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With the increasing demands for crop yield and production mechanization, improvement of plant architecture is getting more imperative in cotton. In the present study, we investigated the plant height (PH) and the node of first fruiting branch (NFFB) of 719 upland cotton accessions in six different environments. We used the 10,511 high‐quality single nucleotide polymorphisms (SNPs) to perform single‐locus and multi‐locus genome‐wide association study (GWAS). As many as 278 associated SNPs were identified, 142 by the mixed linear model (MLM) in the single‐locus model and 192 by six multi‐locus models. A total of 42 SNPs were identified in at least four environment‐traits or methods, of which 28 SNPs were significantly associated with PH, 22 were significantly associated with NFFB, and eight were co‐associated with the two traits. Notably, most of loci were novel besides i33922Gh located in the reported QTL for PH. Furthermore, we identified nine promising candidate genes, among which the three genes Gh_D03G0738, Gh_D10G2028, and Gh_D05G3600 contained non‐synonymous SNP mutation. The accessions with alleles of the mutations resulted in significant phenotypic differences. The expression of these genes showed significant differences between short‐PH and high‐PH varieties. Moreover, overexpression of Gh_D03G0738 led to reduction of PH in Arabidopsis. These results provided insights into genetic basis of plant architecture in cotton. Core Ideas: We identified 278 single nucleotide polymorphisms (SNPs) associated plant height (PH) and node of the first fruiting branch with single‐ and multi‐locus genome‐wide association study by using 719 cotton accessions.A total of 42 SNPs were identified in at least four environment‐traits or methods.Overexpression of Gh_D03G0738 led to reduction of PH in Arabidopsis. [ABSTRACT FROM AUTHOR]

In saline and salinity-affected soils, the global productivity and sustainability of cotton are severely affected by soil salinity. High salt concentrations hinder plant growth and yield formation mainly through the occurrence of osmotic stress, specific ion toxicity, and nutritional imbalance in cotton. A number of agronomic practices have been identified as potential solutions to alleviate the adverse effects induced by salinity. While genetic breeding holds promise in enhancing the salinity tolerance of cotton, agronomic practices that improve the root zone environment, ameliorate soil conditions, and enhance salinity tolerance are currently considered to be more practical. This compressive review highlights the effectiveness of agronomic practices, such as furrow seeding, plastic mulching, their combination, densely planting, and the appropriate application of fertilizer and plant growth regulators, in mitigating the negative impact of salinity on cotton. By implementing these agronomic practices, cotton growers can improve the overall performance and resilience of cotton crops in saline and salinity-affected soils. This review provides valuable insights into practical agronomic measures that can be adopted to counteract the adverse consequences of soil salinity on cotton cultivation. [ABSTRACT FROM AUTHOR]

Weeds seriously affect the yield and quality of crops. Because manual weeding is time-consuming and laborious, the use of herbicides becomes an effective way to solve the harm caused by weeds in fields. Both 5-enolpyruvyl shikimate-3-phosphate synthetase (EPSPS) and acetyltransferase genes (bialaphos resistance, BAR) are widely used to improve crop resistance to herbicides. However, cotton, as the most important natural fiber crop, is not tolerant to herbicides in China, and the EPSPS and BAR family genes have not yet been characterized in cotton. Therefore, we explore the genes of these two families to provide candidate genes for the study of herbicide resistance mechanisms. In this study, 8, 8, 4, and 5 EPSPS genes and 6, 6, 5, and 5 BAR genes were identified in allotetraploid Gossypium hirsutum and Gossypium barbadense, diploid Gossypium arboreum and Gossypium raimondii, respectively. Members of the EPSPS and BAR families were classified into three subgroups based on the distribution of phylogenetic trees, conserved motifs, and gene structures. In addition, the promoter sequences of EPSPS and BAR family members included growth and development, stress, and hormone-related cis-elements. Based on the expression analysis, the family members showed tissue-specific expression and differed significantly in response to abiotic stresses. Finally, qRT-PCR analysis revealed that the expression levels of GhEPSPS3, GhEPSPS4, and GhBAR1 were significantly upregulated after exogenous spraying of herbicides. Overall, we characterized the EPSPS and BAR gene families of cotton at the genome-wide level, which will provide a basis for further studying the functions of EPSPS and BAR genes during growth and development and herbicide stress. [ABSTRACT FROM AUTHOR]

Crops must efficiently allocate their limited energy resources to survival, growth and reproduction, including balancing growth and defense. Thus, investigating the underlying molecular mechanism of crop under stress is crucial for breeding. Chloroplasts immunity is an important facet involving in plant resistance and growth, however, whether and how crop immunity modulated by chloroplast is influenced by epigenetic regulation remains unclear. Here, the cotton lysine 2‐hydroxyisobutyrylation (Khib) and succinylation (Ksuc) modifications are firstly identified and characterized, and discover that the chloroplast proteins are hit most. Both modifications are strongly associated with plant resistance to Verticillium dahliae, reflected by Khib specifically modulating PR and salicylic acid (SA) signal pathway and the identified GhHDA15 and GhSRT1 negatively regulating Verticillium wilt (VW) resistance via removing Khib and Ksuc. Further investigation uncovers that photosystem repair protein GhPSB27 situates in the core hub of both Khib‐ and Ksuc‐modified proteins network. The acylated GhPSB27 regulated by GhHDA15 and GhSRT1 can raise the D1 protein content, further enhancing plant biomass‐ and seed‐yield and disease resistance via increasing photosynthesis and by‐products of chloroplast‐derived reactive oxygen species (cROS). Therefore, this study reveals a mechanism balancing high disease resistance and high yield through epigenetic regulation of chloroplast protein, providing a novel strategy to crop improvements. [ABSTRACT FROM AUTHOR]

Crop rotation and intercropping are important ways to increase agricultural resource utilization efficiency and crop productivity. Alternate intercropping, or transposition intercropping, is a new intercropping pattern in which two crops are intercropped in a wide strip with planting positions switched annually on the same land. Transposition intercropping combines intercropping and rotation and thus performs better than either practice alone. Compared with traditional intercropping or rotation, it can increase yield and net return by 17–21% and 10–23%, respectively, and the land equivalent ratio (LER) by 20% to 30%. In crop growth and development, a balanced root–shoot relation is essential to obtain satisfactory yields and yield quality. Intercropping, rotation, or the combination can alter the original root–shoot relation by changing the ecology and physiology of both root and shoot to achieve a rebalancing of the relation. The crop yield and yield quality are thus regulated by the root–shoot interactions and the resulting rebalancing. The review examines the effects of above- and belowground interactions and rebalancing of root–shoot relations on crop yields under cotton-based intercropping, rotation, and particularly alternate intercropping with the practices combined. The importance of signaling in regulating the rebalancing of root–shoot relations under intercropping, rotation, and the combination was also explored as a possible focus of future research on intercropping and rotation. [ABSTRACT FROM AUTHOR]

Verticillium wilt (VW), a fungal disease caused by Verticillium dahliae, currently devastates cotton fiber yield and quality seriously, yet few resistance germplasm resources have been discovered in Gossypium hirsutum. The cotton variety Nongda601 with suitable VW resistance and high yield was developed in our lab, which supplied elite resources for discovering resistant genes. Early nodulin-like protein (ENODL) is mainly related to nodule formation, and its role in regulating defense response has been seldom studied. Here, 41 conserved ENODLs in G. hirsutum were identified and characterized, which could divide into four subgroups. We found that GhENODL6 was upregulated under V. dahliae stress and hormonal signal and displayed higher transcript levels in resistant cottons than the susceptible. The GhENODL6 was proved to positively regulate VW resistance via overexpression and gene silencing experiments. Overexpression of GhENODL6 significantly enhanced the expressions of salicylic acid (SA) hormone-related transcription factors and pathogenicity-related (PR) protein genes, as well as hydrogen peroxide (H2O2) and SA contents, resulting in improved VW resistance in transgenic Arabidopsis. Correspondingly, in the GhENODL6 silenced cotton, the expression levels of both phenylalanine ammonia lyase (PAL) and 4-coumarate-CoA ligase (4CL) genes significantly decreased, leading to the reduced SA content mediating by the phenylalanine ammonia lyase pathway. Taken together, GhENODL6 played a crucial role in VW resistance by inducing SA signaling pathway and regulating the production of reactive oxygen species (ROS). These findings broaden our understanding of the biological roles of GhENODL and the molecular mechanisms underlying cotton disease resistance. [ABSTRACT FROM AUTHOR]

Fiber quality is a major breeding goal in cotton, but phenotypically direct selection is often hindered. In this study, we identified fiber quality and yield related loci using GWAS based on 2.97 million SNPs obtained from 10.65× resequencing data of 1081 accessions. The results showed that 585 novel fiber loci, including two novel stable SNP peaks associated with fiber length on chromosomes At12 and Dt05 and one novel genome regions linked with fiber strength on chromosome Dt12 were identified. Furthermore, by means of gene expression analysis, GhM_A12G0090 , GhM_D05G1692 , GhM_D12G3135 were identified and GhM_D11G2208 function was identified in Arabidopsis. Additionally, 14 consistent and stable superior haplotypes were identified, and 25 accessions were detected as possessing these 14 superior haplotype in breeding. This study providing fundamental insight relevant to identification of genes associated with fiber quality and yield will enhance future efforts toward improvement of upland cotton. • A total of 909 novel fiber and yield loci were detected via WGRS with 10.65× coverage depth in 1,081 cotton accessions. • Three novel stable SNP peaks associated with FL and FS were found. • GhM_D11G2208 can promote cell elongation based up leaf trichome and dark-grown hypocotyls in Arabidopsis. • 14 consistent and stable superior haplotypes were detected based on 915 SNPs in Dt11 region. [ABSTRACT FROM AUTHOR]

Basal and topdressing split application of nitrogen (N) fertilizer is widely used in cotton in many cotton-growing countries, including China. Recently, in the Yellow River valley of China, one-off basal application of N fertilizer has been applied to meet the challenge of increasing labor costs. However, how one-off basal application of N fertilizer affects cotton yields and N use efficiency and by what mechanisms are not clear. Therefore, an experiment was conducted using full-season (K836) and short-season (LM532) cotton cultivars in a moderate fertility field in the Yellow River valley in 2019 and 2020. A split-plot design was established for each variety with the main plots assigned to a mulching pattern (with or without plastic film mulching) and the subplots assigned to an N rate (0 or 195 kg N ha−1, abbreviated as N0 and N195). Cotton yield and yield components, biomass accumulation and distribution, and total N and 15N absorption and utilization were determined each year. Compared with N0, one-off basal application of N fertilizer (N195) did not increase boll density, boll weight, lint percentage or seedcotton yield regardless of cultivar or mulching. Biomass and total N uptake of cotton increased significantly in N195 compared with N0, but the increases occurred primarily in vegetative organs, leading to reductions in the harvest index and N yield efficiency index. With one-off basal application of N fertilizer, more than 80 % of the N in cotton plants derived from soil. Approximately 28 % of 15N-labeled urea was absorbed by cotton plants, of which only approximately 35 % was used in forming seedcotton yield. Therefore, cotton plants with one-off basal application of N fertilizer only recovered a small amount of fertilizer N, and even less of the fertilizer N was used in yield formation. As a result, the harvest index of cotton decreased, and thus, one-off basal application of N fertilizer failed to increase seedcotton yield. Cultivar and plastic film mulching did not alter the effects of one-off basal application of N fertilizer. Therefore, although one-off basal application of N fertilizer in cotton is a labor-saving approach, it should not be encouraged in moderate fertility soil in the Yellow River valley or other areas with similar ecology. • One-off basal N application did not increase the seedcotton yield compared with no-N fertilization. • One-off N application led to a low proportion of plant N derived from 15N and even less for yield formation. • Both N uptake and N distribution to vegetative organs was improved by one-off basal N application. • Cultivar and plastic mulching did not alter the effects of one-off basal application of N fertilizer. [ABSTRACT FROM AUTHOR]

Productivity and benefits in intercropping systems are influenced by the overlapping period and competitive dynamics between species, which are contingent upon variety selection and planting schedules. However, there is limited research on improving the productivity of intercropping systems by adjusting sowing dates for combinations with minimal plant height differences. A two-year field experiment utilizing a strip intercropping with four rows of cotton and five rows of soybeans was conducted. Three soybean varieties (Qihuang 34, Jidou 12, and Jidou 17) with varying plant heights and types, along with early and late sowing dates, were examined. Intercropping cotton and soybeans resulted in higher yields than monoculture, with Jidou 12 identified as the most suitable variety for intercropping with cotton. The land equivalent ratio (LER) for the cotton-soybean intercropping system averaged between 1.04 and 1.15 over two years. Notably, intercropping cotton with late-sown Qihuang 34, Jidou 12, and Jidou 17 demonstrated increased LER by 4 %, 5 %, and 3 % respectively, compared to early-sown. This demonstrates that adjusting the soybean sowing date can modulate the competition dynamics between cotton and soybean, mitigating interspecific competition. Furthermore, intercropping cotton with late-sown Jidou 12 exhibited superior performance in terms of dry matter, canopy photosynthesis, photosynthetically active radiation, and root morphology in cotton compared to other treatments. Within the distance of 100–150 mm from the soybean, cottons were more competitive than soybeans, indicating subtle interspecific competition between the two species. By carefully selecting soybean varieties and adjusting sowing dates, temporal complementarity and spatial niche differentiation can be achieved, alleviating interspecific competition and enhancing the productivity of cotton-soybean intercropping systems. • Intense competition between cotton and soybean limits intercropping productivity. • Intercropping cotton with late-sown Jidou 12 mitigates interspecific competition. • It enhances niche differentiation through improved light utilization and root growth. • Niche differentiation increases the productivity in intercropping cotton with late-sown Jidou 12. [ABSTRACT FROM AUTHOR]

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]

Cotton has a complex branching pattern including sympodial and vegetative branching. Traditionally managed cotton mainly depends on sympodial branching for formation of yield-contributing fruit. Whether seedcotton yield based solely on vegetative branching is comparable with that based solely on sympodial or both types of branching is unclear. The study determined how terminal removal at first square to avoid formation of sympodial branches (SBs) regulated vegetative branching and yield under different plant densities. A two-year split-plot design field experiment had main plots with plant density (4.5 and 9.0 plants m−2) and subplots with plant pruning mode. Pruning modes were terminal removal at first square (TRS) to avoid formation of sympodial branches but retain only vegetative branches (VBs), removal of VBs (RVB) to retain only SBs, and no pruning (CK), with both branch types remaining intact. Canopy photosynthesis, dry matter accumulation and partitioning, and seedcotton yield and yield components were examined. At low plant density (4.5 plants m−2), compared with other pruning modes, TRS increased seedcotton yield and biological yield but did not affect harvest index. At high plant density (9.0 plants m−2), compared with other pruning modes, TRS decreased seedcotton yield and harvest index, although biological yield increased. The yield increase with TRS at low plant density was attributed to the increase in biological yield, which was due to significantly higher canopy photosynthesis with TRS than with other pruning modes. At high plant density, photosynthesis with TRS was higher than that with no pruning at peak boll-setting and boll-opening stages and higher than that with RVB from peak squaring to boll-opening. Compared with other pruning modes, TRS increased dry matter partitioning to vegetative organs but decreased partitioning to reproductive organs. Pearson correlation analysis revealed a significant positive correlation between canopy apparent photosynthesis and biological yield, biomass partitioning, and harvest index, irrespective of plant pruning and plant density. Plant pruning and plant density interacted to affect seedcotton yield. With TRS, cotton yield at low plant density was higher than that with other pruning modes, which was attributed to an increase in biological yield associated with an increase in canopy photosynthesis. At high plant density, the yield decrease with TRS was attributed to low harvest index associated with reduced reproductive partitioning. Cotton cultivation relying solely on vegetative branching can be an alternative to obtain moderate yields and economic benefits under conditions of low plant density. • Plant pruning and density affected cotton branching and yield formation. • Terminal removal at first square led to the highest seed cotton yield at low plant density. • Terminal removal at first square increased yield by promoting canopy photosynthesis. [ABSTRACT FROM AUTHOR]

Waterlogging stress is an increasing threat to cotton production worldwide. The use of cultivation measures to combat waterlogging stress is a promising approach. As a traditional cultural practice, ridge intertillage is usually conducted before flowering to form a ridge along a row and a furrow between two rows in order to reduce lodging and control weeds in cotton fields. However, it is unclear whether ridge intertillage can alleviate waterlogging stress in field-grown cotton. Flat and ridge intertillage were conducted at 10 days after squaring of cotton to establish flat and ridge–furrow configurations, respectively, with or without 10-d waterlogging. To determine effects of intertillage pattern on mitigating waterlogging stress, changes in rhizosphere bacterial communities and plant physiological parameters were examined in waterlogged cotton. Compared with flat tillage, ridge intertillage significantly decreased hydrogen peroxide production, malonaldehyde content, and alcohol dehydrogenase and pyruvate decarboxylase activities in both roots and leaves of waterlogged cotton but significantly increased nitrogen, phosphorus, and potassium concentrations, leaf area, and plant biomass. Compared with flat intertillage under waterlogging (FIW), ridge intertillage under waterlogging (RIW) changed the abundance and composition of rhizosphere bacterial communities. In addition, several taxa of bacteria with beneficial functions were enriched in the rhizosphere under ridge intertillage. Pearson correlations indicated that changes in rhizosphere bacteria and plant physiological parameters in waterlogged cotton were significantly correlated (P < 0.05), suggesting that adjustments in rhizosphere bacterial communities were involved in the physiological response to waterlogging stress. Moreover, compared with FIW, RIW increased canopy photosynthesis and lint yield of waterlogged cotton by 51.5% and 18.3%, respectively, and decreased lint yield loss by 61.3%. Compared with flat intertillage, ridge intertillage induced adjustments in rhizosphere bacterial communities, reduced oxidative membrane damage, improved nutrient uptake and canopy photosynthesis, and ultimately reduced the stress damage and yield loss of waterlogged cotton. Ridge intertillage before flowering is a promising agronomic measure to combat waterlogging stress in cotton and possibly other major field crops. • Ridge intertillage produced ridge-furrow configuration by piling up the topsoil to cotton plants base before flowering. • Effects of flat and ridge intertillage on waterlogged cotton were compared. • Ridge intertillage adjusted rhizosphere microbe and nutrient uptake of waterlogged cotton. • The adjustments induced a set of physiological changes and reduced the yield loss of waterlogged cotton. [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]

Manual removal of the main-stem growth tip is traditionally used to break the apical dominance of cotton (Gossypium hirsutum L.). Chemical topping with plant growth regulators also effectively inhibits apical dominance. However, the effect of chemical topping on yield increases and whether plant density or ecological conditions affect its efficacy are unclear. Therefore, a three-year field experiment with a split-plot design was conducted to determine the effects of plant topping, plant density, and their interactions on cotton yield and related physiological and agronomical parameters at three sites with different ecological conditions in China. In each site, the main plots were assigned low, moderate, or high plant density and the subplots were assigned no topping, manual topping, or chemical topping. Growth, yield, yield components, earliness, and late-season leaf photosynthesis as well as labor and material inputs were examined each year. Compared with no topping, both chemical and manual topping greatly reduced plant height at all sites. Manual topping increased seed cotton yield and earliness in all tested plant densities and sites. However, plant density but not ecological condition greatly mediated the effect of chemical topping on yield. At low plant density, the yields with chemical topping were 4–6% lower than those with no topping and 5.5–10.8% lower than those with manual topping at the three sites. Although yields with chemical topping were comparable with those of manual topping at moderate and high plant densities, they were 8.6–12.8% higher at moderate density and 13.8–16.4% higher at high plant density than those with no topping across years and sites. Averaged across the sites, chemical topping reduced biological yield by 12.7% at low plant density. Although biological yield decreased slightly, chemical and manual topping increased the harvest index by 12.4% and 13.3% at moderate density and by 15.6% and 17.4% at high density, respectively. In comparison with no topping, the reduction in seed cotton yield with chemical topping at low plant density was attributed to insufficient biological yield, whereas the increase in yield at moderate and high plant densities was mainly due to greater partitioning of assimilates to reproductive tissues. Compared with manual topping, chemical topping produced 23.2% lower net returns as a result of lower seed cotton yield at low plant density but produced 8.1% and 20.9% higher net returns at moderate and high plant densities, respectively, because of savings in labor inputs and comparable seed cotton yields. In addition, chemical topping increased the earliness percentage compared with that of no topping. Overall, this study demonstrates that chemical topping is a promising alternative to traditional manual topping under moderate or high cotton plant density. • Manual topping increased cotton yield regardless of plant densities and ecological conditions relative to non-topping. • Chemical topping decreased yield at low plant density relative to non-topping because of greater biomass reduction. • Chemical topping increased cotton yield at moderate and high plant densities via greater assimilates partitioning to fruits. • Chemical topping could replace manual topping at moderate and high plant densities without ecological dependence. [ABSTRACT FROM AUTHOR]

• Cotton yield did not differ between vegetative branch retention and removal. • Chemical topping increased cotton yield mainly by increasing canopy photosynthesis. • Manual topping increased yield also by increasing reproductive partitioning. • The mechanism of yield formation differed between chemical and manual topping. Fine pruning, or the artificial removal of vegetative branches (VB) and main stem tips (plant topping), is a traditional cotton (Gossypium hirsutum L.) cultivation practice. Pruning can be simplified without reducing yield by retaining the vegetative branches and adopting chemical topping; however, cotton yield formation under different plant pruning modes remains unclear. We aimed to determine if and how simplified pruning results in comparable yields to fine pruning in terms of canopy photosynthesis and photoassimilate partitioning. A two-year field experiment was thus conducted to determine the effects and interactions of vegetative branch management (retaining and removing of vegetative branches) and plant topping pattern (non-topping, manual topping, and chemical topping) on yield, canopy photosynthesis, and photoassimilate partitioning. Seed cotton yield, canopy photosynthesis, and photoassimilate partitioning were significantly affected by VB removal or retention and plant topping modes, but not by their interaction. Boll weight and harvest index under VB retention were reduced compared to VB removal, while boll density and biological yield increased. Compared with non-topping, the biological and seed cotton yield increased and the harvest index decreased under chemical topping, whereas these all increased under manual topping. Seed cotton yield was comparable between chemical and manual topping. The leaf area index (LAI) under VB retention was higher than under VB removal at peak squaring, peak flowering, and peak boll-setting, and comparable at boll-opening. The carbon assimilation rate (CAR) under VB retention increased compared with that under VB removal at peak flowering, peak boll-setting, and boll-opening. Meanwhile, VB retention partitioned more photoassimilates to the vegetative organs, and less to the reproductive organs, than VB removal at peak flowering and peak boll-setting. Compared with no topping, LAI and CAR under chemical and manual topping increased at peak-boll setting and boll-opening. Furthermore, the partitioning of photoassimilates to the reproductive organs under chemical topping was similar to that of non-topping at the peak boll-setting and boll opening stages, whereas this increased under manual topping. Cotton yield did not vary between VB managements due to the coordination between canopy carbon assimilation and assimilate partitioning. Manual topping improved both CAR and photoassimilate partitioning to the bolls, and thus increased the seed cotton yield compared with non-topping. By contrast, chemical topping reduced the photoassimilate partitioning to the reproductive organs, and the increased yield was attributed to the improved carbon assimilation rate. In summary, chemical topping achieved the same yield as manual topping, but the mechanism of yield increase differed from the perspective of photosynthetic production and assimilate partitioning. [ABSTRACT FROM AUTHOR]