Endophytic fungus yt15-1 in gomphus and application thereof

Abstract

The application discloses endophytic fungus YT15-1 of Genus Xylaria and application thereof, and belongs to the technical field of microorganisms. Sarocladium strictum The endophytic fungus YT15-1 of Genus Xylaria is isolated from the root system of Sonchus arvensis L., is classified and named as YT15-1, is preserved in the China Center for Type Culture Collection, and has a preservation number of CCTCC NO: M 20252189. The endophytic fungus YT15-1 can colonize the root system of rice by being co-cultured with the rice, and can effectively enhance the salt stress resistance of the rice seedling stage. Under the condition of high salt stress, compared with a control group, the stem and leaf height, root length and stem and leaf fresh weight of the strain treatment group of the endophytic fungus YT15-1 are increased by 75.54%, 214.71% and 52.63% respectively.

Description

Technical Field

[0001] This invention relates to the field of microbial technology, specifically to an endophytic fungus of the genus Cladosporium YT15-1 and its applications. Background Technology

[0002] rice( White rice Rice (L.) is an important grain widely cultivated in tropical Asia, but it is quite sensitive to salt stress. Salt stress adversely affects rice from seed germination to reproductive growth, impacting root growth. High concentrations of sodium (Na₂O) further exacerbate this problem. + Cl - Osmotic stress caused by ions hinders the absorption of nutrients by rice, leading to a decline in quality and yield, and in severe cases, plant death. Saline-alkali land, as a reserve arable land resource, has vast potential for development and utilization. Traditional improvement measures, such as engineering desalination and the use of chemical amendments, are costly, prone to repetition, and easily cause secondary salinization. Therefore, green and sustainable biological solutions are urgently needed.

[0003] Microbial inoculants, as an emerging biological improvement measure, possess great potential due to their environmental friendliness and high ecological benefits. Microbial agents directly improve the adverse rhizosphere growth environment of plants in saline-alkali soils by leveraging the multiple functions of salt-tolerant microorganisms, effectively mitigating the adverse effects of soil salinization stress on crop growth. They can also work in conjunction with plants to improve the fertility of saline-alkali soils. Furthermore, utilizing endophytic growth-promoting strains to establish a harmonious symbiotic relationship with plants and enhance crop resistance to salt stress is also an effective solution for ensuring crop cultivation in saline-alkali lands.

[0004] Plant endophytic strains are non-pathogenic microorganisms that can infect and colonize healthy plant tissues at least part of their life cycle, and maintain a very stable, long-term interactive relationship with the host plant. In the process of forming a mutualistic symbiotic relationship between plant endophytic strains and their hosts, on the one hand, plant endophytic strains obtain nutrients such as water and minerals necessary for growth from the host; on the other hand, they endow the plant with a rich variety of biological functions, such as promoting plant growth, increasing plant biomass, and enhancing the host plant's resistance to biotic and abiotic stresses.

[0005] Patent document CN118126891A discloses a strain of Bacillus belye C5 and its fermentation broth, which can significantly improve the salt tolerance of rice. However, bacterial biocontrol agents have shortcomings such as poor colonization stability and short field persistence. In contrast, fungal mycelia can penetrate plant cell walls to form typical intracellular or intercellular colonization structures and survive in the host for a long time. Their stress resistance, secondary metabolic diversity, and ecological adaptability are significantly superior to bacteria. However, the exploration of salt-tolerant endophytic fungal resources for rice in saline-alkali land is still scarce, and strains with industrialization potential and supporting biological agents have not yet formed a complete technical system. Therefore, it is necessary to screen and develop novel endophytic fungal strains that can stably colonize in saline-alkali environments and significantly improve the salt tolerance of rice.

[0006] Broom mold ( Sarocladium ) belongs to the order Hypocreales ( Hypocrisy According to reports, genetic studies of strains of this genus show that their endophytic fungi can release volatile substances that inhibit pathogens and cyclosporine-like compounds, and activate the host plant's disease resistance. Patent document CN117165449A discloses *Bryum oryzae* isolated from rice. Sarocladium oryzae JZ4 can be used to control rice blast fungus. Currently, there are no reports of strains of this genus enhancing host plant resistance to salt stress. Summary of the Invention

[0007] The purpose of this invention is to provide a microorganism that can improve the salt tolerance of rice and develop it into a bio-fertilizer for stress resistance and prevention in rice.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention isolates a new strain of the genus *Broomia* from the root system of *Sonchus oleraceus* originating from Yantan Village, Weihai City, Shandong Province. Sarocladium The endophytic fungus YT15-1 exhibits the following biological characteristics: slow colony growth on PDA plates, reaching a diameter of 3.7 cm after 10 days of growth at 25°C; underdeveloped aerial hyphae, creeping along the culture medium surface or appearing as thin, cottony ridges with a flocculent texture; pale orange colonies; slender, transparent hyphae, 1.0-2.5 µm wide, branched and septate; conidia oblong, unicellular, 2-6 µm × 1-1.5 µm. The ITS sequence of this strain is shown in SEQ ID No. 1, and is similar to GenBank accessions MF077236.1 and KC172080.1 (both...). Sarocladium strictum The coverage and similarity of ITS rDNA were 100%. By constructing a five-gene phylogenetic tree of ITS-SSU-LSU-TEF1-MCM7 for this strain and its closely related species, the strain and... Sarocladium strictum The type strain F45 constitutes a monophyletic branch (MLBS 83%) and is located in SarocladiumIt belongs to the core branch.

[0010] Based on morphological and molecular identification, YT15-1 belongs to the kingdom Fungi ( ). Fungi Ascomycota ( Ascomycota ), class of fecal scabies ( Sordariomycetes ), Sarcophyceales ( Hypocrisy ), Sarcoptaceae ( Hypocreaceae ), genus Cladosporium ( Sarocladium Therefore, this strain was classified and named... Sarocladium strictum YT15-1 was deposited on October 9, 2025, at the China Center for Type Culture Collection (CCTCC), Wuhan University, Wuhan, China, with accession number CCTCC NO: M 20252189.

[0011] Furthermore, the culture medium for the endophytic fungus YT15-1 of the genus Cladosporium is potato dextrose agar (PDA) medium, and the culture conditions are dark culture at 20-25℃.

[0012] This invention has found that the endophytic fungus YT15-1 of the genus Cladosporium has a strong ability to colonize roots. When co-cultured with rice plants, the hyphae can penetrate cells and colonize the epidermis, cortex and stele cell layer of the root system.

[0013] Further research revealed that colonizing the endophytic fungus YT15-1 of the genus Cladosporium into the root tissue of rice significantly alleviated the inhibitory effect of high salt stress on rice growth and enhanced the rice's adaptability to adverse environments.

[0014] Therefore, the present invention provides the application of the aforementioned endophytic fungus YT15-1 of the genus Cladosporium in improving the salt stress tolerance of rice.

[0015] Furthermore, the application includes co-culturing the endophytic fungus YT15-1 of the genus *Pterocarya* with rice, allowing the strain to colonize the root tissue of rice plants to alleviate the inhibitory effect of salt damage on rice growth. By colonizing the strain in the root tissue of rice, the salt tolerance of rice is enhanced, and the growth status of rice is improved.

[0016] Furthermore, the co-culture conditions were: 22-25℃, 16 h light / 8 h dark for 15-20 days. Through co-culture, the endophytic fungus YT15-1 of the genus *Cladosporium* colonized the root tissue of rice, forming a mutualistic symbiotic relationship.

[0017] This invention provides a formulation of the endophytic fungus YT15-1 from the genus *Pleurotus*, which is then prepared into a solid microbial fertilizer. The preparation method of the solid microbial fertilizer includes: inoculating the activated endophytic fungus YT15-1 into a liquid fermentation medium, culturing it at 22-25℃ and 100-150 rpm for 7 days; adding 100 mL of fermentation broth per 500 g of wheat grains; and then incubating in the dark at 22-25℃ until the mycelium covers the wheat grains, thus obtaining the solid microbial fertilizer.

[0018] The liquid fermentation medium consists of: 4 g / L soybean meal, 10 g / L corn flour, 0.5 g / L magnesium sulfate, and 1 g / L dipotassium hydrogen phosphate.

[0019] The activation method includes: inoculating the endophytic fungus YT15-1 of the genus Cladosporium into PDA medium and culturing it in the dark at 22-25℃ for 5-7 days.

[0020] The solid microbial fertilizer can be applied by mixing it into the seedling substrate, sowing the germinated crop seeds into the seedling substrate containing the endophytic fungus YT15-1 of the genus Cladosporium, and during the co-cultivation process, the strain colonizes the root tissue of the crop, thereby improving the crop's salt tolerance.

[0021] The present invention also provides the application of the solid microbial fertilizer YT15-1 of the endophytic fungus of the genus Cladosporium in improving the salt stress tolerance of rice, the application comprising: mixing the solid microbial fertilizer into the rice planting substrate.

[0022] Furthermore, the solid microbial fertilizer is applied during rice seedling cultivation. Specifically, germinating rice seeds are sown into a seedling substrate mixed with the solid microbial fertilizer and cultured at 22-25°C under 16 hours of light / 8 hours of darkness, allowing the bacterial strain to colonize the root tissue of the rice plants.

[0023] The beneficial effects of this invention are as follows:

[0024] This invention provides a new strain of *Cladosporium* ( Sarocladium strictum The strain YT15-1, when co-cultured with rice, can colonize the root tissue of rice and effectively enhance the resistance of rice seedlings to salt stress. Under high salt stress conditions, compared with the control group, the stem and leaf height, root length, and fresh weight of stems and leaves in the YT15-1 treatment group increased by 75.54%, 214.71%, and 52.63%, respectively, showing significant differences. Attached Figure Description

[0025] Figure 1 The images show the colony morphology of YT15-1 cells grown on PDA medium for 10 days. A is a front view of the colony, and B is a back view.

[0026] Figure 2 Images show the hyphae and spore morphology of YT15-1 under a microscope. Image A is at 50 µm scale bar, and image B is at 20 µm scale bar.

[0027] Figure 3 Images show the hyphae and spore morphology of YT15-1 under a scanning electron microscope. A and B are images from different fields of view.

[0028] Figure 4 This is a phylogenetic tree of the five genes ITS-SSU-LSU-TEF1-MCM7 in YT15-1. The tree was constructed by concatenating five sequence datasets (ITS, SSU, LSU, TEF1, and MCM7) after MAFFT alignment and TrimAl pruning. The topology is based on the maximum likelihood (ML) inference from the IQ-TREE (PhyloSuite platform); branch values ​​represent ML bootspin support (MLBP, 1000 replicates). The scale bar represents a 0.1 nucleotide substitution site.

[0029] Figure 5 Image of YT15-1 colonized on the roots of rice after electron microscopy with false-color processing. Scale bar is 20 µm.

[0030] Figure 6 This study tested the salt tolerance of YT15-1 strain co-cultured with rice. Figure A shows the effect of YT15-1 strain treatment on rice seedling growth on MS medium with a sodium chloride concentration of 0.3 mol / L. Figures B through D are bar charts showing the effects of YT15-1 strain treatment on root length, stem and leaf height, and seedling fresh weight (data analyzed by independent samples t-test; *, ***, and **** represent independent samples t-test data, respectively). P <0.05, P <0.001, P (Significant difference at the level <0.0001); Blank control was no salt stress treatment without inoculation with YT15-1 strain, NaCl was salt stress treatment without inoculation with YT15-1 strain, and NaCl+YT15-1 was salt stress treatment with inoculation with YT15-1 strain.

[0031] Figure 7 This figure shows the results of a pot experiment in which YT15-1 solid microbial fertilizer improved the growth of rice under salt stress. Figure A shows the effect of strain YT15-1 on improving rice salt stress; Figures B and C are bar charts showing the root length and fresh weight of rice in the control and treatment groups, respectively (data analyzed by independent samples t-test, ** and *** represent independent samples t-test data, respectively). P <0.01 and P(Significant difference at the level <0.001); Blank control was no salt stress treatment without inoculation with YT15-1 strain, NaCl was salt stress treatment without inoculation with YT15-1 strain, and NaCl+YT15-1 was salt stress treatment with inoculation with YT15-1 strain. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the invention are within the scope of the invention.

[0033] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0034] The tested endophytic fungus, *Cladosporium* strain YT15-1, was isolated from the roots of *Sonchus oleraceus* from Yantan Village, Weihai City, Shandong Province. This strain is deposited at the China Center for Type Culture Collection (CCTCC), Wuhan University, Wuhan, China, with accession number CCTCC NO: M 20252189.

[0035] Test plant: Rice White rice L., a common variety, CO39.

[0036] Example 1: Isolation and identification of Cladosporium strain YT15-1

[0037] I. Isolation and Culture of Strains

[0038] 1. Strains Isolation

[0039] (1) Collect samples of sow thistle from Shandong Province, rinse the roots of sow thistle with tap water to wash away soil particles and attached substances on the surface;

[0040] (2) Select healthy root tissues for surface disinfection. Disinfect with 75% alcohol for 2 min, then disinfect with 1% sodium hypochlorite for 4-5 min, and finally rinse with sterile distilled water 4-5 times to remove residual sodium hypochlorite solution.

[0041] (3) Cut the disinfected roots into 5 mm long segments;

[0042] (4) Pour 15 mL of sterilized potato dextrose agar (PDA) medium (with chloramphenicol added to the medium to reach 50 mg / L to inhibit bacterial growth) into 7 cm petri dishes after cooling to 50-60℃; after the medium has cooled and solidified, use tweezers to transfer the cut root segments into the medium for incubation.

[0043] (5) Invert the petri dish and incubate it in a constant temperature incubator at 25℃. After 3-7 days of incubation, pick the hyphae of a single colony and place them on a new PDA plate.

[0044] PDA medium: Each liter contains 20 g glucose, 200 g potato, and 15 g agar. Weigh the required amount of potato according to the volume of the medium to be prepared, boil it in water, mash and dissolve it, filter it, add glucose and agar, and autoclave at 121°C for 20 min.

[0045] A strain, designated YT15-1, was isolated from the root system of *Sonchus oleraceus* from Shandong.

[0046] 2. Culture of strain YT15-1

[0047] The YT15-1 strain was inoculated onto PDA solid medium for activation culture and cultured in the dark at 25°C for 7 days for later use.

[0048] II. Strain Identification

[0049] 1. Morphological identification

[0050] After isolation and purification, strain YT15-1 was inoculated onto PDA medium and cultured at 25°C for 10 days. A small amount of bacterial cells was picked up with a needle, prepared onto a glass slide, and observed, measured, and photographed under a microscope.

[0051] Colony growth status as follows Figure 1 As shown, the colonies grow slowly on PDA plates, reaching a diameter of 3.7 cm after 10 days of growth at 25°C; the aerial hyphae are underdeveloped, creeping along the surface of the culture medium or appearing as thin, cottony ridges with a flocculent texture, and the colonies are light orange in color.

[0052] Mycelial and conidial morphology as follows Figure 2 and Figure 3 As shown, the hyphae are slender, transparent, 1.0-2.5µm wide, branched and without septa; conidiophores are solitary and unbranched; conidia are oblong, unicellular, 2-6 µm × 1-1.5 µm.

[0053] 2. Molecular identification

[0054] (1) DNA extraction

[0055] After culturing strain YT15-1 on a PDA plate at 25℃ for 7 days, mycelia were scraped from the plate with a toothpick and placed into a sterile 1.5 mL centrifuge tube containing 300 μL of extraction buffer. The extraction buffer formulation was: 1 M KCl, 100 mM Tris-HCl, 10 mM EDTA, pH=8.0. The picked mycelia were ground using an electric grinder, and then 300 μL of extraction buffer was added, followed by vigorous shaking for 2 min. The tube was then centrifuged at 10000 rpm for 10 min. The supernatant was collected and transferred to a new centrifuge tube, and the precipitate was discarded. An equal volume of isopropanol (analytical grade) was added to the supernatant, and the mixture was gently inverted several times. The tube was then centrifuged at 12000 rpm for 10 min to precipitate the nucleic acid. The supernatant was gently discarded, and the centrifuge tube containing the precipitate was inverted on absorbent paper to drain excess water. Then, 300 μL of 70% ethanol was added, and the mixture was gently inverted several times. The tube was then centrifuged at 12000 rpm for 2 min. After 1 minute, gently pour off the supernatant and repeat the washing step once; invert the centrifuge tube on absorbent paper to drain the water, and place it at 37℃ for 15 minutes to allow the ethanol to evaporate completely; resuspend the precipitate with 50 μL ddH2O to obtain YT15-1 genomic DNA at a concentration of 30 ng / μL.

[0056] (2) PCR amplification of fungal ITS rDNA gene

[0057] PCR amplification was performed in a 50 μL reaction system containing: 2 μM each of forward and reverse primers, 200 μM dNTPs, 1.5 mM MgCl2, 5 μL 10×PCR buffer, 2 μL template DNA, and 2 U Taq enzyme.

[0058] The upstream primer ITS1 sequence is: 5′-TCCGTAGGTGAACCTGCGG-3′ (SEQ ID No. 2).

[0059] The downstream primer ITS4 sequence is: 5′-TCCTCCGCTTATTGATATGC-3′ (SEQ ID No. 3).

[0060] PCR amplification was performed on a Lange MG96G PCR instrument. Reaction conditions: 94℃ pre-denaturation for 2 min, followed by 35 cycles of: 94℃ denaturation for 30 sec, 55℃ annealing for 40 sec, 72℃ extension for 1 min, and a final extension at 72℃ for 10 min.

[0061] (3) Recovery and purification of PCR products

[0062] After the PCR reaction was completed, the PCR products were detected by 1% agarose gel electrophoresis. Then, the DNA gel purification kit from Aspirin Biotechnology Co., Ltd. was used, following the instructions in the kit's manual. The steps are as follows:

[0063] Add 50 μL of PCR product to the wells of a 1% agarose gel and electrophoresis at 5 V / CM for 30 min. After electrophoresis, cut the gel containing the target DNA fragment under UV light and place it in a 2 mL centrifuge tube, then weigh it. Add DE-A buffer to the 2 mL centrifuge tube containing the gel, following the standard of adding 3 mL of DE-A buffer per 1 mg of gel. Incubate at 75℃ for 10 min, shaking several times until completely dissolved. Add 0.5 times the volume of DE-A buffer (DE-B buffer) and mix well. Transfer the mixture to the 2 mL centrifuge tube and centrifuge at 12000 rpm for 1 min, discarding the supernatant. Return the DNA preparation tube to the 2 mL centrifuge tube, add 500 μL of buffer W1, and centrifuge at 12000 rpm for 30 s. Return the DNA preparation tube to the 2 mL centrifuge tube, add 700 μL of buffer W2, and centrifuge at 12000 rpm for 30 s. Repeat this step once; place the DNA preparation tube back into a 2 mL centrifuge tube and centrifuge at 12000 rpm for 2 min. Drain the washing buffer from the membrane; place the DNA preparation tube back into a 2 mL centrifuge tube, add 50 μL of ddH2O, centrifuge at 10000 rpm for 1 min to elute the DNA, and store at -20℃.

[0064] (4) Gene sequencing and sequence analysis

[0065] The purified and recovered target DNA fragment, after electrophoresis detection, was sent to Shanghai Sangon Biotech for sequencing using an ABIPRIS MA377 automated sequencer. After rigorous verification, the sequencing results yielded a DNA fragment sequence of 552 bp, as shown in SEQ ID No. 1.

[0066] On the NCBI website, the determined nucleotide sequence was searched and compared with homologous or similar nucleotide sequences in the GenBank database using BLAST. After BLAST alignment, the sequence showed 100% coverage and 100% similarity with accession numbers MF077236.1 and KC172080.1. These two sequences are from the genus *Cladosporium* (…). Sarocladium strict The results indicate that the molecular identification was consistent with the morphological identification.

[0067] By constructing a five-gene phylogenetic tree of this strain and its closely related species, ITS-SSU-LSU-TEF1-MCM7 ( Figure 4 ), strain YT15-1 and Sarocladium strictum The type strain F45 constitutes a monophyletic branch (MLBS 83%) and is located in Sarocladium It belongs to the core branch.

[0068] Based on the multi-gene topology and high support value, YT15-1 was confirmed to belong to the kingdom Fungi ( ). Fungi Ascomycota ( Ascomycota ), class of fecal scabies ( Sordariomycetes ), Sarcophyceales ( Hypocrisy ), Sarcoptaceae ( Hypocreaceae ), genus Cladosporium ( Sarocladium ).

[0069] Therefore, strain YT15-1 was named Sarocladium strictum YT15-1 was deposited at the China Center for Type Culture Collection (CCTCC) on October 9, 2025, at Wuhan University, Wuhan, China, with accession number CCTCC NO: M20252189, and was confirmed to be viable on October 16, 2025.

[0070] Example 2: Co-culture of YT15-1 strain with rice roots

[0071] Test plant: Rice White rice L., a common variety, CO39.

[0072] After removing the husks, rice seeds were placed in Erlenmeyer flasks and surface-sterilized with 1% NaClO for 15 min. They were then rinsed three times with sterile water before use. The sterilized seeds were evenly spread on 1 / 2 MS (Murashige and Skoog) medium, sealed with Parafilm, and placed in a 25°C plant incubator (16 h light / 8 h dark). After 3 days, when the seeds began to sprout, they were transferred to tissue culture flasks containing 0.3 M NaCl medium, 10 seeds per flask. Five YT15-1 mycelial blocks (0.5 cm in diameter) were inoculated simultaneously. A sterile PDA agar block served as the control group. Three replicates were performed. When the rice seedlings reached the three-leaf stage (15-20 days), root length, stem length, and fresh weight of stems and leaves were measured. Simultaneously, the colonization of endophytic fungi in the roots was observed using SEM (scanning electron microscopy), and pseudo-color processing was performed using Photoshop.

[0073] Colonization status such as Figure 5As shown, by sectioning and observing the root tissue of rice after co-culture treatment using SEM scanning electron microscopy, we can confirm that YT15-1 has formed a symbiotic relationship with rice, exhibiting a strong ability to colonize roots. The hyphae can penetrate cells and colonize the epidermis, cortex, and stele cell layer of the root system.

[0074] Rice plant growth status as follows Figure 6 As shown, rice seedlings in the NaCl-treated group exhibited severely inhibited growth, stunted plants, and yellowing leaves, indicating that normal physiological metabolism in rice was significantly suppressed under salt stress, with typical stress-induced damage phenotypes observed in both the aboveground parts and roots. In contrast, rice seedlings in the NaCl and YT15-1 co-treatment group showed vigorous growth, with dark green leaves and well-developed root systems. Compared to the NaCl-treated group, the NaCl and YT15-1 co-treatment group showed a 75.54% increase in stem and leaf height, a 214.71% increase in root length, and a 52.63% increase in fresh stem and leaf weight. This demonstrates that strain YT15-1 can significantly alleviate the inhibitory effect of stress on rice growth, enhancing rice's adaptability to adverse environments by promoting root elongation and aboveground biomass accumulation.

[0075] Example 3: The role of YT15-1 solid microbial fertilizer in improving salt stress tolerance in potted rice

[0076] Test plant: Rice White rice L., a common variety, CO39.

[0077] The YT15-1 strain was inoculated onto potato dextrose agar (PDA) solid medium for activation and cultured in the dark at 25°C for 7 days. Mycelial cakes (5 cakes) were then collected using a 0.5 cm diameter punch and inoculated into Erlenmeyer flasks containing 500 mL of liquid fermentation medium. These flasks were then incubated on a shaker (25°C, 150 rpm) for 7 days. The liquid fermentation broth was then inoculated into sterile wheat grain culture bottles (500 g wheat grains / bottle, 100 mL fermentation broth: 500 g wheat grains) and cultured in a dark incubator at 25°C for 10-15 days until the mycelium had completely covered the wheat grains.

[0078] PDA medium: glucose 20 g / L, potato 200 g / L, agar 15 g / L. Weigh the required amount of potato (200 g / L) according to the volume of the medium to be prepared, boil it in water, mash and dissolve it, filter it, add glucose and agar, and autoclave at 121℃ for 20 min.

[0079] Liquid fermentation medium: 4 g / L soybean meal, 10 g / L corn flour, 0.5 g / L magnesium sulfate, and 1 g / L dipotassium hydrogen phosphate. Weigh the required reagents according to the volume of the medium to be prepared, dispense them into Erlenmeyer flasks, and autoclave at 121℃ for 20 min.

[0080] After mixing the fermented solid microbial fertilizer with conventional seedling substrate, the mixture is placed into nutrient pots, with each pot containing 10 g of solid microbial fertilizer. Rice seeds are disinfected by soaking them in a 3000-fold dilution of 25% cyazofamid for two days, then placed in a 30℃ dark incubator for 1-2 days to germinate. Once the seeds show signs of germination, they are evenly sown in the nutrient pots and placed in a glass greenhouse for cultivation, with normal watering management. After 7 days of growth, the rice seedlings are irrigated with a 0.3 M NaCl solution. The growth status of the rice seedlings is observed and recorded after 20 days.

[0081] The results are as follows Figure 7 As shown, under high salt concentrations, rice plants are stunted, with narrow, short leaves and yellowing tips, exhibiting significant browning. After inoculation with YT15-1 at the same salt concentration, the plant phenotype significantly improved, with elongated stems, dark green leaves, a 48.83% increase in fresh weight, and a 30.14% increase in root length.

[0082] In summary, under salt stress, strain YT15-1 can effectively alleviate the inhibitory effect of salt damage on rice, enhance the salt tolerance of rice, and improve the growth of rice.

[0083] The above description is merely a specific embodiment of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. All equivalent modifications or substitutions made based on the essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. An endophytic fungus of the genus *Cladosporium*, YT15-1, characterized in that, The endophytic fungus YT15-1 of the genus *Cladosporium* is classified as follows: Sarocladium strictum YT15-1 is deposited at the China Center for Type Culture Collection (CCTCC), accession number CCTCC NO: M 20252189.

2. The endophytic fungus YT15-1 of the genus *Cladosporium* as described in claim 1, characterized in that, The culture medium for the endophytic fungus YT15-1 of the genus Cladosporium was potato dextrose agar medium, and the culture conditions were dark culture at 20-25℃.

3. The application of the endophytic fungus YT15-1 of the genus Cladosporium as described in claim 1 or 2 in improving the salt stress tolerance of rice.

4. The application as described in claim 3, characterized in that, The application includes co-culturing the endophytic fungus YT15-1 of the genus Cladosporium with rice, so that the strain colonizes in the root tissue of rice plants to alleviate the inhibitory effect of salt damage on rice growth.

5. The application as described in claim 4, characterized in that, The co-culture conditions are: 22-25℃, 16 h light / 8 h dark culture for 15-20 days.

6. A solid microbial fertilizer containing the endophytic fungus YT15-1 of the genus Cladosporium, characterized in that, The method for preparing the solid microbial fertilizer includes: inoculating the activated endophytic fungus YT15-1 of the genus Cladosporium as described in claim 1 or 2 into a liquid fermentation medium, culturing it at 22-25℃ and 100-150 rpm for 7 days, adding 100 mL of fermentation liquid for every 500 g of wheat grains, and then culturing it in the dark at 22-25℃ until the mycelium grows and covers the wheat grains, thereby obtaining the solid microbial fertilizer; The liquid fermentation medium consists of: 4 g / L soybean meal, 10 g / L corn flour, 0.5 g / L magnesium sulfate, and 1 g / L dipotassium hydrogen phosphate.

7. The solid microbial fertilizer of *Cladosporium* endophytic fungi YT15-1 as described in claim 6, characterized in that, The activation method includes: inoculating the endophytic fungus YT15-1 of the genus Cladosporium on potato dextrose agar medium and culturing it in the dark at 22-25°C for 5-7 days.

8. The application of the solid microbial fertilizer of *Cladosporium* endophytic fungus YT15-1 as described in claim 6 or 7 in improving rice salt stress tolerance, characterized in that... The application includes mixing solid microbial fertilizer into rice planting substrate.

9. The application as described in claim 8, characterized in that, The solid microbial fertilizer is applied during rice seedling cultivation.

10. The application as described in claim 9, characterized in that, The application includes: sowing germinating rice seeds into a seedling substrate mixed with the solid microbial fertilizer, and culturing them at 22-25℃ with 16 h of light / 8 h of darkness, so that the strain colonizes in the root tissue of the rice plant.

Images