Serratia marcescens and application thereof

Abstract

The invention discloses serratia marcescens and application thereof, and belongs to the technical field of microorganisms. The invention provides a serratia marcescens CZJ4 which is preserved in the China General Microbiological Culture Collection Center on October 20, 2025, the preservation address is No.3, No.1 yard, Beichen West Road, Chaoyang District, Beijing, and the preservation number is CGMCC No.36254. The serratia marcescens CZJ4 disclosed by the invention has the advantages that the serratia marcescens CZJ4 can be used for preparing a bacterial strain; the strain not only grows fast, but also has the growth promoting functions of nitrogen fixation, phosphorus dissolving, iron production and the like, and a wild barley salt stress experiment proves that the strain has positive effects in improving the growth phenotype of agricultural plants and promoting the growth of the plants.

Description

Technical Field

[0001] This invention relates to the field of microbial technology, and in particular to a strain of Serratia marcescens and its applications. Background Technology

[0002] Soil salinity in agricultural soils refers to the high concentration of soluble salts in soil moisture. These soluble salts create high osmotic pressure, which limits plant water absorption and the balanced absorption of basic nutrient ions by roots, thus affecting plant growth. The formation of saline-alkali land is the result of multiple factors, including long-term over-cultivation leading to soil structure damage, excessive fertilization causing salt accumulation in the soil, and drought causing groundwater salts to rise to the surface with evaporation. The most direct impact of soil salinization is reduced grain yields. Annual crop failures due to salinization pose a serious threat to food security. Improving and rationally utilizing saline-alkali land can not only transform previously low-yield "stagnant soil" into arable land but also directly increase the cultivated land area, playing an irreplaceable role in ensuring stable food supply and maintaining ecological security.

[0003] Beneficial microbial communities in microbial inoculants, through a series of decomposition and synthesis processes such as nitrogen fixation and phosphorus solubilization, can transform soil substances into various nutrients, improving soil fertility and promoting plant growth. Beneficial microorganisms can also secrete various antibiotics and other antibacterial substances, inhibiting the growth and reproduction of pathogens, inducing systemic disease resistance in plants, reducing disease occurrence, and enhancing plant stress resistance. In recent years, the application of microbial technology in saline-alkali soil remediation has received increasing attention and strengthening, mainly focusing on research into enhancing plant salt and alkali tolerance through microorganisms. Existing studies have found that salt-tolerant microorganisms can improve the rhizosphere environment of plants, reduce the inhibitory effect of salt on crop growth, and achieve the goal of improving saline-alkali soil. Other studies have found that strains can promote the emergence rate of mung beans, increase biomass, and reduce disease incidence under NaCl stress. Therefore, microbial activity can, to a certain extent, improve the survival rate and preservation rate of vegetation in saline-alkali soils, playing an important role in the long-term improvement of saline-alkali soils, restoring soil physicochemical properties, and reconstructing the ecological environment of saline-alkali soils. Summary of the Invention

[0004] The purpose of this invention is to provide a strain of *Serratia marcescens* and its applications to address the problems existing in the prior art. The *Serratia marcescens* strain screened in this invention not only grows rapidly but also possesses growth-promoting functions such as nitrogen fixation, phosphorus solubilization, phosphorus dissolution, and iron production. Salt stress experiments with wild barley have demonstrated that this strain plays a positive role in improving the growth phenotype of agricultural plants and promoting their growth.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] In the first aspect, the present invention provides a strain of Serratia marcescens CZJ4, which was deposited on October 20, 2025, at the China General Microbiological Culture Collection Center (CGMCC), located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, with accession number CGMCC No. 36254.

[0007] Secondly, the present invention also provides the application of the aforementioned Serratia marcescens CZJ4 in the preparation of microbial inoculants.

[0008] Thirdly, the present invention also provides a microbial inoculant, wherein the microbial inoculant includes the Serratia marcescens CZJ4.

[0009] Preferably, the method for preparing the microbial agent includes culturing *Serratia marcescens* CZJ4 in a culture medium, collecting the bacterial cells by centrifugation, washing and resuspending, and adjusting the OD value. 600 The step of obtaining the microbial inoculant by boiling it to 0.6-0.8 is called the step of boiling it to 0.6-0.8.

[0010] Fourthly, the present invention also provides the application of the aforementioned Serratia marcescens CZJ4 or the aforementioned microbial agent in promoting the growth of crops in saline-alkali land.

[0011] Preferably, the agricultural plant is wild barley.

[0012] Fifthly, the present invention also provides the application of the aforementioned Serratia marcescens CZJ4 or the aforementioned microbial agent in the preparation of products that promote the growth of agricultural plants in saline-alkali land.

[0013] Preferably, the growth of crops in saline-alkali land is promoted by increasing the root length, plant height, biomass fresh weight, and dry weight of the crops.

[0014] In a sixth aspect, the present invention also provides a product for promoting the growth of crops in saline-alkali land, the product comprising the *Serratia marcescens* CZJ4 or the microbial agent.

[0015] In a seventh aspect, the present invention also provides a method for promoting the growth of crops in saline-alkali land, the method comprising the step of applying the Serratia marcescens CZJ4, the microbial agent, or the product to crops in saline-alkali land.

[0016] The present invention discloses the following technical effects:

[0017] The *Serratia marcescens* CZJ4 strain screened in this invention not only grows rapidly but also possesses growth-promoting functions such as nitrogen fixation, phosphorus solubilization, phosphorus dissolution, and iron production. Salt stress experiments with wild barley have demonstrated that this strain plays a positive role in improving the growth phenotype of agricultural plants and promoting plant growth.

[0018] Preservation information: Serratia marcescens CZJ4 was deposited on October 20, 2025, at the China General Microbiological Culture Collection Center (CGMCC), located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, with accession number CGMCC No. 36254. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The images show the colony morphology of the growth-promoting bacteria screened in this invention; the left side is the front view and the right side is the back view.

[0021] Figure 2 This is a phylogenetic tree diagram for screening growth-promoting bacteria in this invention;

[0022] Figure 3 The growth curves of growth-promoting bacteria at different salt concentrations are shown in the figure for screening the present invention.

[0023] Figure 4 This invention screens for the phosphate-solubilizing plate dissolution zones of growth-promoting bacteria.

[0024] Figure 5 This invention screens the plate dissolution zone of phosphate-solubilizing bacteria.

[0025] Figure 6 The plate dissolution zone for screening growth-promoting bacteria as iron-producing carriers in this invention;

[0026] Figure 7 The results of the screening of growth-promoting bacteria on the morphological growth characteristics of wild barley under saline-alkali or non-saline-alkali environments are presented in this invention.

[0027] Figure 8 The figure shows the results of the screening of growth-promoting bacteria in saline-alkali or non-saline-alkali environments on the growth of wild barley. Among them, AD are the results of the measurement of wild barley plant height (A), root length (B), fresh biomass weight (C), and dry weight (D) under different treatment groups. Detailed Implementation

[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0029] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0030] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0031] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0032] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0033] Unless otherwise specified, all materials used in this embodiment are commercially available products.

[0034] LB medium: 10 g / L tryptone, 5 g / L yeast extract, 10 g / L sodium chloride, 18 g / L agar (solid), pH adjusted to 7.0-7.2.

[0035] LB liquid medium: yeast extract 5 g / L, tryptone 10 g / L, NaCl 10 g / L, pH adjusted to 7.

[0036] Nitrogen-fixing medium (nitrogen-free medium): mannitol 10.0 g / L, CaCO3 5 g / L, KH2PO4 0.2 g / L, MgSO4·7H2O 0.2 g / L, NaCl 0.2 g / L, CaSO4·2H2O 0.2 g / L, agar 20 g / L, pH adjusted to 7.0-7.2.

[0037] Monkina Inorganic Phosphorus Solid Culture Medium: Glucose 10.0 g / L, yeast extract 0.5 g / L, (NH4)2SO4 0.5 g / L, MgSO4·7H2O 0.3 g / L, MnSO4·4H2O 0.03 g / L, KCl 0.3 g / L, FeSO4·7H2O 0.03 g / L, NaCl 0.3 g / L, Ca3(PO4)2 10 g / L, agar 15 g / L, pH adjusted to 7.0-7.5.

[0038] Mongolica organophosphorus solid culture: glucose 10.0 g / L, yeast extract powder 0.4 g / L, (NH4)2SO4 0.5 g / L, MnSO4·4H2O 0.03 g / L, KCl 0.3 g / L, FeSO4·7H2O 0.03 g / L, NaCl 0.3 g / L, CaCO3 5 g / L, egg yolk lecithin 0.2 g / L, agar 20 g / L, pH adjusted to 7.0.

[0039] CAS detection medium: Chromium azurite S (CAS) 60.5 mg / L, cetyltrimethylammonium bromide 72.9 mg / L, FeCl3·6H2O 2.645 mg / L, NaH2PO4·2H2O 295.25 mg / L, Na2HPO4·12H2O 1213.5 mg / L, NH4Cl 125.0 mg / L, KH2PO4 37.5 mg / L, NaCl 62.5 mg / L, agar 9000.0 mg / L, pH adjusted to 6.7-6.9.

[0040] Example 1: Isolation and Identification of Growth-Promoting Bacterial Strains

[0041] 1. Isolation of growth-promoting bacterial strains

[0042] Soil samples were collected from the saline-alkali land of Linze in the Hexi Corridor. The soil collection adopted the five-point sampling method. Five sampling points were determined in the selected area. Soil samples of 10-20 cm were collected from saline-alkali land of different degrees. Equal amounts of soil were collected from each point, mixed, and then placed in sterile bags and sealed. The collection number, collection location, date and other key information were marked. The samples were then brought back to the laboratory and stored at 4℃.

[0043] Soil samples were sieved through a 20-mesh sieve (approximately 1 mm in diameter). 10 g of the sample was weighed and placed in an Erlenmeyer flask containing 90 mL of sterile aqueous solution (containing 10-15 sterile glass beads). The flask was incubated at 28°C and 150 rpm for 2-3 hours, then allowed to stand for 10 minutes to obtain a soil suspension diluted 10 times. This suspension was recorded as 10 g. -1 Diluent. Use a pipette to take 1 mL of 10... -1 Add the diluent to a test tube containing 9 mL of sterile water, mix well by pipetting, and dilute to a 10:1 ratio.-2 Diluent, then dilute in the same manner to prepare 10. -3 10 -4 10 -5 10 -6 10 -7 Prepare a series of gradient dilutions; take 0.1 mL of each gradient dilution and spread it evenly on LB agar plates, repeating each concentration three times. Incubate the plates upside down in a 28°C incubator for 2-3 days.

[0044] Select plates with suitable colony density (30-300 CFU / plate). Strawberry culture of different types from the LB agar plates is performed, and the culture is incubated at 28°C for 2-3 days. Single cells are streaked again, and this process is repeated 2-3 times to obtain pure single-cell cultures of each strain. Single cells from each strain are then inoculated into LB liquid medium and incubated at 28°C with shaking at 150 rpm for 12-24 hours. Strains showing significant growth in the medium are selected for purification and preservation. The pure cultures are cryopreserved in 30% glycerol and named CZJ4.

[0045] 2. Strain identification

[0046] 2.1 Morphological identification

[0047] The purified strain CZJ4 was selected and cultured on LB agar using the streak method at 28°C for 2 days. Colony morphology was then observed.

[0048] The colony morphology of growth-promoting bacteria is as follows: Figure 1 As shown, the colonies of this growth-promoting bacterium are smooth and moist, with regular and neat edges, and the surface of the colonies often exhibits a distinct stickiness.

[0049] 2.2 Molecular biological identification

[0050] The isolated and purified strain CZJ4 was subjected to molecular biological identification by DNA extraction, PCR amplification, and 16S rRNA gene sequencing (forward primer 27F: 5'-AGAGTTTGATCCTGGCTCAG-3', SEQ ID NO.2; reverse primer 1492R: 5'-TACGGCTACCTTACGACTT-3', SEQ ID NO.3).

[0051] The PCR product of the amplified 16S rRNA was sent to Sangon Biotech (Shanghai) Co., Ltd. for sequencing, and the 16S rRNA sequence of the strain was finally obtained. The 16S rRNA sequence of the strain is shown in SEQ ID NO.1.

[0052]

[0053] Homology alignment (BLAST) of nucleic acid sequences was performed using the GenBank database on NCBI. The results showed that *Serratia marcescens* had the highest sequence contrast. A phylogenetic tree was constructed as follows: Figure 2 Analysis revealed that the strain had a high degree of similarity to Serratia marcescens. Therefore, the strain was preliminarily identified as Serratia marcescens and named Serratia marcescens CZJ4.

[0054] Example 2: Salt tolerance test of Serratia marcescens CZJ4

[0055] Preparation of Serratia marcescens CZJ4 seed culture: Single colonies of strain CZJ4 were picked and inoculated into LB liquid medium test tubes and cultured at 28℃ and 180rpm for 24h to prepare the seed culture.

[0056] Saline-alkaline media containing 0 mmol / L, 200 mmol / L, 400 mmol / L, 600 mmol / L, and 800 mmol / L (NaCl:Na₂SO₄ = 1:1) were prepared. CZJ4 strain seed culture was inoculated at a 3% inoculum and cultured for 40 h. The growth curves of strain CZJ4 at different salt concentrations were then determined. The growth curves are shown below. Figure 3 As shown.

[0057] Depend on Figure 3 It can be seen that the time required for strain CZJ4 to enter the logarithmic phase increases with increasing salt concentration in the culture medium; the strain exhibits the best growth at a salt concentration of 200 mmol / L, entering the logarithmic phase after 2 hours of culture; the strain can tolerate a salt concentration of 600 mmol / L, and at a salt concentration of 600 mmol / L, the bacterial concentration OD200 reaches the stationary phase. 600 The value reaches 0.5 or higher.

[0058] In summary, strain CZJ4 can grow normally in culture media with salt concentrations not exceeding 600 mmol / L, maintaining stable viability and tolerance. Strain CZJ4 can also maintain its growth in culture media with a salt concentration of 800 mmol / L. This demonstrates that the strain can grow and reproduce normally and maintain its viability in high-salt culture media. This indicates that the CZJ4 strain screened in this invention can adapt to high-salt, high-osmotic-pressure environments, has a wider range of applications, and can be used for the biological treatment of high-salt wastewater and the improvement of saline-alkali soils.

[0059] Example 3: Determination of nitrogen fixation, phosphorus solubilization, phosphorus lysis, and siderophore production performance of Serratia marcescens CZJ4

[0060] (1) Test method for nitrogen fixation

[0061] Nitrogen-free medium test: Pick a small number of single colonies of strain CZJ4, streak them on a plate of nitrogen-free medium, and observe whether the strain can grow and form colonies on nitrogen-free medium.

[0062] Nitrogenase activity assay (acetylene reduction method): Seed culture of strain CZJ4 was inoculated into LB liquid medium at a 3% inoculum and cultured at 28℃ and 180 rpm for 24 h with shaking. The culture was then transferred to centrifuge tubes and centrifuged at 4℃ and 8000 rpm for 10 min to collect the bacterial cells. The cells were washed 2-3 times with physiological saline and resuspended to adjust the OD concentration. 600 =1.0, prepare a bacterial suspension; take 1 mL of bacterial suspension and add it to a centrifuge tube containing 9 mL of nitrogen-free medium and incubate for 1 h, then measure the nitrogenase activity in the strain.

[0063] The nitrogenase activity of strain CZJ4 was determined to be 89.5503 nmol / (mL×h). This indicates that the strain possesses high nitrogenase activity.

[0064] (2) Test method for phosphorus solubility (inorganic phosphorus)

[0065] Take 5 μL of seed culture of strain CZJ4 and spot it onto the center of a Monkina inorganic phosphorus medium plate. Repeat the process 3 times and incubate at 28℃ for 3-5 days. Observe whether a clear zone is formed around the colony.

[0066] The results are as follows Figure 4 As shown, this strain produces a clear phosphorus-solubilizing zone on the phosphorus-solubilizing medium, indicating that the strain has a significant effect on solubilizing inorganic phosphorus.

[0067] (3) Test method for soluble phosphorus (organic phosphorus)

[0068] Take 5 μL of seed culture of strain CZJ4 and spot it onto the center of a Monkina organophosphate medium plate. Repeat the process 3 times and incubate at 28 ℃ for 3-5 days. Observe whether a clear zone is formed around the colony.

[0069] The results are as follows Figure 5 As shown, this strain produces a clear phosphorus-solubilizing zone on the phosphorus-solubilizing medium, indicating that the strain has a significant effect on solubilizing organic phosphorus.

[0070] (4) Detection methods for iron-producing carrier characteristics

[0071] Take 5 μL of seed culture of strain CZJ4 and spot it in the center of CAS detection medium plate. Repeat 3 times and incubate in 28℃ incubator for 3-5 days. Observe whether an orange-yellow halo is formed around the colony.

[0072] The results are as follows Figure 5As shown, this strain produces a yellow halo on the siderophore detection medium, indicating that the strain has siderophore-producing characteristics.

[0073] In summary, the *Serratia marcescens* CZJ4 strain screened in this invention possesses the characteristics of nitrogen fixation, phosphorus solubilization, phosphorus dissolution, and acting as an iron-carrier strain. It can promote the decomposition and transformation of nutrients (nitrogen, phosphorus, and iron) in the soil, which is beneficial for promoting the absorption of nutrients by plants.

[0074] Example 4: Effects of Serratia marcescens CZJ4 on the growth ability of wild barley under salt stress

[0075] Simulated saline-alkali planting system: A mixed salt solution was added to the loess culture system to simulate the saline-alkali planting environment, and the growth-promoting effect of Serratia marcescens CZJ4 on the seedling growth of wild barley was verified by an experiment.

[0076] Prepare salt solutions with salt concentrations of 0 mmol / L, 200 mmol / L, 400 mmol / L, 600 mmol / L, and 800 mmol / L (NaCl:Na2SO4=1:1).

[0077] Serratia marcescens CZJ4 was cultured in LB broth at 28°C and 180 rpm for 36 h. After culturing, bacterial cells were obtained by centrifugation at 8000 rpm for 10 min, washed once with physiological saline, and then resuspended. OD was adjusted. 600 Within the range of 0.6-0.8, this was used as a microbial inoculant for subsequent experiments.

[0078] Wild barley seeds were disinfected by soaking in 95% alcohol for 2 minutes, stirring in 1% sodium hypochlorite solution for 3 minutes, rinsing 10 times with sterile water, maintaining moisture, and germinating in the dark at 25℃ for 2 days. Germinated seeds with sprouts about 1 cm in length were selected and sown in loess pots, with two groups: a salt-treated + inoculated group and a salt-treated + uninoculated group. Nine seedlings were planted in each treatment group. After sowing, the inoculum amount of microbial agent in the salt-treated + inoculated group was 50 mL / pot, added every 3 days, repeated twice. After each addition of microbial agent, 50 mL / pot of salt solution was added. The salt-treated + uninoculated group served as an inoculation control with an equal volume of PBS buffer, and the salt solution was added in the same manner as in the salt-treated + inoculated group.

[0079] After treatment, the barley seedlings were placed in a smart greenhouse and moistened with appropriate water every two days. After 7 days of cultivation, the seedling height and dry weight of wild barley were measured to evaluate the effect of *Serratia marcescens* CZJ4 on the growth phenotype of wild barley. The results are as follows: Figures 7-8 As shown.

[0080] pass Figures 7-8It can be seen that, phenotypically, when the salt concentration is 400 mmol / L, the plants turn yellow, but the plant height is higher than that of the 600 mmol / L salt treatment. At the same salt concentration, the wild barley plant height of the salt treatment + inoculation group is significantly higher than that of the salt treatment + no inoculation group under the 0 mmol / L and 600 mmol / L salt treatments.

[0081] Significant differences were observed between the inoculated and uninoculated treatments for root length, particularly under salt stress conditions of 400 mmol / L and 800 mmol / L, with a particularly pronounced difference between the salt-treated + uninoculated group and the salt-treated + inoculated group. Data analysis showed that root length was significantly longer in low-salt or stress-free environments than under high-salt stress. Specifically, under 400 mmol / L salt stress, the root length of the inoculated group increased by approximately 25% compared to the uninoculated group, while under 800 mmol / L salt stress, the increase was approximately 18%. This indicates that *Serratia marcescens* CZJ4 significantly promotes root growth in wild barley under salt stress. Further analysis of root length trends under different salt concentrations revealed that root length generally decreased with increasing salt concentration, but the inoculated group mitigated this trend to some extent, allowing wild barley to maintain relatively good root growth even at higher salt concentrations.

[0082] The fresh and dry weight data of biomass showed significant differences between the inoculum-treated and untreated groups under salt stress, indicating that inoculum treatment effectively promotes the growth of wild barley in a saline-alkali environment. Analysis of the fresh and dry weight of biomass revealed that with increasing salt concentration, the biomass of the untreated group decreased significantly, while the decrease in the inoculum-treated group was relatively smaller. This suggests that *Serratia marcescens* CZJ4 not only enhances the biomass accumulation of wild barley under salt stress but also strengthens its adaptability to high-salt environments.

[0083] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A strain of Serratia marcescens CZJ4, characterized in that, This strain was deposited on October 20, 2025, at the China General Microbiological Culture Collection Center (CGMCC), located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, with accession number CGMCC No. 36254.

2. The application of Serratia marcescens CZJ4 as described in claim 1 in the preparation of microbial inoculants.

3. A microbial inoculant, characterized in that, The microbial agent includes Serratia marcescens CZJ4 as described in claim 1.

4. The microbial agent according to claim 3, characterized in that, The preparation method of the microbial agent includes culturing Serratia marcescens CZJ4 in a culture medium, collecting the bacterial cells by centrifugation, washing and resuspending, and adjusting the OD. 600 The step of obtaining the microbial inoculant by boiling it to 0.6-0.8 is called the step of boiling it to 0.6-0.

8.

5. The application of Serratia marcescens CZJ4 as described in claim 1 or the microbial agent as described in claim 3 in promoting the growth of crops in saline-alkali land.

6. The application according to claim 5, characterized in that, The agricultural plant in question is wild barley.

7. The use of Serratia marcescens CZJ4 as described in claim 1 or the microbial agent as described in claim 3 in the preparation of products that promote the growth of crops in saline-alkali land.

8. The application according to claim 7, characterized in that, Promote the growth of crops in saline-alkali land by increasing the root length, plant height, biomass fresh weight, and dry weight of crops.

9. A product that promotes the growth of crops in saline-alkali land, characterized in that, The product includes Serratia marcescens CZJ4 as described in claim 1 or the microbial agent as described in claim 3.

10. A method for promoting the growth of crops in saline-alkali land, characterized in that, The method includes the step of applying the Serratia marcescens CZJ4 of claim 1, the microbial agent of claim 3, or the product of claim 9 to saline-alkali land crops.

Images