A composite microbial seed coating agent for alfalfa in saline-alkali land and its application

Abstract

The present invention belongs to the technical field of agricultural microorganisms, and specifically relates to a composite microbial seed coating agent for alfalfa in saline-alkali land and its application. The present invention relates to YJ42, a pseudomonas with a preservation number of CCTCC NO: M 2024914, and YJ33, a tropical bacillus with a preservation number of CCTCC NO: M 20232194. When acting together with plants, the salt-tolerance growth-promoting effect on plants is better. Among them, Pseudomonas YJ42 has a strong ability to produce IAA and dissolve phosphorus. After screening, the optimal bacterial liquid concentration of Pseudomonas YJ42 and tropical bacillus YJ33 is used as an active ingredient to prepare a composite microbial seed coating agent that specifically acts on alfalfa. It not only maximizes the synergistic effect of the two bacteria, but also can significantly improve the salt tolerance of alfalfa at a salt content of 0.7%, promote its growth, and increase its biomass.

Description

Technical Field

[0001] The invention relates to the technical field of agricultural microorganisms, in particular to a composite microbial seed coating agent for alfalfa in saline-alkali land and application thereof. Background Art

[0002] The global area of ​​salinized land is expanding year by year, posing a serious threat to agricultural production and ecological security. Therefore, the improvement of saline-alkali land remains a top priority in the agricultural sector. Among the many improvement measures, biological improvement can not only rely on the growth and development of salt-tolerant plants to absorb saline and alkali components in the soil to repair saline-alkali land; it can also improve the salt tolerance of plants through the use of microbial agents, coating agents, and other methods. Among them, the application of microorganisms refers to the use of appropriate forms of salt-tolerant plant growth-promoting rhizobacteria (PGPR) to act on plants to form a plant-microorganism co-remediation system to resist salt stress. Among the many salt-tolerant plant growth-promoting rhizobacteria, Pseudomonas and Bacillus both have growth-promoting properties such as IAA production, nitrogen fixation, phosphorus solubilization, and potassium production, and have great application prospects.

[0003] IAA, or indoleacetic acid, is an important regulator of plant root development. IAA plays a key role in plant growth. Salt-tolerant growth-promoting bacteria can synthesize IAA through a tryptophan-dependent pathway, thereby directly promoting the formation of root hairs, the proliferation of lateral roots, and the activity of root apical meristems, thereby expanding the root surface area and enhancing the plant's ability to absorb water and nutrients in saline soils. Some researchers have found that phosphate-solubilizing bacteria such as Pseudomonas can significantly increase the biomass of corn. In addition, the synergistic effect of IAA and ACC deaminase can reduce the level of ethylene precursor (ACC), effectively alleviating the inhibitory effect of salt stress on root growth.

[0004] The use of coating agents is an effective measure to help crops avoid the threat of pests and diseases, promote their growth and development, and increase yield and quality. As a new biotechnology method, microbial coating agents can promote plant root development and enhance stress resistance by coating seeds and introducing beneficial microorganisms. Nowadays, there are many coating agents that can effectively prevent and control pests and diseases and ensure the normal growth and development of plants. However, there are not many studies on composite microbial coating agents that have plant rhizosphere growth-promoting bacteria as the core ingredient and can specifically act on alfalfa to enable it to grow salt-tolerant. Furthermore, microbial coating agents are also an environmentally friendly biological agent that plays an important role in China's green agriculture. Today's coating agent products are mostly chemical pesticides. Therefore, environmentally friendly coating agents with microbial components as the core ingredient still have broad research potential. Summary of the Invention

[0005] In response to the defects and shortcomings of the existing technology, the present invention provides a composite microbial seed coating agent with synergistic effect in promoting salt tolerance and growth promotion of alfalfa in saline-alkali land, as well as a preparation method and application, which facilitates promoting the salt tolerance growth of alfalfa in saline-alkali land and provides scientific support for the improvement and restoration of saline-alkali land.

[0006] The present invention aims to provide a composite microbial seed coating agent with synergistic effect in promoting the salt tolerance and growth of alfalfa in saline-alkali soil, wherein the coating agent has good activity under the condition of high salt content and can promote the emergence and growth of alfalfa seedlings.

[0007] Another object of the present invention is to provide an application of a composite microbial seed coating agent that can synergistically enhance the salt tolerance and growth promotion of alfalfa in saline-alkali soil.

[0008] The above-mentioned object of the present invention is achieved through the following technical solutions:

[0009] In the first aspect, a composite microbial seed coating agent with synergistically enhanced salt tolerance and growth promotion of alfalfa in saline-alkali soil is provided. The composite microorganisms of the seed coating agent are Pseudomonas sp. YJ42 and Bacillus tropicalis YJ33, with preservation numbers of CCTCC NO: M 2024914 and CCTCC NO: M 20232194, respectively. They were preserved in the China Center for Type Culture Collection, Luojiashan, Bayi Road, Wuchang District, Wuhan City, Hubei Province on May 13, 2024 and November 10, 2023, respectively.

[0010] In a second aspect, the present invention provides a composite microbial seed coating agent with synergistic effects on salt tolerance and growth promotion of alfalfa in saline-alkali land. The coating agent is composed of equal proportions of the bacterial body or bacterial liquid of Pseudomonas sp. YJ42 with a preservation number of CCTCC NO: M 2024914 and the bacterial body or bacterial liquid of Bacillus tropicus YJ33 with a preservation number of CCTCC NO: M 20232194.

[0011] Furthermore, when preparing the composite microbial seed coating agent, the concentration of live bacteria was adjusted to 8×10 8 cfu / mL.

[0012] The Pseudomonas sp. YJ42 was screened from the rhizosphere soil of the halophyte Suaeda salsa in the saline-alkali land of the Yellow River Delta, and has the ability to tolerate salt, produce IAA, and solubilize phosphorus and potassium.

[0013] Both the YJ42 and YJ33 bacteria can grow naturally under a 10% salt gradient and have good salt tolerance.

[0014] Furthermore, the composite microbial seed coating agent further comprises one or more of the following components: 10 wt % composite bacterial suspension resuspension, 1 wt % sodium alginate, 0.5 wt % sodium benzoate, 1 wt % sodium carboxymethyl cellulose, 0.3 wt % acid fuchsin, 5 wt % propylene glycol, and the remainder is water to make up 100%.

[0015] Furthermore, the composite microbial seed coating agent also includes 1 wt% of polyacrylamide.

[0016] The present invention also provides a method for using the composite microbial seed coating agent, which is as follows: the mass ratio of the composite microbial seed coating agent to the crop seeds is 1:10-20.

[0017] The coating was carried out using a commercial coating machine, that is, the coating agent to be used was loaded into the liquid container in proportion, the machine was turned on and the speed of the pot was set to 40-60 r / min, seeds were put in after the operation was stable, the air compressor was turned on, the liquid spraying device was turned on after the air pressure was stable, and after the liquid spraying was completed, the liquid spraying device and the air compressor were turned off, the fan was turned on, the drying temperature was set to 40°C, and the pot continued to run to accelerate the drying of the seeds, and the drying time was set to 20-30 minutes.

[0018] In a second aspect, the present invention provides a method for promoting salt-tolerant growth of alfalfa in saline-alkali land, comprising treating the plant with a composite microbial seed coating agent having salt-tolerant growth-promoting capabilities.

[0019] The composite microbial seed coating agent is used in promoting the growth of alfalfa or promoting the growth of alfalfa under salt stress.

[0020] The composite microbial seed coating agent helps plants to grow in a salt-tolerant manner by high-yielding IAA.

[0021] The composite microbial seed coating agent is used to promote the emergence and growth of alfalfa under salt stress.

[0022] In a third aspect, the present invention also provides a method for improving / repairing saline-alkali soil, which uses a composite microbial seed coating agent to increase the salt-tolerant growth rate of plants, thereby indirectly and greenly improving the saline-alkali soil.

[0023] The YJ42 strain and the YJ33 strain described in the present invention both have good salt tolerance and can promote the growth of alfalfa or promote the growth of alfalfa in a saline-alkali soil environment.

[0024] After strains YJ42 and YJ33 were prepared into coating agents, screening for optimal bacterial concentrations revealed that alfalfa maintained healthy growth at a 0.7% salt gradient, demonstrating its ability to tolerate higher salt gradients. Germination of alfalfa in environments with varying salt concentrations and treated with different coating ratios demonstrated varying degrees of growth enhancement. Compared to the blank control, the coating agents significantly increased alfalfa seedling length, root length, seedling weight, and root weight. In the absence of a water-retaining agent, a coating ratio of 1:10 significantly increased alfalfa seedling length and weight, by 47.39% and 19.75%, respectively. Therefore, composite microbial seed coating agents can be used to enhance soil fertility or improve / remediate saline-alkali soils, possessing significant economic value and practical significance for promoting crop growth and improving soil quality in saline-alkali soils.

[0025] Therefore, the following applications of the composite microbial seed coating agent are all within the scope of protection of the present invention:

[0026] Application of composite microbial seed coating agent in promoting plant growth or promoting plant growth under salt stress.

[0027] Application of composite microbial seed coating agent in improving / restoring saline-alkali land.

[0028] Application of composite microbial seed coating agent in soil conditioner or salt-alkali resistant products.

[0029] Application of composite microbial seed coating agent in nitrogen fixation and / or phosphorus solubilization in saline-alkali soil environment.

[0030] Application of composite microbial seed coating agent in the preparation of preparation for increasing soil nitrogen and phosphorus content.

[0031] Beneficial effects of the embodiments of the present invention:

[0032] The present invention provides a composite microbial seed coating agent with salt-tolerant growth-promoting capabilities. A germination test was conducted on alfalfa seeds treated with the coating agent. The alfalfa seeds treated with the coating agent showed good activity at a salt concentration of less than 7‰, which has important practical significance and value for improving saline-alkali soil quality and the ecological environment.

[0033] The composite microbial seed coating agent provided by the present invention acts specifically on alfalfa. It not only has the most suitable concentration for alfalfa emergence and growth screened for alfalfa, but also enables the two bacteria to exert the maximum synergistic gain effect to ensure its salt-tolerant growth-promoting effect in actual alfalfa planting applications; and on the basis of the reference auxiliary ingredients, it innovatively adds a water-retaining agent ingredient, so that it can not only help alfalfa to grow salt-tolerantly, but also increase the survival rate of alfalfa under drought conditions, which is beneficial to its growth. In addition, the composite microbial seed coating agent provided by the present invention is green and pollution-free during use, and is an environmentally friendly coating agent. Its use can significantly improve the salt tolerance of alfalfa under salt stress, slow down salt damage, increase biomass, promote the growth of alfalfa, and improve the physical and chemical properties of saline-alkali soil to a certain extent, while not only not causing pollution to the environment, but also being conducive to sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A morphological diagram of coated alfalfa seeds provided in an embodiment of the present invention;

[0035] Figure 2 Figure 1 shows the results of a test of the IAA production capacity of Pseudomonas sp. YJ42 provided in an embodiment of the present invention;

[0036] Figure 3 The IAA standard curve provided by the embodiment of the present invention;

[0037] Figure 4 A colony morphology diagram of a two-bacteria co-culture provided in an embodiment of the present invention;

[0038] Figure 5 The germination potential of alfalfa after being treated with different resuspensions provided in the embodiments of the present invention;

[0039] Figure 6 The germination rate of alfalfa after being treated with different resuspensions provided in the embodiments of the present invention;

[0040] Figure 7 The length of alfalfa seedlings after being treated with different resuspensions provided in the embodiments of the present invention;

[0041] Figure 8 The weight of alfalfa seedlings after being treated with different resuspensions provided in the embodiments of the present invention;

[0042] Figure 9 The growth diagram of alfalfa after coating with different coating ratios provided in the embodiment of the invention;

[0043] Figure 10 The germination potential and germination rate of alfalfa after coating with different coating ratios provided in the embodiments of the present invention;

[0044] Figure 11The different coating ratios provided in the embodiments of the present invention increase the length and weight of alfalfa seedlings after coating. DETAILED DESCRIPTION

[0045] The following describes embodiments of the present embodiment in more detail with reference to the accompanying drawings. Although certain embodiments of the present embodiment are shown in the accompanying drawings, it should be understood that the present embodiment can be implemented in various forms and should not be construed as limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present embodiment. It should be understood that the drawings and embodiments of the present embodiment are for illustrative purposes only and are not intended to limit the scope of protection of the present embodiment.

[0046] In the embodiment of the present invention, the salt-tolerant rhizosphere growth-promoting bacteria Pseudomonas sp. and Bacillus tropicus are respectively referred to as strain number YJ42, deposit number CCTCC NO: M2024914 and strain YJ33, deposit number CCTCC NO: M 20232194. The composite microbial seed coating agent provided in the embodiment of the present invention can be applied in combination with organic fertilizer or alone.

[0047] Figure 1 A morphological diagram of coated alfalfa seeds provided in an embodiment of the present invention;

[0048] The picture shows the seed morphology of alfalfa seeds after being coated with the composite microbial seed coating agent according to a predetermined coating ratio. It can be seen that the coating is uniform and the color is bright.

[0049] Example 1 Test of IAA production ability of Pseudomonas YJ42, active ingredient of composite microbial seed coating agent

[0050] 1. Qualitative determination

[0051] IAA production by strain YJ42 was qualitatively determined using the Salkowski colorimetric method (Shokri and Emtiazi, 2010). The strain was inoculated into 50 mL of sterilized NB medium containing 200 mg / L of L-tryptophan and cultured on a temperature-controlled shaker at 28°C and 180 rpm for 3–5 days. The culture was then centrifuged at 4°C, 10,000 rpm, and 10 min to obtain 200 μL of supernatant. Positive and blank controls were prepared, consisting of 200 μL each of an IAA standard solution (50 mg / L) and uninoculated culture medium. The supernatant was placed on a white ceramic plate. An equal volume of Salkowski colorimetric solution was then added to each sample and mixed thoroughly. After the color reaction was complete, the ceramic plate was placed in a dark environment (25°C) for 30 minutes. The color turns red, indicating that the strain has the ability to produce IAA. Figure 2 It can be seen that the color of Pseudomonas YJ42 turned red after treatment, proving that it has the ability to produce IAA.

[0052] In the examples, the formula and dosage of the NB culture medium are as follows: 3.0 g beef powder, 5.0 g tryptone, pH = 7.2-7.4, and 1000 mL distilled water.

[0053] 2. Drawing of IAA standard curve

[0054] Accurately weigh 10 mg of IAA and prepare the standard solution system using the gradient dilution method. The specific process is as follows:

[0055] IAA crystals were completely dissolved in anhydrous ethanol as the initial solvent and the volume was adjusted to 100 mL with ultrapure water to obtain 100 μg mL -1 Stock solution; before use, the stock solution was adjusted to 0 (blank control), 0.5, 1.0, 5.0, 10.0, 15.0, 20.0 and 25.0 μg·mL -1 Gradient working solution was obtained by gradient dilution. 2 mL of gradient working solution and 4 mL of Salkowski colorimetric reagent were added to clean glass tubes numbered 0-7, respectively. The tubes were placed in a constant temperature, dark environment at 40°C for color development reaction, and the reaction time was set to 30 min. Colorimetric determination was performed at a wavelength of 530 nm, and a standard curve was drawn with OD value as the horizontal axis and IAA concentration as the vertical axis (Zhang Dongyan et al., 2016). The standard curve is shown in Figure 2. Figure 3 .

[0056] 3. Quantitative determination

[0057] A 4-day culture suspension was placed in a centrifuge tube. Three replicates were run. 2 ml of supernatant was centrifuged and transferred to a test tube. An equal volume of Salkowski colorimetric solution was added. The culture and centrifugation conditions were the same as for the qualitative assay. The test tube was placed in a dark environment and allowed to stand for 30 minutes for a colorimetric reaction. The absorbance of the solution at a wavelength of 530 nm was measured. The measurement results were analyzed and the IAA content per unit volume of fermentation broth was calculated using the obtained standard curve equation. The calculation showed that Pseudomonas YJ42 produced 25.21 ± 0.44 mg / L of IAA. Literature indicates that culture media with different carbon and nitrogen sources produce different amounts of IAA. In the examples of the present invention, Pseudomonas YJ42 still achieved a yield of 25.21 ± 0.44 mg / L when the basal medium contained only beef meal and tryptone, demonstrating that even higher IAA yields can be achieved with optimized culture media.

[0058] Example 2 Antagonism Test of Active Ingredients of Composite Microbial Seed Coating Agent

[0059] The strains YJ42 and YJ33 were inoculated into NA medium in succession, with a total of 4 replicates, and cultured in a 28°C incubator. After 48 h of culture, their growth was observed to determine whether there was antagonism. Figure 4 As shown, strains YJ42 and YJ33 both grew well at the intersection of the lines, indicating that there was no antagonism between the two bacteria and they could be used together as active ingredients of the target composite microbial seed coating agent.

[0060] In this embodiment, the formula and dosage of the NA medium are: 3.0 g beef powder, 5.0 g tryptone, 18.0 g agar, pH = 7.2-7.4, and 1000 mL distilled water.

[0061] Example 3 Screening of active ingredient concentrations of composite microbial seed coating agents

[0062] The seed solution was inoculated at a 3-4% inoculum into a 500 mL conical flask containing 300 mL of sterilized NB medium. The culture was shaken on a temperature-controlled shaker for 24 h at 28°C and 180 rpm. The fermentation broth was then centrifuged in a centrifuge, the supernatant discarded, and the precipitated cells collected. The centrifugation temperature was set at 4°C and the speed was set at 10,000 rpm. The cells were resuspended in sterile water to obtain a concentration of 4 × 10 8 cfu / mL, 8×10 8 cfu / mL, 1.2×10 9cfu / mL resuspension. With sterile water treatment as the control, alfalfa seeds were treated with resuspension and then subjected to a germination test for ten days in sterile water, 3‰, 5‰, and 7‰ salt solutions. The results of germination potential, germination rate, seedling length, and seedling weight were as follows: Figures 5 to 8 It should be noted that Figures 5-8 The red box in the middle is the group with the most significant difference within the same bacterial species treatment group under each salt gradient, represented by a, and the blue box is the group with the most significant difference between different bacterial species treatment groups under each salt gradient, represented by A; Ⅰ, Ⅱ, Ⅲ, and Ⅳ in the figure numbers represent the corresponding data under no salt, 0.3%, 0.5%, and 0.7% salt gradient treatments, respectively.

[0063] The promoting effects of different treatments on alfalfa germination potential, germination rate, seedling length and seedling weight in the figure show that the effect of applying YJ42 and YJ33 in equal proportion is higher than that of applying either fungus alone; 8×10 8 cfu / mL and 1.2×10 9 The effect was higher than 4×10 cfu / mL 8 cfu / mL; considering the test results under different treatments and economic costs, the present invention selected 8×10 8 The resuspension of YJ42 and YJ33 mixed in equal proportions with cfu / mL was used as the active ingredient of the target composite microbial seed coating agent.

[0064] In this embodiment, the formula and dosage of the NB culture medium are as follows: 3.0 g beef powder, 5.0 g tryptone, pH = 7.2-7.4, and 1000 mL distilled water.

[0065] Example 4 Application of composite microbial seed coating agents at different coating ratios to promote the growth of alfalfa under salt stress

[0066] 1. Preparation of active ingredients of composite microbial seed coating agent

[0067] To prepare seed culture, inoculate the activated strains YJ42 and YJ33 into 100 mL of NB medium in a 250 mL Erlenmeyer flask and incubate on a temperature-controlled shaker at 28°C and 180 rpm for 24 hours. Inoculate 3-4% of the seed culture into a 500 mL Erlenmeyer flask containing 300 mL of NB medium and incubate on a temperature-controlled shaker at 28°C and 180 rpm for 24 hours. The fermentation broth was then centrifuged in a centrifuge, the supernatant discarded, and the pelleted cells collected. The centrifugation temperature was set at 4°C and the speed was set at 10,000 rpm.

[0068] The collected precipitated bacteria were resuspended in sterile water, and the effective viable bacterial counts of strains YJ42 and YJ33 were greater than 1.5×10 10 cfu / mL resuspension. Mix the two in equal proportions and dilute with sterile water to prepare resuspensions with different effective viable bacterial counts according to different coating ratios to ensure that the effective viable bacterial count is 8×10 8 cfu / mL.

[0069] 2. Preparation of auxiliary ingredients of composite microbial seed coating agent

[0070] Using the auxiliary agent ingredients and ratios described in Patent Publication No. CN118421536A as a reference, 1 wt% of sodium alginate, 0.5 wt% of sodium benzoate, 1 wt% of sodium carboxymethylcellulose, 0.3 wt% of acid fuchsin, and 5 wt% of propylene glycol were weighed in order and dissolved in sterile water. After uniformity and absence of bubbles, 10 wt% of the composite bacterial suspension resuspension described in the present invention was added, and the volume was made up to 100% with water. This served as the coating agent for Group A1 without a water-retaining agent. Using the water-retaining agent types described in Patent Publication No. CN118667700A as a reference, 1 wt% of polyacrylamide was weighed based on the auxiliary agent ratios of Group A1 coating agent and dissolved in sterile water. After uniformity and absence of bubbles, 10 wt% of the composite bacterial suspension resuspension described in the present invention was added, and the volume was made up to 100% with water. This served as the coating agent for Group A2 with the addition of the water-retaining agent polyacrylamide.

[0071] During the preparation of the above two types of auxiliary ingredients, only the ingredients or ratios are referenced and innovated. The preparation process is unique to the present invention and does not refer to the above two patents.

[0072] 3. Growth-promoting effect of composite microbial seed coating agent under different coating ratios on alfalfa under salt stress

[0073] To verify the growth-promoting effect of composite microbial seed coating agents on alfalfa under salt stress at different coating ratios, this example used double-layer filter paper sterilized at high temperature to conduct a ten-day germination test. This test set up a salt gradient of 3‰; this test set up three coating treatments, namely the sterile water coating control group CK, the water-retaining agent-free coating test group A1, and the water-retaining agent-containing coating test group A2; this test set up five coating ratio treatments, namely 1:10, 1:20, 1:30, 1:40, and 1:50, with a total of five replicates for each treatment. Alfalfa seeds with full grains, uniform size, and no pests and diseases were selected. After treatment, 50 grains / dish were germinated in an incubator. The culture conditions were set to a photoperiod of 16 hours, a temperature of 28°C, a dark treatment of 8 hours, a temperature of 22°C, and a humidity of 50-80%. The germination potential was obtained on the 3rd day after germination, the germination rate was obtained on the 7th day after germination, and the length and weight of the alfalfa seedlings were obtained on the 10th day after germination.

[0074] In this embodiment, the growth of alfalfa seedlings in the two test groups and the control group is as follows: Figure 9 As shown in the figure, it can be seen that under the treatment of coating agent with or without water retaining agent, the alfalfa seedlings under different coating ratios were significantly better than the control A0, and the effect was more stable under the coating ratio of 1:10. The results of germination potential, germination rate, seedling length and seedling weight were as follows: Figures 10-11 It should be noted that Figures 10-11 The red box in the middle is the group with the most significant difference between the treatment groups with or without water retaining agent, represented by a; Figure 10 Figures Ⅰ and Ⅱ represent the corresponding data of germination potential and germination rate of alfalfa under different coating ratios. Figure 11 Figure numbers Ⅰ and Ⅱ represent the corresponding data of alfalfa seedling length and seedling weight under different coating ratios.

[0075] From the promoting effects of different treatments on alfalfa germination potential, germination rate, seedling length and seedling weight in the figure, it can be seen that when no water retaining agent was added, the coating ratio of 1:50 had a more significant promoting effect on the germination potential and germination rate of alfalfa seedlings, increasing by 4.19% and 4.04% respectively, and the effects were not significant under the other coating ratios; the coating ratio of 1:10 had a more significant promoting effect on the seedling length and seedling weight of alfalfa seedlings, increasing by 47.39% and 19.75% respectively, followed by the coating ratio of 1:50, which increased the seedling length and seedling weight of alfalfa seedlings by 37.32% and 13.27% respectively. When a water-retaining agent was added, a coating ratio of 1:10 significantly increased the germination potential of alfalfa seedlings by 4.19%, while the effects were not significant at the other coating ratios. Treatments with different coating ratios significantly increased the length of alfalfa seedlings. Furthermore, coating ratios of 1:10 and 1:40 significantly increased the weight of alfalfa seedlings by 16.8% and 14.15%, respectively. Therefore, the present invention proposes to recommend a coating ratio of 1:10 to 20 as the optimal ratio for the composite microbial seed coating agent. Based on the above test results, it can be seen that the composite microbial seed coating agent at different coating ratios can improve the salt tolerance and growth-promoting ability of alfalfa to varying degrees, alleviate salt damage, increase biomass, and thus promote the growth of alfalfa. Furthermore, it can improve the physical and chemical properties of saline-alkali soil to a certain extent, not only increasing yield but also improving soil quality. Furthermore, the coating agent group with the newly added water-retaining agent component has a more stable effect than the group without the addition, indicating that the coating agent provided by the present invention with the newly added water-retaining agent has a more stable and reliable effect.

[0076] The above embodiments merely illustrate several embodiments of the present invention, and the descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of patent protection. It should be noted that those skilled in the art may make modifications and improvements without departing from the scope of the present invention, and such modifications and improvements are encompassed within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the appended claims.

Claims

1. Use of a composite microbial seed coating agent in promoting the growth of alfalfa under salt stress, characterized in that: The composite microorganism is a composite bacterial suspension composed of a bacterial solution of Pseudomonas sp. YJ42 and a bacterial solution of Bacillus tropicus YJ33 in equal proportions. When preparing the composite microbial seed coating agent, the live bacterial concentration is adjusted to 8×10 8 cfu / mL, the Pseudomonas sp. YJ42 and Bacillus tropicus YJ33, the preservation numbers are CCTCC NO: M 2024914 and CCTCC NO: M20232194, respectively, and were deposited in the China Center for Type Culture Collection, Luojiashan, Bayi Road, Wuchang District, Wuhan City, Hubei Province on May 13, 2024 and November 10, 2023, respectively. The salt stress is a salt concentration of 0.7%, and the promotion of alfalfa growth is the promotion of alfalfa seedling length and seedling weight.

2. Use of the composite microbial seed coating agent according to claim 1 in promoting the growth of alfalfa under salt stress, characterized in that: The composite microbial seed coating agent comprises the following components: 10 wt % composite bacterial suspension resuspension, 1 wt % sodium alginate, 0.5 wt % sodium benzoate, 1 wt % sodium carboxymethyl cellulose, 0.3 wt % acid fuchsin, 5 wt % propylene glycol, and the remainder is water to make up 100%.

3. Use of the composite microbial seed coating agent according to claim 1 in promoting the growth of alfalfa under salt stress, characterized in that: The coating ratio of the composite microbial seed coating agent is 1:10-1:

20.

4. Use of the composite microbial seed coating agent according to claim 1 in promoting the growth of alfalfa under salt stress, characterized in that: The composite microbial seed coating agent further comprises 1 wt% of polyacrylamide.

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