Search

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.

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.

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.

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.

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.

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.

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.

Silicon (Si) can increase plant defence systems against abiotic and biotic stress, but there is little information on UV-B radiation stress alleviation by Si for field crops. Using soybean (Glycine max (L.) Mell) seedlings, we determined how Si may mediate UV-B radiation stress by studying changes in biomass, physiological attributes and antioxidants’ activities. The seedlings were raised with 0, 1.70 and 2.55 mm of Si in the growth chamber under ambient, ambient +2.7 kJ m−2 day and ambient +5.4 kJ m−2 day of UV-B radiation. As expected, plants suffered severe growth limitations under UV-B radiation, but Si alleviated these limitations through improvements in leaf area (LA) and root-to-shoot ratio (R/S). The UV-B radiation stress reduced the LA by 73.9–94.7%, total dry weight (TDW) by 11.8–36.6% and R/S by 9.2–30.2% but induced the activities of soluble protein by 18.4–21.0%, catalase (CAT) by 22.7–54.2%, superoxide dismutase (SOD) by 31.9–63.1%, and peroxidases (POD) by as much as 162.9–381.6%. Further confirmation of stress alleviations by Si was noted from reductions in these stress signals (antioxidant activities) under UV-B radiation: CAT decreased significantly by 78.3–79.4%, SOD by 5.3–7.2% and POD by 49.9–61.9% in silicon-treated UV-B stressed soybean.

We studied the effects of coronatine (COR), a structural and functional analogue of jasmonates, on the drought tolerance of two rice cultivars, Handao 297 (a drought-tolerant upland rice) and Yuefu (a drought-sensitive lowland rice). Seedlings were treated with COR at the three-leaved stage at 0.01 and 0.1 lm for 24 h, followed by imposition of water deficit induced with 20 % polyethylene glycol (PEG). Water stress reduced the biomass of both cultivars and increased leaf lipid peroxidation and solute leakage. Pre-treatment with COR significantly increased the activities of superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase in leaf tissues of water-stressed Handao 297 (0.01 lm) and Yuefu (0.1 lm) seedlings. COR supplement also increased the accumulation of 44 and 32 kDa polypeptides in water-stressed Handao 297 (0.01 and 0.1 lm) and Yuefu (0.1 lm) and significantly induced the expression of 29 kDa polypeptide in Handao 297. The results suggest that COR might alleviate drought stress by activating antioxidant enzymes and inducing proteins, thereby preventing membrane peroxidation and denaturation of bio-molecules. Thus, membrane permeability decreased substantially by 24‐27 % in Handao 297, and 22‐29 % in Yuefu. The optimal concentrations conferring drought resistance were 0.01 for the upland rice and 0.1 lm for the lowland cultivar.

The objective was to study soil water conservation and physiological growth of wheat (Triticum aestivum L.) using composted cattle manure applied either as mulch or incorporated with soil at 20 Mg ha -1 . Haruhikari, a relatively drought-sensitive and Hongmangmai, a relatively drought-tolerant wheat, were the cultivars studied under both adequate and deficit irrigation. Fourteen weeks after sowing (WAS), the number of tillers and leaves was significantly reduced by 19 % and 30 % respectively under deficit irrigation and Hongmangmai produced slightly (10 %) more tillers than Haruhikari. Unlike mulching, the incorporation of manure had favourable effects on plants in terms of shoot dry mass (SDM) by 36 % and number of tillers and leaves by 40 %. Haruhikari produced substantially (29 %) greater root mass under adequate irrigation but Hongmangmai produced slightly (2.7 %) more roots and responded much better to manure use whether under adequate or deficit irrigation. As a result, Hongmangmai suffered less severe reductions in tillers and biomass under water stress. In comparison, the mulched manure treatment saved 15 % and 64 % respectively more water than the control and the treatment incorporating manure, but this advantage in water-saving did not translate to superior plant growth. Leaf water potential (ψ 1 ) under adequate irrigation significantly exceeded that under deficit irrigation by 27 % and the ψ l of Haruhikari exceeded that of Hongmangmai by 15 %. However, Hongmangmai may be considered more tolerant of dehydration since it maintained much higher net photosynthetic rates (P N ) even with a lower leaf water potential. The reduction in the P N and intracellular carbon dioxide concentration (C i ) of the cultivars under deficit irrigation was on account of decreasing stomatal conductance (g s ) and transpiration rate but on average, the g s of Hongmangmai significantly exceeded that of Haruhikari by as much as 0.53 under adequate irrigation and 0.22 under deficit irrigation. In conclusion, we suggest that the drought tolerance of Hongmangmai was related to its superior root growth and greater ability than Haruhikari, to efficiently utilize incorporated manure for growth under water stress.

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.

Cotton is usually managed with a normal planting production system (NPPS) that involves planting in mid-April at a moderate plant density (4.5 plants/m 2 ) in the Yellow River Valley of China, but drought or cold stress in spring often delays cotton planting, and results in reduced yield and maturity at this plant density. Two experiments were conducted for 4 consecutive years, to test if yield and fiber quality can be maintained or improved by increased plant density for relatively late-planted cotton. Results in the first experiment in 2001 and 2002 showed that average lint yields were not significantly affected by plant density (3.0, 4.5, 6.0 or 7.5 plants/m 2 ) or byplanting date (mid-April or early May), but significant interactions between planting date and plant density on lint yield were detected in both years. Normal planted cotton at a plant density of 3.0‐4.5 plants/m 2 , and late-planted cotton at 7.5 plants/m 2 produced higher lint yield than other planting date and density combinations. Experiment 2 compared NPPS with a late planting production system (LPPS) which involves planting in early May at 7.5 plants/m 2 over 2 years. The NPPS and LPPS had similar lint yields in both years. Cotton plants in both systems produced approximately 75% of total lint in the first two harvests, indicating no significantly delayed earliness in LPPS relative to NPPS. Fiber from late-season bolls exhibited reduced strength and micronaire in both systems, but there were no significant differences in fiber properties for early- and midseason fiber between the two systems. In terms of green leaf area index and leaf chlorophyll content, leaf senescence or premature senescence of cotton plants was considerably alleviated by either altered source to sink balance or the uptake of K in LPPS compared to NPPS. It was concluded that the LPPS, a relatively late-planted cotton production system with increased plant density under intensive field management, might be a potential alternative for growing cotton. # 2005 Elsevier B.V. All rights reserved.

Previous studies have indicated that dry mycelium (DM) of Penicillium chrysogenum ( PEN ), a waste product of the pharmaceutical industry, is effective in controlling fungal diseases in crop plants under greenhouse or shade-house conditions. In the present study, cotton was grown in fields amended with DM before planting, or squaring, or both, in Linqing and Liaocheng, Shandong province, China, and disease severity of Fusarium oxysporum f.sp vasinfectum ( Fov ) and Verticillium dahliae ( Vd ) was monitored from 2001 to 2004. Results from the first experiment in 2001 and 2002 showed that DM was effective in protecting, in an application mode-dependent manner, against these two pathogens. At a dose of 30 g m −2 , either basal application alone or basal application plus side dressing of DM provided significant protection against Fusarium wilt and Verticillium wilt, but side dressing alone was not significantly effective in controlling the two diseases. In the second experiment in 2003 and 2004, it was shown that disease-control efficacy of DM was dependent on application rates. Averaged across two sites and both years (2003 and 2004), basal application plus side dressing at doses of 30, 90 and 150 g m −2 provided protection of 20.1, 34.6 and 42.7% against Fov , and of 26.8, 47.8 and 49.6% against Vd , respectively, compared to their corresponding DM-free controls. Increases in lint yield of cotton was also obtained by application of DM each year, which could be attributed to both disease control and nutritional effects of DM. DM (⩽2%) had no effect on mycelial growth of the pathogens in vitro, suggesting that the protection was probably attributable to induced resistance. It is concluded that DM of PEN may serve as an organic product for both disease control and plant nutrition in cotton production.

Bt (Bacillus thuringiensis) transgenic cotton (Gossypiwn hirsutum L.), including the introduced, indigenous Chinese non-hybrid and hybrid cotton, is spreading very rapidly in China. Agronomic and photosynthetic performance as well as the optimum plant density for planting Bt cotton may vary with genotypes. With three types of commercial Bt cotton varieties, two field experiments were conducted to study yield performance and leaf photosynthetic rate (Pn) during 2000 and 2001, and yield interaction between variety and plant density during 2001 and 2002 in Yellow River region in northern China. The first experiment showed that the indigenous Chinese Bt cotton significantly differed from the introduced Bt cotton (IBtC) in plant growth and yield components. As a result of manipulation of boll numbers, boll weight and lint percentage, there was no significant difference in lint yield between Chinese non-hybrid Bt cotton (CBtC) and the IBtC, but two Chinese hybrid Bt cotton (HBtC) varieties exhibited significantly higher lint yield than all other varieties in either 2000 or 2001. Hybrid cotton SCRC15 showed a one-peak curvilinear change in diurnal course of Pn throughout the growing season, while non-hybrid cotton 33B and SCRC16 exhibited severe midday depression in Pn in squaring, flowering or boll-setting stage. The second experiment showed that the main effect of plant population on lint yield was not significant, and yield difference among all treatments was derived from varieties and the interaction between plant density and variety. The optimal plant densities in terms of lint yield for the introduced, indigenous CBtC and HBtC genotypes were 6.0, 4.5 and 3.0 plants m -2 respectively.

Seedling transplanting and plastic mulching are widely adopted intensive planting systems in cotton production in China. Manual removal of early- or late-season flowers may improve seed quality without sacrificing yield through the compensatory growth of cotton plants. Two experiments were conducted, in Yellow River Valley in China from 2002 to 2003, to test if the intensive systems and flower removal can be used for enhancing hybrid seed production. Results in the first experiment show that yields of seed cotton and seed, and seed quality parameters averaged across three plant densities (2.25, 3.00 and 3.75 plants/m 2 ), were significantly improved by either transplanting or plastic mulching relative to conventional planting. The improvements in yield and quality in two intensive planting systems were mainly attributed to longer and earlier flowering period. Transplanted plants did not differ significantly from mulched plants in seed yield, seed maturity and percentage germination, but transplanting decreased lint percentage and increased seed index relative to mulching. In terms of seed yield and quality, the optimum plant density for each planting system was 3.00 plants/m 2 . At the optimum plant density, seed yields averaged across two years for transplanting and mulching systems were 31.3% and 32.6% higher than for conventional planting system, respectively. Flower removal did not significantly affect seed yield, but removal of late-season or both early- and late-season flowers significantly improved seed quality. It was concluded that transplanting or plastic mulching, low plant density (3.00 plants/m 2 ), and removal of late-season or both early- and late-season flowers can be integrated to enhance yield and quality of hybrid seed of cotton.

Rapid adoption of Bacillus thuringiensis (Bt) transgenic hybrid cotton (Gossypium hirsutum L.) in China is greatly attributed to high-quality hybrid seed produced in northern Shandong cotton production area; however, seed yield has reached a plateau in this area in recent years. Shifting the growing season earlier in the year by planting earlier in a greenhouse-like hut and transplanting the raised seedlings to the open fields later may allow the crop to produce more seeds. Four-year consecutive experiments conducted in Huimin County (northern Shandong, China) showed that early-season chilling stress on seedlings was avoided in such a hut, and that the blooming period was extended by about 1 week longer and the peak blooming occurred 5 days earlier in the year in the transplanting system than in the normal planting system. The number of early-season blooms and the number of bolls retained per unit area in transplanting system were significantly higher than those in normal planting system, but there were no significant differences in boll size and lint percentage between the two planting systems. Seed yield and quality parameters were significantly improved in the transplanting system through the increased number of bolls per square metre and earlier blooming respectively. As a result of improvement in seed yield and quality, the net revenue for seed producers with the transplanting system was increased by 20.8 and 22.5 % in 2002 and 2003, respectively, compared with the corresponding net revenue in the normal planting system. Seedling transplanting is a potent way to enhance hybrid seed production in Bt transgenic cotton.

As modern cotton varieties including Bt (Bacillus thuringiensis) transgenic cotton are adopted and yield per unit area continues to increase, potassium deficiency is occurring with rising frequency in many cotton-growing countries. Symptoms of K deficiencies used to occur at the bottom of the plant on the older or mature leaves, but more recently described symptoms show up on young leaves near the top of the plant. Potassium deficiency induces numerous disorders in cotton, including decreased leaf area index, photosynthesis and plant biomass, but enhances specific leaf weight and earliness of maturity. Low supply and uptake of K, adoption of modern cotton varieties particularly Bt transgenic cotton, and environmental stress are obvious contributors to potassium deficiency. Single leaf photosynthesis (Pn) reduction results mainly from decreased stomatal conductance, low chlorophyl content, poor chloroplast ultrastructure, restricted saccharide translocation, and decreased synthesis of RuBP carboxylase under K deficient conditions. Canopy photosynthesis reduction in K-deficient plants is mainly attributed to both inhibited single leaf Pn rate and decreased leaf area index. Potassium concentrations in both blade and petiole of top fully expanded leaves on main stem are good indicators of K deficiency.