Growth-promoting strain SZ-R2 and application of growth-promoting strain SZ-R2 in promoting seed germination and seedling growth and development of sweet corn inbred line

Abstract

The invention relates to the technical field of microorganisms, in particular to a growth-promoting bacterium SZ-R2 and application of the growth-promoting bacterium SZ-R2 in promoting seed germination and seedling growth and development of a sweet corn inbred line, the growth-promoting bacterium is named as bacillus amyloliquefaciens SZ-R2, the preservation unit of the growth-promoting bacterium is China Center for Type Culture Collection, the preservation number is CCTCC M 20241103, and the preservation date is May 30, 2024. The bacillus amyloliquefaciens SZ-R2 provided by the invention has better capabilities in the aspects of phosphate solubilization, nitrogen fixation, potassium solubilization, siderophore production and starch solubilization; the biological agent prepared from the growth-promoting bacterium is used for seed soaking treatment, germination of sweet corn seeds can be promoted, growth and development of seedlings and substance accumulation of the overground part are remarkably improved, and economic benefits are improved on the premise that the environment is not polluted.

Description

Technical Field

[0001] This invention relates to the field of microbial application technology, and in particular to the growth-promoting strain SZ-R2 and its application in promoting seed germination and seedling growth and development of sweet corn inbred lines. Background Technology

[0002] corn( Zea mays Sweet corn (Zea mays), a plant belonging to the genus Zea in the Poaceae family originating in Mexico, North America, is an important food crop and now occupies a significant position in global agricultural production (Jonathan A. Origin and diversification of maize: Two teosinte but different contributions. Molecular Plant, 2024, 17, 233-235.). However, sweet corn inbred lines suffer from low seed vigor and weak growth after emergence, poor stress resistance, stunted plants in later stages, and low seed yield, which is one of the main problems in current sweet corn seed production.

[0003] Beneficial microbiomes in soil, also known as plant growth-promoting bacteria (PGPR), are beneficial microbial communities in the soil that promote healthy plant growth, improve soil fertility, and enhance soil structure. Among them, growth-promoting bacteria, represented by Bacillus and Pseudomonas, can enhance plant resistance to stress by inhibiting plant pathogen infection and promote the absorption and utilization of nutrients such as nitrogen, phosphorus, and potassium by crops. Therefore, the characteristics of growth-promoting bacteria, such as phosphate solubility, biological nitrogen fixation, and siderophore production, can serve as important indicators for evaluating the growth-promoting effects of strains (Souza, RD Plant growth-promoting bacteria as inoculants in agriculturalsoils. Genetics and Molecular Biology, 2015, 38, 401-419.). For example, the invention patent with publication number CN115094003B discloses "a growth-promoting bacterium with phosphorus-solubilizing, iron-producing, and heavy metal-resistant properties and its application". The inventor isolated a xylose-oxidizing colorless bacillus from wild rice tissue. This bacterium can stimulate plant growth and enhance nutrient absorption by secreting plant growth hormones, solubilizing phosphorus, and producing iron, and has great application value in promoting plant growth.

[0004] In conclusion, the research and application of novel biological agents such as growth-promoting bacteria can not only provide crops with more natural and environmentally friendly nutritional support, thereby reducing dependence on chemical fertilizers and pesticides, but also help improve crop productivity, achieve comprehensive management of soil fertility, and promote the sustainable development of ecological agriculture. Summary of the Invention

[0005] This invention provides a growth-promoting strain SZ-R2 and its application in promoting seed germination and seedling growth and development of sweet corn inbred lines.

[0006] The specific technical solution is as follows: The first objective of this invention is to provide a growth-promoting strain SZ-R2, named Bacillus amyloliquefaciens (Bacillus amyloliquefaciens). Bacillus amyloliquefaciens SZ-R2, accession number CCTCC M 20241103, deposited at China Center for Type Culture Collection, on May 30, 2024.

[0007] Furthermore, the gyrB sequence of the Bacillus amyloliquefaciens strain SZ-R2 includes the sequence shown in SEQ ID No. 1.

[0008] A second object of the present invention is to provide a biological agent containing at least one of the following as an active ingredient: A1) The Bacillus amyloliquefaciens SZ-R2 described; A2) The culture of Bacillus amyloliquefaciens SZ-R2 described above; A3) Metabolites obtained by culturing the Bacillus amyloliquefaciens SZ-R2.

[0009] Preferably, the culture of Bacillus amyloliquefaciens SZ-R2 is prepared by the following method: Bacillus amyloliquefaciens SZ-R2 is inoculated into LB liquid medium and cultured to obtain the culture of Bacillus amyloliquefaciens SZ-R2.

[0010] Preferably, the concentration of Bacillus amyloliquefaciens SZ-R2 in the biological agent is 1×10⁻⁶. 7 ~1×10 9 CFU·mL -1 .

[0011] More preferably, the concentration of Bacillus amyloliquefaciens SZ-R2 in the biological agent is 1×10⁻⁶. 8 CFU·mL -1 .

[0012] A third object of the present invention is to provide the use of the aforementioned Bacillus amyloliquefaciens SZ-R2 or the aforementioned biological agent in at least one of the following: B1) Decomposes inorganic phosphorus; B2) Nitrogen fixation; B3) Potassium phosphate decomposition; B4) Iron production capacity; B5) Detoxifies starch; B6) Promotes corn seed germination; B7) Promotes the growth and development of corn seedlings.

[0013] Preferably, the corn is sweet corn.

[0014] More preferably, the corn is a sweet corn inbred line.

[0015] Preferably, promoting corn seed germination means increasing the seed germination rate.

[0016] Preferably, the promotion of corn seedling growth and development is manifested in increasing seedling height, seedling fresh weight, and seedling dry weight.

[0017] A fourth objective of this invention is to provide a method for promoting the germination of seeds and / or the growth and development of seedlings of sweet corn inbred lines, comprising the following steps: applying the aforementioned Bacillus amyloliquefaciens SZ-R2 or the aforementioned biological agent to corn seeds.

[0018] Preferably, the corn seeds are applied by soaking them in the aforementioned Bacillus amyloliquefaciens SZ-R2 or the aforementioned biological agent.

[0019] More preferably, the soaking time is 6–12 hours.

[0020] More preferably, the soaking time is 8 hours.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) The Bacillus amyloliquefaciens SZ-R2 provided by the present invention has the functions of decomposing inorganic phosphorus, fixing nitrogen, solubilizing potassium, secreting iron ion carriers, and solubilizing starch, thereby promoting plant growth. The biological agent prepared by it can be used to soak sweet corn inbred line seeds, which can significantly improve the seed germination rate, seedling height, seedling fresh weight and seedling dry weight, etc., and promote seed germination and seedling growth and development, laying the foundation for ensuring seed production yield.

[0022] (2) The Bacillus amyloliquefaciens SZ-R2 or biological agent provided by the present invention belongs to the field of microbial fertilizer. It mainly relies on microorganisms and their metabolites to produce effects. It is environmentally friendly and does not produce pollution. Moreover, it comes from the rhizosphere soil of corn plants, which is environmentally friendly and does not produce pollution. It is in line with the future agricultural development trend. The production process is simple and suitable for promotion. Attached Figure Description

[0023] Figure 1 The results of the indoor plate growth promotion characteristics test of three different growth-promoting strains, including Bacillus amyloliquefaciens SZ-R2, in Example 1 are shown. Among them, A is Assumption medium for nitrogen-fixing bacteria, B is silicate bacteria medium, C is organic phosphorus bacteria medium, D is inorganic phosphorus bacteria medium, and E is CAS detection medium.

[0024] Figure 2 This shows the growth of Bacillus amyloliquefaciens SZ-R2 on LB plates in Example 2.

[0025] Figure 3 This is a phylogenetic tree of Bacillus amyloliquefaciens SZ-R2 constructed based on the gyrB sequence in Example 2.

[0026] Figure 4 The image shows the growth and development of seedlings of the sweet corn inbred line “S74-1-2-1-1” in Example 3 after being soaked in sterile water (CK) and three different growth-promoting bacterial agents, including SZ-R2. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0028] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The experimental materials used in the embodiments of this invention are all conventional experimental materials in the art and are commercially available. Experimental methods not specifying detailed conditions are performed according to conventional experimental methods or the operating instructions recommended by the supplier.

[0029] Example 1: Isolation, screening, and verification of growth-promoting ability of growth-promoting bacteria 1. Test materials Soil samples were collected from the rhizosphere soil of healthy corn plants in Yazhou District, Sanya City, Hainan Province, and Dong'an Village, Shangzhi City, Harbin City, Heilongjiang Province, and stored in a laboratory refrigerator at 4°C.

[0030] Seeds used for testing: Sweet corn inbred line “S622-432” seeds, provided by the Institute of Modern Seed Industry, Zhejiang University.

[0031] Seed germination bag (30 cm × 25.5 cm): purchased from the Phytoic brand.

[0032] LB broth medium (1000 mL): 10.0 g tryptone, 5.0 g yeast extract, 10.0 g sodium chloride, distilled water to a final volume of 1000 mL, sterilized at 121°C for 20 min by moist heat.

[0033] LB agar medium: 10 g tryptone, 5 g yeast extract, 10 g sodium chloride, 15 g agar, distilled water to a final volume of 1000 mL, pH 7.0; sterilize at 121°C for 20 min by moist heat.

[0034] CAS detection medium (1000 mL): Chromium azurite S (CAS) 0.0605 g, hexadecyltrimethylammonium bromide (HDTMA) 0.0729 g, ferric chloride hexahydrate 0.002645 g, potassium dihydrogen phosphate 0.0375 g, ammonium chloride 0.125 g, sodium dihydrogen phosphate dihydrate 0.29525 g, disodium hydrogen phosphate dodecahydrate 1.2135 g, sodium chloride 0.0625 g, agar 9.0 g, distilled water to a final volume of 1000 mL, sterilized by moist heat at 121℃ for 15 min.

[0035] Inorganic phosphorus bacteria culture medium (1000 mL): glucose 10.0 g, ammonium sulfate 0.5 g, yeast extract 0.5 g, sodium chloride 0.3 g, potassium chloride 0.3 g, magnesium sulfate 0.3 g, ferrous sulfate 0.03 g, manganese sulfate 0.03 g, calcium phosphate 5.0 g, agar 15.0 g, distilled water to a final volume of 1000 mL, sterilize at 121℃ for 20 min.

[0036] Organophosphate bacteria culture medium (1000 mL): glucose 10.0 g, ammonium sulfate 0.5 g, sodium chloride 0.3 g, yeast extract 0.5 g, potassium chloride 0.3 g, magnesium sulfate 0.3 g, ferrous sulfate 0.03 g, manganese sulfate 0.03 g, lecithin 0.2 g, calcium carbonate 1.0 g, agar 15.0 g, distilled water to a final volume of 1000 mL, sterilize at 121℃ for 20 min.

[0037] Silicate bacteria culture medium (1000 mL): sucrose 5.0 g, magnesium sulfate 0.5 g, calcium carbonate 0.1 g, disodium hydrogen phosphate 2.0 g, ferric chloride 0.005 g, glass powder 0.5 g, agar 15.0 g, distilled water to a final volume of 1000 mL, sterilize at 121℃ for 20 min.

[0038] Assumption medium (1000 mL) was used for nitrogen-fixing bacteria: 0.2 g dihydrogen phosphate, 0.2 g magnesium sulfate, 0.2 g sodium chloride, 5.0 g calcium carbonate, 10.0 g mannitol, 0.1 g calcium sulfate, 15.0 g agar, and distilled water to a final volume of 1000 mL. The mixture was then sterilized by moist heat at 121°C for 20 min.

[0039] Hogland nutrient solution (1000 mL): Potassium sulfate 607 mg, ammonium dihydrogen phosphate 115 mg, magnesium sulfate 493 mg, EDTA iron sodium salt 20 mg, ferrous sulfate 15 mg, boric acid 2.86 mg, borax 4.5 mg, trace elements 3 mg, bring to a final volume of 1000 mL, and sterilize at 115℃ for 20 min by moist heat.

[0040] Live bacterial suspension of growth-promoting bacteria: Growth-promoting bacteria were inoculated onto LB agar medium and incubated at 28℃ for 24 h for activation. Activated bacterial pellets were collected using a 5 mm diameter colony punch and placed into shaker tubes containing LB broth medium, then incubated at 200 r·min. -1 After incubating the culture on a shaker at 30°C for 24 h, transfer 5 mL of the bacterial suspension to an Erlenmeyer flask containing 250 mL of LB broth and shake for 48 h to prepare a bacterial suspension. Transfer the bacterial suspension to a 50 mL centrifuge tube and centrifuge at 8000 r·min. -1 After incubation at 28℃ for 10 minutes, discard the supernatant and adjust the concentration to 1×10⁻⁶ with sterile water. 8 CFU·mL -1 Prepare the bacterial suspension for later use.

[0041] 2. Test Methods (1) Isolation and screening of rhizosphere soil bacteria The rhizosphere soil bacteria of maize plants were isolated using the dilution plate spread method. 5 g of soil sample was weighed and placed in an Erlenmeyer flask, along with 3 steel balls and 100 mL of sterile water. The flask was then incubated at 37℃ and 180 r·min. -1 Shake thoroughly in a constant temperature shaker for 1 hour, remove and let stand for 15 minutes. Under aseptic conditions, take 5 mL of the supernatant and dilute to 1×10⁻⁶. -1 1×10 -2 1×10 -3 1×10 -4 1×10 -5 Five gradient dilutions were prepared, with 100 μL of each diluted solution spread onto LB plates and incubated at 28°C for 72 h. After single colonies grew, single colonies with different morphological characteristics were selected and streaked onto fresh LB agar medium. The purification was repeated 2-3 times, and the obtained strains were inoculated into LB broth medium. The bacterial culture was then mixed with 50% glycerol at a 1:1 ratio and stored at -80°C for later use.

[0042] The purified bacterial strains were screened using various selection media, including those for phosphate-solubilizing bacteria, nitrogen-fixing bacteria, potassium-solubilizing bacteria, and siderogenic bacteria. The preserved bacterial culture was diluted to 1×10⁻⁶. -3 Spread the culture onto LB agar medium and incubate at 37°C for 24 h. Pick single colonies and incubate on LB broth medium at 200 rpm. -1After culturing on a shaker at 37℃ for 24 h, 100 μL of the bacterial solution was spread onto LB agar medium and cultured for another 24 h. The culture was then punched into 5 mm diameter bacterial cakes for later use. These bacterial cakes were inoculated onto Assab's medium for nitrogen-fixing bacteria, and strains exhibiting normal growth were selected as having nitrogen-fixing properties. Bacteria were inoculated onto silicate bacteria medium; strains exhibiting an oil droplet morphology were considered to have potassium-solubilizing properties. These bacteria, verified to have nitrogen-fixing and potassium-solubilizing properties, were then inoculated onto inorganic phosphorus bacteria medium, organic phosphorus bacteria medium, and CAS medium, respectively. Strains producing a clear zone around the bacteria exhibiting phosphate-solubilizing, organic phosphorus-decomposing, and siderophore-producing properties.

[0043] (2) Verification of the growth-promoting ability of growth-promoting bacteria The growth-promoting ability of the growth-promoting bacteria was verified using the sweet corn inbred line “S622-432”. The bacterial suspensions of the three selected growth-promoting bacteria were inoculated onto seeds via seed soaking. Seed germination and seedling growth were evaluated to further screen for strains with significant growth-promoting effects. First, surface-sterilized corn seeds were soaked in 1×10⁻⁶ water. 8 CFU·mL -1 After treating the seeds with a growth-promoting bacterial suspension for 8 h, the suspension was discarded, and the seeds were air-dried at room temperature. Seeds were then soaked in sterile water as a control (CK). The treated seeds were transferred to germination bags, with 100 mL of Hoagland's nutrient solution added to each bag. The germination bags were then placed in an incubator and cultured at 25°C for 7 days under alternating 12 h of 9000 Lux light and 12 h of dark conditions. Germination rates and seedling rooting were recorded for different treatments. Seedling root length, seedling height, aboveground fresh and dry weight, and underground fresh and dry weight were measured. One hundred seeds constituted one replicate, and each treatment was repeated three times.

[0044] Statistical analysis: The Duncan method was used with SPSS 27.0 software to analyze the significance of differences between data processed in different ways. P <0.05).

[0045] 3. Experimental Results (1) Growth-promoting characteristics of growth-promoting bacteria SZ-R2 127 bacterial strains were isolated and purified from the tested soil samples. Through screening on a series of growth-promoting characteristic selection media, three strains with good overall growth-promoting characteristics—YZ-B23, SZ-R2, and SZ-S3—were obtained. Screening on nitrogen-fixing selection media showed that all three growth-promoting strains could grow normally and exhibit nitrogen-fixing activity. Figure 1 A); In silicate culture medium, the colony surface of all three bacteria showed oil droplet-like structures, indicating potassium-solubilizing activity. Figure 1 B); In organic phosphorus culture medium, the colonies of bacteria YZ-B23 and SZ-S3 produced hydrolysis zones, indicating their ability to decompose organic phosphorus. Figure 1C); YZ-B23 and SZ-R2 can dissolve phosphates, producing hydrolysis zones around colonies on inorganic phosphorus media. Figure 1 D); All three types of bacteria produced hydrolysis zones around their colonies on CAS medium, and all exhibited the characteristic of producing siderophores. Figure 1 E).

[0046] (2) Growth-promoting ability of growth-promoting bacteria SZ-R2 After the seeds of the sweet corn inbred line “S622-432” were treated with bacterial suspensions of three tested bacteria (YZ-B23, SZ-R2, and SZ-S33), the germination rate of the seeds treated with strain SZ-R2 was the highest, reaching 60.00%, which was 5 percentage points higher than the control, indicating that the growth-promoting bacterium SZ-R2 could significantly improve the seed germination rate (Table 1). As for the indicators closely related to seedling growth and development, such as seedling height, fresh weight, and dry weight, the SZ-R2 bacterial suspension treatment group was significantly better than the control group and the YZ-B23 and SZ-S3 treatment groups, indicating that SZ-R2 can significantly increase the biomass of seedlings and has the best growth-promoting effect.

[0047] In addition, after treatment with bacterial suspensions of three tested bacteria, namely YZ-B23, SZ-R2 and SZ-S3, there were no significant differences in rooting rate, root length and root weight of seedlings compared with the control. This indicates that the growth-promoting bacterium SZ-R2 has a significant promoting effect on the aboveground growth and development of sweet corn inbred line “S622-432” seedlings, but has no significant effect on the underground parts (Table 2).

[0048] Table 1. Effects of SZ-R2 bacterial suspension treatment on seed germination and aboveground growth of seedlings of the inbred line S622-432.

[0049] Note: Different lowercase letters after the data indicate significant differences between different treatment groups (P < 0.05, Duncan), the same applies below. Table 2. Effects of SZ-R2 bacterial suspension treatment on root growth promotion of "inbred line S622-432"

[0050] Example 2 Identification of growth-promoting bacteria SZ-R2 1. Test culture medium and reagents 15% gelatin culture medium (1000 mL): 5.0 g peptone, 150.0 g gelatin, distilled water to a final volume of 1000 mL, sterilize at 121°C for 15 min, and dispense into shaker tubes, approximately 8 mL per tube.

[0051] VP test medium (1000 mL): 5.0 g peptone, 5.0 g glucose, 5.0 g dipotassium hydrogen phosphate, distilled water to a final volume of 1000 mL, sterilized by moist heat at 121℃ for 15 min.

[0052] Methyl red test medium (1000 mL): 5.0 g peptone, 5.0 g glucose, 5.0 g dipotassium hydrogen phosphate, distilled water to a final volume of 1000 mL, sterilized by moist heat at 121℃ for 15 min.

[0053] Nitrate reducing medium (1000 mL): 5.0 g peptone, 1.0 g potassium nitrate, distilled water to a final volume of 1000 mL, sterilized by moist heat at 121°C for 15 min.

[0054] Nitrite reducing medium (1000 mL): 10.0 g beef extract, 5.0 g peptone, 1.0 g sodium nitrite, distilled water to a final volume of 1000 mL, sterilized at 121℃ for 15 min by moist heat.

[0055] Lead acetate medium (1000 mL): 10.0 g peptone, 3.0 g beef extract, 5.0 g sodium chloride, 2.5 g sodium thiosulfate, 12.0 g agar, and distilled water to a final volume of 1000 mL. Dispense 100 mL into Erlenmeyer flasks, sterilize at 121°C for 15 min, and when cooled to approximately 50°C, add 1 mL of 10% lead acetate solution (sterilized by passing through a 0.22 μm filter), mix well, dispense approximately 8 mL into test tubes, and cool for later use.

[0056] Toluidine blue-DNase agar (1000 mL): 0.3 g deoxyribonucleic acid (DNA), 1.1 g calcium chloride, 10.0 g sodium chloride, 6.1 g tris(hydroxymethyl)aminomethane (Tris), 10.0 g agar, distilled water to a final volume of 1000 mL, sterilized by moist heat at 121°C for 15 min.

[0057] Starch hydrolysis medium (1000 mL): 2.0 g soluble starch, 10.0 g peptone, 3.0 g beef extract, 5.0 g sodium chloride, 15.0 g agar, distilled water to a final volume of 1000 mL, sterilized at 121°C for 15 min by moist heat.

[0058] Catalase assay reagent: 3%~10% hydrogen peroxide solution. Methyl red assay indicator: 0.1 g methyl red, 300 mL 95% ethanol, 200 mL distilled water. VP assay indicator: 40% NaOH solution (containing 0.3% creatine). Amylase assay indicator: Lugol's iodine solution.

[0059] Nitrate reduction test reagent: Griess reagent (solution A + solution B).

[0060] Hogland nutrient solution (100 ml): Potassium sulfate 607 mg, ammonium dihydrogen phosphate 115 mg, magnesium sulfate 493 mg, EDTA iron sodium salt 20 mg, ferrous sulfate 15 mg, boric acid 2.86 mg, borax 4.5 mg, trace elements 3 mg, bring to a final volume of 1000 mL, and sterilize at 115℃ for 20 min.

[0061] 2. Test Methods (1) Morphological and physiological biochemical identification of growth-promoting bacteria SZ-R2 Following the methods described in the "Handbook of Systematic Identification of Common Bacteria" by Dong Xiuzhu et al., the morphological identification and physiological and biochemical characteristics of the growth-promoting bacterium SZ-R2 strain were performed.

[0062] (2) Molecular identification of growth-promoting bacteria SZ-R2 DNA was extracted from the screened antagonistic strains using the OMEGA bacterial DNA extraction kit. The gyrB gene fragment of this biocontrol bacterium was amplified using a PCR amplification kit, with the extracted genomic DNA product as a template. The sequence used for amplifying the gyrB gene is as follows: The forward primer sequence is: 5'-GAAGTCATCATGACCGTTCTGCAYGCNGGNGGNAARTTYGA-3'; The reverse primer sequence is: 5'-AGCAGGATACGGATGTGCGAGCCRTCNACRTCNGCRTCNGTCATPCR-3'.

[0063] After agarose gel electrophoresis, the products were sent to Hangzhou Shangya Biotechnology Co., Ltd. for DNA sequencing. The sequencing results were aligned to BLAST on NCBI, and sequence analysis was performed using Mega 11 software. A phylogenetic tree was constructed using a Neighbor-joining tree.

[0064] 3. Experimental Results (1) Morphological and physiological biochemical identification of growth-promoting bacteria SZ-R2 SZ-R2 colonies appear as opaque milky white on LB agar medium. Single colonies have a rough, raised surface and irregular edges. Figure 2 The gelatin was positive for catalase, citrate utilization, amylase, acetylmethylethanol, acetamide, aescin hydrolysis, glucose hydrolysis, and bile aescin hydrolysis tests, while it was negative for other tests such as gelatin liquefaction, oxidase production, and hydrogen sulfide production (Table 3).

[0065] Table 3. Physiological and biochemical identification results of strain SZ-R2

[0066] (2) Molecular identification results of growth-promoting bacteria SZ-R2 SZ-R2 according to bacteria gyrB Gene sequence sequencing results were compared using BLAST at NCBI, and strain SZ-R2 was found to be... Bacillus amyloliquefaciens On the same branch, it was identified as Bacillus amyloliquefaciens (B. amyloliquefaciens). Figure 3 The amplified product was sequenced, yielding a sequence with a length of 1129. gyrB The gene, whose base sequence is shown in the sequence listing (SEQ ID NO.1).

[0067] Example 3: Growth-promoting effect of growth-promoting bacterium SZ-R2 on the sweet corn inbred line “S74-1-2-1-1” Example 1 confirmed that strain SZ-R2 has a significant promoting effect on the growth and development of sweet corn inbred line seedlings. This example further verifies the growth-promoting effect of growth-promoting bacterium SZ-R2 on the growth and development of sweet corn inbred line “S74-1-2-1-1” seedlings.

[0068] 1. Test materials and reagents Seeds used for testing: Sweet corn inbred line “S74-1-2-1-1” seeds, provided by the Institute of Modern Seed Industry, Zhejiang University.

[0069] Seed germination bag: Same as in Example 1.

[0070] Hogland nutrient solution: Same as in Example 1.

[0071] Live bacterial suspension of growth-promoting bacteria: Same as in Example 1. 2. Test Methods Three growth-promoting bacteria, including strain SZ-R2, were used in Example 1 to treat seeds by soaking them in bacterial suspension. The growth-promoting effect of strain SZ-R2 was verified by evaluating the seedling growth after germination. The treatment method was the same as in Example 1. After 7 days of cultivation, the seed germination rate was recorded, and the seedling height, fresh weight, and dry weight were measured. 100 seeds constituted one replicate, and each treatment was repeated three times.

[0072] Statistical analysis: The Duncan method of SPSS 27.0 software was used to analyze the significance of differences between data processed in different ways. P <0.05).

[0073] 3. Experimental Results From Table 4 and Figure 4As shown, after treating seeds of the sweet corn inbred line "S74-1-2-1-1" with bacterial suspensions of three tested bacteria, including SZ-R2, the seeds treated with strain SZ-R2 showed the highest germination rate, reaching 78.70%, significantly higher than the control by 14 percentage points. This indicates that the growth-promoting bacterium SZ-R2 can significantly promote seed germination. Indicators closely related to seedling growth and development, such as seedling height, fresh weight, and dry weight, also showed significantly better results in the SZ-R2 bacterial suspension treatment group compared to the control group and the YZ-B23 and SZ-S3 treatment groups, further demonstrating that the growth-promoting bacterium SZ-R2 can significantly improve seed germination rate and promote the aboveground growth and development of seedlings.

[0074] Table 4. Effects of growth-promoting bacterium SZ-R2 on seed germination and aboveground growth of sweet corn inbred line “S74-1-2-1-1”.

Claims

1. A growth-promoting bacterium SZ-R2, characterized in that, It possesses the characteristics of phosphorus solubilization, potassium solubilization, nitrogen fixation, and iron production carrier, and is named Bacillus amyloliquefaciens (Bacillus). Bacillus amyloliquefaciens SZ-R2, accession number CCTCC M 20241103, deposited at China Center for Type Culture Collection, on May 30, 2024.

2. The growth-promoting bacterium SZ-R2 as described in claim 1, characterized in that, The gyrB sequence of the Bacillus amyloliquefaciens SZ-R2 contains the sequence shown in SEQ ID No.

1.

3. A biological agent, characterized in that, It contains at least one of the following as an active ingredient: A1) The Bacillus amyloliquefaciens SZ-R2 as described in claim 1; A2) The culture of Bacillus amyloliquefaciens SZ-R2 described above; A3) Metabolites obtained by culturing the Bacillus amyloliquefaciens SZ-R2.

4. The biological agent as described in claim 3, characterized in that, The concentration of the growth-promoting strain SZ-R2 in the biological agent is 1×10⁻⁶. 7 ~1×10 9 CFU·mL -1 .

5. The use of Bacillus amyloliquefaciens SZ-R2 according to any one of claims 1-2 or the biological agent according to any one of claims 3-4 in at least one of the following: B1) Decomposes inorganic phosphorus; B2) Nitrogen fixation; B3) Potassium phosphate decomposition; B4) Iron production capacity; B5) Detoxifies starch; B6) Promotes corn seed germination; B7) Promotes the growth and development of corn seedlings.

6. The application according to claim 5, characterized in that, The corn in question is a sweet corn inbred line.

7. A method for promoting seed germination and / or seedling growth and development of sweet corn inbred lines, characterized in that, Includes the following steps: Apply Bacillus amyloliquefaciens SZ-R2 as described in any one of claims 1 to 2 or the biological agent as described in any one of claims 3 to 4 to corn seeds.

8. The method according to claim 7, characterized in that, The corn seeds are applied by soaking them in the aforementioned Bacillus amyloliquefaciens SZ-R2 or a biological agent.

9. The method according to claim 7, characterized in that, Soaking time is 6–12 hours.

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