Drought significantly reduces cotton boll yields across various fruiting branches (FBs). Potassium (K) application can partially mitigate the drought-induced damage by modifying the biosynthesis of photoassimilates in the leaf subtending to cotton boll (LSCB) and facilitating their transport to the subtending bolls, although its effects vary among FBs. The underlying mechanisms remain unclear. To investigate this, potting experiments were conducted at three soil relative water content (SRWC): 75 +/- 5 % (W75), 60 +/- 5 % (W60), and 45 +/- 5 % (W45), along with K rates of 0 (K0), 150 (K150) and 300 (K300) kg K2O ha-1. Compared to W75, the W60 and W45 treatments reduced the photosynthesis of LSCBs in different FBs, adversely affecting carbohydrate accumulation in the subtending cotton bolls. K application can mitigate this negative impact, with the most pronounced effects observed in the middle and upper FBs. K application (K150 and K300) enhanced the net photosynthetic rate, stomatal conductance, maximum mass yield of PSII and chlorophyll content of LSCB in the middle and upper FBs compared to K0 under drought conditions. Additionally, K application significantly increased K content in LSCBs within the middle and upper FBs, which in turn elevated sucrose phosphate synthase (SPS), and sucrose synthase (SuSy) activities, reducing the conversion of sucrose into starch, ultimately facilitating carbohydrate exports to the subtending bolls. In summary, we propose a model that elucidates how K application mitigates drought damage by enhancing the exports of photoassimilates from the middle and upper FBs to their respective subtending cotton bolls.

Introduction Verticillium wilt is a severe soil-borne disease that affects cotton growth and yield. Traditional monitoring methods, which rely on manual investigation, are inefficient and impractical for large-scale applications. This study introduces a novel approach combining machine learning with feature selection to identify sensitive spectral features for accurate and efficient detection of cotton Verticillium wilt.Methods We conducted comprehensive hyperspectral measurements using handheld devices (350-2500 nm) to analyze cotton leaves in a controlled greenhouse environment and employed Unmanned Aerial Vehicle (UAV) hyperspectral imaging (400-995 nm) to capture canopy-level data in field conditions. The hyperspectral data were pre-processed to extract wavelet coefficients and spectral indices (SIs), enabling the derivation of disease-specific spectral features (DSSFs) through advanced feature selection techniques. Using these DSSFs, we developed detection models to assess both the incidence and severity of leaf damage by Verticillium wilt at the leaf scale and the incidence at the canopy scale. Initial analysis identified critical spectral reflectance bands, wavelet coefficients, and SIs that exhibited dynamic responses as the disease progressed.Results Model validation demonstrated that the incidence detection models at the leaf scale achieved a peak classification accuracy of 85.83%, which is about 10% higher than traditional methods without feature selection. The severity detection models showed improved precision as disease severity of damage increased, with accuracy ranging from 46.82% to 93.10%. At the canopy scale, UAV-based hyperspectral data achieved a remarkable classification accuracy of 93.0% for disease incidence detection.Discussion This study highlights the significant impact of feature selection on enhancing the performance of hyperspectral-based remote sensing models for cotton wilt monitoring. It also explores the transferability of sensitive spectral features across different scales, laying the groundwork for future large-scale early warning systems and monitoring cotton Verticillium wilt.

Drought stress negatively affects cotton pollen fertility, which in turn leads to a decrease in seed number per boll and boll weight. Exogenous melatonin application significantly enhances pollen fertility under drought conditions, while the specific underlying mechanisms remain unclear. A pot experiment was conducted using a cultivar Yuzaomian 9110 under two moisture treatments (soil relative water content at 75 +/- 5 % and 45 +/- 5 %) with two melatonin concentration (0 and 200 mu M) to investigate the effects of exogenous melatonin on the structural traits and physiological metabolism of cotton anthers and its' relationships with pollen fertility. Results demonstrated the significant impact of drought on anthers development and metabolism, with damage to the anther tapetum and decreased starch and adenosine triphosphate (ATP) contents, subsequently resulting in reduced pollen germination rate, seed number per boll and boll weight. Melatonin application in water-deficit anthers up-regulated the expression of sucrose transporter protein (GhSWEET55) and phosphate sucrose synthetase, promoting sucrose import and synthesis, respectively. However, it also increased sucrose synthase and acid convertase, accelerating sucrose decomposition and reducing its content. Additionally, melatonin application promoted starch accumulation in water-deficit anthers by enhancing activities of adenosine diphosphate glucose pyrophosphorylase and soluble starch synthase, meaning that potential energy storage was increased, which facilitated the formation of pollen fertility. Although melatonin application reduced the expression of pyruvate kinase (GhPK) and glucose 6-phosphogluconate dehydrogenase (GhG6PD) genes in water-deficit anthers, it upregulated hexokinase (GhHXK) and citrate synthase (GhCIT) expression, enhancing ATP content, and ultimately pollen fertility, seed number and boll weight under drought. In summary, exogenous melatonin preserved cotton pollen fertility under drought stress by regulating carbohydrate and energy metabolism, especially enhancing starch and ATP accumulation in anthers.

Cotton is a highly sensitive crop to drought stress. Consequently, it is crucial to devise strategies that optimize crop production in conditions of limited water availability. While potassium silicate has demonstrated effectiveness in mitigating drought stress in various crops, its specific impact on different cotton cultivars under drought conditions remains not fully clarified. This research aimed to assess the efficacy of six potassium silicate levels (0, 100, 200, 300, 400 and 500 mg L-1) on four cotton genotypes (Zong main-113, Xin Nong-525, Xin lu Zhong-55, and Xin lu Zhong-66) under two field capacity levels (80% and 50% FC) in a sand culture. Foliar applied potassium silicate significantly improved photosynthetic efficiency, shoot biomass, root biomass, and leaf area under water stress (50% FC). The most substantial reduction in H2O2, malondialdehyde levels, and electrolyte leakage was recorded with potassium silicate applied at a rate of 400 mg L-1. This concentration effectively mitigated reactive oxygen species accumulation, safeguarding plants against oxidative damage at 50% FC. Furthermore, potassium silicate contributed to maintaining water status, resulting in increased leaf water content and elevated water-soluble proteins in cotton plants. The order of drought resistance (50% FC) with the application of potassium silicate at 400 mg L-1 was Zong Mian-113, Xin Nong-525, Xin lu Zhong-55, and Xin lu Zhong-66. The findings could help in selection of drought resistance cultivars of cotton in water limited conditions.

By improving soil properties, cover crops can reduce wind erosion and sand damage to emerging cotton (Gossypium hirsutum L.) plants. However, on the Texas High Plains, questions regarding cover crop water use and management factors that affect cotton lint yield are common and limit conservation adoption by regional producers. Studies were conducted near Lamesa, TX, USA, in 2017-2020 to evaluate cover crop species selection, seeding rate, and termination timing on cover crop biomass production and cotton yield in conventional and no-tillage systems. The no-till systems included two cover crop species, rye (Secale cereale L.) and wheat (Triticum aestivum L.) and were compared to a conventional tillage system. The cover crops were planted at two seeding rates, 34 and 68 kg ha(-1), and each plot was split into two termination timings: optimum, six to eight weeks prior to the planting of cotton, and late, which was two weeks after the optimum termination. Herbage mass was greater in the rye than the wheat cover crop in three of the four years tested, while the 68 kg ha(-1) seeding rate was greater than the low seeding rate in only one of four years for both rye and wheat. The later termination timing produced more herbage mass than the optimum in all four years. Treatments did not affect cotton plant populations and had a variable effect on yield. In general, cover crop biomass production did not reduce lint production compared to the conventional system.

Reproductive failure in cotton caused by drought has been reported to be closely associated with alterations in pistil fertility; however, the mechanism of the effect of drought on pistil fertility in cotton is less studied. We hypothesized that drought would inhibit the ovule formation to alter pistil potential fertility. To address this hypothesis, we conducted a water deficit induction experiment with a cotton cultivar, Dexiamian 1. Results showed that drought damaged the cytological structure of the developing ovules. This resulted in a lower ovule number, finally leading to lower cottonseed number and boll weight. And the decreased ovule number was closely related to the reactive oxygen species (ROS) accumulation in pistil during ovule development. Further analysis of antioxidant metabolism found that in the enzymatic antioxidant system, drought decreased the activities of superoxide dismutase (SOD) and catalase (CAT), resulting in the accumulation of superoxide anion (O2 center dot-$$ {{\mathrm{O}}_2}{\bullet -} $$) and hydrogen peroxide (H2O2). Regarding the non-enzymatic antioxidant system, the elevated glutathione reductase gene (GhGR) expression under drought promoted the glutathione (GSH) accumulation; however, the decreased dehydroascorbate reductase gene (GhDHAR2) expression under drought inhibited the conversion of GSH to ascorbic acid (AsA). Although the increased monodehydroascorbate reductase gene (GhMDHAR) expression under drought promoted AsA accumulation, drought-induced reduced ascorbate peroxidase gene (GhAPX) expression inhibited the reduction of H2O2 by AsA, which ultimately led to higher AsA content and H2O2 content. We conclude that drought impedes the ovule formation by disturbing pistil's antioxidant metabolic homeostasis to destruct the cytological structure of the developing ovules.

Excessive salt content in soil has adverse effects on cotton production, especially during the germination and seedling stages. gamma-aminobutyric acid (GABA) is an important active substance that is expected to improve the resistance of plants to abiotic stresses. This study focused on two cotton cultivars (Gossypium hirsutum L.: Tahe 2 and Xinluzhong 62) and investigated the impact of exogenous GABA (0, 1, 2, 3, and 4 mM) on seed germination, seedling growth, and related morphological, physiological, and biochemical indicators under salt stress (150 mM NaCl). The results showed that salt stress significantly reduced the germination rate and germination index of cotton seeds (decreased by 20.34% and 32.14% for Tahe 2 and Xinluzhong 62, respectively), leading to decreased seedling height and biomass and causing leaf yellowing. Salt stress induced osmotic stress in seedlings, resulting in ion imbalance (marked reduction in K+/Na+ ratio) and oxidative damage. Under salt stress conditions, exogenous GABA increased the germination rate (increased by 10.64 similar to 23.40% and 2.63 similar to 31.58% for Tahe 2 and Xinluzhong 62, respectively) and germination index of cotton seeds, as well as plant height and biomass. GABA treatment improved leaf yellowing. Exogenous GABA treatment increased the content of proline and soluble sugars, with varying effects on betaine. Exogenous GABA treatment reduced the Na+ content in seedlings, increased the K+ content, and increased the K+/Na+ ratio (increased by 20.44 similar to 28.08% and 29.54 similar to 76.33% for Tahe 2 and Xinluzhong 62, respectively). Exogenous GABA treatment enhanced the activities of superoxide dismutase and peroxidase, and reduced the accumulation of hydrogen peroxide and malondialdehyde, but had a negative impact on catalase activity. In conclusion, exogenous GABA effectively improved cotton seed germination. By regulating osmoprotectant levels, maintaining ion homeostasis, and alleviating oxidative stress, GABA mitigated the adverse effects of salt stress on cotton seedling growth.