A method for screening low phosphorus tolerant cotton varieties

Abstract

The present application relates to the field of cotton breeding technology, and particularly relates to a method for screening low-phosphorus-tolerant cotton varieties. The present application combines the phosphorus absorption and utilization rules of cotton and the characteristics of the interaction between crop root architecture and low phosphorus, introduces the root architecture index closely related to the low-phosphorus-tolerance ability, and combines other agronomic traits to screen the low-phosphorus-tolerant cotton varieties, which can effectively improve the accuracy and efficiency of screening. Meanwhile, the present application determines the important trait indexes that have a significant influence on the low-phosphorus-tolerance ability of cotton; and based on the principal component analysis, system clustering analysis and regression analysis, a comprehensive evaluation method for the low-phosphorus-tolerant cotton types is constructed. The method has high accuracy, relatively few trait indexes, relatively simple operation and higher screening efficiency. The screening method provides a scientific theoretical basis for cultivating low-phosphorus-tolerant cotton varieties in production, and has important significance for promoting the green and sustainable development of cotton planting industry.

Description

Technical Field

[0001] This invention relates to the field of cotton variety screening technology, and in particular to a method for screening low-phosphorus tolerant cotton varieties. Background Technology

[0002] Phosphorus is one of the essential macronutrients for crop growth and development, playing a vital role in crop quality and yield. Phosphorus has a low diffusion coefficient in soil; most of the phosphate fertilizer applied to the soil is adsorbed, fixed, and precipitated into insoluble phosphates, making it difficult for crops to absorb and utilize.

[0003] Cotton is an important economic crop in my country, and phosphorus is a limiting factor for nutrients in cotton fields in Xinjiang. During cotton production, a lack of available phosphorus in the soil delays cotton maturity and significantly reduces yield and quality. The seedling stage of cotton is a critical period for phosphorus nutrient availability, and different genotypes of cotton varieties exhibit significant phenotypic differences in the seedling stage in response to changes in environmental phosphorus levels. Screening low-phosphorus-tolerant cotton varieties and establishing methods for evaluating low-phosphorus tolerance in cotton are of great significance for future breeding of low-phosphorus-tolerant cotton varieties and for promoting the green and sustainable development of cotton cultivation. Summary of the Invention

[0004] In view of the above-mentioned problems, the present invention provides a method for screening low-phosphorus tolerant cotton varieties. The cotton varieties screened by this method still maintain good growth when planted in low-phosphorus environments. The present invention is of great significance for promoting the green and sustainable development of cotton planting industry.

[0005] The technical solution for achieving the above-mentioned objective of this invention is as follows:

[0006] A method for screening low-phosphorus tolerant cotton varieties includes the following steps:

[0007] S1. Six key indicators for evaluating the low phosphorus tolerance of cotton varieties were selected. The six key indicators are total dry weight, specific root tip density, total root length, root fresh weight, root surface area, and total phosphorus accumulation.

[0008] Wherein, total dry weight = aboveground dry weight + underground dry weight, and total phosphorus accumulation = aboveground phosphorus accumulation + underground phosphorus accumulation;

[0009] S2. Germinate cotton seeds and cultivate cotton seedlings under normal phosphorus and low phosphorus stress conditions, respectively;

[0010] S3. After cultivation, six key indicators of cotton seedlings under normal phosphorus and low phosphorus stress conditions were measured.

[0011] S4. Calculate the low phosphorus tolerance coefficient X for each key indicator according to formula (1):

[0012] X = treatment value LP / control value CK × 100% (1),

[0013] Among them, the treatment value LP is the measured value of each key indicator of cotton seedlings under low phosphorus stress, and the control value CK is the measured value of each key indicator of cotton seedlings under normal phosphorus conditions.

[0014] S5. Calculate the D value of the cotton variety according to the multiple regression equation in equation (2):

[0015] D=0.08+0.34X1+0.46X2+0.27X3+0.19X4+0.23X5+0.31X6 (2),

[0016] Where X1 represents the low phosphorus tolerance coefficient of total dry weight, X2 represents the low phosphorus tolerance coefficient of root tip density, X3 represents the low phosphorus tolerance coefficient of total root length, X4 represents the low phosphorus tolerance coefficient of root fresh weight, X5 represents the low phosphorus tolerance coefficient of root surface area, and X6 represents the low phosphorus tolerance coefficient of relative total phosphorus accumulation.

[0017] S6. Cotton varieties are divided into four groups: low-phosphorus sensitive, low-phosphorus tolerant, medium-phosphorus tolerant, and high-phosphorus tolerant. When the D value is < 0.33, the cotton variety is a low-phosphorus sensitive variety; when 0.33 ≤ D value ≤ 0.40, the cotton variety is a low-phosphorus tolerant variety; when the D value is 0.41 ≤ D value ≤ 0.54, the cotton variety is a medium-phosphorus tolerant variety; and when the D value is > 0.55, the cotton variety is a high-phosphorus tolerant variety. The cotton variety group is determined according to the D value.

[0018] Furthermore, the method for screening and evaluating key indicators of low phosphorus tolerance in cotton varieties is as follows:

[0019] S1-1. The selected cotton varieties were subjected to normal phosphorus treatment and low phosphorus stress treatment respectively.

[0020] S1-2. Determine relevant conventional indicators for cotton varieties after normal phosphorus treatment and low phosphorus stress treatment, respectively.

[0021] S1-3. Based on the conventional indicators measured in step S1-2, calculate the low phosphorus tolerance coefficient X of each conventional indicator of the cotton variety using formula (3). i :

[0022] ,

[0023] Among them, Y Lpi Y represents the measured value of the i-th conventional index under low phosphorus stress treatment. CKi is the measured value of the i-th conventional index under normal phosphorus treatment;

[0024] S1-4. Based on the low phosphorus tolerance coefficients of various indicators of cotton varieties, principal component analysis is used to transform multiple conventional indicators of cotton varieties into a few independent comprehensive indicators, and the values ​​of each comprehensive indicator are calculated using equation (4):

[0025] ,

[0026] Where i = 1, 2, 3, …, n; j = 1, 2, 3, …, n; X k Let be the value of the k-th comprehensive index, aij be the eigenvector corresponding to the eigenvalue of each individual conventional index, and Xij be the standardized value of each individual conventional index.

[0027] S1-5. Based on the comprehensive index value, use equation (5) to convert the comprehensive index value into a membership function value:

[0028] ,

[0029] Among them, X k X represents the value of the k-th comprehensive index. min Let X represent the minimum value of the j-th conventional index for all cotton varieties. max This represents the maximum value of the j-th conventional index for all cotton varieties;

[0030] S1-6. Calculate the weight of each comprehensive indicator in the cumulative contribution rate using formula (4):

[0031] ,

[0032] Among them, W k P represents the weight of the k-th comprehensive indicator among all comprehensive indicators. k This represents the contribution rate of the k-th comprehensive index of different cotton varieties obtained through principal component analysis;

[0033] S1-7. Calculate the comprehensive low phosphorus tolerance evaluation value D for different cotton varieties using formula (7):

[0034] ,

[0035] S1-8. Based on the comprehensive low-phosphorus tolerance evaluation value obtained in step five, using this as the dependent variable and each individual indicator as the independent variable, the stepwise regression method is used to analyze the relationship between the comprehensive low-phosphorus tolerance evaluation value and the individual indicators to obtain the optimal regression equation:

[0036] ,

[0037] Where X1 represents the low phosphorus tolerance coefficient of total dry weight, X2 represents the low phosphorus tolerance coefficient of root tip density, X3 represents the low phosphorus tolerance coefficient of total root length, X4 represents the low phosphorus tolerance coefficient of root fresh weight, X5 represents the low phosphorus tolerance coefficient of root surface area, and X6 represents the low phosphorus tolerance coefficient of relative total phosphorus accumulation;

[0038] The combined results of correlation analysis and multiple stepwise regression analysis indicate that six conventional indicators—total dry weight, specific root tip density, fresh root weight, total root length, root surface area, and total phosphorus accumulation—can serve as key indicators for evaluating the low phosphorus tolerance of different cotton genotypes.

[0039] Furthermore, the concentrations of KH₂PO₄ in the Hogrange nutrient solutions used under the normal phosphorus conditions and low phosphorus conditions were 500 µM and 10 µM, respectively, with other components remaining consistent: 2.5 mM Ca(NO₃)₂·4H₂O, 0.5 mM KH₂PO₄, 1 mM MgSO₄·7H₂O, 0.1 mM EDTA·Fe·Na, 46 µM H₃BO₃, 4 µM MnCl₂·4H₂O, 2 µM ZnSO₄·7H₂O, 0.3 µM CuSO₄·5H₂O, and 0.12 µM (NH₄)₆Mo₇O. 24 ·4H2O.

[0040] Furthermore, before the cotton varieties germinate, they must be soaked in hydrogen peroxide solution for disinfection, and then cleaned thoroughly for later use.

[0041] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0042] 1. This invention uses the low phosphorus tolerance coefficient as the mathematical analysis object. Through various calculation methods and analysis techniques, a large amount of data is transformed into an intuitive comprehensive evaluation value of low phosphorus tolerance. This can eliminate the inherent differences between cotton varieties and make the results more accurate and reliable.

[0043] 2. This invention is the first method to evaluate the low phosphorus tolerance of cotton. Through extensive data analysis and deduction, a highly feasible result has been obtained. It is characterized by its scientific nature, applicability, high efficiency, and speed.

[0044] 3. This invention obtains the optimal regression equation through regression analysis. It only requires testing 6 key indicators of cotton seedlings to determine the strength of low phosphorus tolerance, effectively reducing the number of trait indicators and greatly reducing the workload.

[0045] 4. The cotton low phosphorus tolerance evaluation method described in this invention was obtained using 140 cotton micro-core varieties as research materials. The research materials have large genotypic differences and long genetic distances, so this method can evaluate both the low phosphorus tolerance of existing cotton varieties and the low phosphorus tolerance of future bred varieties (lines). Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0047] Figure 1 Population genetic analysis was conducted on 140 cotton varieties. Among them, Figure 1 (a) Attenuation analysis of linkage disequilibrium (LD) across the whole genome in 140 cotton varieties; Figure 1 (b) Analysis of genetic diversity and population differentiation of three populations of 140 cotton varieties. The value in the circle represents the genetic diversity of the population (θπ), and the value between the circles represents the population differentiation between the populations (Fst).

[0048] Figure 2 This is a principal component dispersion plot of the low phosphorus tolerance index for 140 cotton varieties in Example 1. Wherein, ADW: aboveground dry weight (g); UDW: underground dry weight (g); TDW: total dry weight (g); TRL: taproot length (cm); RSA: root surface area (cm²). 2 RVE: Root-average volume (cm³) 3 TRH: Total root length (cm); RAD: Average root diameter (mm); SRL: Specific root length (cm·g) -1 SRA: Specific root area (cm·g) -2 RTD: Root tissue density (g·cm³) -3 RTN: Root tip number; SRTD: Specific root tip density (g) -1 ); SFW: Fresh weight of aboveground parts (g); RFW: Fresh weight of underground parts (g); R / S: Root-to-shoot ratio (%); SPAD: Relative chlorophyll content; TPC: Total phosphorus content (mg / g); TPA: Total phosphorus accumulation (g / g); PUE: Phosphorus use efficiency (g) 2 ·mg -1 PUtE: Phosphorus absorption efficiency (mg·g) -1 ).

[0049] Figure 3 The correlation coefficients between the low phosphorus stress tolerance index and the low phosphorus tolerance comprehensive evaluation value (D) of various indicators of cotton for 140 cotton varieties are given. * indicates a significant correlation at the 0.05 level. Detailed Implementation

[0050] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0051] Example 1

[0052] S1. Select 140 cotton varieties with significant differences in genetic background as needed. Select cotton seeds with intact, plump and uniform grains, soak them in distilled water for 20 minutes, disinfect them with 0.1% hydrogen peroxide solution for 20 minutes, rinse them repeatedly with pure water 3 times, and then place them in a petri dish for germination.

[0053] The 140 cotton varieties were from various major cotton-producing countries. Population structure analysis showed that they could be clustered into three groups: G1, G2, and G3. Linkage disequilibrium (LD) decreased with increasing physical distance between SNPs across all cotton groups. Figure 1 a). When r2 decreased to half of its maximum value (0.92), the LD degree for each group was calculated as chromosome distance. All three decay values ​​covered the values ​​reported by Fang et al. (1000 kb, 2017), which were higher than those reported by Wang et al. (296 kb, 2017) and Ma et al. (742.7 kb, 2018), indicating that the genetic diversity of this population of 140 is representative of the existing cotton germplasm resource population. The genetic differentiation value (Fst) among the three groups ranged from 0.116 to 0.184 ( Figure 1 b), which is much higher than the values ​​within improved cotton varieties (0.032-0.049, Ma et al., 2018; 0.019-0.067, He et al., 2021), which means that there are relatively large genotypic differences among varieties in different groups in this study.

[0054] The cotton varieties to be selected are shown in Table 1:

[0055] Table 1. Cotton varieties to be screened

[0056]

[0057]

[0058] S2. Four to six days after germination, until the cotton cotyledons have fully expanded, select seedlings of the same variety with uniform growth vigor and transfer them to hydroponic boxes. Use a modified Hoagland nutrient solution for hydroponic cultivation. Two treatments were set up: a low-phosphorus treatment and a normal-phosphorus treatment. Each treatment was replicated three times, with two seedlings planted in each replicate. The nutrient solution was configured with two phosphorus levels: low-phosphorus level LP (10µM KH2PO4) and normal-phosphorus level CK (500µM KH2PO4). Other components of the nutrient solution remained consistent: 2.5mM Ca(NO3)2·4H2O, 1 mM KCl, 1mM MgSO4·7H2O, 0.1 mM EDTA·Fe·Na, 46µM H3BO3, 4µM MnCl2·4H2O, 2µM ZnSO4·7H2O, 0.3µM CuSO4·5H2O, and 0.12µM (NH4)6Mo7O. 24 • 4H2O, maintain the pH of the nutrient solution at 5.5±0.5, and change the nutrient solution every 7 days;

[0059] S3. After 28 days of cultivation, the morphological and physiological indicators of cotton seedlings (hereinafter referred to as conventional indicators) were measured. The morphological and physiological indicators included plant height, stem diameter, leaf area, chlorophyll content, net photosynthetic rate, stem and leaf dry weight, total root length, root surface area, root dry weight, root-shoot ratio, stem and leaf phosphorus content, and root phosphorus content.

[0060] Based on the measured values ​​of each conventional index, the low phosphorus tolerance coefficient X of each conventional index is calculated according to formula (1). i :

[0061] ,

[0062] Among them, Y Lpi Y represents the measured value of the i-th conventional index under low phosphorus treatment. CKi is the measured value of the i-th conventional index under normal phosphorus level treatment.

[0063] Different cotton varieties (lines) respond differently to various conventional indicators at different phosphorus levels, as shown in Table 2 below:

[0064] Table 2. Measured values ​​of various conventional indicators for 140 varieties under different phosphorus levels.

[0065]

[0066]

[0067] Table 2 shows that, compared with normal phosphorus treatment, under low phosphorus stress, all 10 indicators of cotton varieties, including aboveground dry weight, total dry weight, taproot length, total root length, specific root length, root tissue density, stem fresh weight, SPAD value, total phosphorus content, and total phosphorus accumulation, decreased, indicating that low phosphorus treatment has a significant impact on cotton growth and development. Among these, the largest decreases were in total phosphorus accumulation (93.82%), total phosphorus content (85.4%), aboveground dry weight (54.1%), and total dry weight (48.4%), while taproot length (0.5%), total root length (7.2%), and SPAD value (5.5%) decreased. This indicates that low phosphorus treatment has a greater response to low phosphorus stress in terms of biomass and phosphorus accumulation, while its effect on root length and SPAD value is relatively small.

[0068] Analysis of variance results (Table 2) showed that there were extremely significant differences in each indicator among varieties and different phosphorus levels (P < 0.01). The interaction between phosphorus level and varieties also reached a significant level, indicating that the traits of different varieties were significantly different under the two phosphorus treatments and were representative.

[0069] The cotton traits under different phosphorus levels showed a certain degree of variability, indicating that the tested cotton varieties have relatively wide genetic differences in various traits, which provides a possibility for screening low-phosphorus tolerant cotton varieties. Under normal phosphorus treatment, the coefficient of variation for each indicator ranged from 3.80% to 37.15%; under low phosphorus treatment, the coefficient of variation for each indicator ranged from 6.1% to 47.8% (Table 2). Under low phosphorus conditions, the coefficients of variation for root system indicators such as specific root tip density, number of root tips, specific root length, specific root area, and root volume were all higher than those under normal phosphorus treatment, indicating that low phosphorus treatment increased the dispersion of various indicators among cotton seedling roots, that is, the differences between varieties were more significant. Therefore, it is easier to screen low-phosphorus tolerant varieties under low phosphorus treatment conditions. Under both phosphorus level treatments, the coefficients of variation for underground dry weight, total dry weight, total phosphorus accumulation, root-to-stalk ratio, and phosphorus absorption and utilization efficiency were all high, indicating a sensitive response to phosphorus levels (Table 2). Therefore, in order to eliminate the inherent biological and genetic differences between varieties, the following comprehensive analysis of low phosphorus tolerance was conducted based on the low phosphorus tolerance coefficients of each indicator.

[0070] S4. Convert individual routine indicators into mutually independent comprehensive indicators.

[0071] Principal component analysis was used to analyze and screen comprehensive indicators for 21 common indicators of cotton. The screening criteria for comprehensive indicators were that the cumulative contribution rate of variance was greater than 75% and the eigenvalue of the comprehensive indicator was greater than 1. Specific results are shown in (…). Figure 2 (and Table 3).

[0072] Table 3. Coefficients and cumulative contribution rates of various comprehensive indicators of cotton under different phosphorus supply conditions.

[0073]

[0074] The results showed that the aboveground dry weight (coefficient 0.40, same below, Table 3), total dry weight (0.42), stem fresh weight (0.36), root fresh weight (0.32), total phosphorus accumulation (0.32), and phosphorus use efficiency (0.32) had the largest projections on the PC1 axis, and all of these indicators had a positive impact on PC1. On the PC2 axis, the root traits with the largest positive projections were specific root area (0.40), root surface area (0.35), and root volume (0.34), while the underground dry weight (-0.16), root-to-stem ratio (-0.19), and total phosphorus content (-0.24) had a significant negative impact on PC2. PC3... The positive projections of the root length in the axial region (0.36), total phosphorus content (0.32), and total phosphorus accumulation (0.33) were much larger than those of other indicators. The total root length (0.18), root tip density (0.17), and root area (0.15) had a certain positive effect on PC3. The underground dry weight (-0.35), root-to-stem ratio (-0.45), phosphorus absorption efficiency (-0.35), and root surface area (-0.16) had a significant negative effect on PC3.

[0075] The sensitivity of each comprehensive index to different phosphorus levels was PC1>PC2>PC3>PC4>PC5>PC6, with a cumulative variance contribution rate of 77.21%. Based on the contribution rate of each comprehensive index, it can be seen that the low phosphorus tolerance of cotton is closely related to indicators such as biomass, phosphorus efficiency parameters, and root-related traits.

[0076] S5. Comprehensive Variety Evaluation

[0077] Using the formula mentioned in this invention Calculate the comprehensive index values ​​corresponding to 140 cotton varieties; using the membership function U(X) mentioned in this invention. k )=(X k -X min ) / (X max -X min The transformation process is performed using the comprehensive index weight calculation formula mentioned in this invention. Further utilize the comprehensive evaluation formula mentioned in this invention. .

[0078] Correlation analysis of low phosphorus tolerance coefficients and low phosphorus tolerance comprehensive evaluation value (D) for 21 conventional indicators ( Figure 3The results showed that the correlation between the low phosphorus stress tolerance index and the D value of 13 indicators, including aboveground dry weight, total dry weight, taproot length, root surface area, average root volume, total root length, number of root tips, specific root tip density, stem fresh weight, root fresh weight, root-shoot ratio, total phosphorus accumulation, and phosphorus use efficiency, was extremely significant (P < 0.01). Among them, the correlation coefficients of the three conventional indicators, aboveground dry weight, total dry weight, and total phosphorus accumulation, were relatively high compared with the other conventional indicators, at 0.72, 0.72, and 0.68, respectively.

[0079] A multiple stepwise regression analysis model was established based on the D value and the low-phosphorus tolerance coefficients of relevant conventional indicators. The multicollinearity effects of aboveground dry matter and root-to-stem ratio on the model were excluded. The resulting multiple regression equation for the dependent variable D and six independent variables was: D = 0.08 + 0.34X1 + 0.46X2 + 0.27X3 + 0.19X4 + 0.23X5 + 0.31X6 (Table 3). X1 represents the low-phosphorus tolerance coefficient of TDB (Total Dry Weight), X2 represents the low-phosphorus tolerance coefficient of PUE (Specific Root Tip Density), X3 represents the low-phosphorus tolerance coefficient of TRH (Total Root Length), X4 represents the low-phosphorus tolerance coefficient of RFW (Fresh Root Weight), X5 represents the low-phosphorus tolerance coefficient of RSA (Root Surface Area), and X6 represents the low-phosphorus tolerance coefficient of TPA (Total Phosphorus Accumulation). The coefficients of each key indicator represent the influence weight of each key indicator on the comprehensive low-phosphorus tolerance evaluation value D. The coefficient of determination for this regression equation is R² = 0.99. (P < 0.01) indicates that the reliability of the equation in comprehensively evaluating the low phosphorus tolerance of cotton is 99%, and the F test reached a highly significant level, indicating that the model has a good fit and the regression equation has a certain explanatory power (Table 4).

[0080] Table 4. Correlation between the optimal model prediction and different comprehensive evaluation indicators for cotton varieties with low phosphorus tolerance.

[0081]

[0082] The combined results of correlation analysis and multiple stepwise regression analysis indicate that six conventional indicators—total dry weight, specific root tip density, fresh root weight, total root length, root surface area, and total phosphorus accumulation—can serve as key indicators for evaluating the low phosphorus tolerance of different cotton genotypes.

[0083] S8. Screening of Low-Phosphorus-Tolerant Cotton Varieties (Lines): Using the low-phosphorus tolerance coefficients of six key indicators, a hierarchical cluster analysis was conducted using the average Euclidean distance method. Based on the clustering results, 140 cotton varieties (lines) were divided into three categories. Category I consisted of 47 varieties (lines), with an average comprehensive evaluation value (D) of 0.34, ranging from 0.25 to 0.38. Category II consisted of 29 varieties (lines), with an average comprehensive evaluation value (D) of 0.41, ranging from 0.33 to 0.45. Category III consisted of 64 varieties (lines), with an average comprehensive evaluation value (D) of 0.51, ranging from 0.39 to 0.65.

[0084] Based on the comprehensive analysis of the clustering results, Category I is classified as low-phosphorus tolerant, Category II as intermediate, and Category III as low-phosphorus intolerant. According to the clustering analysis results and the comprehensive low-phosphorus tolerance evaluation value D, varieties such as Zongxu No. 1, Luyuan 343, Lambright GL-N, Brazil 014, Nandanlihu cotton, Suyuan 1028, and gL2g13 were selected as low-phosphorus tolerant cotton varieties. Varieties such as Shan 2812, FJA, Xiao 2168, and Donglanating large-flowered cotton have poor low-phosphorus tolerance and are classified as low-phosphorus intolerant.

Claims

1. A method for screening low-phosphorus tolerant cotton varieties, characterized in that... Includes the following steps: S1. Six key indicators for evaluating the low phosphorus tolerance of cotton varieties were selected. The six key indicators are total dry weight, specific root tip density, total root length, root fresh weight, root surface area, and total phosphorus accumulation. Wherein, total dry weight = aboveground dry weight + underground dry weight, and total phosphorus accumulation = aboveground phosphorus accumulation + underground phosphorus accumulation; S2. Germinate cotton seeds and cultivate cotton seedlings under normal phosphorus and low phosphorus stress conditions, respectively; S3. After cultivation, six key indicators of cotton seedlings under normal phosphorus and low phosphorus stress conditions were measured. S4. Calculate the low phosphorus tolerance coefficient X for each key indicator according to formula (1): X = treatment value LP / control value CK × 100% (1), Among them, the treatment value LP is the measured value of each key indicator of cotton seedlings under low phosphorus stress, and the control value CK is the measured value of each key indicator of cotton seedlings under normal phosphorus conditions. S5. Calculate the D value of the cotton variety according to the multiple regression equation in equation (2): D=0.08+0.34X1+0.46X2+0.27X3+0.19X4+0.23X5+0.31X6 (2), Where X1 represents the low phosphorus tolerance coefficient of total dry weight, X2 represents the low phosphorus tolerance coefficient of root tip density, X3 represents the low phosphorus tolerance coefficient of total root length, X4 represents the low phosphorus tolerance coefficient of root fresh weight, X5 represents the low phosphorus tolerance coefficient of root surface area, and X6 represents the low phosphorus tolerance coefficient of relative total phosphorus accumulation. S6. Cotton varieties are divided into four groups: low-phosphorus sensitive, low-phosphorus tolerant, medium-phosphorus tolerant, and high-phosphorus tolerant. When the D value is < 0.33, the cotton variety is a low-phosphorus sensitive variety; when 0.33 ≤ D value ≤ 0.40, the cotton variety is a low-phosphorus tolerant variety; when the D value is 0.41 ≤ D value ≤ 0.54, the cotton variety is a medium-phosphorus tolerant variety; and when the D value is > 0.55, the cotton variety is a high-phosphorus tolerant variety. The cotton variety group is determined according to the D value.

2. The method for screening low-phosphorus tolerant cotton varieties according to claim 1, characterized in that... The method for screening and evaluating key indicators of low phosphorus tolerance in cotton varieties is as follows: S1-1. The selected cotton varieties were subjected to normal phosphorus treatment and low phosphorus stress treatment respectively. S1-2. Determine relevant conventional indicators for cotton varieties after normal phosphorus treatment and low phosphorus stress treatment, respectively. S1-3. Based on the conventional indicators measured in step S1-2, calculate the low phosphorus tolerance coefficient X of each conventional indicator of the cotton variety using formula (3). i : ， Among them, Y Lpi Y represents the measured value of the i-th conventional index under low phosphorus stress treatment. CKi is the measured value of the i-th conventional index under normal phosphorus treatment; S1-4. Based on the low phosphorus tolerance coefficients of various indicators of cotton varieties, principal component analysis is used to transform multiple conventional indicators of cotton varieties into a few independent comprehensive indicators, and the values ​​of each comprehensive indicator are calculated using equation (4): ， Where i = 1, 2, 3, …, n; j = 1, 2, 3, …, n; X k Let be the value of the k-th comprehensive index, aij be the eigenvector corresponding to the eigenvalue of each individual conventional index, and Xij be the standardized value of each individual conventional index. S1-5. Based on the comprehensive index value, use equation (5) to convert the comprehensive index value into a membership function value: ， Among them, X k X represents the value of the k-th comprehensive index. min Let X represent the minimum value of the j-th conventional index for all cotton varieties. max This represents the maximum value of the j-th conventional index for all cotton varieties; S1-6. Calculate the weight of each comprehensive indicator in the cumulative contribution rate using formula (4): ， Among them, W k P represents the weight of the k-th comprehensive indicator among all comprehensive indicators. k This represents the contribution rate of the k-th comprehensive index of different cotton varieties obtained through principal component analysis; S1-7. Calculate the comprehensive low phosphorus tolerance evaluation value D for different cotton varieties using formula (7): ， S1-8. Based on the comprehensive low-phosphorus tolerance evaluation value obtained in step five, using this as the dependent variable and each individual indicator as the independent variable, the stepwise regression method is used to analyze the relationship between the comprehensive low-phosphorus tolerance evaluation value and the individual indicators to obtain the optimal regression equation: ， Where X1 represents the low phosphorus tolerance coefficient of total dry weight, X2 represents the low phosphorus tolerance coefficient of root tip density, X3 represents the low phosphorus tolerance coefficient of total root length, X4 represents the low phosphorus tolerance coefficient of root fresh weight, X5 represents the low phosphorus tolerance coefficient of root surface area, and X6 represents the low phosphorus tolerance coefficient of relative total phosphorus accumulation; The combined results of correlation analysis and multiple stepwise regression analysis indicate that six conventional indicators—total dry weight, specific root tip density, fresh root weight, total root length, root surface area, and total phosphorus accumulation—can serve as key indicators for evaluating the low phosphorus tolerance of different cotton genotypes.

3. The method for screening low-phosphorus tolerant cotton varieties according to claim 1, characterized in that: The concentrations of KH₂PO₄ in the Hogrange nutrient solution used under normal phosphorus and low phosphorus conditions were 500 µM and 10 µM, respectively, with other components remaining the same: 2.5 mM Ca(NO₃)₂·4H₂O, 0.5 mM KH₂PO₄, 1 mM MgSO₄·7H₂O, 0.1 mM EDTA·Fe·Na, 46 µM H₃BO₃, 4 µM MnCl₂·4H₂O, 2 µM ZnSO₄·7H₂O, 0.3 µM CuSO₄·5H₂O, and 0.12 µM (NH₄)₆Mo₇O. 24 ·4H2O.

4. The method for screening low-phosphorus tolerant cotton varieties according to claim 1, characterized in that: Before the cotton varieties germinate, they must be soaked in hydrogen peroxide solution for disinfection, and then cleaned thoroughly for use.

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