[Objective] Na₂SO₄ stress is a major type of salt stress in Xinjiang and has seriously restricted the cotton production in Xinjiang. This study aims to explore the effect of Na₂SO₄ stress on cotton metabolism and to investigate the key metabolites and metabolic pathways in the stress response of cotton. [Method] The metabolic analysis was applied in cotton roots and leaves under two treatment settings, including control (CK) and sulfate stress (Na₂SO₄, SS), to explore the changes of metabolite content and metabolic pathways in cotton under Na₂SO₄ stress. [Result] Sulfate stress significantly inhibited the growth of cotton. Compared with CK, the dry mass of leaves, stems, and roots, and total mass of plant under SS treatment decreased by 46.9%, 50.9%, 43.0% and 47.9%, respectively. Under sulfate stress, there were 42 up-regulated and 10 down-regulated organic acids, 32 up-regulated and 16 down-regulated amino acids and amino acid derivatives, 23 up-regulated and 1 down-regulated carbohydrate in root. There were 37 up-regulated organic acids and 7 down-regulated organic acids, 16 up-regulated and 17 down-regulated amino acids and amino acids derivatives, 16 up-regulated and 4 down-regulated carbohydrate in leaves. A total of 30 differential metabolic pathways were selected in roots, including 9 pathways related to amino acid metabolism, 7 pathways related to organic acid metabolism, and 7 pathways related to carbohydrate metabolism. A total of 17 differential metabolic pathways were selected in leaves, including 7 pathways related to amino acid metabolism, 4 pathways related to organic acid metabolism, and 3 pathways related to carbohydrate metabolism. [Conclusion] Cotton responded to sulfate stress by accumulating organic acids, carbohydrate and alcohols in roots and leaves. The up-regulation of citric acid, succinic acid, pyruvic acid and linoleic acid in leaves suggested the enhanced tricarboxylic acid (TCA) cycle and β-enhanced oxidation. And up-regulation of citric acid, succinic acid and pyruvic acid in roots indicated the enhanced TCA cycle. This study explored the mechanism of Na₂SO₄ stress response in cotton and provided a theoretical basis for cotton cultivation in Xinjiang.

[Objective] The aim of this study is to explore the elite gene/quantitative trait loci (QTL) resources of yield and fiber quality, and to provide useful information for developing cotton varieties with high yield and excellent fiber quality. [Methods] A superior chromosome segment substitution line MBI9626, and a high-yield and wide-adaptability upland cotton CCRI 36 were selected to construct a secondary segregation population BC₆F₂ which contained 152 individuals. And 109 selected simple sequence repeat(SSR) markers were used to genotyping parents and the population, and QTL mapping for yield and fiber quality traits was conducted based on genotype data and phenotype data. [Results] Genotyping resutts showed MBI9626 recovered to 94.8% of the genetic background of CCRI 36. A total of 28 QTLs related to yield and fiber quality traits were detected in BC₆F₂, BC₆F_2:3, and BC₆F_2:4 populations, which were distributed on 6 chromosomes. Among them, there are 16 QTLs related to yield, accounting for 2.25%-6.14% of the phenotypic variation, including 6 stable QTLs; 12 QTLs related to quality traits, accounting for 2.49%-12.30% of the phenotypic variation, including 2 stable QTLs. There were 19 newly discovered QTLs, including 5 stable QTLs. And 233 genes were identified in a QTL cluster with 6 QTLs on D3 chromosome. Based on gene ontology (GO) cluster and Kyoto encyclopedia of genes and genomes (KEGG) analysis and TM-1 transcriptome data, 6 candidate genes were screened to be involved in fiber development, namely GH_D03G1428、GH_D03G1466, GH_D03G1518, GH_D03G1570, GH_D03G1586, and GH_D03G1640. [Conclusion] Twenty-eight stable QTLs related to cotton yield and fiber quality were identified and would lay a solid foundation for fine mapping and cloning of candidates genes and marker assisted selection.

[Objective] The purpose of this study is to study the influence of cotton-wheat cropping modes on yield and cotton maturity in the Yellow River Basin, to provide technical support for the whole-process mechanization management under the machine-harvested cotton mode. [Method] The experiments were carried out in Anyang, Henan in 2017/2018 and 2018/2019 seasons including 6 treatments with 2 cotton varieties (ZM50, ZM79) and 3 cropping modes, W6C2 (6 rows wheat and 2 rows cotton), W3C1 (3 rows wheat and 1 row cotton) and W2C1 (2 rows wheat and 1 row cotton) under the machine-harvested cotton row space (76 cm) cultivation. Some key indexes such as the wheat yield and side effects, and cotton biomass accumulation, the time distribution of cotton bolls, percentage of seed-cotton yield before frost, and fiber quality were compared and analyzed. [Result] The wheat yield was significantly higher in the mode W3C1 than the mode W2C1 and W6C2 by 16.2%-43.3% and 28.4%-52.3% respectively; the number of effective panicles significantly increased by 29.2%-47.5% and 34.9%-53.6%, respectively; however, the indexes such as wheat yield(2019) and effective panicles per hectare(2018) of W3C1 were significantly lower than W6C2. No significant differences in fiber length, breaking tenacity, and micronaire were found among different cropping modes. There was no significant difference in the seed cotton yield and harvest index(HI) of ZM50 under different modes，while the seed cotton yield and HI of ZM79 in the mode W3C1 in 2018 was lower than that in W6C2 and W2C1. Under W3C1 mode, short season cotton ZM50, compared with ZM79, showed an earlier maturity performance, such as a lower node/branch ratio, and faster reproductive growth, higher ratio of the middle season bolls between July 16 and August 15, lower cotton boll shell ratio, and higher percentage of seed-cotton yield before frost by 38.7%-54.2%; moreover, land equivalent ratio (LER) of this mode is over 1.689-1.697, significantly higher than other modes. [Conclusion] It is suggested that under the machine-harvested cotton row space in the Yellow River Basin, adopting the short-season cotton ZM50 and mode W3C1 can obtain a higher LER and percentage of seed-cotton yield before frost, and is conducive to increasing crop uniformity and yield of wheat. So, taking this configuration for wheat-cotton cropping in the Yellow River Basin is helpful to improve the mechanized management level of the crops and the planting benefit.

[Objective] At the seedling stage, plant growth regulators and their appropriate concentrations were screened to improve the high temperature tolerance of cotton, and the alleviating effects were determined at the flowering and boll setting stage. [Method] In this study, the cotton cultivar Zhongmian 425 was selected as the test material. Two kinds of temperature treatments were set: normal temperature (average temperature was 28 ℃, and maximum/minimum temperature were 24 ℃/32 ℃) and high temperature (average temperature was 38 ℃, and maximum/minimum temperature were 42 ℃/34 ℃). Water, 200, 400, 600 μmol·L^-1 1-methylcyclopropene (1-MCP), 0.01, 0.02, 0.05 μmol·L^-1 coronidine (COR) and 0.5, 1.0, 2.0 μmol·L^-1 2, 4-epibrassinolide (EBR) spraying treatments were set at the seedling stage. Water and 400 μmol·L^-1 1-MCP spraying treatment were set at the flowering and boll setting stage. The effects of different plant growth regulators on the dry mass, leaf photosynthetic characteristics, chlorophyll content, antioxidant enzyme activity, yield and fiber quality of cotton under the normal temperature and high temperature conditions were explored. [Result] The results showed that the suitable concentrations of three plant growth regulators could improve the high temperature tolerance of cotton. Under high temperature stress at the seedling stage, compared with water treatment, spraying 400 μmol·L^-1 1-MCP could significantly increase the dry mass of aboveground and underground parts of cotton, and increase the net photosynthetic rate, the contents of chlorophyll a and chlorophyll b, and the activities of antioxidant enzymes (superoxide dismutase, peroxidase, glutathione peroxidase and ascorbate peroxidase), and decrease malondialdehyde content in newly expanded cotton leaves. Principal component analysis proved that 400 μmol·L^-1 1-MCP could effectively improve the high temperature tolerance of cotton. Meanwhile, under high temperature stress at the flowering and boll setting stage, spraying 400 μmol·L^-1 1-MCP could significantly improve the net photosynthetic rate, stomatal conductance and transpiration rate of subtending leaves to cotton bolls, the number of bolls per plant, boll weight, seed cotton yield per plant and fiber quality compared with spraying water. [Conclusion] 400 μmol·L^-1 1-MCP can increase the chlorophyll content, photosynthetic capacity and antioxidant enzyme activity, and reduce the accumulation of malondialdehyde and other harmful substances in cotton leaves, thus enhancing the high temperature tolerance of cotton, and finally improve the cotton yield and fiber quality to a certain extent.

[Objective] Deficit irrigation is an effective irrigation method used in water-saving agriculture. This study aims to quantitatively analyze the influence on cotton yield and irrigation water productivity under deficit irrigation in China, and to provide the reference for further application of deficit irrigation in China. [Method] A meta-analysis was used to quantitatively evaluate the influence of different factors on cotton yield and irrigation water productivity under deficit irrigation in China by integrating 53 literatures published from 2010 to 2022. [Result] The result showed that compared with full irrigation, the average yield of seed cotton under deficit irrigation was decreased by 16.2%, while the irrigation water productivity was increased by 32.2% on average. The subgroup analysis showed that the highest increase of irrigation water productivity was observed in Northwest China under deficit irrigation, particularly in Xinjiang which had the best effect with less yield reduction. Field plantation and areas with relatively low precipitation had increased efficiency of water productivity under irrigation deficit condition. In areas with the annual average temperature ≥ 10 ℃, adopting the planting method of dry sowing and wet emergence, and moderately increasing irrigation frequency can effectively reduce the risk of yield reduction under deficit irrigation condition. Under the condition of soil bulk density <1.5 kg·cm^-3, the risk of seed cotton yield reduction was lower than that of the high soil bulk density under deficit irrigation condition. The application of 80%-100% of full irrigation, and application rate of 200-300 kg·hm^-2 nitrogen, 100-150 kg·hm^-2 potassium and 150-200 kg·hm^-2 phosphorus can effectively promote water utilization rate and reduce the risk of yield reduction under deficit irrigation condition. [Conclusion] It is suggested that the planting method of dry sowing and wet emergence is suitable to conserve water and stabilize yield under mild deficit irrigation condition in the Northwest China arid region with relatively high temperature. And appropriate increase of irrigation frequency and moderate fertilizer application rate can reduce the influence of deficit irrigation on cotton production.

[Objective] The acyl-coenzyme A oxidase (ACX) gene family was identified in Gossypium hirsutum and their expression patterns were analyzed, which would lay the foundation for further studies of the function of ACX genes. [Method] The members of ACX gene family in G. hirsutum genome were identified by bioinformatics method, and their physical and chemical properties, gene structure, evolutionary relationships, gene replication, cis-acting elements in promoter region and expression patterns were analyzed systematically, and the virus-induced gene silencing (VIGS) technique was used to preliminary explore the function of GhACX16 gene. [Results] A total of 20 ACX genes were identified in G. hirsutum genome and distributed on 13 chromosomes, which were divided into 4 subfamilies by cluster analysis. The results of non-synonymous mutation rate/synonymous mutation rate (K_a/K_s) analysis showed that the ACX genes in G. hirsutum had undergone strong purifying selection. The promoter region of ACX genes contain cis-acting elements related to heat stress, drought, plant hormone responses, etc. The expression patterns under abiotic stresses showed that the ACX genes responded obviously to high-temperature, low-temperature, salt, and simulated drought stress. The expression patterns of ACX genes in the anthers at different developmental stages of high temperature-tolerant/sensitive cotton lines under high temperature conditions were analyzed, and it was found that the expression levels of GhACX5 and GhACX16 changed obviously. Compared with the negative control, the GhACX16 silenced cotton seedlings showed obvious characteristics of high temperature tolerance, and the proline content, chlorophyll content, and catalase activity were significantly higher, while the malondialdehyde content was significantly lower in the leaves. [Conclusion] The identification and expression patterns of ACX genes in G. hirsutum showed that ACX genes were widely involved in abiotic stresses response, and GhACX16 gene was preliminary speculated to play an important role in high temperature stress response according to the VIGS verification and physiological and biochemical analysis.

[Objective] The effect of arbuscular mycorrhizal fungi (AMF) inoculation on photosynthetic characteristics and mesophyll cell ultrastructure in cotton under arsenic stress were studied. [Method] Cotton germplasm Dalingmian 69 were used as the test material in the pot experiment. Two species of AMF including Rhizophagus intraradices and Funneliformis mosseae were inoculated into the cotton roots respectively in order to investigate the effects of AMF on stomatal morphological characteristics, gas exchange parameters, chlorophyll fluorescence parameters and mesophyll cell ultrastructure under different arsenic concentrations (0, 100, 200 mg·kg^-1) in soil. [Result] (1) Arsenic stress significantly reduced stomatal length, width, density, conductance, transpiration rate, intercellular CO₂ concentration and net photosynthetic rate, and significantly affected chlorophyll fluorescence parameters of cotton leaves. However, compared with the control treatment, inoculation of AMF increased the length, width, aperture, density, and conductance of cotton stomata, and significantly increased the net photosynthetic rate, transpiration rate, intercellular CO₂ concentration, actual photosynthetic efficiency, the maximum photochemical quantum yield and photochemical quenching coefficient, and reduced the non-photochemical quenching coefficient under different concentrations of arsenic. Under 100 and 200 mg·kg^-1 arsenic concentration, the net photosynthetic rate and actual photosynthetic efficiency of F. mosseae treatment were significantly higher than those of R. intraradices treatment. (2) Arsenic stress led to the gradual swelling of chloroplast, the overall structure was destroyed, the disordered and uneven arrangement of grana thylakoids, the loose and deformed arrangement of cristae in mitochondria, the appearance of voids in some mitochondrial structures, and the fuzzy double-layer membrane structure. However, under arsenic stress, the lamellae of chloroplast grana in the mesophyll cells of cotton inoculated with AMF were clearly visible, and the cristae in mitochondria were closely arranged, and the degree of arsenic damage was significantly reduced. The palliative effect of F. mosseae was even stronger. [Conclusion] Under arsenic stress, inoculation of F. mosseae and R. intraradices significantly increased the net photosynthetic rate and light energy utilization efficiency, and improved the photosynthetic capacity of cotton, and reduced the damage of arsenic to the ultrastructure of mesophyll cells. And the inoculation effect of F. mosseae was better.

[Objective] The effects of adjuvants on the physicochemical properties, evaporation resistance, deposition and distribution of droplet, and control effect of nanopesticide against cotton aphid were studied through spray tests carried out by plant protection unmanned aerial vehicle (UAV) in cotton field. [Method] The dynamic light scatterometer, automatic interfacial tensiometer, BP100 tensiometer, contact angle meter and super depth of field photography system were used to evaluate influences of adding adjuvants (0.1% volume fraction of Youruopai, 0.1% volume fraction of Jiexiaofeng, 0.6% volume fraction of Aero-Mate 320) on the physicochemical properties and anti-evaporation of solutions with 20% reduced nanopesticide 8% (mass fraction, the same as below) dinieramine dinotefuran compared to the recommended dosage of 1 200 g·hm^-2, in the laboratory. The effect of droplets with adjuvant on the deposition and distribution in the canopy of cotton and its effect on the cotton aphid were explored. [Result] The physicochemical properties of the solutions were improved by adding Youruopai, Jiexiaofeng and Aero-Mate 320 adjuvants into the nanopesticide solutions with 20% reduced dosage. The static surface tension of solutions decreased from 36.43 mN·m^-1 to 31.82-34.99 mN·m^-1. The contact angles decreased to 12.25°-14.85°, which were decreased by about 22.97%-36.46%. The wetting areas increased by 18.34%-33.57% and the inhibition rates of spray evaporation reached 27.72%-73.40%. The results of field test showed that, the median diameters of the droplets in the upper and lower canopy of cotton were significantly increased from 122.4 μm and 106.7 μm to 154.3 μm and 148.5 μm, respectively. After 7 days of application, the control efficacy of treatment with 20% reduction of nanopesticide against aphids was 47.6%. However, the efficacies increased to 63.2%, 65.0% and 73.3%, respectively, after three adjuvants were added in the above treatments. The efficiencies were comparable to that of conventional dosage sprayed by UAV (71.8%) and traditional pesticide sprayed by artificial knapsack sprayer (74.9%). [Conclusion] The results indicated that adding adjuvant could improve physicochemical properties, enhance wetting area, reduce evaporation and drift of droplets, and increase the efficiency of nanopesticide against A. gossypii.

[Objective] Cadmium (Cd) is one of the serious environmental pollutants, and Cd stress affects seed germination. Melatonin (MT), as an antioxidant, and can promotes seed germination. In this study, the effects of MT on cotton seed germination, antioxidant activity, and osmotic adjustment content under Cd stress were analyzed to clarify the regulatory effect of MT on cotton seed germination under Cd stress. [Method] Seeds of the transgenic insect-resistant cotton variety Nongdamian 601 were used as material, Cd concentration and MT concentration were screened. And four treatments, CK (control, water), MT (melatonin treatment, 50 μmol·L^-1), Cd (cadmium stress 100 μmol·L^-1 treatment), CM (cadmium + melatonin treatment) were set. The germination potential, germination rate, seedling biomass, antioxidant enzyme activity, and osmotic adjustment content of cotton seed under different treatments were studied. [Result] Cd stress of 100 μmol·L^-1 significantly decreased the germination potential, the germination rate, the length of radicle and plumule, the fresh and dry mass of radicle, but had no significant effect on the fresh or dry mass of plumule. Under the stress of Cd, the activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and soluble protein content of cotton seed were decreased. The content of proline, soluble sugar and malondialdehyde (MDA) were increased. Application of MT (50 μmol·L^-1) increased the germination potential and germination rate of cotton seed under Cd stress, the activity of SOD, POD and CAT, the content of soluble protein, soluble sugar and proline, while decreased the content of MDA, significantly increased the length of radicle and plumule, and significantly increased radicle biomass. [Conclusion] Exogenous MT (50 μmol·L^-1) could effectively alleviate the inhibitory effeet of Cd stress (100 μmol·L^-1) on cotton seed germination.

[Objective] Frego bract can greatly reduce the attachment of bract to boll and help to reduce the percentage of trash of machine-harvested cotton. In this study, we aimed to fine mapping the frego bract fg gene in cotton, so as to provide reference for its cloning and breeding utilization. [Method] Two F₂ segregating populations were constructed by crossing Gossypium hirsutum T582 (as the female parent) with G. hirsutum TM-1 and G. barbadense 3-79, respectively. Population 1 (T582 × TM-1) included 370 individual plants, and population 2(T582 × 3-79) contained 2 667 individual plants. The developed Indel (insertion-deletion) markers based on the reference genomic data of TM-1 and 3-79 were used to fine mapping fg. Functional annotation and expression pattern analysis of genes within the mapped sequence were performed using cotton functional genomics and multi-omics data. [Result] Genetic analysis showed that frego bract is controlled by a single recessive gene. Based on the previous mapping result of fg gene, cotton fg gene was further mapped between molecular markers M3 and M4 on chromosome A03, with an interval size of 188 kb in this study. A total of fourteen annotated functional genes were predicted in the mapping region. Among them, Gh_A03G021700, Gh_A03G021900, Gh_A03G022600 and Gh_A03G022700 were highly expressed in sepal and epicalyx. [Conclusion] Frego bract fg gene was finely mapped on chromosome A03, with an interval size of 188 kb, and 14 candidate genes in the mapping interval were preliminarily analyzed, which lays the foundation for map-based cloning of this gene.

[Objective] In order to establish a theoretical basis for sustainable development of dry-sowing and wet-emergence, and determine the critical content of salinity in soil for cotton seedling development under this planting mode, this study analyzed the effects of dry-sowing and wet-emergence technique on emergence rates and the development of cotton seedling under different levels of salt stress. [Method] The pot experiment was conducted to study the agronomic traits, dry weight and K⁺/Na⁺ ratio of cotton with dry-sowing and wet-emergence technique under salt stress. A control treatment (CK, soil salt content: 0.30 g·kg^-1) and ten treatments with different soil salt content (T1: 1.13 g·kg^-1, T2: 2.47 g·kg^-1, T3: 4.03 g·kg^-1, T4: 5.43 g·kg^-1, T5: 6.75 g·kg^-1, T6: 7.96 g·kg^-1, T7: 9.31 g·kg^-1, T8: 10.66 g·kg^-1, T9: 12.10 g·kg^-1, T10: 13.48 g·kg^-1) were applied. Additionally, the experiment of sowing under suitable moisture was applied to compare the effect of dry-sowing and wet-emergence mode on the seedling emergence rates. [Result] Soil salinity significantly inhibited the germination and emergence of cotton seeds. By using the dry-sowing and wet-emergence technique, the germination rate of cotton significantly improved under salt stress. Compared with sowing under suitable moisture, treatments of T4-T10 using dry-sowing and wet-emergence technique resulted in an increase in the emergence rate to 69.1%-93.3%. Salt stress had significant effects on agronomic traits and dry matter accumulation in cotton by dry-sowing and wet-emergence technique. Plant height, stem diameter, leaf number, square number, and dry matter accumulation of cotton were significantly decreased with the increase of soil salt content. And above-mentioned indexes of CK, T1, and T2 are significantly higher than that of T4-T10. The K⁺/Na⁺ value of cotton plant was also decreased significantly with the increase of soil salt content, in which treatments of T4-T10 were significantly lower than CK, T1, and T2. The result of the principal component analysis based on cotton growth indexes indicated that soil salt stress had a more significant effect on cotton growth and development in T4-T10 compared with CK, T1-T3. [Conclusion] The findings showed that when the soil salt content surpassed that of the T3 treatment (4.03 g·kg^-1), the salt stress significantly inhibited the seedling growth and dry matter accumulation of cotton, while the K⁺/Na⁺ value in cotton plant were significantly decreased. Despite the dry-sowing and wet-emergence technique significantly increased the emergence rate, it mitigated the negative impact of salt stress on the growth and development of cotton. Based on the result of this study, the critical value of soil salt content for the development of cotton seedling under dry-sowing and wet-emergence mode was 4.03 g·kg^-1.

[Objective] The glycosylphosphatidylinositol-anchored lipid transfer protein (LTPG) genes were identified from the whole genome of Gossypium hirsutum to provide support for subsequent research. [Method] Bioinformatics methods were used to screen and identify the LTPG gene family from the TM-1 genome, and the physicochemical properties of proteins, phylogenetic relationship, gene duplication, gene structure, and cis-acting elements in the promoter region were predicted and analyzed. Transcriptome data and real-time quantitative polymerase chain reaction (qRT-PCR) were used to analyze their expression pattern in different tissues and organs and under different abiotic stresses. The subcellular localization of the target proteins was identified by transient transformation in tobacco leaves. [Result] Ninety-five GhLTPG genes were identified in the G. hirsutum genome, which were clustered into 5 categories by phylogenetic tree analysis. Segment duplication is the main reason for the expansion of the GhLTPG gene family. K_a/K_s analysis indicated that GhLTPG underwent strong purification selection. Transcriptome data analysis showed that some GhLTPG responded to low temperature, high temperature, salt, or drought stress. The results of qRT-PCR analysis showed that GhLTPG11/14/52/62 responded to low temperature, high temperature, salt and drought stress, and GhLTPG24/56 responded to low temperature, salt, or drought stress. Subcellular localization experiments showed that both GhLTPG24 and GhLTPG62 were localized in the cell membrane. [Conclusion] Ninety-five GhLTPG genes were identified in the whole genome of G. hirsutum. Some GhLTPG genes responded to abiotic stresses such as low temperature, high temperature, salt and drought, which laid a foundation for in-depth analysis of the function of specific GhLTPG gene.

Based on the dataset of planting area of individual cotton varieties released by National Extension and Service Center of Agricultural Technology in the past 40 years, the varieties with planting area ranking the first in the main cotton producing regions in one year, or with more than 0.33 million hm² planting area and ranking the top three in one or more years were defined as mega varieties. The cumulative planting area, the maximum annual area, the number of years with area ranking in top three, and the planting area percentage of the mega varieties were analyzed. Around forty-four cotton mega varieties were selected in the main cotton production regions (i.e. the Yellow River basin, the Yangtze River basin and the Northwest inland cotton production region) in the past 40 years, among of which the cultivar Lumianyan 15 was found to be a mega cultivar both in the Yellow River basin and the Yangtze River basin cotton production regions. The total number of cotton varieties applied in production every year was generally on the rise during 1981-2020. The increase step of variety number was slow during 1981-2000, but speeded up during 2001-2020. Meanwhile, the proportion of mega varieties planting area to the total area of main cotton producing regions in each year showed significant historical characteristics. The proportion was relatively stable during 1981-1995, with a proportion of around 61%, 36%, and 83% in the Yellow River basin, the Yangtze River basin and the Northwest inland cotton production regions respectively. After then, the area proportion of mega varieties suffered a sharp decline to about 20% on average during 1996-2006, and followed by a slow drop period to around 15% on average till 2020. Cotton mega varieties contributed greatly indeed to the stability and development of cotton production in the history. However, the cotton breeding target at current and also in the future will be more functional and regional oriented to meet the versatile needs of seed industry and market development.

[Objective] This study aims to set up a near infrared spectrum(NIR) calibration model for the protein content and oil content in fuzz cottonseed. [Method] In this study, the SPXY (sample set partitioning based on joint X-Y distance sampling) method was used to divide the 426 samples into 320 as calibration set and 106 as prediction set according to the ratio of 3∶1, and the model was optimized by combining spectral pretreatment methods such as multiplicative scatter correction and first derivative. Three methods, linear partial least square method (PLS), support vector machine (SVM), and random forest (RF) were used to build the NIR rapid determination models of cotton seeds protein content and oil content. The coefficient of determination (R²), root mean square error (RMSE), and residual prediction deviation (RPD) were used as the evaluation indexes of the models. [Result] The results showed that the SVM model and PLS model performed better in the calibration set with R² more than 0.8, but with R² less than 0.8 in the prediction set, indicating that the models were overfitting. While the RF model was very well trained on both the calibration set and prediction sets with R² more than 0.9. The R², predicted RMSE, and RPD of RF model were 0.945 9, 0.935 2, and 4.539 1 for protein content, and 0.909 7, 0.770 4, and 3.489 1 for oil content, respectively. [Conclusion] The prediction model based on RF method can be well applied to the NIR spectroscopy determination of protein content and oil content of fuzz cottonseed, which could replace the chemical method. The results of the study not only lay a foundation for the rapid and nondestructive evaluation of the nutritional quality of cotton seed for seed quality breeding, processing production and marketing, but also provide technical references for the nondestructive analysis of seeds of other crops.

[Objective] Gibberellin 20 oxidase gene GhGA20ox6 was cloned and the preliminary functional analysis was performed for plant height. [Method] The GhGA20ox6 gene was successfully cloned from the stem of upland cotton standard line TM-1. The evolutionary relationships of GhGA20ox6 and its homologous genes in Arabidopsis thaliana and rice were confirmed by phylogenetic analysis and multiple alignment of amino acid sequences. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to analyse the expression pattern of GhGA20ox6 in multiple tissues of TM-1. In addition, subcellular localization was used to analyze its specific subcellular localization. And its function in Arabidopsis was analysed. [Result] The open reading frame of GhGA20ox6 is 1 155 bp and encodes 384 amino acids. The molecular mass of GhGA20ox6 is 43.32 ku and the predicted isoelectric point is 6.37. Phylogenetic analysis showed that GhGA20ox6 was highly similar to the green revolution gene sd1(OsGA20ox2) in rice. The qRT-PCR results showed that GhGA20ox6 was higher expressed in the stem than in other tissues of TM-1. Furthermore, according to the results of subcellular localization analysis in tobacco epidermd cells, GhGA20ox6 was localized in the cell membrane. Overexpression of GhGA20ox6 in Arabidopsis significantly increased the expression of a downstream gene GID1 (gibberellin insensitive dwarf1), resulting in the increase of plant height and earlier bolting. [Conclusion] Based on the cloning and functional analysis of GhGA20ox6, it is speculated that the gene may be related to gibberellin synthesis in cotton, and may affect the plant height of cotton. These results lay a foundation for further molecular verification of the biological function of GhGA20ox6 in cotton growth and development.

[Objective] The effects of nitrogen application depth and amount on cotton dry matter and nitrogen accumulation, distribution and yield in rape-cotton rotation cropping system around Dongting Lake cotton planting region were studied, so as to provide a scientific basis for reducing the application and increasing the efficiency of chemical fertilizer of direct seeding cotton after harvesting rape. [Method] The nitrogen application experiment was carried out at Changde, Hunan Province in 2018 and 2019. A field experiment was conducted using Xiang FZ001 with the treatments of two nitrogen application depths (15 cm and 5 cm, marked by H₁₅ and H₅), and five nitrogen rates (0, 90, 180, 270 and 360 kg·hm^-2, marked by N₀, N₉₀, N₁₈₀, N₂₇₀, N₃₆₀, respectively). [Result] The trends of cotton nitrogen and dry matter accumulation were consistent, and the accumulation dynamics were in line with the logistic model. Deep application of nitrogen fertilizer increased the accumulation of nitrogen and dry matter in cotton plants and their distribution proportion in reproductive organs. With the increase of nitrogen application rate, the accumulation of nitrogen and dry matter and their distribution proportion in reproductive organs all showed a trend of increase at first and decrease afterward. Under the interaction of nitrogen application depth and amount, the accumulation of nitrogen was maximum under H₁₅N₂₇₀; the proportion of nitrogen distribution in reproductive organs, dry matter accumulation and its distribution proportion in reproductive organs were maximum under H₁₅N₁₈₀. From the characteristic values of nitrogen and dry matter accumulation, it could be seen that the accumulation and distribution of nitrogen and dry matter in cotton was basically sychronized, with the average rapid accumulation of nitrogen starting slightly earlier than that of dry matter accumulation, indicating that cotton nitrogen absorption was likely the basis and premise of dry matter accumulation. Compared with H₅, H₁₅ improved the utilization efficiency of nitrogen fertilizer, and the apparent utilization rate, agronomic utilization rate and biased productivity of nitrogen fertilizer decreased with the increase of nitrogen application rate. With the interaction of nitrogen application depth and amount, the H₁₅N₁₈₀ treatment could obtain desirable apparent utilization rate, agronomic utilization rate, biased productivity and production efficiency and highest seed cotton yield. [Conclusion] This study indicated that applying suitable nitrogen application rate and increasing fertilization depth could promote high yield. And it was recommended that the depth of nitrogen application should be increased from 5 cm to 15 cm,and the quantity should be reduced from 270-300 kg·hm^-2 to 180 kg·hm^-2 for the tested region.

[Objective] This study aimed to explore the effects of water and nitrogen management on cotton growth and development, water and nitrogen use efficiency, and soil greenhouse gas emissions under non-film drip irrigation cotton fields in Xinjiang. [Method] Two irrigation quotas (W1: 450 m³·hm^-2, W2: 540 m³·hm^-2) and three nitrogen application rates (150 kg·hm^-2, 225 kg·hm^-2, 300 kg·hm^-2 nitrogen) were set. The differences of total nitrogen content of soil and plant, cotton plant height, cotton stem diameter, seed cotton yield, water and nitrogen use efficiency and soil greenhouse gas emissions were analyzed under different water and nitrogen treatments. [Result] At 225 kg·hm^-2 and 300 kg·hm^-2 nitrogen application rates, the average total nitrogen content in the 0-80 cm soil layer of W1 was higher than that in the W2 treatment at different growth stages. At the same nitrogen application level, the cumulative emissions of soil CO₂, CH₄, N₂O, global warming potential (GWP), greenhouse gas emission intensity (GHGI) and water use efficiency under W1 treatment were all increased compared with W2. Under W1 treatment, the average total nitrogen content of 0-80 cm soil layer at seedling and squaring periods, cotton plant height and stem diameter at different growth stages, seed cotton yield and water use efficiency all increased with the increase of nitrogen application rate. The cumulative emissions of soil CO₂ and CH₄, GWP, GHGI and partial productivity of nitrogen fertilizer decreased with the increase of nitrogen application rate, while the total nitrogen content of plant increased first and then decreased with the increase of nitrogen application rate. Under W2 breatment, total nitrogen content of cotton plant, seed cotton yield and water use efficiency all increased first and then decreased with the increase of nitrogen application rate. The cumulative emissions of soil CO₂ and CH₄, GWP and partial productivity of nitrogen fertilizer all decreased with the increase of nitrogen application rate, while cotton plant height and stem diameter increased with the increase of nitrogen application rate. Through fitting analysis, it was found that the fitting curves of seed cotton yield under W1 treatment and that under W2 treatment intersected when the nitrogen application rate was 278.07 kg·hm^-2. [Conclusion] For the Southern Xinjiang region with water shortage, 450 m³·hm^-2 irrigation quota and 300 kg·hm^-2 nitrogen application rate are efficient water and nitrogen application modes for increasing water use efficiency and cotton yield and reducing emission of soil greenhouse gas under non-film drip irrigation condition.

Crop maturity is the comprehensive performance reflection of crop growth, development and maturation. It is usually expressed by the growth period or life cycle from seedling emergence to harvest. It is also a critical indicator of crop ecological adaptability. The selection of cotton varieties with appropriate maturity is an important prerequisite to ensure normal maturity, high yield, superior fiber quality, and timely harvest. Accurate evaluation of cotton crop maturity is an important basis for cotton cultivation management and genetic improvement. Due to the indeterminate growth characteristic of cotton, the evaluation of cotton crop maturity is complicated, and there are still controversies so far. This manuscript clarifies the concept of cotton crop maturity, and discusses its main influencing factors (genetic factors, environmental factors, and cultivation measures), and reviews predictors and methods used for cotton crop maturity evaluation based on growth characteristics (the first fruit branch node, fruit branch occurrence speed and flowering time interval, pre-frost seed cotton rate, etc.), growth process (growth period, physiological termination period, the number of fruit branches above cracked boll, early maturity index, etc.) and the comprehensive index. In the end, the following suggestions have been given: enhancing the innovation of evaluation predictors for cotton crop maturity, establishment of the evaluation system for cotton crop maturity, and creation of an innovative information collection system, which will provide theoretical and technical support for cotton simplified and mechanized production.

[Objective] This research aims to investigate the effects of male sterile cytoplasm of Gossypium harknessii (CMS-D2) and Gossypium trilobum (CMS-D8) on ATP and H₂O₂ contents. [Method] The contents of ATP and H₂O₂ in leaves and flower buds of CMS-D2 and CMS-D8 "three lines" (sterile line, maintainer line, and restorer line) at different developmental stages were determined, and combined with the subject of existing research, ATP and H₂O₂ contents in Arabidopsis plants overexpressing the sterile candidate gene orf610a were determined. The expression levels of ATP synthesis-related genes in the flower buds of sterile lines, maintainer lines and transgenic Arabidopsis were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR). [Result] During the development of cotton, compared with its maintainer line and restorer line, the leaves of CMS-D2 sterile line showed an extremely significant decrease in ATP content and an extremely significant increase in H₂O₂ content at both the bud stage and boll stage; the leaves of CMS-D8 sterile line showed an extremely significant decrease in ATP content and an extremely significant increase in H₂O₂ content at the bud stage, and an extremely significant increase in ATP content at the boll stage. The ATP content in 3 mm and 4 mm flower buds of CMS-D2 sterile line was extremely significantly decreased, and the H₂O₂ content in 4 mm flower buds was extremely significantly increased; the ATP contents in 5 mm and 6 mm flower buds of CMS-D8 sterile line were extremely significantly decreased. Compared with the maintainer lines, the expression levels of several ATP synthesis-related genes in the flower buds of the CMS-D2 and CMS-D8 sterile lines were extremely significantly reduced. Compared with wild-type Arabidopsis, the H₂O₂ contents in siliques and flower buds of orf610a-overexpressed Arabidopsis were significantly increased, and the ATP content were extremely significantly decreased, and most ATP synthesis-related genes were extremely significantly down-regulated. [Conclusion] The male sterile cytoplasm have certain effects on the contents of ATP and H₂O₂ in leaves and flower buds at different developmental stages of cotton, and the disruption of the dynamic balance may affect the development of pollen.

[Objective] Adenosine diphosphate-glucose pyrophosphorylase(AGPase) is the rate limiting enzyme in the starch biosynthesis pathway, which plays an important role in starch synthesis and accumulation of plant "source" and "sink" organs. However, the systematic study of AGPase gene family has not been carried out in cotton. [Method] In this study, the whole genome identification of AGPase gene family was carried out by bioinformatics based on the published genomic data of Gossypium hirsutum standard line TM-1. The physical and chemical properties, evolutionary relationship, gene structure, cis-acting elements in the promoter region were systematically analyzed. Transcriptomic data and real-time quantitative polymerase chain reaction (qRT-PCR) were used to analyze the expression patterns of AGPase family genes in different tissues and under various abiotic stresses. [Result] A total of 20 AGPase genes (GhAGP) were identified in G. hirsutum, and they were unevenly distributed on 16 chromosomes. There were 12 AGPase gene encoding AGPase large subunit and 8 AGPase gene encoding AGPase small subunit, and had similar conserved motifs and exon-intron structure in different groups. The promoter region of GhAGP had multiple cis-acting elements related to plant hormones and abiotic stress response. Expression analysis showed that GhAGP had different tissue expression patterns. The expression level analysis under abiotic stress showed that most GhAGP were induced by low temperature, high temperature, salt and drought stress, in which GhAGPL1 and GhAGPL7 were involved in the response to a variety of stresses in cotton. [Conclusion] The distribution, structural and phylogenetic characteristics of AGPase genes were clarified in G. hirsutum, and the function of AGPase gene family in response to external environmental stress was preliminarily revealed, which provide important candidate gene resources for genetic improvement of starch traits and stress resistance breeding in cotton.