Breeding method of saline-alkali resistant cotton variety

Abstract

The invention discloses a breeding method of a cotton saline-alkali-resistant variety, and relates to the technical field of agricultural biologication.The breeding method comprises the following steps that initial salt stress concentration setting is conducted, specifically, according to physiological characteristics and salt tolerance of cotton in the seedling stage, the low initial salt concentration is set as an initial stress condition, and the initial salt stress concentration is set; according to the salt tolerance characteristics of different growth stages of cotton, a plurality of stages are finely divided, the salt concentration is dynamically adjusted in each stage, and the salt concentration is gradually increased from the initial 50 mmol / L of the seedling stage to the higher concentration of the vegetative growth stage and the reproductive growth stage; the dynamically changing salt stress gradient not only accurately simulates the actual change condition of salt in the saline-alkali soil in the natural environment, but also enables the cotton to gradually adapt to and improve the salt resistance in a gradually enhanced stress environment, so that varieties with stable salt and alkali resistance are more effectively screened out, the pertinence and success rate of breeding are greatly improved, and the method is suitable for large-scale popularization and application. And a new way is opened up for the cultivation of saline-alkali-resistant cotton varieties.

Description

Technical Field

[0001] The invention relates to the field of agricultural biotechnology, in particular to a method for breeding saline-alkali resistant cotton varieties. Background Art

[0002] With the influence of global climate change and unreasonable irrigation factors, the area of ​​saline-alkali land has continued to expand, posing a serious threat to agricultural production. As one of the world's important economic crops, the yield and quality of cotton are directly restricted by the saline-alkali environment. Therefore, breeding cotton varieties that can grow stably in saline-alkali land and have high yield and quality is of great significance to ensuring food security and promoting sustainable agricultural development. In recent years, with the rapid development of molecular biology and genetic biotechnology, the breeding technology of salt-alkali resistant cotton varieties has also made significant progress.

[0003] In the process of breeding salt-alkali resistant cotton varieties, salt stress treatment is an important means of screening salt-resistant materials. However, traditional technologies often have many shortcomings in this link. In the past, researchers may only use a few fixed salt concentrations for stress treatment. This method ignores the differences in salt tolerance of cotton at different growth stages, and cannot fully simulate the complexity of salt changes in saline-alkali land over time and environment. Therefore, the selected varieties often show low adaptability and stability in practical applications. Specifically, the fixed salt concentration cannot accurately simulate the dynamic change process of salt in saline-alkali land, resulting in the selected varieties showing weaker salt resistance when facing complex saline-alkali environments. In addition, due to the failure to fully consider the physiological changes and salt tolerance mechanisms during cotton growth, the varieties bred by traditional methods also have deficiencies in genetic stability and yield performance.

[0004] Therefore, in view of the deficiencies and shortcomings of the prior art, the present invention proposes a method for breeding salt-alkali resistant cotton varieties. By designing a multi-stage dynamic salt stress gradient, the stress stages are finely divided according to the salt tolerance characteristics of cotton at different growth stages, and the salt concentration is dynamically adjusted in each stage. This not only accurately simulates the actual changes in salt content in saline-alkali land, but also enables cotton to gradually adapt to and improve its salt resistance in the gradually increasing stress environment. Summary of the invention

[0005] The purpose of the present invention is to make up for the shortcomings of the prior art and provide a method for breeding salt-alkali resistant cotton varieties. By designing a multi-stage dynamic salt stress gradient, the method realizes the accurate simulation and gradual improvement of the salt tolerance characteristics of cotton at different growth stages. This method overcomes the limitations of fixed salt concentration treatment in traditional breeding technology, making the breeding process closer to the dynamic changes of the natural saline-alkali environment, thereby effectively improving the adaptability and stability of the bred cotton varieties in saline-alkali land.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for breeding salt-alkali resistant cotton varieties, the specific steps of the breeding method are: S100, initial salt stress concentration setting: according to the physiological characteristics and salt tolerance of cotton seedlings, a lower initial salt concentration was set as the initial stress condition; S200, multi-stage dynamic salt stress gradient design: according to the salt tolerance characteristics of cotton at different growth stages, the salt stress concentration gradient is designed and gradually increased. Starting from the initial concentration in the seedling stage, the salt concentration is gradually increased at regular intervals according to the growth status of cotton and the improvement of salt tolerance until the highest salt concentration of the target saline-alkali land is reached; S300, multi-generation salt stress treatment and breeding: select cotton germplasm resources with potential salt resistance as the initial material, and carry out stress treatment for multiple generations according to the designed multi-stage dynamic salt stress gradient. After each generation of treatment, comprehensively evaluate the growth status, yield, quality and physiological indicators of cotton plants, and select individuals with excellent performance as the breeding material for the next generation; S400, genetic stability assessment: genetic stability assessment of cotton varieties that have been bred for multiple generations, observing and recording the stability of their growth performance and yield, and selecting varieties that can maintain good growth performance and yield in different generations and different salt concentrations as the final salt-alkali resistant varieties; S500, variety promotion and application: the selected salt-alkali resistant cotton varieties will be promoted for large-scale planting in saline-alkali land.

[0007] Furthermore, in S100, the initial salt stress concentration is set by selecting salt solutions of different concentrations to test the salt tolerance of cotton seedlings, and by observing and recording the growth performance of the seedlings under different salt concentrations, the salt concentration range that the seedlings can tolerate without causing significant growth inhibition is determined, and a relatively low salt concentration is selected as the initial salt stress concentration.

[0008] Furthermore, in S100, the initial salt stress concentration is set by selecting salt solutions of different concentrations to test the salt tolerance of cotton seedlings, and by observing and recording the growth performance of the seedlings under different salt concentrations, the salt concentration range that the seedlings can tolerate without causing significant growth inhibition is determined, and a relatively low salt concentration is selected as the initial salt stress concentration.

[0009] Furthermore, the S200, multi-stage dynamic salt stress gradient design clearly divides the seedling stage, vegetative growth stage and reproductive growth stage of cotton, sets the expected target salt concentration for each stage, and designs the incremental increase and frequency of salt concentration in each growth stage, regularly monitors the growth status of cotton and the improvement of salt tolerance, and dynamically adjusts the incremental increase and time of salt concentration according to the growth status, physiological indicators and salt damage symptoms of cotton.

[0010] Furthermore, the S200, multi-stage dynamic salt stress gradient design sets the initial salt stress concentration of the cotton seedling stage to 50mmol / L NaCl solution, evaluates the growth of the seedlings every week, and the seedlings grow normally within one week without obvious symptoms of salt damage. At the end of the second and third weeks, the salt concentration is gradually increased to 70mmol / L and 100mmol / L, respectively.

[0011] Furthermore, the S200, multi-stage dynamic salt stress gradient design, cotton receives a salt concentration of 100mmol / L at the end of the seedling stage in the early stage of the vegetative growth period, and monitors and evaluates the plant branching, leaf quantity and size changes and root development in detail every week. If the cotton plants grow vigorously, the salt concentration is increased to 130mmol / L at the end of the second week, and then gradually increased to 150mmol / L at a rate of 10-20mmol / L every 2 weeks under good growth conditions. In the late stage of the vegetative growth period, the treatment is continued based on 150mmol / L, and the growth performance and physiological indicators are comprehensively evaluated every 2 weeks. The cotton plants perform stably and the physiological indicators are normal. At the end of the second week, the salt concentration is increased to 170-180mmol / L, and then gradually increased to 200mmol / L at a rate of 20-30mmol / L every 1-2 weeks according to the adaptation situation.

[0012] Furthermore, the S200 multi-stage dynamic salt stress gradient design takes the salt concentration in the late vegetative growth period as the starting point after entering the reproductive growth period, evaluates the bud development, the overall growth status of the plant and the salt stress adaptation performance every 2 weeks in the bud stage, increases the salt concentration by 20-30mmol / L at the end of the second week, closely observes the flower opening, quantity and quality and plant response after entering the flowering period, increases the salt concentration by 10-20mmol / L every 1-2 weeks according to the actual situation, and fine-tunes the salt concentration every week according to the growth status of the cotton bolls and the salt tolerance of the plants after entering the boll stage, so as to gradually approach the maximum salt concentration of the target saline-alkali land, while always paying close attention to the growth and yield performance of cotton.

[0013] Furthermore, the S300, multi-generation salt stress treatment and breeding selects cotton germplasm resources with potential salt resistance as initial breeding materials, and implements salt stress treatment according to a multi-stage dynamic salt stress gradient on them and their offspring for multiple generations. After each generation of treatment, the growth condition, yield, quality and physiological indicators of the cotton plants are comprehensively evaluated. According to the evaluation results, individuals with excellent performance are selected as the next generation breeding materials, and the multi-generation breeding process is repeated, and the salt stress gradient and breeding strategy are continuously optimized according to the feedback of each generation until a new cotton variety with stable genetics, high salt resistance, high yield and high quality is successfully bred.

[0014] Furthermore, the S400, genetic stability assessment, selects representative samples from cotton varieties that have undergone multi-generation salt stress treatment and breeding, plants the samples and conducts unified field management, regularly records and analyzes growth performance data and harvest yield data, calculates genetic stability indicators based on the data and combines comprehensive evaluation of multi-condition performance, selects excellent varieties and then conducts result verification tests.

[0015] Furthermore, the S400, genetic stability assessment, strictly controls light, temperature, and humidity during unified field management to ensure that the environmental conditions between groups are consistent.

[0016] Compared with the prior art, the breeding method of the cotton salt-alkali resistant variety has the following beneficial effects: 1. The present invention divides the cotton into multiple stages according to its salt tolerance in different growth stages, and dynamically adjusts the salt concentration in each stage, gradually increasing from the initial 50 mmol / L in the seedling stage to higher concentrations in the vegetative growth stage and the reproductive growth stage. This dynamically changing salt stress gradient not only accurately simulates the actual changes in salinity in saline-alkali land in the natural environment, but also enables cotton to gradually adapt to and improve its salt resistance in the gradually increasing stress environment, thereby more effectively screening out varieties with stable salt-alkali resistance, greatly improving the pertinence and success rate of breeding, and opening up a new way for the cultivation of salt-alkali-resistant cotton varieties.

[0017] 2. The multi-stage dynamic salt stress gradient design in the present invention not only optimizes the stress treatment method, but also significantly improves the breeding efficiency and variety adaptability. By gradually increasing the salt concentration, cotton plants gradually accumulate the physiological mechanism and genetic basis for coping with high-salt environment in continuous stress treatment. This gradual adaptation process enables the bred varieties to not only maintain stable growth and yield under high salt concentration, but also have stronger environmental adaptability and genetic stability. Compared with traditional methods, this method can complete multiple generations of breeding in a shorter time, and the bred varieties are more adaptable to complex saline-alkali land environments, providing strong variety support for the agricultural utilization of saline-alkali land.

[0018] Other advantages, objectives and features of the present invention will be set forth in part in the following description and, in part, will be apparent to those skilled in the art based on an examination of the following or may be taught from the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 The present invention is a flow chart of a method for breeding salt-alkali resistant cotton varieties. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example

[0022] This embodiment provides a method for breeding saline-alkali resistant cotton varieties, comprising the following steps: S100, initial salt stress concentration setting. The salt tolerance of seedlings of 10 collected cotton germplasm resources was tested. The seedlings were planted in seedling media containing different concentrations of NaCl solution (30mmol / L, 40mmol / L, 50mmol / L, 60mmol / L). After one week of observation, it was found that when the concentration of NaCl solution was 50mmol / L, the seedlings grew normally, with only a few leaves showing slight curling on the edges, and the overall growth rate was not significantly affected. Therefore, 50mmol / L was determined as the initial salt stress concentration.

[0023] S200, multi-stage dynamic salt stress gradient design: Seedling stage (weeks 1-4): Start with 50mmol / L NaCl solution and observe the growth of seedlings every week. At the end of the second week, due to the good growth of seedlings, the salt concentration was increased to 70mmol / L. At the end of the third week, it was further increased to 90mmol / L. At the end of the fourth week, the seedlings were still strong, so the salt concentration was further increased to 100mmol / L. Vegetative growth period (weeks 5-12): Early stage (weeks 5-8): Continue with the 100mmol / L salt concentration at the end of the seedling stage, monitor plant growth every week, at the end of the 6th week, due to vigorous plant growth, increase the salt concentration to 120mmol / L, and then gradually increase by 15mmol / L every 2 weeks according to growth conditions, reaching 150mmol / L at the 8th week; Late stage (weeks 9-12): Based on 150mmol / L, evaluate every 2 weeks, at the end of the 10th week, the plant performance is stable, and the salt concentration is increased to 180mmol / L, and then gradually increased by 25mmol / L every 1 week to 200mmol / L according to adaptation conditions; Reproductive growth period (weeks 13-20): Bud stage (weeks 13-15): starting from 200mmol / L, evaluate every 2 weeks. At the end of week 15, if the buds develop normally, increase the salt concentration to 230mmol / L; Flowering period (weeks 16-18): closely observe the opening of flowers, increase the salt concentration by 15mmol / L every week according to the plant response; Boll stage (weeks 19-20): fine-tune the salt concentration every week according to the growth of cotton bolls, and gradually approach the maximum salt concentration of the target saline-alkali land (the maximum salt concentration of the test field was tested to be 280mmol / L).

[0024] S300, multi-generation salt stress treatment and breeding, selected 5 germplasm resources with relatively good performance in each stage from 10 germplasm resources as the first generation breeding materials, and after the first generation treatment, comprehensively evaluated the growth status, yield, quality and physiological indicators, and found that one of the cotton varieties performed outstandingly in plant height, number of bolls per plant and antioxidant enzyme activity, so it was used as the key material for the second generation breeding, and was hybridized with other individuals with better performance. During the second generation breeding process, it continued to be treated according to the multi-stage dynamic salt stress gradient, and the breeding strategy was continuously optimized according to the evaluation results. After three generations of breeding, a cotton variety with stable genetics, high salt resistance, high yield and high quality potential was finally obtained.

[0025] S400, genetic stability assessment, selected multiple samples of cotton varieties that had been bred for three generations, and planted them in test plots with different salt concentrations (200mmol / L, 250mmol / L, 300mmol / L). The area of ​​each plot was 10 square meters. The light, temperature, and humidity environmental conditions of each plot were kept consistent. The growth performance data of the cotton were regularly observed and recorded, and the yield data was measured at the harvest time. After statistical analysis, the genetic stability index of the variety under different salt concentrations was calculated. The results showed that the growth performance and yield of this variety were relatively stable under various salt concentrations, and it had good genetic stability.

[0026] S500, variety promotion and application, promotes the large-scale planting of the selected cotton variety in this experimental field and similar saline-alkali land in the surrounding area, and provides detailed planting technical guidance, including reasonable planting density, irrigation management and fertilization plan. Example

[0027] This embodiment provides a method for breeding saline-alkali resistant cotton varieties, comprising the following steps: S100, initial salt stress concentration setting. The salt tolerance of seedlings of 8 cotton varieties was tested. NaCl solutions of different concentrations (40mmol / L, 50mmol / L, 60mmol / L) were set for irrigation. After one week of observation, it was found that when the concentration of NaCl solution was 50mmol / L, although the seedlings of various varieties had a certain growth pressure, they could still maintain the basic growth trend and there was no large-scale death. Therefore, 50mmol / L was determined as the initial salt stress concentration.

[0028] S200, multi-stage dynamic salt stress gradient design: Seedling stage (weeks 1-3): start with 50mmol / L NaCl solution and observe the growth of seedlings every 2 days. At the end of the 3rd week, increase the salt concentration to 80mmol / L based on the growth performance of the seedlings. Vegetative growth period (weeks 4-8): Early stage (weeks 4-6): Based on 80mmol / L, evaluate the growth of the plants every week. At the end of the 5th week, if the plants grow well, increase the salt concentration to 110mmol / L, and then gradually increase it to 140mmol / L by 10mmol / L every 2 weeks according to the growth status; Late stage (weeks 7-8): Starting from 140mmol / L, conduct a comprehensive evaluation every 2 weeks. At the end of the 8th week, if the plants perform stably, increase the salt concentration to 170mmol / L. Reproductive growth period (weeks 9-16): Bud stage (weeks 9-11): start with 170mmol / L as the salt concentration, observe the development of the flower buds every 2 weeks, and at the end of the 11th week, if the flower buds develop normally, increase the salt concentration to 200mmol / L; Flowering period (weeks 12-14): pay close attention to the opening of flowers and the growth of plants, and increase the salt concentration by 10mmol / L every week according to the actual situation; Boll stage (weeks 15-16): according to the growth of cotton bolls, carefully adjust the salt concentration every week, gradually approaching the highest salt concentration in the area (about 250mmol / L).

[0029] S300, multi-generation salt stress treatment and breeding, 8 cotton varieties and their offspring were treated with salt stress for three consecutive generations. After each generation of treatment, various indicators were comprehensively evaluated to screen out individuals with excellent performance. In the first generation, 3 varieties were found to have good performance in salt tolerance and yield. They were selected as key breeding objects for self-pollination. During the second generation breeding process, the salt stress gradient was optimized according to the evaluation results of the previous generation, which further improved the targeted breeding. After three generations of breeding, new cotton varieties that adapt to the local saline-alkali environment were cultivated.

[0030] S400, genetic stability assessment, selected multiple samples of the newly bred cotton varieties, planted in test plots with different salt concentration gradients (180mmol / L, 220mmol / L, 250mmol / L), strictly controlled the light, temperature and humidity conditions of each plot to ensure consistency, regularly recorded the growth performance and yield data of the cotton, and conducted data analysis. By calculating the genetic stability index, it was found that the variety has high stability under different salt concentrations and can adapt to the complex local saline-alkali environment.

[0031] S500, variety promotion and application, promotes the large-scale planting of this new cotton variety in local saline-alkali land, and cooperates with local agricultural departments to carry out technical training and guidance to improve farmers' planting technology. Example

[0032] This embodiment provides a method for breeding saline-alkali resistant cotton varieties, comprising the following steps: S100, initial salt stress concentration setting. The salt tolerance of seedlings of 6 cotton germplasm resources was tested. They were treated with NaCl solutions of different concentrations (45mmol / L, 50mmol / L, 55mmol / L). After a week of observation and comparison, it was found that when the concentration of NaCl solution was 50mmol / L, the growth of seedlings was affected to a certain extent, but they could still maintain a certain vitality, and the differences between various germplasm resources were relatively small. Therefore, 50mmol / L was determined as the initial salt stress concentration.

[0033] S200, multi-stage dynamic salt stress gradient design: Seedling stage (weeks 1-3): Start with 50mmol / L NaCl solution and observe the growth of the seedlings every 3 days. At the end of the second week, if the seedlings grow normally, increase the salt concentration to 65mmol / L. At the end of the third week, if the seedlings continue to adapt well, further increase it to 80mmol / L. Vegetative growth period (weeks 4-7): Early stage (weeks 4-5): Based on 80mmol / L, evaluate the growth of the plants every 2 weeks. At the end of the 5th week, if the plants are growing vigorously, increase the salt concentration to 100mmol / L, and then gradually increase it to 130mmol / L by 10mmol / L every 2 weeks according to the growth status; Late stage (weeks 6-7): Starting from 130mmol / L, conduct a comprehensive evaluation every 2 weeks. At the end of the 7th week, if the plants are stable, increase the salt concentration to 160mmol / L; Reproductive growth period (weeks 8-14): Bud stage (weeks 8-10): start with 160mmol / L as the salt concentration, observe the development of the flower buds every 2 weeks, and at the end of the 10th week, if the flower buds develop normally, increase the salt concentration to 180mmol / L; Flowering period (weeks 11-12): pay close attention to the opening of flowers and plant growth, and increase the salt concentration by 8mmol / L every week according to actual conditions; Boll stage (weeks 13-14): fine-tune the salt concentration every week according to the growth of cotton bolls, and gradually approach the highest salt concentration in the area (about 220mmol / L).

[0034] S300, multi-generation salt stress treatment and breeding, six germplasm resources and their offspring were treated with salt stress for four consecutive generations. After each generation of treatment, a comprehensive evaluation was conducted based on growth conditions, yield, quality and physiological indicators. In the first generation, two germplasm resources with relatively good performance were selected for key cultivation. In the subsequent breeding process, a combination of hybridization and self-pollination was adopted to continuously optimize the breeding materials. After four generations of breeding, a new cotton variety with high salt resistance and good adaptability was successfully bred.

[0035] S400, genetic stability assessment, selected multiple samples of the newly bred cotton varieties, planted them in test areas with different salt concentrations (150mmol / L, 180mmol / L, 200mmol / L), ensured that the light, temperature and humidity in each area were consistent, regularly recorded the growth performance and yield data of the cotton, and conducted detailed statistical analysis. By calculating the genetic stability index, the stability and adaptability of the variety under different salt concentrations were verified.

[0036] S500, variety promotion and application, is widely promoted and planted in the saline-alkali land of the inland arid area. We cooperate with local farmers and agricultural enterprises to establish demonstration fields to show the advantages and planting techniques of this new cotton variety. At the same time, we provide professional technical support and after-sales service to ensure high and stable yields of cotton.

[0037] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for breeding saline-alkali resistant cotton varieties, characterized in that: The specific steps of the breeding method are: S100, initial salt stress concentration setting: according to the physiological characteristics and salt tolerance of cotton seedlings, a lower initial salt concentration was set as the initial stress condition; S200, multi-stage dynamic salt stress gradient design: according to the salt tolerance characteristics of cotton at different growth stages, the salt stress concentration gradient is designed and gradually increased. Starting from the initial concentration in the seedling stage, the salt concentration is gradually increased at regular intervals according to the growth status of cotton and the improvement of salt tolerance until the highest salt concentration of the target saline-alkali land is reached; S300, multi-generation salt stress treatment and breeding: select cotton germplasm resources with potential salt resistance as the initial material, and carry out stress treatment for multiple generations according to the designed multi-stage dynamic salt stress gradient. After each generation of treatment, comprehensively evaluate the growth status, yield, quality and physiological indicators of cotton plants, and select individuals with excellent performance as the breeding material for the next generation; S400, genetic stability assessment: genetic stability assessment of cotton varieties that have been bred for multiple generations, observing and recording the stability of their growth performance and yield, and selecting varieties that can maintain good growth performance and yield in different generations and different salt concentrations as the final salt-alkali resistant varieties; S500, variety promotion and application: the selected salt-alkali resistant cotton varieties will be promoted for large-scale planting in saline-alkali land.

2. The method for breeding salt-alkali resistant cotton varieties according to claim 1, characterized in that: In S100, the initial salt stress concentration is set by selecting salt solutions of different concentrations to test the salt tolerance of cotton seedlings, and by observing and recording the growth performance of the seedlings under different salt concentrations, the salt concentration range that the seedlings can tolerate without causing significant growth inhibition is determined, and a relatively low salt concentration is selected as the initial salt stress concentration.

3. The method for breeding a salt-alkali resistant cotton variety according to claim 2, characterized in that: In S100, the initial salt stress concentration is set by selecting salt solutions of different concentrations to test the salt tolerance of cotton seedlings, and by observing and recording the growth performance of the seedlings under different salt concentrations, the salt concentration range that the seedlings can tolerate without causing significant growth inhibition is determined, and a relatively low salt concentration is selected as the initial salt stress concentration.

4. The method for breeding salt-alkali resistant cotton varieties according to claim 1, characterized in that: The S200, multi-stage dynamic salt stress gradient design clearly divides the seedling stage, vegetative growth stage and reproductive growth stage of cotton, sets the expected target salt concentration for each stage, and designs the incremental increase and frequency of salt concentration in each growth stage, regularly monitors the growth status of cotton and the improvement of salt tolerance, and dynamically adjusts the incremental increase and time of salt concentration according to the growth status, physiological indicators and salt damage symptoms of cotton.

5. The method for breeding salt-alkali resistant cotton varieties according to claim 4, characterized in that: The S200, multi-stage dynamic salt stress gradient design sets the initial salt stress concentration of cotton seedlings to 50mmol / L NaCl solution, evaluates the growth of seedlings every week, and the seedlings grow normally within one week without obvious salt damage symptoms. At the end of the second and third weeks, the salt concentration is gradually increased to 70mmol / L and 100mmol / L, respectively.

6. The method for breeding salt-alkali resistant cotton varieties according to claim 4, characterized in that: The S200, multi-stage dynamic salt stress gradient design, adopts the 100mmol / L salt concentration at the end of the seedling stage in the early stage of the vegetative growth period of cotton, monitors and evaluates the plant branching, leaf quantity and size changes and root development in detail every week, increases the salt concentration to 130mmol / L at the end of the second week when the cotton plants grow vigorously, and then gradually increases it to 150mmol / L at a rate of 10-20mmol / L every 2 weeks under good growth conditions, and continues to be treated on the basis of 150mmol / L in the late stage of the vegetative growth period, and comprehensively evaluates the growth performance and physiological indicators every 2 weeks. The cotton plants perform stably and the physiological indicators are normal, and at the end of the second week, increases the salt concentration to 170-180mmol / L, and then gradually increases it to 200mmol / L at a rate of 20-30mmol / L every 1-2 weeks according to the adaptation situation.

7. The method for breeding salt-alkali resistant cotton varieties according to claim 4, characterized in that: The S200 multi-stage dynamic salt stress gradient design takes the salt concentration in the late vegetative growth period as the starting point after entering the reproductive growth period, evaluates the bud development, the overall growth status of the plant and the salt stress adaptation performance every 2 weeks during the bud stage, increases the salt concentration by 20-30mmol / L at the end of the second week, closely observes the flower opening, quantity and quality and plant response after entering the flowering period, increases the salt concentration by 10-20mmol / L every 1-2 weeks according to the actual situation, and fine-tunes the salt concentration every week according to the growth status of the cotton bolls and the salt tolerance performance of the plants after entering the boll stage, so as to gradually approach the maximum salt concentration of the target saline-alkali land, while always paying close attention to the growth and yield performance of cotton.

8. The method for breeding salt-alkali resistant cotton varieties according to claim 1, characterized in that: The S300, multi-generation salt stress treatment and breeding, selects cotton germplasm resources with potential salt resistance as initial breeding materials, and subjecting them and their offspring to salt stress treatment according to a multi-stage dynamic salt stress gradient for multiple generations. After each generation of treatment, the growth status, yield, quality and physiological indicators of the cotton plants are comprehensively evaluated. Based on the evaluation results, individuals with excellent performance are screened out as the next generation of breeding materials. The multi-generation breeding process is repeated, and the salt stress gradient and breeding strategy are continuously optimized according to the feedback of each generation, until a new cotton variety with stable genetics, high salt resistance, high yield and high quality is successfully bred.

9. The method for breeding salt-alkali resistant cotton varieties according to claim 1, characterized in that: The S400, genetic stability assessment, selects representative samples from cotton varieties that have undergone multi-generation salt stress treatment and breeding, plants the samples and conducts unified field management, regularly records and analyzes growth performance data and harvest yield data, calculates genetic stability indicators based on the data and combines comprehensive evaluation of multi-condition performance, selects excellent varieties and conducts result verification tests.

10. The method for breeding salt-alkali resistant cotton varieties according to claim 1, characterized in that: The S400, genetic stability assessment was conducted during the unified field management period, with strict control of light, temperature, and humidity to ensure that the environmental conditions among the groups were consistent.

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