mixed in equal volumes to obtain the synthetic bacterial agent.

[0032] Based on the above advantages, the present invention provides the use of the alfalfa Sinorhizobium NFB5 described in the above technical scheme, or the synthetic bacterial community described in the above technical scheme, or the synthetic bacterial agent described in the above technical scheme, or the synthetic bacterial agent prepared by the preparation method described in the above technical scheme in breaking the dormancy of alfalfa seeds and / or promoting the growth of alfalfa seedlings.

[0033] As an embodiment, breaking the dormancy of alfalfa seeds includes: increasing the germination rate and / or germination potential of alfalfa seeds; promoting the growth of alfalfa seedlings includes: increasing one or more of the plant height, root length, stem weight and root weight of alfalfa seedlings.

[0034] Based on the above advantages, the present invention provides a method for breaking alfalfa seed dormancy, comprising the following steps: The sterilized alfalfa seeds are soaked in a microbial solution, and the soaked alfalfa seeds are germinated; the microbial solution includes the alfalfa Sinorhizobium NFB5 described in the above technical solution, or the synthetic bacterial community described in the above technical solution, or the synthetic bacterial agent described in the above technical solution, or the synthetic bacterial agent prepared by the preparation method described in the above technical solution.

[0035] Based on the above advantages, the present invention provides a method for promoting the growth of alfalfa seedlings, comprising: applying a microbial solution to soil in which alfalfa seedlings are planted; the microbial solution comprises the alfalfa Sinorhizobium NFB5 described in the above technical scheme or the synthetic bacterial community described in the above technical scheme or the synthetic bacterial agent described in the above technical scheme or the synthetic bacterial agent prepared by the preparation method described in the above technical scheme.

[0036] To further illustrate the present invention, a synthetic bacterial community for breaking alfalfa seed dormancy and promoting seedling growth and its application provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0037] Example 1 (1) Isolation and identification of bacterial strains EB3: Take fresh nutrient roots of Stipa brevis, rinse them repeatedly with sterile water for 3-4 times, soak them in 75% alcohol by volume for 1 min, rinse them with sterile water for 3-4 times, disinfect them with 1% sodium hypochlorite solution by mass for 30 s, rinse them with sterile water for 3-4 times, and dry them with sterile filter paper. Select 0.1 g of the sterilized roots, cut them into small pieces of about 1 cm in length with sterile scissors under sterile conditions, place them in a sterile mortar, add 1 mL of sterile water, and grind the roots thoroughly into a homogenate. Take 200 µL of the ground homogenate and spread it on NB medium, invert and culture at 30°C; according to the morphology of the colonies, pick colonies of different morphologies under sterile conditions, inoculate them on LB purification medium, and pass them three times to obtain pure cultured bacteria, which are recorded as EB3.

[0038] NFB5: Take 1 g of rhizosphere soil of yellow alfalfa and dilute it to 10 with 10 mL of sterile water. -1 , 10 -2 , 10 -3 and 10 -4The diluted suspensions were spread on NFM nitrogen-fixing medium and inverted at 30°C. According to the morphology of the colonies, colonies of different morphologies were picked under sterile conditions and inoculated on LB purification medium. After three subcultures, pure cultured bacteria were obtained, which were recorded as NFB5.

[0039] Total bacterial DNA was extracted, and 16S rDNA universal primers were selected for PCR amplification. The DNA was sent to Shanghai Meiji Biological Technology Co., Ltd. for sequencing. Through sequence comparison, it was preliminarily determined that the EB3 strain belonged to the genus Brevibacillus, and the 16SrRNA gene similarity with the known model bacteria of the genus Brevibacillus was 99.02%. The NFB5 strain belonged to the genus Meliloti, and the 16SrRNA gene similarity with the known model bacteria of the genus Meliloti was 99.85%.

[0040] (2) Physiological and biochemical identification of EB3 and NFB5 The EB3 strain and the NFB5 strain were inoculated into LB solid medium, respectively, and cultured for 72 h at a temperature of 28-32 °C and a pH of 7.0. The colony morphology was observed. Figure 1 The results showed that the colony morphology of the EB3 strain was rod-shaped, oval, slightly yellow, opaque, with a rough surface and irregular edges; the colony morphology of the NFB5 strain was rod-shaped, oval, slightly yellow, with a smooth surface and egg white.

[0041] In summary, the EB3 strain was named as Halophilus brevis EB3, and deposited in the China General Microbiological Culture Collection Center with a deposit number of CGMCC NO.33617; the NFB5 strain was named as Sinorhizobium alfalfa NFB5, and deposited in the China General Microbiological Culture Collection Center with a deposit number of CGMCC NO.33618.

[0042] Example 2 1. Preparation of bacterial suspensions of different strains: Prepare 100 mL of LB liquid culture medium, sterilize and cool, add Bacillus PS06, salt-tolerant Bacillus brevis EB3 and Sinorhizobium meliloti NFB5 screened in Example 1, and culture at 28°C and 150 r / min for 36 h. Use the uninoculated culture medium as a negative control to measure the bacterial growth. 600 The value was adjusted to 0.2, and the mixture was centrifuged at 5000 r / min for 10 min. The supernatant was discarded, and the bacteria adhering to the bottom of the centrifuge tube were washed with sterile water to obtain the OD 600 The value of 3 bacterial suspensions was 0.2 (respectively denoted as PS06, EB3 and NFB5).

[0043] 2. Synthetic bacterial suspension of PS06+EB3+NFB5: Mix the three bacterial suspensions prepared in step 1 in equal volumes, add sterile water and raise the OD of the mixed bacterial suspension to600 The value was adjusted to 0.2 to obtain the bacterial suspension of synthetic bacterial colony 1.

[0044] 3. Synthetic bacterial suspension of bacterial colony 2 (PS06+EB3): Mix the PS06 and EB3 bacterial suspensions prepared in step 1 in equal volumes, add sterile water and raise the OD of the mixed bacterial suspension to 600 The value was adjusted to 0.2 to obtain the bacterial suspension of synthetic bacterial colony 2.

[0045] 4. Synthetic bacterial suspension of bacterial group 3 (EB3+NFB5): Mix equal volumes of the EB3 and NFB5 suspensions prepared in step 1, add sterile water and raise the OD of the mixed suspension to 600 The value was adjusted to 0.2 to obtain the bacterial suspension of synthetic bacterial colony 3.

[0046] 5. Synthetic bacterial suspension of bacterial community 4 (PS06+NFB5): Mix the PS06 and NFB5 bacterial suspensions prepared in step 1 in equal volumes, add sterile water and raise the OD of the mixed bacterial suspension to 600 The value was adjusted to 0.2 to obtain the bacterial suspension of synthetic bacterial colony 4.

[0047] Comparative Example 1 A synthetic supernatant is prepared by the following method: after the bacterial suspensions of the three strains configured in Example 2 are centrifuged respectively, equal volumes of the supernatants are taken and mixed to obtain the synthetic supernatant.

[0048] Test Case Sterile water was added to the bacterial suspensions of the three strains prepared in Example 2 to raise the OD 600 The value was adjusted to 0.2, and the test bacterial solutions of the three strains were obtained.

[0049] The bacterial suspensions of the synthetic bacterial communities 1 to 4 configured in Example 2, the test bacterial solutions of the three strains, sterile water, LB liquid culture medium, and the synthetic supernatant in Comparative Example 1 were used as test agents to conduct germination experiments and potted experiments in alfalfa. Each seed was subjected to three parallel repeated experiments using each test agent. The steps were as follows: 1. Alfalfa seed selection: Select yellow alfalfa seeds and purple alfalfa seeds with a hardness rate of 57% respectively.

[0050] 2. Seed disinfection: Soak the alfalfa seeds in sterile water for 5 minutes, then disinfect them with 1% sodium hypochlorite for 30 seconds, and then wash them three times with sterile water.

[0051] 3. Inoculation treatment: Add the sterilized alfalfa seeds into 5 mL of the test agent and shake at 30°C and 150 r / min for 6 hours.

[0052] 4. Germination experiment: After pouring out the suspension of synthetic bacteria, the seeds were placed on sterile filter paper, and after absorbing the water, they were placed in a culture dish covered with two layers of moist filter paper. 100 seeds were placed in each dish, and 3 replicates were placed in a light incubator. They were cultured at a constant temperature of 20°C, 8 hours of light, and 16 hours of darkness. The initial count began on the 4th day, and the number of germinated seedlings was counted daily. The last count day was the 10th day, and the number of normal seedlings, abnormal seedlings, hard seeds, dead seeds, germination rate, and germination potential were finally counted.

[0053] Germination rate = (number of seeds germinated within the specified germination days / total number of seeds tested) × 100%; Germination potential = (total number of seeds germinated when the germination number reaches the peak / number of seeds tested) × 100%.

[0054] 5. Pot experiment: Select normal seedlings with consistent germination and plant them in pots (11 cm high × 12 cm in diameter) filled with 500 g sterilized soil. Plant 5 pots for each treatment, add 20 mL of the test agent diluted 3 times, and cultivate at a constant temperature of 25°C, 16 hours of light, 8 hours of darkness, and water regularly. After 60 days of cultivation, measure the plant height, root length, stem weight and root weight. Some results are shown in Figure 2 .

[0055] The preparation method of the sterilized soil is as follows: after removing roots, dead branches and gravel from the collected soil with a 2 mm sieve, vermiculite is added in a volume ratio of soil: vermiculite = 7:3, sterilized at 120° C. for 20 minutes, and sterilized again after an interval of 12 hours.

[0056] The results are shown in Tables 1~4.

[0057] Table 1 Effects of different tested agents on the germination rate of yellow alfalfa seeds

[0058] Note: Different lowercase letters represent significant differences, the same applies to the following table.

[0059] Table 2 Effects of different tested agents on the morphological characteristics of yellow-flowered alfalfa seedlings

[0060] Table 3 Effects of different tested agents on the germination rate of alfalfa seeds

[0061] Table 4 Effects of different tested agents on morphological characteristics of alfalfa seedlings

[0062] The test results show that the treatment of yellow alfalfa and purple alfalfa seeds with the synthetic bacterial flora constructed by the present invention can significantly ( P <0.05) reduced the number of hard seeds, significantly ( P <0.05) to improve the germination rate and germination potential of seeds, and the synthetic bacterial community 1 (PS06+EB3+NFB5) had the best effect, indicating that the synthetic bacterial community can effectively break the dormancy of alfalfa seeds without causing damage to the seeds and reducing the seed quality (Tables 1 and 3). In addition, the synthetic bacterial community also has a significant growth-promoting effect, which can significantly ( P <0.05) increased seedling height, root length, stem weight and root weight (Table 2 and Table 4), and the synthetic bacterial community 1 (PS06+EB3+NFB5) had the best effect ( Figure 3 ).

[0063] In summary, the strain and synthetic bacterial flora provided by the present invention can break the dormancy of alfalfa seeds and promote the growth of alfalfa seedlings and roots.

[0064] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A strain of Sinorhizobium meliloti ( Sinorhizobium meliloti ) NFB5, characterized in that The deposit number is CGMCC NO.33618.

2. A synthetic bacterial community, characterized in that: The synthetic bacterial community is composed of the Chinese Rhizobium meliloti NFB5 described in claim 1 and other microorganisms; the other microorganisms include Bacillus ( Bacillus pratensis ) PS06 and / or Bacillus brevis halotolerant ( Brevibacillus halotolerans ) EB3; the preservation number of the salt-tolerant Bacillus brevis EB3 is CGMCC NO.33617.

3. A synthetic bacterial agent, characterized in that: The synthetic bacterial agent comprises the synthetic bacterial flora according to claim 2; the OD of the synthetic bacterial flora in the synthetic bacterial agent is 600 Value ≥ 0.

2.

4. The synthetic bacterial agent according to claim 3, characterized in that The OD values ​​of the halodurable Brevibacillus EB3 and Bacillus PS06 were 600 The OD values ​​of the salt-tolerant Brevibacillus EB3 and the alfalfa Sinorhizobium NFB5 were the same as those of the 600 The OD values ​​of Bacillus PS06 and Sinorhizobium meliloti NFB5 were the same. 600 The values ​​are the same.

5. The method for preparing the synthetic bacterial agent according to claim 3 or 4, characterized in that: The following steps are involved: The strains in the synthetic bacterial community are cultured separately to obtain a bacterial suspension of each strain; the culture medium used in the culture includes LB culture medium; The bacterial suspensions of each strain are mixed to obtain the synthetic bacterial agent.

6. The preparation method according to claim 5, characterized in that: The culture conditions include: temperature of 28-32° C. and pH of 6.8-7.

2.

7. Use of the alfalfa Sinorhizobium NFB5 described in claim 1, the synthetic bacterial community described in claim 2, the synthetic bacterial agent described in claim 3 or 4, or the synthetic bacterial agent prepared by the preparation method described in claim 5 or 6 in breaking the dormancy of alfalfa seeds and / or promoting the growth of alfalfa seedlings.

8. The use according to claim 7, characterized in that: The method of breaking the dormancy of alfalfa seeds includes: increasing the germination rate and / or germination potential of alfalfa seeds; and the method of promoting the growth of alfalfa seedlings includes: increasing one or more of the plant height, root length, stem weight and root weight of the alfalfa seedlings.

9. A method for breaking alfalfa seed dormancy, characterized in that: The following steps are involved: The sterilized alfalfa seeds are soaked in a microbial solution, and the soaked alfalfa seeds are germinated; the microbial solution includes the alfalfa Sinorhizobium NFB5 described in claim 1 or the synthetic bacterial community described in claim 2 or the synthetic bacterial agent described in claim 3 or 4 or the synthetic bacterial agent prepared by the preparation method described in claim 5 or 6.

10. A method for promoting the growth of alfalfa seedlings, characterized in that: include: A microbial liquid is applied to the soil where alfalfa seedlings are planted; the microbial liquid includes the alfalfa Sinorhizobium NFB5 described in claim 1 or the synthetic bacterial community described in claim 2 or the synthetic bacterial agent described in claim 3 or 4 or the synthetic bacterial agent prepared by the preparation method described in claim 5 or 6.

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