Growth-promoting rhizobacteria and application thereof

Abstract

Provided are a bacterial strain for promoting plant growth and an application thereof, the bacterial strain being selected from at least one of the following: a strain 1 comprising a 16S rDNA sequence as shown in SEQ ID NO: 1 or a complementary sequence thereof or a sequence at least 85% identical to SEQ ID NO: 1; the strain 2 comprises a 16S rDNA sequence as shown in SEQ ID NO: 2 or comprises a sequence which is at least 85% identical with the sequence as shown in SEQ ID NO: 2; a strain 3 comprising a 16S rDNA sequence as shown in SEQ ID NO: 3 or comprising a sequence at least 85% identical to the sequence as shown in SEQ ID NO: 3; and a strain 4 comprising the 16S rDNA sequence as shown in SEQ ID NO: 4 or comprising a sequence at least 85% identical to SEQ ID NO: 4.

Description

[0001] Cross - reference to related applications

[0002] This application is a divisional application of the application with the filing date of July 22, 2022, application number: 2022109115753, and invention title "Plant growth - promoting rhizobacteria and their applications". Technical field

[0003] This application relates to the field of microorganisms, specifically to plant growth - promoting rhizobacteria and their applications. Background art

[0004] Microorganisms are a large group of organisms including bacteria, viruses, fungi, etc. They are tiny in size and are closely related to plants. Microorganisms exist in various parts of plants such as roots, stems, leaves, flowers, and seeds. All kinds of physiological functions of plant growth are affected by microorganisms. For example, microorganisms can promote plant growth and development, reduce the toxicity of soil heavy metals, enhance the resistance of plants to extreme environments (drought, flood, heat), and prevent and control pests and diseases.

[0005] Microorganisms and plant hosts have experienced a co - evolution process of millions of years. As a hot spot for energy and material exchange between plants and microorganisms, the root microbiome uses 40% of the carbon source fixed by photosynthesis in plant roots as a nutrient source, signal transduction, and source of antimicrobial active substances for root - zone soil microorganisms.

[0006] Therefore, it is urgent to develop plant growth - promoting rhizobacteria to promote the growth and development of a wide range of plants. Summary of the invention

[0007] For this reason, embodiments of the present application provide plant growth - promoting rhizobacteria and their applications.

[0008] The first - aspect embodiments of the present application propose a bacterial strain for promoting plant growth, wherein the bacterial strain is selected from at least one of the following:

[0009] Strain 1, which contains the 16S rDNA sequence shown in SEQ ID NO: 1 or its complementary sequence or a sequence with at least 85% identity compared to SEQ ID NO: 1;

[0010] Strain 2, which contains the 16S rDNA sequence shown in SEQ ID NO: 2 or a sequence with at least 85% identity compared to SEQ ID NO: 2;

[0011] Strain 3, which contains the 16S rDNA sequence shown in SEQ ID NO: 3 or a sequence with at least 85% identity compared to SEQ ID NO: 3; and

[0012] Strain 4, comprising the 16S rDNA sequence shown in SEQ ID NO: 4 or comprising a sequence with at least 85% identity compared to SEQ ID NO: 4.

[0013] In some embodiments, the strain 1 is Arthrobacter sp. In some embodiments, the strain 1 has the 16S rDNA sequence shown in SEQ ID NO: 1. In some embodiments, the strain 1 is Arthrobacter sp. Arth4 with the deposit number GDMCC No: 62566.

[0014] In some embodiments, the strain 2 is Bacillus sp. In some embodiments, the strain 2 is Bacillus paralicheniformis. In some embodiments, the strain 2 has the 16S rDNA sequence shown in SEQ ID NO: 2. In some embodiments, the strain 2 is Bacillus paralicheniformis Bacil9 with the deposit number GDMCC No: 62569.

[0015] In some embodiments, the strain 3 is Priestia sp. In some embodiments, the strain 3 is Priestia megaterium. In some embodiments, the strain 3 has the 16S rDNA sequence shown in SEQ ID NO: 3. In some embodiments, the strain 3 is Priestia megaterium Bacif4 with the deposit number GDMCC No: 62567.

[0016] In some embodiments, the strain 4 is Bacillus sp. In some embodiments, the strain 4 is Bacillus velezensis. In some embodiments, the strain 4 has the 16S rDNA sequence shown in SEQ ID NO: 4. In some embodiments, the strain 4 is Bacillus velezensis Baci5 with the deposit number GDMCC No: 62568.

[0017] An embodiment of the second aspect of the present application provides an agricultural preparation, wherein the agricultural preparation comprises the bacterial strain as described in any embodiment of the first aspect of the present application.

[0018] In some embodiments, the agricultural preparation further comprises excipients.

[0019] In some embodiments, the dosage form of the agricultural preparation is selected from: wettable powder, water dispersible granule, suspending agent, emulsion in water, granule, seed coating agent, or a combination thereof.

[0020] In the third aspect of the embodiments of the present application, there is provided the use of the bacterial strain as described in any one of the first aspect of the present application in the preparation of an agricultural preparation.

[0021] In the fourth aspect of the embodiments of the present application, there is provided a method for promoting plant growth, the method comprising applying to the plant the bacterial strain as described in any one of the first aspect of the present application or the agricultural preparation as described in any one of the second aspect of the present application.

[0022] The embodiments of the present application achieve the following beneficial effects:

[0023] The present application first proposes four strains, namely Arthrobacter sp. Arth4, Bacillus paralicheniformis Bacil9, Priestia megaterium Bacif4, and Bacillus velezensis Baci5, and their applications in improving the agronomic traits of plants. In particular, the bacterial genera and species to which the four strains belong can effectively promote the elongation of plant roots and the growth of stems, thereby improving the nutrient absorption and accumulation of plants, and thus increasing the yield of crops. The plant growth-promoting rhizobacteria proposed in the embodiments of the present application are of great significance for increasing the yield of crops. At the same time, by making Arth4, Bacil9, Bacif4, and Baci5 into microbial fertilizers suitable for agricultural production, the amount of chemical fertilizers used can be reduced, promoting green agricultural production. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 It is a clustering diagram of Arth4 according to Embodiment 2 of the present application;

[0026] Figure 2 It is a clustering diagram of Bacil9 according to Embodiment 2 of the present application;

[0027] Figure 3 It is a clustering diagram of Bacif4 according to Embodiment 2 of the present application;

[0028] Figure 4 It is a clustering diagram of Baci5 according to Embodiment 2 of the present application;

[0029] Figure 5 It is the flat growth diagram according to Embodiment 3 of the present application;

[0030] Figure 6 It is the sterile soil growth diagram of the seedlings according to Embodiment 4 of the present application;

[0031] Figure 7 It is the field growth diagram of Huagu 12 according to Embodiment 5 of the present application;

[0032] Figure 8 It is another field growth diagram of Huagu 12 according to Embodiment 5 of the present application.

[0033] Description of strain preservation:

[0034] Arthrobacter sp. Arth4: The preservation registration number is GDMCC No: 62566, the preservation institution is: Guangdong Provincial Microbial Culture Collection Center; The address of the preservation unit is: 5th Floor, Experimental Building, No. 100 Compound, Xianlie Middle Road, Yuexiu District, Guangzhou City, Guangdong Province; The preservation time is June 28, 2022.

[0035] Bacillus paralicheniformis Bacil9: The preservation registration number is GDMCC No: 62569, the preservation institution is: Guangdong Provincial Microbial Culture Collection Center; The address of the preservation unit is: 5th Floor, Experimental Building, No. 100 Compound, Xianlie Middle Road, Yuexiu District, Guangzhou City, Guangdong Province; The preservation time is June 28, 2022.

[0036] Priestia megaterium Bacif4: The preservation registration number is GDMCC No: 62567, the preservation institution is: Guangdong Provincial Microbial Culture Collection Center; The address of the preservation unit is: 5th Floor, Experimental Building, No. 100 Compound, Xianlie Middle Road, Yuexiu District, Guangzhou City, Guangdong Province; The preservation time is June 28, 2022.

[0037] Bacillus velezensis Baci5: The preservation registration number is GDMCC No: 62568, the preservation institution is: Guangdong Provincial Microbial Culture Collection Center; The address of the preservation unit is: 5th Floor, Experimental Building, No. 100 Compound, Xianlie Middle Road, Yuexiu District, Guangzhou City, Guangdong Province; The preservation time is June 28, 2022. Detailed implementation manners

[0038] The present invention will be further described in detail below in combination with the specific implementation manners. The provided embodiments are only for clarifying the present invention and do not limit the scope of the present invention. The following provided embodiments can be used as a guide for those of ordinary skill in the art to make further improvements and do not constitute any limitation to the present invention in any way.

[0039] This application is made based on the following understanding of the inventors:

[0040] Soil is a treasure trove of microbial resources, with a complex composition and a wide variety of microorganisms. Approximately 2,000 - 18,000 species of microorganisms are contained in 1 g of soil. Rhizosphere microorganisms are extremely susceptible to the influence of plant hosts, soil types, nutritional status, and climate factors. The selection of microorganisms by plant hosts does not seem to be completely random. It seems that by secreting specific small-molecule nutrients, some potentially beneficial plant probiotics for plant growth are attracted to colonize around them, while modifying the soil pH and improving soil quality, etc. However, how microorganisms help plants grow and increase crop yields remains unknown.

[0041] Research shows that compared with non-plant-related microorganisms, plant-related microorganisms (such as rhizosphere microorganisms and rhizoplane microorganisms) have evolved a large number of functional gene elements to adapt to the plant environment, such as plant root nodules, nitrogen fixation reactions, phytohormone synthesis, T3SS and T6SS secretion systems, and flagellar motility, etc.

[0042] Understanding the microbial composition around plants, analyzing the interactions between microorganisms, plant growth, and environmental conditions, finding the optimal microbial composition required for plant growth, establishing a controllable model for microbial-assisted crop health, efficient growth, and high yields, and promoting maximum food production. This requires finding these potential plant probiotics and functional characteristics by establishing correlation analyses between large-scale plant-related microbial compositions and functional gene information and crop growth and yield phenotypes. Under the guidance of big data analysis results, purposefully screening potential probiotics with application value can provide possibilities for agricultural applications.

[0043] In the embodiments of this application, sequencing studies were conducted on the rhizoplane microbial compositions of different strains of foxtail millet, and at the same time, data on foxtail millet growth and yield phenotypes were collected. Key microbial groups (marker bacteria) related to foxtail millet growth and yield phenotypes were identified by constructing a linear model. By isolating single bacterial strains from the rhizosphere soil of foxtail millet and performing 16S rRNA sequence alignment, it was found that 4 of them were marker strains significantly related to foxtail millet growth and yield. Further, in the embodiments of this application, a series of experiments such as plate growth promotion experiments, sterile soil experiments, and field experiments were carried out to verify the growth-promoting functions of these strains.

[0044] In the first aspect of the embodiments of this application, a bacterial strain for promoting plant growth is proposed, wherein the bacterial strain is selected from at least one of the following:

[0045] Strain 1, comprising the 16S rDNA sequence shown in SEQ ID NO: 1 or its complementary sequence or a sequence with at least 85% identity compared to SEQ ID NO: 1;

[0046] Strain 2, comprising the 16S rDNA sequence shown in SEQ ID NO: 2 or a sequence having at least 85% identity compared to SEQ ID NO: 2;

[0047] Strain 3, comprising the 16S rDNA sequence shown in SEQ ID NO: 3 or a sequence having at least 85% identity compared to SEQ ID NO: 3; and

[0048] Strain 4, comprising the 16S rDNA sequence shown in SEQ ID NO: 4 or a sequence having at least 85% identity compared to SEQ ID NO: 4.

[0049] In the embodiments of the present application, the percentage of identity generally describes the degree of identity between two sequences, that is, it generally describes the percentage of nucleotides that are the same as the reference sequence at their sequence positions. In the embodiments of the present application, the "sequence with at least 85% identity" refers to a sequence having an identity of any value between 85% and 100% (including the endpoint values) compared to the sequences shown in SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, and SEQ ID NO: 4, respectively. For example, it can have a sequence identity of 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%, as well as the sequence identity shown by countless decimals between two adjacent integers. For example, having a sequence identity of at least 98.57%, 99.64%, 99.7%, 99.8%, or 99.9% compared to the sequences shown in SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, and SEQ ID NO: 4.

[0050] In the embodiments of the present application, Strain 1 is of the genus Arthrobacter. In some embodiments, Strain 1 has the sequence shown in SEQ ID NO: 1. In some embodiments, Strain 1 can be Arthrobacter sp. Arth4 with the accession number GDMCC No: 62566.

[0051] Arthrobacter is a Gram-positive bacterium with an obvious rod-shaped to spherical growth cycle on a complex medium, and its typical species is Arthrobacter globiformis. Through phylogenetic tree analysis, Arth4 proposed in the embodiments of the present application is a new species under the genus Arthrobacter. Arth4 is a kind of Arthrobacter, which belongs to the genus Arthrobacter, and is named Arthrobacter sp. Arth4; the preservation registration number is GDMCC No: 62566, and the preservation institution is: Guangdong Microbial Culture Collection Center; the address of the preservation unit is: 5th Floor, Experimental Building, 100th Yard, Xianlie Middle Road, Yuexiu District, Guangzhou, Guangdong Province; the preservation time is June 28, 2022.

[0052] In the embodiments of the present application, the strain Arth4 with the sequence shown in SEQ ID NO: 1 can be understood by those skilled in the art as the original strain. A strain with a genomic sequence having at least 85% identity to the sequence shown in SEQ ID NO: 1 can be understood by those skilled in the art as a variant strain of the strain Arth4 with the sequence shown in SEQ ID NO: 1. It can be understood that a strain such as strain Arth4 can undergo spontaneous mutation or be artificially cultured to form a variant strain, for example, nucleotide deletion, nucleotide addition, or nucleotide substitution. The "variant strain" has a highly identical gene sequence and extremely similar biological functions to the "strain Arth4", and the mutated genes basically do not affect the conserved sequence of the strain Arth4, thus not affecting the genetic stability of the strain Arth4. More specifically, this "variant strain" is also a strain of the Arth4 species and exhibits the physiological activity characteristics of the Arth4 species. All the specific genera and species under the genus corresponding to strain 1 also fall within the protection scope of the present application.

[0053] In the embodiments of the present application, strain 2 is Bacillus sp. In some embodiments, strain 2 is Bacillus paralicheniformis. In some embodiments, strain 2 has the sequence shown in SEQ ID NO: 2. In some embodiments, strain 2 can be Bacillus paralicheniformis Bacil9 with the preservation number GDMCC No: 62569.

[0054] In the embodiments of the present application, strain 3 is Priestia sp. In some embodiments, strain 3 is Priestia megaterium. In some embodiments, strain 3 has the sequence shown in SEQ ID NO: 3. In some embodiments, strain 3 can be Priestia megaterium Bacif4 with the preservation number GDMCC No: 62567.

[0055] In the embodiments of the present application, strain 4 is of the genus Bacillus (Bacillus sp.). In some embodiments, strain 4 is of the species Bacillus velezensis. In some embodiments, strain 4 has the sequence shown in SEQ ID NO: 4. In some embodiments, strain 4 can be Bacillus velezensis Baci5 with the preservation number GDMCC No: 62568.

[0056] Bacil9 is a Bacillus paralicheniformis, which belongs to the genus Bacillus and is named Bacillus paralicheniformis Bacil9; the preservation registration number is GDMCC No: 62569, the preservation institution is: Guangdong Microbial Culture Collection Center; the address of the preservation unit is: 5th Floor, Experimental Building, No. 100 Yard, Middle Xianlie Road, Yuexiu District, Guangzhou City, Guangdong Province; the preservation time is June 28, 2022.

[0057] Bacif4 is a Priestia megaterium, which belongs to the genus Priestia and is named Priestia megaterium Bacif4; the preservation registration number is GDMCC No: 62567, the preservation institution is: Guangdong Microbial Culture Collection Center; the address of the preservation unit is: 5th Floor, Experimental Building, No. 100 Yard, Middle Xianlie Road, Yuexiu District, Guangzhou City, Guangdong Province; the preservation time is June 28, 2022.

[0058] Baci5 is a Bacillus velezensis, which belongs to the genus Bacillus and is named Bacillus velezensis Baci5; the preservation registration number is GDMCC No: 62568, the preservation institution is: Guangdong Microbial Culture Collection Center; the address of the preservation unit is: 5th Floor, Experimental Building, No. 100 Yard, Middle Xianlie Road, Yuexiu District, Guangzhou City, Guangdong Province; the preservation time is June 28, 2022.

[0059] Bacillus belongs to the Bacillaceae family and the genus Bacillus. It is a type of Gram-positive bacteria that can produce resistant endospores. The cells are rod-shaped and covered with a large amount of calcium picolinate on the outer layer. Its cortex is located between the core and the spore shell and is rich in peptidoglycan; the core is a highly concentrated, inert chromosome; the outermost wall is a layer of peptidoglycan wall, and one or more layers of protein spore coat. Bacillus also has a broad spectrum of bacillary activity and can produce bacteriocins to inhibit pathogens. The important characteristic of this genus of bacteria is that it can produce spores that are particularly resistant to adverse conditions. At present, the most commonly used types of Bacillus are Bacillus subtilis, Bacillus licheniformis, Bacillus cereus, etc. In the examples of the present application, strains 2-4 all belong to the genus Bacillus, and through further phylogenetic tree analysis, it is concluded that Bacil9 isolated in the examples of the present application is a new strain under the species Bacillus paralicheniformis; Bacif4 isolated in the examples of the present application is a new strain under the species Priestia megaterium; Baci5 isolated in the examples of the present application is a new strain under the species Bacillus velezensis.

[0060] It can be understood that, as discussed above for the strain 1 variant, the strain variant having a sequence that is at least 85% or the like compared to the sequences shown in SEQ ID NO: 2, SEQ ID NO: 3, and SEQ ID NO: 4, respectively, also belongs to the genus Bacillus and its corresponding species, and also has similar physiological activity characteristics as strains 2-4. The specific genus corresponding to strains 2-4 and all species under it also fall within the protection scope of this application.

[0061] The four new strains of Arth4, Bacil9, Bacif4, and Baci5 isolated in the examples of the present application can be effectively used to improve the agronomic traits of plants when used alone or in combination, especially the bacterial genus and species to which the four strains belong can effectively promote the elongation of plant roots and the growth of stems, thereby improving the absorption and accumulation of nutrients by plants, thereby increasing crop yields. The rhizosphere growth-promoting bacteria proposed in the examples of the present application are of great significance for increasing crop yields.

[0062] The second aspect of the embodiments of the present application further provides an agricultural preparation, which contains the bacterial strain as described in any embodiment of the first aspect of the present application.

[0063] In the embodiments of the present application, the agricultural preparation may contain any of the above bacterial strains, where the bacterial strains include: strain 1, containing the 16S rDNA sequence shown in SEQ ID NO: 1 or its complementary sequence or a sequence with at least 85% identity compared to SEQ ID NO: 1; strain 2, containing the 16S rDNA sequence shown in SEQ ID NO: 2 or containing a sequence with at least 85% identity compared to SEQ ID NO: 2; strain 3, containing the 16S rDNA sequence shown in SEQ ID NO: 3 or containing a sequence with at least 85% identity compared to SEQ ID NO: 3; and strain 4, containing the 16S rDNA sequence shown in SEQ ID NO: 4 or containing a sequence with at least 85% identity compared to SEQ ID NO: 4. Thus, the agricultural preparation in the embodiments of the present application can be a single strain of strain 1-4 or any combination between strain 1-4; at the same time, since the above strains also include mutant strains of the same genus as strain 1-4, the specific genus of strain 1-4 and all species under its genus also fall within the protection scope of the agricultural preparation of the present application.

[0064] In the embodiments of the present application, strain 2 belongs to the genus Bacillus. In some embodiments, strain 2 is Bacillus paralicheniformis. In some embodiments, strain 2 has the sequence shown in SEQ ID NO: 2. In some embodiments, strain 2 can be Bacillus paralicheniformis Bacil9 with the deposit number GDMCC No: 62569.

[0065] In the embodiments of the present application, strain 3 belongs to the genus Priestia. In some embodiments, strain 3 is Priestia megaterium. In some embodiments, strain 3 has the sequence shown in SEQ ID NO: 3. In some embodiments, strain 3 can be Priestia megaterium Bacif4 with the deposit number GDMCC No: 62567.

[0066] In the embodiments of the present application, strain 4 belongs to the genus Bacillus. In some embodiments, strain 4 is Bacillus velezensis. In some embodiments, strain 4 has the sequence shown in SEQ ID NO: 4. In some embodiments, strain 4 can be Bacillus velezensis Baci5 with the deposit number GDMCC No: 62568.

[0067] In the embodiments of the present application, the agricultural preparation further includes auxiliary materials, where the auxiliary materials can be organic matter and / or inorganic matter. In the embodiments of the present application, the organic matter can be additional bacterial fertilizers other than strains 1-4 that can promote plant growth. For example: bacterial fertilizers that increase soil nitrogen and crop nitrogen nutrition, such as rhizobium fertilizer, azotobacter fertilizer, nitrogen-fixing blue-green algae fertilizer, etc.; bacterial fertilizers that decompose soil organic matter, such as organic phosphorus bacteria fertilizer, comprehensive bacterial fertilizer; bacterial fertilizers that decompose insoluble minerals in the soil, such as phosphorus bacteria fertilizer, potassium bacteria fertilizer, mycorrhizal fungal fertilizer; bacterial fertilizers that stimulate plant growth, such as growth-promoting bacterial fertilizer; bacterial fertilizers that increase the stress resistance of crop roots, such as antibiotic bacterial fertilizer, stress-resistant bacterial fertilizer. In the embodiments of the present application, the organic matter can also be organic fertilizers required for plant growth, such as manure, etc. It can be understood that the organic matter in the embodiments of the present application, alone or in combination, as long as it can ensure a promoting effect on plant growth, is not limited in this application.

[0068] In the embodiments of the present application, the inorganic matter can be chemical components that can be used in agriculture, such as agriculturally acceptable carriers, excipients, diluents, adjuvants, media, excipients, carriers or combinations thereof, and / or inorganic fertilizers that do not affect the microbial activity concentration in the agricultural preparation, and this application is not limited thereto.

[0069] In the embodiments of the present application, the dosage form of the agricultural preparation can be selected from: wettable powder, water dispersible granule, suspension, emulsion in water, granule, seed coating agent, or a combination thereof. It can be understood that the dosage form of the agricultural preparation in the embodiments of the present application, as long as it can ensure that it can be applied to plants in a certain form, is not limited in this application.

[0070] The agricultural preparation proposed in the embodiments of the present application, by using Arth4, Bacil9, Bacif4, Baci5 alone or in combination, can be effectively used to improve the agronomic traits of plants. In particular, the bacterial genera and species to which the 4 strains belong can effectively promote the elongation of plant roots and the growth of stems, thereby improving the nutrient absorption and accumulation of plants, and thus increasing the yield of agricultural crops. The rhizosphere growth-promoting bacteria proposed in the embodiments of the present application are of great significance for increasing the yield of agricultural crops. In addition, by making Arth4, Bacil9, Bacif4, Baci5 into microbial bacterial fertilizers suitable for agricultural production, the use amount of chemical fertilizers can be reduced, and green agricultural production can be promoted.

[0071] The third aspect of the embodiments of the present application also proposes a use of the bacterial strain as described in any one of the first aspects of the present application in the preparation of an agricultural preparation.

[0072] The fourth aspect of the embodiments of the present application also proposes a method for promoting plant growth, including applying the bacterial strain as described in any one of the first aspects of the present application or the agricultural preparation as described in any one of the second aspects of the present application.

[0073] In the experimental methods of the following examples, unless otherwise specified, they are all conventional methods, carried out according to the techniques or conditions described in the literature in this field or according to the product instructions. The materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0074] Unless otherwise specified, in the following examples, quantitative tests are all set up with three repeated experiments, and the results are averaged.

[0075] Example 1: Isolation of strains

[0076] Collect rhizosphere soil samples of foxtail millet planted in Yangling, Shaanxi, dilute them into soil solutions with sterile PBS-S buffer, and then centrifuge the soil dilution buffer at 1200 rpm for 5 minutes to collect the supernatant. Dilute the supernatant into gradient concentrations from 10 -1 to 10 -7 , and respectively take 2 μl of the dilution solutions with concentrations of 10 -4 and 10 -6 and inoculate them into a 96-well microtiter plate containing LB medium, incubate at 28 °C for 48 - 72 hours, and then aspirate the culture solution and subculture it three times on LB solid medium to obtain strain monoclonal colonies. Sequence the 16S rRNA gene of the monoclonal strains, and find microbial strains 1 - 4 with growth-promoting functions. The specific information is as follows.

[0077] Strain 1: Arth4, and its 16S rDNA gene sequence is shown as SEQ ID NO: 1 below.

[0078] AACGATGATCTCCAGCTTGCTGGGGGGATTAGTGGCGAACGGGTGAGTAACACGTGA

[0079] GTAACCTGCCCTTGACTCTGGGATAAGCCTGGGAAACTGGGTCTAATACCGGATATGA

[0080] CCATTCCACGCATGTGGTGGTGGTGGAAAGCTTTTGCGGTTTTGGATGGACTCGCGGC

[0081] CTATCAGCTTGTTGGTGGGGTAATGGCCTACCAAGGCGACGACGGGTAGCCGGCCTGA

[0082] GAGGGTGACCGGCCACACTGGGACTGAGACACGGCCCAGACTCCTACGGGAGGCAG

[0083] CAGTGGGGAATATTGCACAATGGGCGGAAGCCTGATGCAGCGACGCCGCGTGAGGGA

[0084] TGACGGCCTTCGGGTTGTAAACCTCTTTCAGTAGGGAAGAAGCGTAAGTGACGGTACC

[0085] TGCAGAAGAAGCGCCGGCTAACTACGTGCCAGCAGCCGCGGTAATACGTAGGGCGCA

[0086] AGCGTTATCCGGAATTATTGGGCGTAAAGAGCTCGTAGGCGGTTTGTCGCGTCTGCTGT

[0087] GAAAGACCGGGGCTCAACTCCGGTTCTGCAGTGGGTACGGGCAGACTAGAGTGCAGT

[0088] AGGGGAGACTGGAATTCCTGGTGTAGCGGTGAAATGCGCAGATATCAGGAGGAACAC

[0089] CGATGGCGAAGGCAGGTCTCTGGGCTGTAACTGACGCTGAGGAGCGAAAGCATGGGG

[0090] AGCGAACAGGATTAGATACCCTGGTAGTCCATGCCGTAAACGTTGGGCACTAGGTGTG

[0091] GGGGACATTCCACGTTTTCCGCGCCGTAGCTAACGCATTAAGTGCCCCGCCTGGGGAG

[0092] TACGGCCGCAAGGCTAAAACTCAAAGGAATTGACGGGGGCCCGCACAAGCGGCGGA

[0093] GCATGCGGATTAATTCGATGCAACGCGAAGAACCTTACCAAGGCTTGACATGGACTGG

[0094] AAAGATCTGGAGACAGGTCCCCCGCTTGCGGTCGGTTCACAGGTGGTGCATGGTTGTC

[0095] GTCAGCTCGTGTCGTGAGATGTTGGGTTAAGTCCCGCAACGAGCGCAACCCTCGTTCT

[0096] ATGTTGCCAGCGCGTTATGGCGGGGACTCATAGGAGACTGCCGGGGTCAACTCGGAG

[0097] GAAGGTGGGGACGACGTCAAATCATCATGCCCCTTATGTCTTGGGCTTCACGCATGCT

[0098] ACAATGGCCGGTACAAAGGGTTGCGATACTGTGAGGTGGAGCTAATCCCAAAAAGCC

[0099] GGTCTCAGTTCGGATTGGGGTCTGCAACTCGACCCCATGAAGTCGGAGTCGCTAGTAA

[0100] TCGCAGATCAGCAACGCTGCGGTGAATACGTTCCCGGGCCTTGTACACACCGCCCGTCAAGTCACGAAAGTTGGTAACACCCGAAGC(SEQ ID NO:1)

[0101] Strain 2: Bacil9, and its 16S rDNA gene sequence is shown as SEQ ID NO: 2 below.

[0102] AGCGGACAGATGGGAGCTTGCTCCCTGATGTTAGCGGCGGACGGGTGAGTAACACGT

[0103] GGGTAACCTGCCTGTAAGACTGGGATAACTCCGGGAAACCGGGGCTAATACCGGATGC

[0104] TTGATTGAACCGCATGGTTCAATTATAAAAGGTGGCTTTTAGCTACCACTTACAGATGG

[0105] ACCCGCGGCGCATTACCTAGTTGGTGAGGTAACGGCTCACCAAGGCAACAATGCGTAC

[0106] CCAACCTGAAAGGGTGATCGGCCACACTGGGACTGAAACACGGCCCAAACTCCTACG

[0107] GGAGGCAGCAGTAGGGAATCTTCCGCAATGGACAAAAGTCTGACGGAGCAACGCCGC

[0108] GTGAGTGATGAAGGTTTTCGGATCGTAAAACTCTGTTGTTAGGGAAAAACAAGTACCG

[0109] TTCGAATAGGGCGGTACCTTGACGGTACCTAACCAAAAAGCCACGGCTAACTACGTGC

[0110] CACCAGCCGCGGTAATACGTAGGTGGCAAGCGTTGTCCGGAATTATTGGGCGTAAAGC

[0111] GCGCGCAGGCGGTTTCTTAAGTCTGATGTGAAAGCCCCCGGCTCAACCGGGGAGGGT

[0112] CATTGGAAACTGGGGAACTTGAGTGCAAAAAAGGAGAGTGGAATTCCACGTGTAGCG

[0113] GTGAAATGCGTAAAGATGTGGAGGAACACCAGTGGCGAAGGCGACTCTCTGGTCTGT

[0114] AACTGACGCTGAGGCGCGAAAGCGTGGGGAGCGAACAGGATTAGATACCCTGGTAGT

[0115] CCACGCCGTAAACGATGAGTGCTAAGTGTTAGAGGGTTTCCGCCCTTTAGTGCTGCAG

[0116] CAAACGCATTAAGCACTCCGCCTGGGGAGTACGGTCGCAAGACTGAAACTCAAAGGA

[0117] ATTGACGGGGGCCCGCACAAGCGGTGGAGCATGTGGTTTAATTCGAAGCAACGCGAA

[0118] GAACCTTACCAGGTCTTGACATCCTCTGACAACCCTAGAGATAGGGCTTCCCCTTCGG

[0119] GGGCAGAGTGACAGGTGGTGCATGGTTGTCGTCAGCTCGTGTCGTGAGATGTTGGGTT

[0120] AAGTCCCGCAACGAGCGCAACCCTTGATCTTAGTTGCCAGCATTCAGTTGGGCACTCT

[0121] AAGGTGACTGCCGGTGACAAACCGGAGGAAGGTGGGGATGACGTCAAATCATCATGC

[0122] CCCTTATGACCTGGGCTACACACGTGCTACAATGGGCAGAACAAAGGGCAGCGAAGC

[0123] CGCGAGGCTAAGCCAATCCCACAAATCTGTTCTCAGTTCGGATCGCAGTCTGCAACTC

[0124] GACTGCGTGAAGCTGGAATCGCTAGTAATCGCGGATCAGCATGCCGCGGTGAATACGTTCCCGGGCCTTGTACACACCGCCCGTCACACCACGAGAGTTTGTAACACCCG(SEQ ID NO:2)

[0125] Strain 3: Bacif4, whose 16S rDNA gene sequence is shown as SEQ ID NO: 3 below.

[0126] AGCGAACTGATTAGAAGCTTGCTTCTATGACGTTAGCGGCGGACGGGTGAGTAACACG

[0127] TGGGCAACCTGCCTGTAAGACTGGGATAACTTCGGGAAACCGAAGCTAATACCGGATA

[0128] GGATCTTCTCCTTCATGGGAGATGATTGAAAGATGGTTTCGGCTATCACTTACAGATGG

[0129] GCCCGCGGTGCATTAGCTAGTTGGTGAGGTAACGGCTCACCAAGGCAACGATGCATAG

[0130] CCGACCTGAGAGGGTGATCGGCCACACTGGGACTGAGACACGGCCCAGACTCCTACG

[0131] GGAGGCAGCAGTAGGGAATCTTCCGCAATGGACGAAAGTCTGACGGAGCAACGCCGC

[0132] GTGAGTGATGAAGGCTTTCGGGTCGTAAAACTCTGTTGTTAGGGAAGAACAAGTACG

[0133] AGAGTAACTGCTTGTACCTTGACGGTACCTAACCAGAAAGCCACGGCTAACTACGTGC

[0134] CAGCAGCCGCGGTAATACGTAGGTGGCAAGCGTTATCCGGAATTATTGGGCGTAAAGC

[0135] GCGCGCAGGCGGTTTCTTAAGTCTGATGTGAAAGCCCACGGCTCAACCGTGGAGGGT

[0136] CATTGGAAACTGGGGAACTTGAGTGCAGAAGAGAAAAGCGGAATTCCACGTGTAGCG

[0137] GTGAAATGCGTAGAGATGTGGAGGAACACCAGTGGCGAAGGCGGCTTTTTGGTCTGT

[0138] AACTGACGCTGAGGCGCGAAAGCGTGGGGAGCAAACAGGATTAGATACCCTGGTAGT

[0139] CCACGCCGTAAACGATGAGTGCTAAGTGTTAGAGGGTTTCCGCCCTTTAGTGCTGCAG

[0140] CTAACGCATTAAGCACTCCGCCTGGGGAGTACGGTCGCAAGACTGAAACTCAAAGGA

[0141] ATTGACGGGGGCCCGCACAAGCGGTGGAGCATGTGGTTTAATTCGAAGCAACGCGAA

[0142] GAACCTTACCAGGTCTTGACATCCTCTGACAACTCTAGAGATAGAGCGTTCCCCTTCG

[0143] GGGGACAGAGTGACAGGTGGTGCATGGTTGTCGTCAGCTCGTGTCGTGAGATGTTGG

[0144] GTTAAGTCCCGCAACGAGCGCAACCCTTGATCTTAGTTGCCAGCATTTAGTTGGGCAC

[0145] TCTAAGGTGACTGCCGGTGACAAACCGGAGGAAGGTGGGGATGACGTCAAATCATCA

[0146] TGCCCCTTATGACCTGGGCTACACACGTGCTACAATGGATGGTACAAAGGGCTGCAAG

[0147] ACCGCGAGGTCAAGCCAATCCCATAAAACCATTCTCAGTTCGGATTGTAGGCTGCAAC

[0148] TCGCCTACATGAAGCTGGAATCGCTAGTAATCGCGGATCAGCATGCCGCGGTGAATAC

[0149] GTTCCCGGGCCTTGTACACACCGCCCGTCACACCACGAGAGTTTGTAACACCCGAAGTCGGTGGAGTA(SEQ ID NO:3)

[0150] Strain 4: Baci5, whose 16S rDNA gene sequence is shown as SEQ ID NO: 4 below.

[0151] GAGCGGACAGATGGGAGCTTGCTCCCTGATGTTAGCGGCGGACGGGTGAGTAACACG

[0152] TGGGTAACCTGCCTGTAAGACTGGGATAACTCCGGGAAACCGGGGCTAATACCGGATG

[0153] GTTGTTTGAACCGCATGGTTCAGACATAAAAGGTGGCTTCGGCTACCACTTACAGATG

[0154] GACCCGCGGCGCATTAGCTAGTTGGTGAGGTAACGGCTCACCAAGGCGACGATGCGT

[0155] AGCCGACCTGAGAGGGTGATCGGCCACACTGGGACTGAGACACGGCCCAGACTCCTA

[0156] CGGGAGGCAGCAGTAGGGAATCTTCCGCAATGGACGAAAGTCTGACGGAGCAACGCC

[0157] GCGTGAGTGATGAAGGTTTTCGGATCGTAAAGCTCTGTTGTTAGGGAAGAACAAGTGC

[0158] CGTTCAAATAGGGCGGCACCTTGACGGTACCTAACCAGAAAGCCACGGCTAACTACGT

[0159] GCCAGCAGCCGCGGTAATACGTAGGTGGCAAGCGTTGTCCGGAATTATTGGGCGTAAA

[0160] GGGCTCGCAGGCGGTTTCTTAAGTCTGATGTGAAAGCCCCCGGCTCAACCGGGGAGG

[0161] GTCATTGGAAACTGGGGAACTTGAGTGCAGAAGAGGAGAGTGGAATTCCACGTGTAG

[0162] CGGTGAAATGCGTAGAGATGTGGAGGAACACCAGTGGCGAAGGCGACTCTCTGGTCT

[0163] GTAACTGACGCTGAGGAGCGAAAGCGTGGGGAGCGAACAGGATTAGATACCCTGGTA

[0164] GTCCACGCCGTAAACGATGAGTGCTAAGTGTTAGGGGGTTTCCGCCCCTTAGTGCTGC

[0165] AGCTAACGCATTAAGCACTCCGCCTGGGGAGTACGGTCGCAAGACTGAAACTCAAAG

[0166] GAATTGACGGGGGCCCGCACAAGCGGTGGAGCATGTGGTTTAATTCGAAGCAACGCG

[0167] AAGAACCTTACCAGGTCTTGACATCCTCTGACAATCCTAGAGATAGGACGTCCCCTTC

[0168] GGGGGCAGAGTGACAGGTGGTGCATGGTTGTCGTCAGCTCGTGTCGTGAGATGTTGG

[0169] GTTAAGTCCCGCAACGAGCGCAACCCTTGATCTTAGTTGCCAGCATTCAGTTGGGCAC

[0170] TCTAAGGTGACTGCCGGTGACAAACCGGAGGAAGGTGGGGATGACGTCAAATCATCA

[0171] TGCCCCTTATGACCTGGGCTACACACGTGCTACAATGGACAGAACAAAGGGCAGCGA

[0172] AACCGCGAGGTTAAGCCAATCCCACAAATCTGTTCTCAGTTCGGATCGCAGTCTGCAA

[0173] CTCGACTGCGTGAAGCTGGAATCGCTAGTAATCGCGGATCAGCATGCCGCGGTGAATA

[0174] CGTTCCCGGGCCTTGTACACACCGCCCGTCACACCACGAGAGTTTGTAACACCCGAAGTCGGTGAGGTAACCTTTA(SEQ ID NO:4)

[0175] Example 2: Identification of the isolated strains

[0176] The inventors further identified the strains 1-4 isolated in Example 1 by aligning the 16S rRNA sequences of the strains 1-4 with the database.

[0177] 2.1 Arth4 (Strain 1)

[0178] The approximately 1.4 Kb sequence of Arth4, which is nearly the full-length 16S rDNA obtained by sequencing (Arth4_16S_rRNA_gene, i.e., SEQ ID NO: 1), was aligned in the 16S rRNA gene database of EzBioCloud to preliminarily obtain the species classification information of Strain 1. According to the alignment results, the two strains with the highest homology to the 16S rRNA gene of Arth4 in the database are Arthrobacter bambusae GM18 (accession number: KF150696) and Paenarthrobacter aurescens NBRC12136 (accession number: BJMD01000050), with similarity rates of 98.57% and 98.50% respectively. Based on the 16S rRNA information, it can be preliminarily determined that Arth4 is a new species belonging to the genus Arthrobacter.

[0179] Furthermore, the sequences of the related strains of Arth4 were used to construct a phylogenetic tree by the neighbor-joining method using MAGA, and the result is as Figure 1 shown. It can be seen from Figure 1 this that Arth4 does not cluster with the bacteria of other species, which also proves that the Strain 1 isolated in Example 1 is a new species under the genus Arthrobacter.

[0180] Meanwhile, perform whole-genome sequencing on Arth4, and use the FastANI software to perform whole-genome average nucleotide identity (ANI) analysis on its genomic sequence with the genomic sequences of the strains Arthrobacter_bambusae (Genebank accession number: GCA_022606295.1) and Paenarthrobacter aurescens NBRC 12136 (Genebank accession number: GCA_006538985.1) with the highest similarity. ANI is an indicator for comparing the genetic relationship between two genomes at the nucleotide level. ANI is defined as the average base similarity between homologous fragments of two microbial genomes, and its characteristic is that it has a high discrimination degree among closely related species. The analysis results show that the ANI of the whole genome of Arth4 with the genomes of Arthrobacter_bambusae and Paenarthrobacter aurescens NBRC 12136 is only 80.5% and 84.4% respectively, far lower than the ANI value of 95% for the same species (see Jain C, Rodriguez-R L M, Phillippy A M, et al. High throughput ANI analysis of 90K prokaryotic genomes reveals clear species boundaries[J]. Nature Communications, 2018, 9(1):5114, 95% is considered the threshold for determining whether they are the same species). Therefore, it is further determined that Arth4 is a new strain under the genus Arthrobacter, named Arthrobacter sp. Arth4, and deposited in the Guangdong Provincial Culture Collection Center of Microorganisms, with the deposit number GDMCC No: 62566.

[0181] 2.2 Baci9 (Strain 2)

[0182] Similarly, the approximately 1.4 Kb sequence of Bacil9 that is nearly the full length of the 16S rDNA obtained by sequencing (Bacil9_16S_rRNA_gene, i.e., SEQ ID NO: 2) was aligned in the 16S rRNA gene database of EzBioCloud to preliminarily obtain the species classification information of strain 2. According to the alignment results, the strain with the highest homology to the 16S rRNA gene of Bacil9 in the database is Bacillus paralicheniformis (serial number: KY694465), with a sequence similarity of 98.98%. Based on the information of 16S rRNA, it can be preliminarily determined that Bacil9 belongs to the species Bacillus paralicheniformis.

[0183] Furthermore, the sequences of the related strains of Bacil9 were used to construct a phylogenetic tree by the neighbor-joining method using MAGA, and the results are as Figure 2 shown. It can be Figure 2 seen that Bacil9 clusters together with Bacillus paralicheniformis KJ-16 (Genebank serial number: GCA_001042485.2), which also verifies that the strain 2 isolated in Example 1 belongs to the species Bacillus paralicheniformis.

[0184] Meanwhile, the whole genome of Bacil9 was sequenced, and the ANI analysis was also performed on the genome sequence of Bacil9 with the genome of the strain Bacillus paralicheniformis KJ-16 (Genebank serial number: GCA_001042485.2) with the highest similarity using the FastANI software. The analysis results showed that the ANI of the whole genome of Bacil9 with the genome of Bacillus paralicheniformis KJ-16 (Genebank serial number: GCA_001042485.2) reached 99.24% (greater than 95%). Thus, it was further determined that Bacil9 is a new strain under Bacillus paralicheniformis, and it was named Bacillus paralicheniformis Bacil9 and deposited in the Guangdong Provincial Culture Collection of Microorganisms with the deposit number GDMCC No: 62569.

[0185] 2.3 Bacif4 (strain 3)

[0186] Similarly, the nearly full-length 1.4 Kb 16S rDNA sequence of Bacif4 obtained by sequencing (Bacif4_16S_rRNA_gene, i.e., SEQ ID NO: 3) was aligned in the 16S rRNA gene database of EzBioCloud to preliminarily obtain the species classification information of strain 3. According to the alignment results, the strain with the highest homology to the 16S rRNA gene of Bacif4 in the database is Priestia megaterium NBRC 15308 (sequence number: JJMH01000057), with a similarity of 99.93%. Based on the information of 16S rRNA, it can be preliminarily determined that Bacif4 belongs to the species Priestia megaterium.

[0187] Furthermore, the sequences of the related strains of Bacif4 were used to construct a phylogenetic tree by the neighbor-joining method using MAGA, and the results are as Figure 3 shown. It can be Figure 3 seen that Bacif4 is closely related to Priestia megaterium NBRC 15308 (Genebank accession number: GCA_009935415.1), which also verifies that the strain 3 isolated in Example 1 belongs to the species Priestia megaterium.

[0188] Meanwhile, the whole genome of Bacif4 was sequenced, and the ANI analysis was also performed on the genome sequence of Bacif4 and the genome of Priestia megaterium NBRC 15308 (Genebank accession number: GCA_009935415.1) with the highest similarity using the FastANI software. The analysis results showed that the ANI of the whole genome of Bacif4 and the genome of Priestia megaterium NBRC 15308 (Genebank accession number: GCA_009935415.1) reached 99.18% (greater than 95%). Thus, it was further determined that Bacif4 is a new strain under Priestia megaterium, and it was named Priestia megaterium Bacif4 and deposited in the Guangdong Provincial Culture Collection Center of Microorganisms, with the deposit number GDMCC No: 62567.

[0189] 2.4 Baci5 (strain 4)

[0190] Similarly, the nearly full-length 16S rDNA sequence (Baci5_16S_rRNA_gene, i.e., SEQ ID NO: 4) of 1.4 Kb of Baci5 obtained by sequencing was aligned in the 16S rRNA gene database of EzBioCloud to preliminarily obtain the species classification information of strain 4. According to the alignment results, the strains with the highest homology to the 16S rRNA gene of Baci5 in the database are Bacillus siamensis KCTC 13613 (accession number: AJVF01000043) and Bacillus velezensis CR-502 (accession number: AY603658), and the similarity is 99.93% for both. Based on the information of 16S rRNA, it can be preliminarily determined that Baci5 belongs to the genus Bacillus.

[0191] Furthermore, the sequences of the related strains of Baci5 were used to construct a phylogenetic tree by the neighbor-joining method using MAGA, and the results are as Figure 4 shown. It can be Figure 4 seen that Baci5 clusters together with Bacillus siamensis KCTC 13613 (Genebank accession number: GCA_000262045.1) and Bacillus velezensis CR-502 (Genebank accession number: GCA_001461825.1), which also verifies that the strain 4 isolated in Example 1 belongs to the genus Bacillus.

[0192] Meanwhile, the whole genome of Baci5 was sequenced, and the genomic sequences of Baci5 and the strains Bacillus siamensis KCTC 13613 (Genebank accession number: GCA_000262045.1) and Bacillus velezensis (Genebank accession number: GCA_001461825.1) with the highest similarity were analyzed by ANI using the FastANI software. The analysis results showed that the ANIs of the Baci5 genome with the genomes of Bacillus siamensis KCTC 13613 (Genebank accession number: GCA_000262045.1) and Bacillus velezensis (Genebank accession number: GCA_001461825.1) were 93.88% and 97.97%, respectively. Therefore, it was further determined that Bacif5 did not belong to Bacillus siamensis, but was a new strain under Bacillus velezensis. It was named Bacillus velezensis Baci5 and deposited in the Guangdong Provincial Microbial Culture Collection Center with the deposit number GDMCC No: 62568.

[0193] Example 3: Plate growth promotion experiment

[0194] 3.1 After activating strains 1-4, they were inoculated into NY medium and fermented by shaking at 28 °C and 180 r / min. Then, the OD of the bacterial solution was 600 adjusted to 0.5. The bacterial solution was taken, centrifuged at 5000 rpm for 10 min, the supernatant was removed, and the cells were resuspended with sterile water for use.

[0195] 3.2 The Huagu 12 seeds were surface-sterilized with 1% sodium hypochlorite for 5 min and then rinsed 5 times with sterile water. In a sterile petri dish, the seeds were sown on sterile double-layer filter paper, with 15-20 seeds evenly placed on each piece of filter paper. 2 ml of the bacterial solutions 1-4 obtained in step 3.1 were respectively sprayed on the seeds and taken out after 7 days. The number of germinated seeds was counted, and the root length and plant height of the seedlings were recorded. Three parallel experimental groups were set for each treatment. The control group was sprayed with sterile water.

[0196] 3.3 After culturing for 25 days, the root length and plant height of the seedlings were measured, and the specific measured values (averages) are shown in Table 1 and Table 2 respectively. The growth conditions of the treatment group and the control group are as Figure 5 shown.

[0197] Table 1

[0198] Strain Root length (average: cm) Adjusted P value Control group 3.63 / Bacif4 3.41 4.07E-01 Bacil9 3.95 2.12E-01 Baci5 3.96 2.12E-01 Arth4 4.30 2.40E-02

[0199] Table 2

[0200] Strain Plant height (average: cm) Adjusted P value Control group 2.13 / Bacif4 2.83 1.10E-01 Bacil9 3.40 1.02E-08 Baci5 2.23 2.34E-03 Arth4 2.82 4.34E-06

[0201] Table 1 and Table 2 show the root length and plant height of seedlings after treatment with bacterial agents in the petri dish experiment, respectively. As can be seen from Table 1, under petri dish culture, compared with the control group, the root length of seedlings treated with bacterial agent 1 (i.e., Arth4) was significantly longer than that of the control group at the 5% level (*, p < 0.05). At the same time, as can be seen from Table 2, compared with the control group, the average root length of seedlings treated with bacterial agents 1-4 was longer than that of the control group, and there was an extremely significant difference between bacterial agent 1 (i.e., Arth4) and bacterial agent 2 (i.e., Bacil9) (***, p < 0.001), and bacterial agent 4 (i.e., Baci5) showed a significant difference at the 0.1% level (**, p < 0.01). Thus, it is proved that strains 1-4 have a good promoting effect on the root length, especially the plant height, of plants.

[0202] Example 4: Growth promotion experiment in sterile soil

[0203] The surfaces of millet seeds were disinfected with 1% sodium hypochlorite solution for 5 min and rinsed 5 times with sterile distilled water. The disinfected seeds were planted in sterile soil pots, where the sterile soil was obtained by high-temperature sterilization of the soil for field growth of millet at 120 °C. 5-10 plants were planted in each pot. 5 days after the seeds germinated, 5 ml of bacterial solutions 1-4 were respectively poured around the roots of the germinated plants in each pot. Three parallel groups were set for each treatment, and the control group was irrigated with sterile water. Irrigation was carried out once every 5 days for a total of 3 times. 25 days later, the plants in the pots were taken out and their root lengths and plant heights were measured. The specific measured values (averages) are shown in Table 3 and Table 4 below. The growth conditions of the treatment group and the control group are as Figure 6 shown.

[0204] Table 3

[0205] Strain Root length (average: cm) Adjusted P value Control group 3.39 / Bacif4 4.73 5.06E-04 Bacil9 4.43 1.33E-03 Baci5 4.13 3.29E-02 Arth4 3.95 6.86E-02

[0206] Table 4

[0207] Strain Plant height (average: cm) Adjusted P value Control group 7.56 / Bacif4 9.20 2.71E-02 Bacil9 9.12 1.09E-02 Baci5 8.83 2.35E-02 Arth4 10.81 9.60E-07

[0208] Table 3 and Table 4 show the root length and plant height of seedlings after treatment with bacterial solutions in the sterile soil experiment, respectively. As can be seen from Table 3, under the culture with sterile soil as the substrate, compared with the control group, the average root length of seedlings treated with bacterial agents 1-4 was longer than that of the control group, indicating that bacterial agents 1-4 all have a promoting effect on the growth of plant roots. Moreover, there was an extremely significant difference between bacterial agent 4 (i.e., Baci5) and bacterial agent 3 (i.e., Bacif4) (***, p < 0.001), and bacterial agent 2 (i.e., Bacil9) showed a significant difference at the 0.1% level (**, p < 0.01), indicating that strains 2-4 can significantly promote the growth of plant roots.

[0209] In terms of plant height, as can be seen from Table 4, under the cultivation with sterile soil as the substrate, compared with the control group, the average plant heights of the seedlings treated with Bacterial agents 1-4 are all greater than that of the control group, indicating that Strains 1-4 all have a promoting effect on the growth of plant height. Moreover, the plant heights of the seedlings treated with Bacterial agents 2-4 are significantly higher than those of the control group at the 5% level (*, p<0.05), and there is a highly significant difference between Bacterial agent 1 (i.e., Arth4) and the control group (***, p<0.001). Thus, it is proved that Strains 1-4 have a significant promoting effect on the height growth of plants.

[0210] In summary, Strains 1-4 proposed in the embodiments of the present application can be effectively used to promote plant growth.

[0211] Example 5: Field experiment

[0212] Huagu 12 was planted in large pots filled with field soil and irrigated with Bacterial solutions 1-4 respectively. After the plants grew up, the growth traits of the plants were measured. Three parallel experiments were set for each treatment, and the control group was irrigated with sterile water. The specific measurement data (average values) are shown in Tables 5-7. The growth conditions of the treatment group and the control group are as Figure 7 and Figure 8 shown.

[0213] Table 5

[0214] Strain Main stem diameter (average: mm) Adjusted P value Control group 5.58 / Arth4 5.84 0.395 Bacil9 6.03 0.2779 Bacif4 5.56 0.9237 Baci5 5.73 0.6621

[0215] Table 6

[0216] Strain Main stem spike diameter (average: mm) Adjusted P value Control group 14.36 / Arth4 17.64 0.0145 Bacil9 18.74 0.0116 Bacif4 15.45 0.3889 Baci5 14.77 0.7299

[0217] Table 7

[0218] Strain Plant height (average: cm) Adjusted P value Control group 86 / Arth4 92.18 0.0852 Bacil9 90 0.3464 Bacif4 85.54 0.9036 Baci5 78.97 0.0637

[0219] From Figure 7 and 8 it can be seen that in the field experiment, the plants after applying Bacterial agents 1-4 grow more lushly compared with the control group. The plants are generally taller, stronger and more upright, and the leaves are dark green, indicating that Strains 1-4 in the embodiments of the present application have a good promoting effect on the growth of the stems and leaves of plants. At the same time, from the Figure 7 seed setting situation of the millet, it can be seen that compared with the control group, the millet plants treated with Bacterial agents 1-4 have more spikes and the earheads are large and plump, indicating that Strains 1-4 can enable plants to absorb and accumulate more nutrients, and improve the seed setting situation of plants after promoting the overall growth of plants, thereby increasing the crop yield.

[0220] Table 5-7 shows the specific measured values of the main stem and plant height of the plants in the treatment group and the control group, which are the specific quantified values of the growth conditions of the plants. As can be seen from Table 5, the average main stem diameter of the plants treated with Bacif4 strain is comparable to that of the control group, and those treated with other inoculants (Arth4, Bacil9, and Baci5) are larger than the control group, demonstrating that strains 1-4 can promote the growth of plant stems. Among them, Bacil9 (i.e., strain 2) has the thickest main stem, indicating that Bacil9 can effectively promote the growth of plant stems. In terms of plant height, as can be seen from Table 7, in the field experiment, the average plant height of the treatment group treated with Baci5 strain is less than that of the control group, the average plant height of the plants treated with Bacif4 strain is comparable to that of the control group, and the average plant heights of the plants treated with Arth4 and Bacil9 are higher than that of the control group. In terms of the main stem ear diameter, the average main stem ear diameters of the plants treated with inoculants 1-4 are all larger than that of the control group. Since the fruiting situation can directly reflect the nutrient absorption and accumulation status of plants, the data in Table 6 prove that inoculants 1-4 can effectively promote the nutrient absorption of plants.

[0221] Therefore, the rhizosphere growth-promoting strains 1-4 newly isolated and identified in the embodiments of the present application have a good promoting effect on the growth of plants. Further, the promotion of the growth of plant roots by strains 1-4 can effectively improve the nutrient absorption in the rhizosphere of plants, thereby increasing the yield of crops.

[0222] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0223] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A bacterial strain for promoting plant growth, wherein the bacterial strain is: Strain 3, comprising the 16S rDNA sequence shown in SEQ ID NO: 3 or comprising a sequence with at least 85% identity compared to SEQ ID NO:

3.

2. The bacterial strain according to claim 1, wherein the Strain 3 is Priestiamegaterium, having the 16S rDNA sequence shown in SEQ ID NO: 3, and the Strain 3 is named Priestiamegaterium Bacif4, which was deposited at the Guangdong Microbial Culture Collection Center on June 28, 2022, with the deposit number: GDMCC No: 62567.

3. An agricultural preparation, wherein the agricultural preparation comprises the bacterial strain according to claim 1 or 2.

4. The agricultural preparation according to claim 3, wherein the agricultural preparation further comprises excipients.

5. The agricultural preparation according to claim 3 or 4, wherein the dosage form of the agricultural preparation is selected from: wettable powder, water dispersible granule, suspension, emulsion in water, granule, seed coating agent or a combination thereof.

6. Use of the bacterial strain according to claim 1 or 2 in the preparation of an agricultural preparation.

7. A method for promoting plant growth, the method comprising applying to the plant the bacterial strain according to claim 1 or 2 or the agricultural preparation according to any one of claims 3 to 5.

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