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Mechanical monoseeding has been widely adopted in cotton planting; however, it can result in either double seedlings per hole or a decrease in seedling density due to missed seeding or seedling mortality. The impact of these conditions on cotton yield remains uncertain. In this study, we hypothesized that neither double seedlings per hole nor a reduction in seedling density would negatively affect cotton yield. Furthermore, we propose that yield stability can be achieved by manipulating vegetative branching and photoassimilate partitioning. We conducted two experiments in 2020, 2021 and 2022. The first experiment included a monoseeding treatment, where one seed per hole was sown without seedling thinning after emergence, and a cluster seeding treatment, where ten seeds per hole were sown and one seedling was left after emergence. In the second experiment, a double seedlings per hole (2 S) treatment was set up by sowing ten seeds per hole and leaving two seedlings per hole after thinning, while a one seedling per hole (1 S) treatment with the same plant density served as the control. The growth of vegetative branches (VB), boll-setting on both vegetative and sympodial branches (SB), yield, canopy apparent photosynthesis (CAP), and assimilate partitioning were evaluated. In the first experiment, monoseeding decreased the final plant density by 16.8% compared to cluster seeding, but there was no difference in seedcotton yield between the two treatments. Monoseeding exhibited higher values for VB biomass, number of bolls on VB, and their contribution to yield, indicating improved vegetative branching and VB fruiting, compensating for the yield loss due to plant density reduction. Although monoseeding did not show superiority in terms of leaf area and CAP, it increased photoassimilate partitioning to VB and VB bolls by 1.4 and 2 times compared to cluster seeding, respectively, which played a key role in the improved vegetative branching under monoseeding. In the second experiment, there were no difference in leaf area index, CAP and seedcotton yield between 2 S and 1 S. However, the VB biomass and its percentage to total biomass, the number of bolls on VB an their percentage contribution to yield under 2 S significantly decreased relative to 1 S, indicating inhibited vegetative branching and VB fruiting. Furthermore, the photoassimilate partitioning of 2 S to VB and VB bolls decreased by 32.6% and 29.4% compared with 1 S, but the partitionging to SB and bolls on SB increased by 2.4 and 4.1 times, respectively. Thus, the yield stability was achieved by suppressing vegetative branching while promoting sympodial branching under the 2 S treatment. The expression patterns of phytohormone (IAA, GA and CKs)-related genes and hormone contents in the VB tips were consistent with the observed changes in vegetative branching. This study indicated that the reduced seedling density and double plants per hole caused by monoseeding did not reduce cotton yield, which was achieved through manipulation of photoassimilate partitioning and vegetative branching associated with the expression of phytohormone-related genes and phytohormone levels in VB tips. This study provides a strong evidence in favor of monoseeding, and offers new insights into enhancing yield stability through manipulation of photoassimilate partitioning and branching in cotton. • Monoseeding may lead to double seedlings per hole or reduced seedling density. • Neither double seedlings nor seedling density reduction decreased cotton yield. • Yield stability was due to vegetative branching and photoassimilate partitioning. • The study provides new insights for monoseeding without seedling thinning. [ABSTRACT FROM AUTHOR]

Plastic film mulching has been widely applied to improve crop productivity of full-season cotton (Gossypium hirsutum L.). However, in a previous study, plastic mulching did not increase seed cotton yield of short-season cotton compared with non-mulching. The aim of this study was to determine why plastic mulching fails to increase seed cotton yield of short-season cotton. A short-season cultivar Lumian 532 was planted with or without plastic mulching at an experimental station in Linqing in the Yellow River valley of China in 2020 and 2021. Yield, yield components, leaf senescence, photoassimilate accumulation and partitioning, photohormone contents, expression of senescence-related genes, and root traits were examined each year. Seed cotton yield produced with plastic mulching was not significantly different from that produced with non-mulching in short-season cotton. Although number and size of early- and mid-season bolls were significantly greater with plastic mulching than with non-mulching, plastic mulching decreased number and size of late-season bolls by 34.0% and 8.8%, respectively. At the initial boll opening stage, photosynthetic rate and chlorophyll content in main-stem functional leaves were 36.2% and 24.1% lower, respectively, with plastic mulching than with non-mulching, but malondialdehyde content was 34.2% higher, suggesting that plastic mulching accelerated late-season leaf senescence. Canopy photosynthesis and photoassimilate partitioning to reproductive organs at the initial boll-opening stage were 68.1% and 9.4% lower, respectively, with plastic mulching than with non-mulching. Compared with non-mulching, plastic mulching increased abscisic acid and methyl jasmonate contents but decreased those of cytokinins content because of differential expression of hormone metabolism-related genes in late-season main-stem leaves. Plastic mulching also increased root distribution in the shallow soil layer and lowered root vigor in the late season, compared with non-mulching. Overall, plastic mulching negatively affected root distribution and function and altered expression of senescence-related genes and hormone metabolism-related genes to affect hormone balance, which led to accelerated late-season leaf senescence. Because of late-season leaf senescence, canopy photosynthesis and photoassimilate partitioning to cotton bolls were suppressed with plastic mulching, which led to fewer and smaller late-season bolls than those with non-mulching. Thus, plastic mulching failed to improve the seed cotton yield. This study provides a clear explanation of how plastic mulching causes late-season leaf senescence and further demonstrates that plastic film mulching is not required for planting short-season cotton in the Yellow River valley of China or in other cotton growing areas with similar ecology. • Plastic mulching did not increase yield compared with non-mulching because of fewer and smaller late-season bolls in short-season cotton. • Reduced number and size of late-season cotton bolls was attributed to accelerated late-season leaf senescence in short-season cotton. • Accelerated leaf senescence was due to shallow root distribution and weak root vigor, and differential expression of senescence-related genes. [ABSTRACT FROM AUTHOR]

Waterlogging stress hampers cotton growth and development, ultimately causing yield loss. Nitric oxide (NO) was previously found to alleviate waterlogging damage to cotton plants, but it is unclear whether NO can enhance compensatory growth after waterlogging relief. Herein, field-grown cotton (Gossypium hirsutum L.) plants at peak flowering were subjected to a 10-day waterlogging stress treatment, and the effects of foliar spraying of sodium nitroprusside (SNP)—a NO donor—during waterlogging were evaluated. The NO concentrations in the plant tissues, plant biomass, and related physiological events at 10 d post-waterlogging relief, as well as the seedcotton yield and yield components at harvest, were measured over two consecutive years. Non-waterlogged and waterlogged cotton exhibited 38.5% and 48.3% increased plant biomass at 10 d post-waterlogging relief, respectively, compared with that on the day of stress relief, indicating that significant compensatory growth occurred following stress relief. Foliar spraying cotton with SNP during waterlogging not only increased the NO concentration (40–183%) before stress relief, but also increased the NO concentration (30–75%) after stress relief compared with no SNP application. As the NO concentration increased, plant biomass at 10 d post-waterlogging, as well as biological yield, boll density, and seedcotton yield of waterlogged cotton at harvest, were increased by 54.4%, 8.0%, 7.5%, and 7.6% under foliar SNP spraying compared to no SNP spraying, indicating that NO promoted compensatory growth and reduced the yield loss of waterlogged cotton. Correlation analysis showed that yield loss reduction was positively correlated with compensatory growth (R2 = 0.83**). Foliar spraying of SNP decreased the malondialdehyde content and the activities of alcohol dehydrogenase and pyruvate decarboxylase in waterlogged cotton at 10-d post stress relief by 15.2%, 42.4%, and 38.2%, but increased the contents of auxin (IAA), gibberellic acid (GA), and chlorophyll and the photosynthetic rate by 28.6%, 59.6%, 12.1%, and 6.4%, respectively, and decreased the abscisic acid (ABA) and ethylene contents by 12.5% and 8.5%, respectively, compared to no SNP spraying. In conclusion, foliar spraying of SNP increased the content of NO in waterlogged cotton plants even at 10-d post stress. Hormonal rebalance was realized through increased IAA and GA and reduced ABA and ethylene due to the elevated NO content, which promoted photosynthetic recovery and compensatory growth after stress relief, ultimately reducing yield loss. The overall results indicated that enhancing the compensatory growth of cotton after waterlogging is an important mechanism by which NO mitigates waterlogging stress. • Nitric oxide enhanced the compensatory growth of waterlogged cotton and reduced the yield loss. • Enhanced compensatory growth by nitric oxide was achieved through physiological adjustments after waterlogging relief. • The reduction of yield loss was correlated with the compensatory growth of waterlogged cotton. • Enhanced compensatory growth by NO is an important attribute to the yield loss reduction under waterlogging. [ABSTRACT FROM AUTHOR]

Abstract: Plant density and nitrogen fertilization are two important practices for field-grown cotton (Gossypium hirsutum L.). The objective of this study was to investigate the effects of plant density and N fertilization rate, especially their interactions, on yield, yield components, late-season leaf senescence and Cry1Ac expression in Bt (Bacillus thuringiensis) cotton under salinity conditions. To achieve this goal, we conducted a three-year experiment with a high-yielding Bt cotton cultivar (SCRC 28) in a moderately saline (ECe=11dS/m) field, using a split-plot design in the Yellow River Delta of China. The main plots were assigned to low, medium and high plant densities (3.0, 5.25 and 7.5plants/m2), while low, moderate and high nitrogen rates (120, 225 and 300kgN/ha) were assigned to the subplots. Biological yield, lint yield, yield components, harvest index, boll load, Cry1Ac expression and leaf senescence were significantly affected by plant density and N rate. Lint yield was also affected by plant density×N rate interaction. Increased plant density or N rate enhanced biological yield, but reduced harvest index. Considerably high lint yield (1604kg/ha) was achieved only with a high dose of N fertilizer under low plant density, but comparable yields (1693 and 1643kg/ha) were achieved with moderate and low N rate under medium and high plant density. Increased plant density and N rate reduced boll load, which had highly significant negative correlation with late-season leaf photosynthesis (r =−0.928) and significant correlation with Cry1Ac protein concentration (r =−0.8131). Leaf senescence was delayed by increasing plant density and N rate mainly due to reduced boll load and a combination of reduced boll load and nutritional effect. Medium plant density with moderate N rate or high plant density with low N rate would enhance cotton yield and moderate Cry1Ac expression at reduced cost in the Yellow River Delta of China and other areas with similar ecologies. [Copyright &y& Elsevier]