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Cotton (Gossypium hirsutum L.) is a globally important crop that is often damaged by pests and diseases. Current cotton pests and diseases management is dependent on chemical pesticides. Although chemical pesticides are usually effective, long-term application of these pesticides often leads to increased insecticide resistance in the pests, fewer natural enemies, reduced natural control, and a degraded environment. Because of increased environmental awareness and the need for sustainable cotton production, the control of cotton pests and diseases using biological means like intercropping is increasingly receiving attention. Intercropping of cotton with other crops can often boost the total yield and output of the intercropping system and provide significant economic benefits without sacrificing cotton quality. Intercropping also increases the number of natural enemies, and reduces the occurrence of cotton pests and diseases by altering the ecological structure and environmental conditions in the fields. Cotton-based intercropping is an effective strategy to reduce the competition between cotton and grain or other economic crops for arable land. It is also an important way to increase the populations of natural enemies in cotton fields for the management of pests and diseases. However, inappropriate intercropping can also increase labor requirements and even result in inadequate control of pests and diseases. This review focuses on the performance and the mechanisms of intercropping for reducing cotton pests and disease as well as on the effective management of intercropping systems. The risks and limitations, as well as the study approaches needed and the prospects of intercropping for the control of cotton pests and diseases, are also discussed. This information is intended to aid researchers and growers in designing economically viable and ecologically friendly pest and disease management strategies that will reduce the use of chemicals and the cost of cotton production.

Over the last few decades, waterlogging stress has increasingly threatened global cotton production. Waterlogging results in reduced soil oxygen, impairing the growth and development of this valuable crop and often resulting in severe yield loss or crop failure. However, as cotton has an indeterminate growth habit, it is able to adapt to waterlogging stress by activating three mechanisms: the escape, quiescence, and self-regulating compensation mechanisms. The escape mechanism includes accelerated growth, formation of adventitious roots, and production of aerenchyma. The quiescence mechanism involves reduced biomass accumulation and energy dissipation via physiological, biochemical, and molecular events. The self-regulation compensation mechanism allows plants to exploit their indeterminate growth habit and compensatory growth ability by accelerating growth and development following relief from waterlogging stress. We review how the growth and development of cotton is impaired by waterlogging, focusing on the three strategies associated with tolerance and adaptation to the stress. We discuss agronomic measures and prospects for mitigating the adverse effects of waterlogging stress.

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.

Wheat-cotton double cropping has improved crop productivity and economic benefits per unit land area in many countries, including China. However, relay intercropping of full-season cotton and wheat, the most commonly adopted mode, is labor-intensive and unconducive to mechanization. The direct sowing of short-season cotton after wheat (CAW) has been successful, but cotton yields and economic benefits are greatly reduced. Whether the relay intercropping of short-season cotton before the wheat harvest increases cotton yields remains unclear, as does the earliness and fiber quality relative to those for CAW. Therefore, we directly planted short-season cotton after wheat harvest on 15 June (CAW) as the control and interplanted short-season cotton in wheat on 15 May (S1), 25 May (S2) and 5 June (S3), which were 30, 20 and 10 days prior to wheat harvest, respectively, from 2016 to 2018. The crop growth, yield, yield components, boll distribution, and earliness of the cotton were evaluated. The yields and earliness of short-season cotton under relay intercropping were 26.7–30.6% and 20.4–42.9% higher than those under CAW, respectively. Compared with CAW, relay intercropping treatments increased the boll density, boll weight and lint percentage by 5.6–13.1%, 12.5–24.5% and 5.8–12.7%, respectively. The dry matter accumulation and harvest index under the relay intercropping treatments were also greater than those under CAW, which might be attributed to the greater partitioning of dry matter to the seed cotton than to the boll shells. Among the relay intercropping treatments (S1, S2 and S3), the lint yield did not differ, but S1 and S2 were considerably better than S3 based on earliness and fiber quality. The analysis of the within-plant spatial boll distribution showed that more bolls were formed on the lower to middle fruiting branches and at the first fruiting sites for S1 and S2 than for S3 and CAW. Therefore, the increased earliness and fiber quality induced through early relay intercropping (S1 and S2) could be attributed to an improved spatial boll distribution compared to late relay intercropping (S3) or CAW. Conclusively, compared to late relay intercropping and CAW, early relay intercropping considerably increased the lint yield, fiber quality, and earliness by improving the yield components, boll distribution, and dry matter accumulation and partitioning. The relay intercropping of short-season cotton 20 to 30 days before wheat harvest represents a promising alternative to CAW in wheat-cotton double-cropping systems in the Yellow River Basin of China and other regions with similar conditions.

Cotton plants have complex branching patterns formed by distal fruiting branches (FB) and basal vegetative branches (VB). Our prior study showed that cotton’s vegetative branching was considerably inhibited under high plant density via altered hormone contents in VB tips and photosynthetic production in VB leaves. Here, our current objective was to determine whether or not shading of VB reduced vegetative branching, and whether this effect was elicited via a similar mechanism(s) as that under high plant density. To this end, cotton was planted on 76-cm row widths at a moderate density (5 plants m−2). Vegetative branches of cotton plants were shaded to approximate 60% of full solar exposure by using polyethylene nets during squaring; those without shading served as the control. The growth and development of VB, as well as underlying agronomic, physiological and molecular events of both shaded and control plants were examined. Shading VB reduced its numbers by 56.2%; its length by 88.8% and the ratio of VB biomass to total biomass by 91.3%, but it increased FB biomass by 30.8%, compared with the control at 69 days after seeding. Compared with control, shading did not reduce seedcotton yield, suggesting a yield stability similar to that found previously under high plant density. The net photosynthetic rate, chlorophyll content and ribulose-1,5-bisphosphate carboxylase activity in VB leaves were considerably decreased by shading. The sucrose biosynthesis gene GhCYFBP in leaves and GhphyB gene in tips of VB were down-regulated under its shading, followed by lower soluble sugar and starch contents. Suppressed photosynthetic production in leaves of VB was a key reason for poor vegetative branching under shaded conditions. Shading diminished both the auxin (IAA) content and auxin transport from VB tips by decreasing the expression of corresponding genes for auxin biosynthesis (GhYUC5) and transport (GhPIN1and GhPIN5). This treatment also reduced the content of cytokinins (CTKs) in the VB tips by decreasing the expression of the CTKs biosynthesis gene, GhIPT3. By contrast, the SL receptor gene, GhD14 was upregulated in the VB tips, followed by a greater content of strigolactones (SLs). We proposed that lower IAA, CTKs and brassinosteroid contents plus higher SLs content due to differential expression of hormone-related genes in the VB tips suppressed vegetative branching when shaded. Our results suggest this mechanism is not unlike how high plant density inhibits vegetative branching in cotton.

Manual removal of vegetative branches (VB) is a traditional cultural practice widely adopted in Chinese cotton production, but the increasing labor cost in the country has reduced its cost-effectiveness. It is well known that high plant density inhibits the VB growth of cotton and can be a potential alternative to the traditional practice, but the underlying mechanisms are poorly understood. This study mainly aimed to determine how the VB growth of cotton could be inhibited by increasing plant density. Cotton was planted on 76-cm row widths at low (3 plants m−2), moderate (6 plants m−2) and high (9 plants m−2) plant densities. The VB growth and development, as well as the underlying agronomic, physiological and molecular events were examined. The high plant density decreased the number of VB by 67.3% and the ratio of VB biomass to total biomass by 95.0% at 125 days after seeding (DAS) compared with the low plant density. The net photosynthetic (Pn) rate, chlorophyll content and ribulose-1, 5-bisphosphate (RuBP) carboxylase activity in VB leaves were considerably decreased under high plant density, followed by reduced soluble sugar and starch contents, suggesting a suppressed photosynthetic production in the leaves. This decreased photosynthesis resulting from reduced RuBP carboxylase activity and chlorophyll content was one of the reasons for the poor VB growth under high plant density. High plant density increased the auxin (IAA) content and promoted auxin polar transport by increasing the expression of the auxin biosynthesis gene, GhYUC5 and auxin polar transport gene, GhPIN1. It also increased the content of cytokinins (CKs) by increasing the expression of the CKs biosynthesis gene, GhIPT3 in the main-stem tips, and decreasing the IAA and CKs contents as well as auxin polar transport by reducing the expression of GhYUC5, GhPIN1, GhPIN5 and GhIPT3 in the VB tips. The GhPhyB gene was down-regulated by high plant density, but the strigolactones (SLs) content was increased by up-regulating the SL receptor gene, GhD14 in the VB tips. The decreased IAA, CKs, GA and BR contents plus the increased content of SLs due to differential expression of hormone-related genes in the VB tips was another reason for the inhibition of vegetative branching. Although high plant density did not increase seedcotton yield, it improved the fiber quality by decreasing the number of VB-sourced bolls. Our results suggested that high plant density can be a substitute for the traditional plant pruning.

Prolonged drought stress could accelerate plant death. In this study the mechanisms of the acetic acid to increase the survival rate of cotton under drought stress were studied. Twenty-day-old cotton seedlings were grown for 9 days in the presence or absence of acetic acid under natural drought conditions in which the relative water content (RWC) of the soil decreased below 60% at 6 days after treatment (DAT). The water potential, photosynthesis (Pn), chlorophyll (Chl) content, stomatal conductance (Cond), and transpiration (Tr) of the control plants started to decrease at 6 DAT. However, acetic acid treatment caused a decrease in Cond and Tr at 3 DAT. Abscisic acid (ABA) and jasmonic acid (JA) contents and the expression of ABA biosynthesis genes (NCED2, NCED3, and NCED9) and JA biosynthesis genes (GhAOS6, GhLOX3, and GhOPR11) in cotton leaves were increased by acetic acid treatment at 3 DAT, and these variables were increased in control and acetic acid-treated plants at 6 and 9 DAT. These results indicate that acetic acid can increase ABA and JA contents by upregulating the expression of their biosynthesis genes, thus decreasing the Cond and Tr, and therefore, increasing the RWC of the soil and increasing the survival of cotton under drought stress.

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.

Cluster seeding is the dominant sowing pattern of cotton in the Yellow River valley of China, but it expends a large amount of seeds and usually results in slender and long-legged seedlings. The subsequent thinning and final singling of seedlings in cluster seeding are also time-and labor-intensive. Monoseeding may be an alternative sowing pattern to solve these problems. In this study, monoseeding, double seeding and cluster seeding treatments were established by sowing one, two and ten seeds each hill to study their effects on emergence, stand establishment and seedcotton yield as well as the underlying physiological and molecular events during emergence. Results showed that monoseeding, double seeding and cluster seeding were not significantly different in seed emergence rate. But in monoseeding pattern, the stand establishment rate and seedling hypocotyl diameter were increased by 16.3–21.2% and 29.2–34.3%, respectively, while the percentage of seedlings with shell attached, disease incidence and hypocotyl length were reduced by 82.2–91.5%, 36.6–37.2% and 26.9–35.8% respectively when compared with those of cluster seedling. These results indicated that monoseeding not only produced stronger seedlings than double or cluster seeding but also improved stand establishment. Additionally, the apical hook angle of seedlings before emergence under monoseeding was 69.1–71.1% smaller than that under cluster seeding, suggesting improved apical hook formation under monoseeding. The ethylene, IAA, and GA contents in seedlings under monoseeding were higher but the JA content was lower than those under cluster seeding during emergence, suggesting that ethylene, IAA, and GA promoted but JA inhibited the apical formation of seedlings. The increased ethylene content under monoseeding was possibly due to the increased expression of ethylene biosynthesis gene ACO1. Monoseeding also increased the expression of apical hook formation promoting genes COP1 and HLS1, but decreased the expression of hook formation inhibiting gene ARF2. The expression of hypocotyl elongation related gene ERF1 under monoseeding increased relative to cluster seeding, which might be an important reason for the shorter and thicker hypocotyl formation under monoseeding than cluster seeding. Monoseeding considerably reduced seeding rate and labor input for thinning and singling of seedlings but produced comparable cotton yield to double or cluster planting. The results suggested that mononseeding improved stand establishment through regulating the expression of apical hook formation- and hypocotyl elongation-related genes as well as changes of some endogenous phytohormones. It was also suggested that monoseeding is a promising seeding pattern to reduce seed and labor inputs without sacrificing yield for cotton production in the Yellow River valley of China and other areas with similar ecology.

Previous research shows that removal of early fruiting branches (FB) alters the sink/source ratio and delays leaf senescence in cotton. However, how the altered sink/source ratio regulates leaf senescence and yield formation is still poorly understood. In this study, 2 or 4 early FB were removed from two near isogenic cotton lines, late- and early-senescence lines, while plants with intact FB served as controls. The leaf chlorophyll content (Chl) and photosynthetic (Pn) rate in the late-senescence line were higher than those in the early-senescence line, but the malondialdehyde (MDA) accumulation and boll load per leaf area (BLLA) in the late-senescence line were lower than those in the early-senescence line. Removal of FB decreased the BLLA and MDA accumulation but increased the Pn rate, Chl concentration, and the expression of GhLHCB gene in both cotton lines, suggesting that FB removal reduced sink/source ratio and suppressed leaf senescence. However, it decreased ABA and JA contents by decreasing their biosynthesis related genes and increasing the expression of ABA catabolic related genes. Although FB removal increased the iP + iPA content, it had little effects on Z + ZR or DHZ + DHZR contents. The results suggest that the delayed leaf senescence following the decreased sink/source ratio associated with FB removal might be attributed to the increased iP + iPA and reduced ABA and JA contents, as well as the differentially expressed biosynthesis and catabolic related genes. Seedcotton yield increased by 6.3–10.2% following the removal of 2 FB but decreased by 5.7–11.7% following the removal of 4 FB in the early-senescence line; in the late-senescence line, the removal (whether of 2 or 4 FB) significantly decreased yield. Removal of 2 or 4 FB in the late-senescence line and 4 FB in early-senescence line significantly suppressed earliness. The overall results suggested that removal of early fruiting branches would practically regulate the sink/source relationship and suppress leaf senescence in cotton. Delaying leaf senescence would not necessarily increase cotton yield unless when earliness is not affected or when normal maturity is achieved.

Nitrogen (N) fertilization plays an important role in yield formation of field-grown cotton (Gossypium hirsutum L.), but little is known of its interaction with mode of application or plant density under irrigated production. Our objective was to determine the effects of N application rate on cotton yield, leaf senescence and N use efficiency as mediated by mode of application and plant density. To achieve this goal, two field experiments which were conducted from 2015 to 2016 using a split-plot design in randomized complete blocks. In the first experiment, the main plots were assigned to N application modes (conventional application and drip fertigation) and the subplots to N rates (375, 319, 264 and 0 kg N/ha). In the second experiment, the main plots were assigned to plant density (12 plants/m2-low density and 19.5 plants/m2-high density) and the subplots to N rates (330, 264 and 0 kg N/ha). The N rate of 264 kg/ha under drip fertigation or high plant density did not reduce cotton yield. Agronomic nitrogen use efficiency (aNUE) and nitrogen recovery efficiency (NRE) were the highest at 264 kg N/ha under drip fertigation and high plant density. Although a reduced N rate increased boll load, fertigation or high plant density relatively reduced boll load and delayed late-season leaf senescence as indicated by the increased photosynthetic rate and chlorophyll content as well as the reduced malondialdehyde concentration compared to conventional application or low plant density. The yield stability across N rates (264–375 kg N/ha) was probably due to the delayed leaf senescence and improved N use efficiency. The results suggest that the N rate could be reduced to 264 kg/ha, or 20–30% from the traditionally recommended rate, without sacrificing yield under high plant density or drip fertigation. These results are beneficial to the formulation of a scientific and rational use of N fertilizer for sustainable cotton production and environmental health.

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.

Since the beginning of the 21 st century, the rapid economic development and accelerated urbanization of China have caused major changes to the country's cotton cultivation technology. China has not replicated the completely mechanized approach used in developed countries. Rather, taking into account the underdeveloped economy and family-scale based cotton growing, China has established and implemented a light and simplified system of sustainable cotton production. Light and simplified cultivation (LSC) involves using modern agricultural equipment and technology adapted to the local economic level and mode of management of cotton production instead of manual operations. This method reduces labor intensity, simplifies cultivation management, reduces the frequency of field operations, integrates agricultural machinery and agronomic technology, and uses high-quality seeds and improved techniques to achieve light, simplified, and cost-effective cotton production. Cotton LSC includes the following key technologies: Single-seed precision sowing, simplified plant pruning, light and simplified fertilization, water and fertilization integration technology, and plant population structure control. Single seed precision sowing technology ensures robust seedling growth via differential expression of the key genes controlling hook formation and hypocotyl elongation at seed germination. Cotton planting at a relatively high plant density inhibits the growth of vegetative branches via differential expression of genes for hormone metabolism and compartmentation of hormones within a cotton plant. The high and stable yield of LSC lies in the adaptive coordination between the cotton yield components and between the biomass and the harvest index. According to the appropriate leaf area index and its dynamics, quantitative indicators such as suitable plant height, the ratio of fruiting nodes to branches in number, and the ratio of seed cotton to stalks in weight can produce plant populations with high solar efficiency. The basis of light and simplified fertilization is that the absorption of fertilizer N by cotton is concentrated within 20 days after flowering, and the fertilizer applied at early flowering was mainly distributed to reproductive organs and had higher N use efficiency than that applied at other stages. The water saving mechanism of partial root-zone irrigation is that methyl jasmonate serves as a signal substance to enhance the water absorption from the hydrated root side. Future development of cotton cultivation must include an in-depth investigation of the ecophysiology of LSC to further reform and optimize the planting systems and patterns. Innovation in cultivation technologies, development of new materials and equipment, and integration of agronomic technology and materials may provide solid theoretical and technical support for LSC and promote the sustainable cotton production in China.

The early planting of full-season cotton (Gossypium hirsutum L.) at a moderate plant density under plastic mulching is a traditional means of growing cotton in the Yellow River valley of China. However, it is labor intensive, consumes a large amount of materials, and also results in residual plastic pollution in the soil. While our previous studies indicated that late planted short-season cotton under plastic mulching greatly reduces labor and material inputs and increases net revenue, the residual plastic pollution remains an issue. It is unclear if short-season cotton can be managed without yield loss in the absence of plastic mulching. A field experiment was therefore conducted using a random complete block design with four treatments, including the early planting of full-season cotton with (FCM) and without plastic mulching (FC), and the late planting of short-season cotton with (SCM) and without plastic mulching (SC), in the Yellow River valley from 2017 to 2019. The yield, yield components, input and output values, earliness, dynamics of flowering and boll setting, and late-season leaf senescence in cotton were examined. The results showed that early planted full-season cotton under mulching (FCM) produced a 21.1 and 20.4 % higher seedcotton yield and boll density, respectively, and improved earliness over the non-mulched treatment, while the boll weight did not differ significantly. Short-season cotton without plastic mulching produced comparable seedcotton yields to that with mulching (SCM), and there was no significant difference in average boll weight, boll density, or earliness between the mulching and non-mulching treatments. However, SC had a 7.0 and 12.1 % smaller boll density and boll weight, respectively, than FCM and thus produced a 17.9 % lower seedcotton yield. Therefore, SC produced 14.9 and 14.4 % greater net returns than SCM and FCM, respectively, because it consumed less labor and material inputs. Short-season cotton without plastic mulching delayed leaf senescence due to reduced boll load and thus increased boll weight in the late season compared with SCM. In addition, SC exhibited improved earliness as a result of a higher flowering rate, faster fruiting, and more concentrated boll opening than FCM. Short-season cotton without plastic mulching also avoided the residual film pollution in the soil. The overall results demonstrated that the late planting of short-season cotton without mulching is a promising alternative for sustainable cotton production in the Yellow River valley region of China as well as other cotton growing areas with similar ecology.

Plant density, nitrogen (N) fertilization rate and plant pruning are important measures used globally to cultivate cotton. A typical combination of 52,500 plants ha−1, intensive pruning and 255 kg N ha−1 has been widely applied in the Yellow River Valley of China. The main objective of this study is to determine whether more beneficial combinations exist than the typical one for profitable cotton production in this region. Using a split–split plot design with four replications, we conducted a three-year field experiment to study the individual and interaction effects of plant density (52,500 and 82,500 plants ha−1), plant pruning (intensive and extensive) and N fertilizer rate (195 and 255 kg N ha−1) on yield, plant biomass and partitioning, N uptake and use efficiency, as well as input and output values. The results showed that cotton yield was affected by individual and interaction effects of the three agronomic factors. When planted at a moderate density (52,500 plants ha−1), the seedcotton yield of intensively pruned cotton under a low N rate (195 kg N ha−1) and of extensively pruned cotton under low and high (255 kg N ha−1) N rates was reduced by 6.9, 6.7 and 5.4%, respectively, whereas the four combinations with high plant density (82,500 plants ha−1) produced a yield value that was comparable to that of the typical combination, indicating a relatively stable yield at high plant density irrespective of pruning mode and N rate. Vegetative branches of the extensively pruned cotton accounted for 18.7–23.6% of the total biomass at moderate plant density compared with only 2.8–2.9% of the total biomass at high plant density. At moderate plant density, intensively pruned cotton exhibited a higher harvest index than the extensively pruned plants. By contrast, the harvest index for the four combinations with high plant density did not differ, suggesting a relatively stable harvest index among these combinations. There was no difference in the N biomass utility index (NBI) among all combinations. The combination of high plant density, extensive pruning and reduced N rate had a 6.7% lower nitrogen yield utility index (NYI) than the typical combination but a 5.4% higher NYI than the combination of high plant density, extensive pruning and high N rate. More importantly, the combination of high plant density, extensive pruning and reduced N rate produced comparable yield with less input, leading to 21.7% more net revenue than the typical combination. Our results support the use of high plant density, reduced N rate and extensive pruning to ensure profitable cotton production in the Yellow River Valley and other cotton-growing areas with similar ecologies.

The northwest inland is currently the most dominant cotton-growing region in China. In 2015, the region measured 2.3 million hectares with a total output of 4.28 million tons of cotton. The unit yield was 1900 kg hm−2, which was not only 21, 41 and 121% higher than the national averages of China, Brazil and the United States, respectively, but also 2.37 times as much as that of the world’s average. Enhanced cotton production, particularly the high unit yield, can largely be attributed to the adoption of a series of key cultivation techniques. These techniques, including earliness-stimulating cultivation for full utilization of accumulated heat, close planting and short plant height for adequate use of light energy, and drip irrigation under plastic mulching for water saving and yield improvement, have been recently established and applied in the northwest inland of China. At the same time, a series of labor and cost-saving technologies or practices have been adopted to increase net production returns. Mechanization and precision seeding has greatly reduced labor inputs, rational high-density planting techniques combined with chemical regulation has simplified plant pruning and harvesting, and the integrated application of water and fertilizer has reduced the inputs and costs in field management. In particular, the integration of these agronomic techniques and material equipment has not only enhanced yields, but is also convenient, cost-effective and simple. These factors have all led to the establishment of the northwest inland as the largest predominantly cotton-growing area in China. However, the region is currently facing major issues including stagnated cotton yields, serious plastic film pollution, continuous degradation in fiber quality, substantial increases in the cost of cotton production and continuously declining profits. These factors necessitate that cotton cultivation strategies in the region need to be further optimized. Yields can be enhanced by exploring heat and water potential, while quality and economic benefits can be improved by exploring light potential, fertigation and integrating agronomic techniques with mechanization. Greater attention should be paid to seed quality and seeding processes to further reduce costs and improve efficiency. Comprehensive steps for improving the cultivation system at all stages of production should also be taken to enhance the quality of the cotton fiber.

Relay intercropping of garlic with full-season cotton is currently one of the dominant cropping systems in China, but the net benefit is decreasing because the system is labor-intensive. Direct planting of short-season cotton after garlic harvest may increase net revenue through reducing labor and material input. Three field experiments were consecutively conducted in Jinxiang County of China, to determine the effects of plant density and soil fertility on yield, yield components, boll load and leaf senescence in the 1st and 2nd experiments. In the third experiment, we compared the economic benefits of the two cropping systems. Data from the 1st experiment showed that plant density affected yield and yield components, with the optimum plant density being 3.0 plants m −2 for full-season cotton and 9.0 plants m −2 for short-season cotton. In the 2nd experiment, the seedcotton yield of full-season cotton was 9.1% higher under high than medium soil fertility, but there was no yield difference between the two soil fertility levels for short-season cotton. Full-season cotton exhibited larger boll load, earlier leaf senescence and lower boll weight under medium than high fertility. Results of the third experiment showed that seedcotton yield or output value of short-season cotton was 14.5% lower than that of full-season cotton, but the gross return for short-season cotton was 69.2% higher than that for full-season cotton because the short-season cotton required 27.3% less labor and material inputs. The overall results showed that late planted short-season cotton after garlic harvest can be a promising alternative for enhancing the benefits of garlic-cotton production in China.

Waterlogging is a major abiotic stress that reduces crop growth and productivity. Nitric oxide (NO) is an essential signaling molecule involved in abiotic stress responses in many plant species. However, it is unclear if and how NO mitigates waterlogging stress in field-grown cotton. In this study, the NO donor sodium nitroprusside (SNP) or its scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl -imidazoline-1-1-oxyl-3-oxide (cPTIO) was foliar-applied to waterlogged and non-waterlogged cotton plants. The NO concentrations in different plant parts, plant growth, yield and yield components, as well as related physiological and molecular events, were examined over three consecutive years under field conditions. Foliar application of SNP increased NO concentration in leaves by 83.6 and roots by 80.2 % under waterlogging, while cPTIO decreased the NO concentration by 18.9 and 5.3 %, respectively. Biomass and lint yield were reduced by 17.2 and 36.0 % under waterlogging without the application of SNP or cPTIO, but the reductions were 8.8 and 28.4 % following SNP application and 29.5 and 43.4 % respectively, following cPTIO application. Foliar applied SNP increased biomass by 10.2 % and lint yield by 12.0 % under waterlogging, whereas cPTIO caused 5.0 and 11.5 % reductions in biomass and lint yield. Quantitative real-time PCR analysis showed that the SNP up-regulated the NO synthesis gene (GhNIR), but down-regulated the genes involved in glycolysis and fermentation (GhADH2 and GhPDC), ethylene production (GhACO and GhACS8), and abscisic acid (ABA) synthesis (GhNCED2). It also reduced hydrogen peroxide (H2O2) production and malonaldehyde (MDA) content in the leaves, but increased the leaf chlorophyll content and photosynthetic rate. The levels of auxin (IAA) and gibberellic acid (GA) were increased by SNP but those of ABA and ethylene contents as well as the activities of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC) in leaves were decreased. The cPTIO showed an opposite effect to SNP in almost all physiological and molecular responses to waterlogging. The overall results indicated that increasing the concentrations of NO in plant tissues via the foliar application of SNP mitigates waterlogging stress through a series of physiological and molecular events, ultimately reducing biological and lint yield loss under waterlogging. Therefore, increasing the concentration of NO in plant tissues by genetic breeding or agronomic measures might be a potential strategy for improving waterlogging tolerance and reducing yield loss in cotton.

Deficit irrigation is a new strategy to increase water use efficiency of cotton in arid areas, but it is not clear if it interacts with plant density. The objective of this study was to determine the effects of deficit irrigation and plant density as well as their interaction on the growth, yield and fiber quality of irrigated cotton. Two field experiments were conducted at three sites in 2013 and one site from 2014 to 2015 in an arid area of Xinjiang. A randomized complete block design with three replicates was used to determine the effects of 6 irrigation regimes on seedcotton yield in the first experiment, while a split-plot design was used in the second experiment with the main plots assigned to irrigation regime (saturation, regular and deficit) and the subplots to plant density (high, medium and low) to examine cotton yield, fiber quality and water productivity as affected by plant density under deficit irrigation. Averaged across the three sites, drip irrigation ranging from 3650 to 4700 m 3 /ha did not significantly affect cotton yield, but seedcotton yield under 3650 m 3 /ha in S1 was 6.3% lower than that under 4000 m 3 /ha. Thus, it is quite appropriate to regularly drip-irrigate at 4000 m 3 /ha in the experimental area. Deficit irrigation at high plant density also maintained a relatively higher leaf area index (LAI) and net assimilation rate (NAR), particularly at late stages of plant growth and development, than saturation or regular irrigation. Plant density ranging from 18 to 24 plants/m 2 produced more seedcotton than 12 plants/m 2 under regular irrigation. Increasing irrigation to saturation levels had little effects on cotton yield regardless of plant density; saturation irrigation at high plant density even reduced cotton yield compared with regular irrigation at medium plant density. Under deficit irrigation, the high plant density produced 9.1-17% greater yield and 9.3-16.8% higher irrigation water productivity (IWP) than low or medium plant density, and comparable yield to medium or high plant density under regular irrigation. This high yield under deficit irrigation at high plant density was due to increased plant biomass occasioned by high plant population and improved harvest index. Deficit irrigation did not affect fiber quality in 2014, but reduced fiber length and increased fiber micronaire value in 2015. Conclusively, use of high plant density under deficit irrigation can be a promising alternative for water saving without compromising cotton yield under arid conditions.

Cotton may suffer from waterlogging from seedling to boll-setting stage, but little is known of how it responds to temporal waterlogging. In this study, cotton was grown in a rain-shelter and subjected to 0 (control)-, 10-, 15- and 20-d waterlogging at squaring (WLS), flowering (WLF) and boll-setting (WLB) stages. The effects of timing (growth stage) and duration of waterlogging on the growth, yield and yield components as well as some physiological and molecular features of cotton were examined. The lint yield was significantly affected by timing and duration of waterlogging as well as their interaction. On average, the 10-, 15-, and 20-d waterlogging reduced lint yield by 53, 59 and 63% at squaring; 27, 37 and 55% at flowering, and 13, 15 and 24% at boll-setting. The more pronounced yield reduction under WLS than later waterlogging (under WLF and WLB) was attributed to greater reductions in biological yield, harvest index, and the resulting boll density and boll weight. Variations in yield loss due to temporal waterlogging was associated with some physiological and molecular changes: a) the chlorophyll synthesis associated gene (GhLHCB) in the main-stem leaves was down-regulated under WLS to a larger extent, leading to lower leaf photosynthesis than that under WLF or WLB; b) cotton alcohol dehydrogenase (GhADH) and pyruvate decarboxylase (PDC) genes were better up-regulated, resulting to greater activity of lactate dehydrogenase (LDH), alcohol dehydrogenase (ADH) and PDC plus lower activity of SOD, POD and CAT and higher accumulation of malondialdehyde (MDA) and H2O2 under WLS than under WLF and WLB; c) more pronounced reductions in GA and IAA content were observed under WLS than WLF and WLB. Higher sensitivity to earlier waterlogging than later waterlogging in cotton was attributed to the greater reductions in biological yield and harvest index resulting from differences in physiological and molecular adjustments of the plants.

Senescence in cotton is a gradual deterioration process that terminates plant growth and development and ultimately leads to plant death. Maturity performance refers to the senescence appearance of cotton during the boll-opening stage, which is the manifestation and result of senescence. Maturity performance categories include premature senescence, late maturity and normal maturity. Premature senescence and late maturity are anomalies of cotton growth caused by genotype and environment interactions. They result from differential expression of a large number of senescence-associated genes during late growth and development stage. In this paper, we review and summarize research progress on the physiology, ecology, and molecular basis of cotton senescence and maturity performance. Strategies for achieving normal maturity performance with maximum cotton yield and quality should include development of optimized varieties, rational application of plant growth regulators, and use of agronomic measures to regulate cotton growth, development and senescence.

Cotton/peanut intercropping and their rotation have been widely studied and adopted in many cotton and peanut growing countries including China. However, it is impossible to harvest two crops in the same year under the cotton/peanut rotation. And continuous cropping constraints as indicated by inhibited crop growth and development as well as yield decline remain under continuous cotton/peanut intercropping. We hypothesized that a combination of intercropping and rotation can resolve these constraints or challenges. In a preliminary experiment, the traditional intercropping (TIC) of cotton and peanut was established and studied using monocultures of cotton (MC) or peanut (MP) as the control. Field experiments were then conducted to develop an alternate intercropping (AIC) of wide-strip cotton/peanut intercropping in combination with strip rotation (strips of the two crops were grown inter-annually in an alternate manner). Crop productivity, leaf photosynthesis, dry matter accumulation and partitioning, and main nutrient uptake as well as input-output and net returns of the new system were evaluated as compared with TIC, MC and MP for two consecutive years. Results showed that crop productivity varied significantly with cropping systems. On average, the TIC increased seed cotton yield by 16.9% and decreased peanut yield by 5.6%, while the AIC increased cotton yield by 21% without sacrificing peanut yield. The AIC increased the biological yield of peanut by 3.8% and harvest index by 2.4%; it increased the biological yield of cotton by 3.8% compared to TIC. AIC increased uptake of N, P and K in peanut by 6.3, 11.5 and 7.3%, as well as net photosynthetic rate, chlorophyll content and maximum leaf area index of peanut by 7.2, 8.9 and 4.4%, respectively, relative to TIC. Crop output value under AIC was 4.5% higher than that under TIC but the input value was the same; thus the net return under AIC exceeded that under TIC by 10%. The AIC increased crop productivity and economic return without additional input compared to traditional intercropping, thus is a promising alternative cropping system in the Yellow River valley and other areas with similar ecology.

Cotton (Gossypium hirsutum L.) yield under extensive field management across a certain range of plant population densities can be stabilized by manipulating the number of bolls and boll weight, but little is known of similar yield stability under intensive management and how the yield stability is achieved by dry matter accumulation and partitioning under various plant densities. A field experiment was conducted to study the effects of plant density (1.5, 3.3, 5.1, 6.9, 8.7 and 10.5 plants m−2) on dry matter accumulation and partitioning in relation to cotton yield. The seedcotton and lint yields at 1.5 plants m−2 were significantly lower than those at other plant densities, but there was little difference in either seedcotton or lint yield among plant densities ranging from 3.3 to 10.5 plants m−2. Plant biomass increased gradually with increasing plant density. The ratio of dry weight of fruiting forms to plant biomass (DWFF/PB) at 135 days after sowing (DAS) at 1.5 plants m−2 exceeded those under 5.1 plants m−2 by 12.3%, 6.9 plants m−2 by 12.7%, 8.7 plants m−2 by 20.5% and 10.5 plants m−2 by 21.8%. Also, the harvest index at 1.5 plants m−2 exceeded those at 5.1, 6.9, 8.7 and 10.5 plants m−2 densities by 16.2, 16.2, 34.3, 38.7%, respectively. Seedcotton yield was positively correlated with total biomass at extremely low plant density (1.5 plants m−2), but was better correlated with DWFF/PB at higher densities (5.1–10.5 plants m−2). The boll weight of the last harvest was 6.0–6.3% lower than those of the first two harvests at 1.5 plants m−2. Leaf senescence as indicated by reduced Pn and leaf area index (LAI) in later season occurred earlier at 1.5 plants m−2 than other plant densities. It was concluded that cotton yield is relatively stable across a wide range of plant densities even under intensive field management. The stability was achieved mainly through manipulation of dry matter accumulation and partitioning. The reduced boll weight of the last harvest was mainly due to earlier leaf senescence at 1.5 plants m−2, which might explain the lower cotton productivity per unit ground area at such a low plant density.

In the Yangtze and Yellow River Valleys of China, cotton usually suffers from waterlogging stress at peak flowering. The effects of waterlogging stress on cotton growth and yield are well documented, but little is known of its effects on the biomass allocation to reproductive parts and what determines waterlogging tolerance at physiological and molecular levels. Cotton was grown in a rain-shelter and subjected to a 10 day-waterlogging period to monitor plant growth and yield as well as physiology and expression of genes responsive for waterlogging tolerance. Plant growth and development as indicated by leaf area, plant biomass, biological yield and lint yield were significantly reduced by waterlogging stress. Averaged across the three years of study, the reductions were 26.3, 15.5, 19.8 and 26.1%, respectively. Boll weight and the number of bolls were also significantly reduced by waterlogging stress. The reduced lint yield was ascribed to the decreased boll weight and the number of bolls, as well as reduced plant dry matter accumulation and harvest index. Waterlogging reduced plant photosynthetic ( P n ) rate by 16.9% and NO concentration by 17.5% but increased malondialdehyde (MDA) accumulation by 22.2%. The reduced photosynthetic performance was likely due to cell membrane damage resulting from H 2 O 2 accumulation under hypoxic conditions. Waterlogging stress significantly regulated the expression of a set of genes associated with leaf photosynthesis, ROS scavenging, anaerobic metabolism or cell growth like LHCB, CSD, ACS6 , ADH , PDC , ERF s, XTH s and EXPA s, which was the likely mechanism of cotton adaptability to waterlogging stress.

Soil or foliar application of nitrogen (N) can increase plant growth and salinity tolerance in cotton, but a combination of both methods is seldom studied under salinity stress. A pot experiment was conducted to study the effects of soil application (S), foliar application (F), and a combination of both (S+F) with labeled nitrogen (15N) on cotton growth, N uptake and translocation under salinity stress (ECe = 12.5 dS m−1). Plant biomass, leaf area, leaf chlorophyll (Chl) content, leaf net photosynthetic (Pn) rate, levels of 15N and [Na+] and K+/ Na+ ratio in plant tissues were determined at 3, 7, 14 and 28 days after N application (DAN). Results showed that soil or foliar nitrogen fertilization improved plant biomass, leaf area per plant and leaf photosynthesis, and a combination of soil- plus foliar-applied N was superior to either S or F alone under salinity stress. Although foliar application favored a rapid accumulation of leaf N and soil application a rapid accumulation of root N, S+F enhanced N accu...

The effects of nitrogen (N) forms (ammonium- or nitrate-N) on plant growth under salinity stress [150 mmol sodium chloride (NaCl)] were studied in hydroponically cultured cotton. Net fluxes of sodium (Na+), ammonium (NH4+), and nitrate (NO3−) were also determined using the Non-Invasive Micro-Test Technology. Plant growth was impaired under salinity stress, but nitrate-fed plants were less sensitive to salinity than ammonium-fed plants due mainly to superior root growth by the nitrate-fed plants. The root length, root surface area, root volume, and root viability of seedlings treated with NO3-N were greater than those treated with NH4-N with or without salinity stress. Under salinity stress, the Na+ content of seedlings treated with NO3-N was lower than that in seedlings treated with NH4-N owing to higher root Na+ efflux. A lower net NO3− efflux was observed in roots of nitrate-fed plants relative to the net NH4+ efflux from roots of ammonium-fed plants. This resulted in much more nitrogen accumulation in ...

Intensive plant pruning involving removal of vegetative branches, topping, and continuously excising old leaves, growth tips of fruiting branches, excessive buds and empty fruit branches, has been widely adopted in the field management of cotton (Gossypium hirsutum L.) in China, but this practice is facing a serious of challenges because it is labor-intensive and time-consuming. In the present study, an extensive (simplified) pruning system was designed by concurrent removal of vegetative branches and the main-stem leaves below the first fruiting branch at squaring, topping by mid-July when there are 10–12 fruiting branches per plant, and omitting other pruning measures. The objective was to determine if the extensive pruning is better than intensive pruning and non-pruning (plant topping only) in yield and economic benefits. To achieve this goal, two field experiments were conducted at one site from 2011 to 2012 and at five sites in 2013 in the Yellow River delta of China. A split-plot design was used in both experiments with the main plots assigned to cotton cultivars and the subplots assigned to plant pruning (non-pruning, intensive pruning and extensive pruning). The effects of plant pruning, cultivar and their interactions on seed cotton yield were evaluated in both experiments, and on plant growth, harvest index, earliness, yield components and labor input in the first experiment. Both the intensive and extensive plant pruning were beneficial to plant height, harvest index, boll weight and seed cotton yield regardless of cotton cultivar. The extensive pruning was comparable to the intensive pruning system in cotton yield in the first experiment, but produced 4.3% and 4.8% more seed cotton than non-pruning in 2011 and 2012. Greater increases in cotton yield under extensive pruning were obtained in the multi-site experiment in 2013, with an average seed cotton yield increase of 7.7% compared with non-pruning. Both intensive and extensive pruning consumed more labor days than non-pruning, but the labor input under extensive pruning was 76–81% less than that under intensive pruning. Compared with non-pruning, extensive pruning increased the net revenue by 7.9% as a result of improved cotton yield, but intensive pruning decreased net revenue by 3.5% due to increased labor input. The overall results showed that extensive plant pruning is more simplified and beneficial than the traditional intensive pruning and should be a promising alternative in the Yellow River valley of China and other regions with similar ecological conditions.

Two experiments were conducted to determine if improved nutrient uptake increases salinity tolerance of cotton (Gossypium hirsutum L.). A transgenic cotton line (CMO3) with increased salt tolerance and its wild line (SM3) were grown in pots containing substrate (peat:vermiculite = 1:1, v/v) in the first experiment, while cotton (‘SCRC 28’) was cultured in hydroponics with a split-root system in the second experiment. Contents of essential nutrient elements and Na+ in plant tissues, leaf photosynthesis (Pn) and chlorophyll (Chl) concentration and plant biomass were determined after salinity [sodium chloride (NaCl)] treatment in both experiments. In the first experiment, salinity stress with 150 mM NaCl reduced plant biomass and photosynthesis (Pn) of both SM3 and CMO3 compared with their non-stressed controls, but the CMO3 suffered significantly lower reductions than SM3, suggesting an increased salinity tolerance of CMO3 relative to SM3. Total uptake and contents of main nutrient elements [nitrogen (N), p...

With the wide adoption of transgenic Bacillus thuringiensis (Bt) cotton, the incidence of bollworm has reduced significantly, but secondary pests such as cotton spider mites have become serious problems in Bt cotton fields. The objective of the present study was to investigate the underlying mechanism of increased incidence of secondary pests in Bt cotton. Two transgenic cotton varieties, sGK321 and Bt-C12, and their non-transformed counterparts, SY321 and C12, were used to study differences in the incidence of spider mites in relation to secondary metabolites. Plants of each cotton cultivar were infested with five female adult spider mites and then isolated. Leaf samples with a pair of adult mites of the same age were transferred individually into Petri dishes for examination of egg laying and duration of development stages. The number of spider mites on Bt-C12 and sGK321 was more than that on C12 and SY321. The cotton spider mites feeding on Bt-C12 laid significantly more eggs than those feeding on C12; those feeding on sGK321 laid significantly more eggs than those feeding on SY321. The generation time of spider mites feeding on Bt-C12 was greatly reduced relative to those feeding on C12. Also, the generation time of mites feeding on sGK321 was shorter than those feeding on SY321. Gossypol and tannin contents in leaves of Bt-C12 were substantially lower than those in C12, and the contents in leaves of sGK321 were significantly lower than those in leaves of SY321. The occurrence of spider mites was more serious on Bt than non-Bt cotton, and the fitness of the mites on Bt cotton was higher than on non-Bt cotton. Reductions in gossypol and tannin contents in Bt cotton decreased the generation time and increased the number of eggs of cotton spider mites.

Cotton (Gossypium hirsutum L.) production in China has developed rapidly during the last 60 years. In 2012, the planting area and total output in the country were 5.3 million hectares and 7.62 million tons, respectively, and the unit yield was 85% higher than the world average. China currently accounts for about 30% of the world's cotton output with only 15% of the world's cotton land. Enhanced cotton production, particularly the high unit yield is largely due to adoption of a series of intensive farming technologies and cultural practices. The intensive farming technologies for cotton production in China mainly include seedling transplanting, plastic mulching, double cropping, plant training and super-high plant density technique, which have played important roles in promoting unit yield and total output. Although such intensive farming technologies meet the need of a growing population under limited arable land in China, they are labor-intensive and involve large input of various kinds of chemical products like fertilizers, pesticides, and plastic films. Thus, there are increasing challenges from soil pollution and labor shortage. Here, the achievements, challenges, countermeasures and prospects for intensive cotton cultivation in China are reviewed. An important conclusion from this review is that the establishment of a new farming technology through reform of the current intensive technology is inevitable to support sustainable cotton production in the nation. A series of comprehensive countermeasures should be taken to reduce soil pollution through rational use of plastic film and chemicals, labor saving through simplifying field managements and mechanization and increasing benefits by reforming the cropping system and management mode. China's cotton production would be sustainable with a bright prospect if supported by new farming technologies.

Exogenous H2O2 improves seed germination with the involvement of ABA and GA in a number of plant species but how it affects cotton seed germination under salinity stress is not well documented. In this study, we found that the marked inhibition of cotton seed germination under salinity stress was considerably alleviated by pretreatment with H2O2. Salt stress increased the ABA content by upregulating ABA biosynthesis genes, NCED2, NCED5 and NCED9 and downregulating the ABA catabolism gene, CYP707A2. It also decreased the GA content by increasing the expression of GA catabolism gene, GA2ox1 and decreasing that of the GA biosynthesis gene, GA20ox1 during germination. Pretreatment with H2O2 downregulated the ABA biosynthesis genes, NCED5 and NCED9, thereby decreasing the ABA content in germinating seeds. Concurrently, it increased the GA content by downregulating the GA catabolism gene, GA2ox1. These results suggest that pretreatment with H2O2 improved cotton seed germination by mediating the downregulation of ABA catabolism and GA biosynthesis under salt stress.

Nitric oxide (NO) is a signaling molecule which plays an important role in delaying leaf senescence and increasing abiotic stress tolerance, but it is not clear if and how exogenous NO delays salt-induced leaf senescence in cotton. In this study, uniform cotton seedlings with five true main-stem leaves were cultured in hydroponics for 20 days and subjected to 150 mM NaCl. Seedlings were then treated with foliar spray of 300 μM sodium nitroprusside (SNP), a nitric oxide donor, and those with water spray were used as control. The effects of SNP on leaf senescence and expression of senescence-related genes were examined. Foliar spray with SNP significantly delayed leaf senescence in terms of the increased chlorophyll (Chl) content, photosynthetic (Pn) rate and expression of LHCB gene at 22 days after salt stress (DAS). The SNP significantly (p

Understanding salinity and fertilizer interaction is of great economic importance to improving crop yield and fertilizer use efficiency. The objective of this study was to investigate the effects of nitrogen (N) rate on cotton yield and N use efficiency (NUE), and relate this to the optimum N fertilizer rate under saline field conditions. To achieve this goal, we conducted a two-year experiment in two nearby fields with similar fertility but varying salinity, using a split-plot design in the Yellow River Delta of China. The main plots were assigned to moderate (electrical conductivity of soil saturated paste extract, ECe = 6.3 dS/m) and high (ECe = 12.5 dS/m) salinity levels, while N-free (0 kg/ha), low (120 kg/ha), moderate (210 kg/ha) and high (300 kg N/ha) nitrogen rates were assigned to the subplots. The high-salinity soil produced 35% lower biological yield but 8.9% higher harvest index than the moderate-salinity soil. Biological yields were increased by 30% at low N rate, 35% at moderate N rate and 37% at high N rate. Under moderate salinity, moderate N rate produced more lint than other N rates; under the high salinity field, the low N rate produced lint yield comparable to the high- and moderate-N rates, being about 33% greater than that from 0-N rate. Moderate N rate was superior to high N rate but comparable to low rate based on agronomic NUE (aNUE), physiological NUE (pNUE), internal NUE (iNUE) and N recovery efficiency (NRE) under moderate salinity; under high salinity, the low N rate produced the greatest aNUE and NRE, and higher pNUE and iNUE than high N rate. Our overall results supported the use of moderate N rate for moderate salinity cotton fields and low N rate for high salinity fields in the saline Yellow River Delta and other cotton-growing areas with similar ecologies.

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 = 11 dS/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 7.5 plants/m2), while low, moderate and high nitrogen rates (120, 225 and 300 kg N/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 (1604 kg/ha) was achieved only with a high dose of N fertilizer under low plant density, but comparable yields (1693 and 1643 kg/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.

Many studies have shown that root–shoot imbalance influences vegetative growth and development of cotton (Gossypium hirsutum L.), but few have examined changes in leaf senescence and endogenous hormones due to stem girdling. The objective of this study was to determine the correlation between some endogenous phytohormones, particularly cytokinins and abscisic acid (ABA), and leaf senescence following stem girdling. Field-grown cotton plants were girdled on the main stem 5 days after squaring (DAS), while the non-girdled plants served as control. Plant biomass, seed cotton yield, main-stem leaf photosynthetic (Pn) rate, chlorophyll (Chl) and malondialdehyde (MDA) concentrations, as well as levels of cytokinins and ABA in main-stem leaves and xylem sap were determined after girdling or at harvest. Main-stem girdling decreased the dry root weight and root/shoot ratio from 5 to 70 days after girdling (DAG) and reduced seed cotton yield at harvest. Main-stem leaf Pn and Chl concentration in girdled plants were significantly lower than in control plants. Much higher levels of MDA were observed in main-stem leaves from 5 to 70 DAG, suggesting that stem girdling accelerated leaf senescence. Girdled plants contained less trans-zeatin and its riboside (t-Z + t-ZR), dihydrozeatin and its riboside (DHZ + DHZR), and isopentenyladenine and its riboside (iP + iPA), but more ABA than control plants in both main-stem leaves and xylem sap. These results suggested that main-stem girdling accelerated leaf senescence due to reduced levels of cytokinin and/or increased ABA. Cytokinin and ABA are involved in leaf senescence following main-stem girdling.

As the most important cultural practices for cotton production, the single effects of plant density and [nitrogen (N) and potassium (K)] fertilization on yield and yield components are well documented but their combined effects on Bt cotton are poorly understood. Using a split–split plot design with four replications, we conducted a two-year field experiment in two fields, one with lower fertility and the other with higher fertility, in the Yellow River Valley of China. The aim was to evaluate both the individual and combined effects of plant density and nitrogen and potassium fertilization on yield, yield components and uptake of major nutrients. The main plots were assigned to plant density (4.5 and 7.5 plants/m 2 ), while nitrogen (0 and 240 kg N/ha) and potassium fertilization (0 and 150 kg K/ha) were assigned to the sub- and sub–subplots. Lint yield was improved with high plant density (7.5 plants/m 2 ) in the lower fertility field, particularly without N and K application, but not in the higher fertility field. Nitrogen or K application also increased lint yield, and a combination of high plant density, N and K application further improved lint yield in the lower fertility field, while only K application increased lint yield in the higher fertility field. Lint percentage was not affected by any of the variables studied. Thus, the yield increase due to plant density, fertilization or their combinations was attributed to increases in boll number or boll weight. The ratio of seed cotton to stalk (RSS) was linearly correlated with harvest index, and thus can be a simple indicator of dry matter allocation to reproductive structures. Increased yield due to plant density and fertilization was mainly attributed to the enhanced biological yield in the lower fertility field, while the yield increase due to K fertilization was mainly due to increased RSS in the higher fertility field. The plants used approximately equal N and P to produce 100 kg lint in both fields, but the uptake of K to produce 100 kg lint in the higher fertility field was about 21% more than that in the lower fertility field. Ratios of N:P:K were 1:0.159:0.604 in the lower fertility field and 1:0.159:0.734 in higher fertility field. This study suggests that K fertilization was extremely important for maintaining high yield, although luxury consumption occurred in the higher fertility field; N was applied more than required in the highly fertile field, and increased plant density would be beneficial to cotton yield in the lower fertility field.

Normal planting of full-season cotton ( Gossypium hirsutum L.) (NPF) in saline fi elds of the Yellow River valley, China, is currently faced with poor stand establishment, late maturity, and increas-ing cost of inputs. Our objective was to determine if late planting of short-season cotton (LPS) may alleviate these problems. In the fi rst experiment, the effects of cultivar, planting date, seeding rate, and their interactions on stand establishment and seedling Na + and malondialdehyde concen-trations were studied. We also compared varietal effects, input costs, and gross economic returns under NPF and LPS. Late planting improved stand establishment due to increased tempera-ture and reduced Na + and malondialdehyde concentrations in cotton tissues. The LPS at 21 kg seeds ha –1 (LPSM) and NPF at 30 kg seeds ha –1 (NPFH) yielded better than other treatment combinations. Varietal effects on lint yield were not signifi cant. The output value of both systems was comparable; however, the net revenue from LPSM was 32% greater than that from NPFH due to lower material cost and labor inputs. Late planting of short-season cotton is a promising option for cotton production in saline areas of the Yellow River delta and probably in other cotton-growing areas with similar ecologies.Cotton Research Center, Provincial Key Lab. for Cotton Culture and Phys-iology, Shandong Academy of Agricultural Sciences, Jinan 250100, China. Received 3 Apr. 2009. *Corresponding author (donghz@saas.ac.cn).

A two-year field experiment was conducted to determine the effects of removal of early-fruiting branches (REFB) on yield, quality, and endotoxin expression in transgenic Bt (Bacillus thuringiensis) cotton (Gossypium hirsutum L.). Two early-fruiting branches of field-grown cotton plants were removed and retained at squaring to form the REFB and the control treatments, respectively. Lint yield, yield components, fibre quality, and Cry1Ac protein concentration in the first fully expanded young leaves on the main stem were measured. Results show that lint yields were increased by 5.1 and 5.5% with REFB compared with control in 2004 and 2005, respectively. There was no difference in fibre quality in the first two harvests between REFB and control, but fibre strength and micronarie in the third harvest were improved with REFB. Levels of total N, soluble protein, and Cry1Ac protein as well as glutamic-pyruvic transaminase (GPT) activity in leaves were higher in REFB than in the control. Laboratory bioas...

Numerous studies have shown that early-fruit removal enhances vegetative growth and development of cotton (Gossypium hirsutum L.). However, few studies have examined changes in leaf senescence and endogenous hormones due to fruit removal. The objective of this study was to determine the correlation between some endogenous phytohormones, particularly the cytokinins and abscisic acid (ABA), and leaf senescence following fruit removal. Cotton was grown in pots and in the field during 2005 and 2006. Two early-fruiting branches were excised from plants at squaring to form the fruit removal treatment while the non-excised plants served as control. Plant biomass, seed cotton yield, cytokinins and ABA levels in main-stem leaves and xylem sap as well as main-stem leaf photosynthetic rate (Pn) and chlorophyll (Chl) concentration were determined after removal or at harvest. Fruit removals increased the leaf area, root and shoot dry weight and plant biomass at 35 days after removal (DAR), whether in potted or field-grown cotton; under field conditions, it also improved plant biomass and seed cotton yield at harvest. The Pn and Chl concentration in excised plants were significantly higher than in control plants from 5 to 35 DAR, suggesting that fruit removal considerably delayed leaf senescence. Fruit-excised plants contained more trans-zeatin and its riboside (t-Z + t-ZR), dihydrozeatin and its riboside (DHZ + DHZR), and isopentenyladenine and its riboside (iP + iPA) but less ABA in both main-stem leaves and xylem sap than control plants from 5 to 35 DAR. These results suggest that removal of early fruiting branches delays main-stem leaf senescence, which can be attributed to increased cytokinin and/or reduced ABA. Cytokinin and ABA are involved in leaf senescence following early fruit removal.

Row covering with polyethylene film (plastic mulching) is a common practice for improving emergence, plant growth and yield of cotton in China. This is usually applied after sowing (conventional mulching, CM), but pre-sowing evaporation in spring would cause accumulation of salts and moisture loss in the surface layer of saline soils. Two experiments were conducted in Yellow River delta from 2004 to 2005 and during 2006, respectively to determine if row covering with plastic film 30 d before sowing (early mulching, EM) supports better productivity of cotton than CM in saline fields. In the first experiment, we studied the effects of EM versus CM and no-mulching (NM), on soil microclimate, seedling physiology, cotton yield and earliness. The second experiment was conducted in seven sites to compare cotton yield between the two mulching systems. Results from the first experiment showed that both EM and CM could effectively improve stand establishment, plant growth, earliness and lint yield of cotton relative to NM control. However, compared with CM, EM increased stand establishment rate by 11.4% and plant biomass by 9.9% and lint yield by 7.1%. EM, relative to CM and NM, increased the photosynthesis (Pn) rate 6.8% and decreased malondialdehyde (MDA) concentration 7.4% and Na + level 8%. These improvements were due mainly to delayed accumulation of salts, elevation of soil temperature and reduction of moisture loss with EM. The revenue from EM was higher than that from CM and NM, suggesting the increased yield by EM was enough compensate for additional costs. The multi-site experiment in 2006 showed that the yield advantage of EM over CM was not significant in two sites with lower salinity (ECe = ∼6 dS/m), but substantial (from 9 to 14%) in five sites with higher salinity (ECe = 10–12 dS/m). The overall results suggest that EM is a promising cotton production technique in the saline Yellow River Delta and other cotton-growing areas with similar ecologies.

Salinity, waterlogging and a combination of both stresses are severe threats to plant growth, development and yield of field-grown cotton (Gossypium hirsutum L.), but their individual or combined effects on insecticidal efficacy of Bacillus thuringiensis (Bt) transgenic cotton and the underlying mechanisms are not well understood. In the present study, two cotton cultivars (33B and SCRC17) containing the Cry1Ac insecticidal protein gene were planted in 10 L pots filled with soil and allowed to grow in a greenhouse. The potted plants were either treated with NaCl (5 mg/g, w/w), waterlogging, or a combination of both stresses at the three true-leaf stage, and levels of total soluble protein, Bt insecticidal protein, gossypol and the control efficacy as indicated by mortality of bollworm larvae were examined at 7-day intervals after stress. Waterlogging and a combination of salinity and waterlogging reduced total protein content by 40–46% and 45–65% and Bt protein content by 38–50% and 45–72% from 7 to 21 days after stress, relative to the non-stressed control, respectively. The control efficacy was significantly reduced by either waterlogging or the combined stress. Regression analysis indicated that Bt protein content was correlated to total soluble protein content (R2 = 0.7677*), while Bt cotton efficacy was correlated to Bt protein level (R2 = 0.7917**). Salinity reduced Bt protein by 11–22% and total soluble protein by 5.7–7.2% from 7 to 21 days after NaCl stress, but did not result in reduction in control efficacy. It is concluded that reduced bollworm control efficacy under waterlogging or the combined stress could be mainly attributed to the declined levels of Bt protein, which is closely associated with the inhibited nitrogen metabolism by stresses. As one of the secondary compounds that are toxic to pests, increases in gossypol may be involved in maintaining the efficacy when Bt protein level was reduced under salinity.

Glycine betaine is an osmoprotectant that plays an important role and accumulates rapidly in many plants during salinity or drought stress. Choline monooxygenase (CMO) is a major catalyst in the synthesis of glycine betaine. In our previous study, a CMO gene (AhCMO) cloned from Atriplex hortensis was introduced into cotton (Gossypium hirsutum L.) via Agrobacterium mediation to enhance resistance to salinity stress. However, there is little or no knowledge of the salinity tolerance of the transgenic plants, particularly under saline-field conditions. In the present study, two transgenic AhCMO cotton lines of the T3 generation were used to study the AhCMO gene expression, and to determine their salinity tolerance in both greenhouse and field under salinity stress. Molecular analysis confirmed that the transgenic plants expressed the AhCMO gene. Greenhouse study showed that on average, seedlings of the transgenic lines accumulated 26 and 131% more glycine betaine than those of non-transgenic plants (SM3) under normal and salt-stress (150 mmol l−1 NaCl) conditions, respectively. The osmotic potential, electrolyte leakage and malondialdehyde (MDA) accumulation were significantly lower in leaves of the transgenic lines than in those of SM3 after salt stress. The net photosynthesis rate and Fv/Fm in transgenic cotton leaves were less affected by salinity than in non-transgenic cotton leaves. Therefore, transgenic cotton over-expressing AhCMO was more tolerant to salt stress due to elevated accumulation of glycine betaine, which provided greater protection of the cell membrane and photosynthetic capacity than in non-transgenic cotton. The seed cotton yield of the transgenic plants was lower under normal conditions, but was significantly higher than that of non-transgenic plants under salt-stressed field conditions. The results indicate that over-expression of AhCMO in cotton enhanced salt stress tolerance, which is of great value in cotton production in the saline fields.

Uniform stand establishment is essential for profitable cotton (Gossypium hirsutum L.) production in saline fields. This study was conducted during 2003 and 2004 to determine if furrow-bed seeding and plastic mulching improve stand establishment and cotton lint yield in a saline field. The experiment was arranged in a split-plot design with seeding patterns (flat-seeded and furrow-seeded) as main plots and mulching (with or without plastic mulching) as subplots. The effects of seeding patterns, mulching, and their interactions on root-zone salinity, soil temperature, stand establishment, and lint yield were monitored. Furrow seeding reduced the root-zone salinity, while plastic mulching both reduced salinity and increased soil temperatures. As a result, furrow-seeded cotton under plastic mulching increased stand establishment and lint yield by 103 and 25% in 2003, and 92 and 22% in 2004, compared with flat-seeded cotton without mulching, respectively. Plastic mulching and furrow seeding also enhanced earliness as indicated by the percentage of the first two harvests. Physiological assay 30 d after seeding (DAS) showed that plastic mulching and furrow seeding substantially reduced Na + accumulation both in root and leaf tissues, inhibited peroxidation oflipids, and improved leaf photosynthesis (Pn) and dry matter production. The overall results suggest that use of plastic mulching plus furrow-bed seeding would be a suitable cultural practice for enhancing cotton production in saline soils.

Plastic mulching and seedling transplanting are widely adopted intensive planting systems for cotton production in China. Previous studies have demonstrated considerable yield increases by individual use of mulching or transplanting compared with conventional planting. In the present study, two experiments were conducted to test if an integration of transplanting and plastic mulching is more beneficial than individual use of transplanting for enhancing cotton production, in northern Shandong, Yellow River Valley of China from 2003 to 2005. In the first experiment in 2003 and 2004, a hybrid Bt cotton cultivar SCRC 15 was planted in a greenhouse-like hut in early April, and the raised seedlings were transplanted to mulched or non-mulched field plots in early May. Plant growth and development, yield and yield components, and earliness of cotton were evaluated. In the second experiment in 2004 and 2005, three hybrid and three non-hybrid Bt cotton cultivars were managed with the integrated system or with transplanting alone, and yields of each cultivar were examined. Results from the first experiment showed that plant growth and development, yield and yield components, and earliness of cotton were significantly enhanced by an integration of mulching and transplanting compared with individual use of transplanting in either 2003 or 2004. Lint yields and the number of bolls per unit ground area were increased by 17.4% and 14.6% in 2003, and 17.1% and 15.3% in 2004 with plastic mulching in comparison with non-mulching, respectively. Such enhancement was mainly attributed to significantly increased soil temperature during early season after transplanting. The size of soil blocks for seedling nursing had significant and non-significant enhancement on final lint yield in 2003 and 2004, respectively. In the second experiment, average lint yields of hybrid cotton were increased by 17.8% in 2003 and 16.9% in 2004, and those of non-hybrid cotton were 13.3% in 2003 and 13.5% in 2004 with mulching in comparison with non-mulching (individual use of transplanting). It was concluded that an integration of plastic mulching and seedling transplanting can be more effective than individual use of transplanting to enhance cotton production in northern Shandong and other heat-limited areas.