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Abstract Background Natural and synthetic plant growth regulators are essential for plant health, likewise these regulators also play a role in increasing organic production productivity and improving quality and yield stability. In the present study, we have evaluated the effects of foliar applied plant growth regulators, i.e., moringa leaf extract (MLE) and mepiquat chloride (MC) alone and in combination MC and MLE on the conventional cotton cultivar (CIM 573) and transgenic one (CIM 598). The growth regulators were applied at the start of bloom, 45 and 90 days after blooming. Results The application of MC and MLE at 90 days after blooming significantly improved the relative growth rate, net assimilation rate, the number of bolls per plant, and seed cotton yield. Likewise, the combined application of MLE and MC at 90 days after blooming significantly boosted the nitrogen uptake in locules, as well as the phosphorus and potassium uptake in the leaves of both cotton cultivars. The application of MLE alone has considerably improved the nitrogen uptake in leaves, and phosphorus and potassium contents in locules of Bt and conventional cotton cultivars. Similarly, Bt cotton treated with MLE at 90 days after blooming produced significantly higher ginning out turn and oil contents. Treatment in combination (MLE + MC) at 90 days after blooming produced considerably higher micronaire value, fiber strength, and staple length in conventional cultivar. Conclusion The natural growth enhancer, MLE is a rich source of minerals and zeatin, improving the nutrient absorption and quality of cotton fiber in both conventional and Bt cotton cultivars.

Background: Natural and synthetic plant growth regulators are essential for plant health, likewise these regulators also play a role in increasing organic production productivity and improving quality and yield stability. In the present study, we have evaluated the effects of foliar applied plant growth regulators, i.e., moringa leaf extract (MLE) and mepiquat chloride (MC) alone and in combination MC and MLE on the conventional cotton cultivar (CIM 573) and transgenic one (CIM 598). The growth regulators were applied at the start of bloom, 45 and 90 days after blooming. Results: The application of MC and MLE at 90 days after blooming significantly improved the relative growth rate, net assimilation rate, the number of bolls per plant, and seed cotton yield. Likewise, the combined application of MLE and MC at 90 days after blooming significantly boosted the nitrogen uptake in locules, as well as the phosphorus and potassium uptake in the leaves of both cotton cultivars. The application of MLE alone has considerably improved the nitrogen uptake in leaves, and phosphorus and potassium contents in locules of Bt and conventional cotton cultivars. Similarly, Bt cotton treated with MLE at 90 days after blooming produced significantly higher ginning out turn and oil contents. Treatment in combination (MLE + MC) at 90 days after blooming produced considerably higher micronaire value, fiber strength, and staple length in conventional cultivar. Conclusion: The natural growth enhancer, MLE is a rich source of minerals and zeatin, improving the nutrient absorption and quality of cotton fiber in both conventional and Bt cotton cultivars. [ABSTRACT FROM AUTHOR]

Background: Mepiquat chloride (MC) application and plant population density (PPD) increasing are required for modern cotton production. However, their interactive effects on leaf physiology and carbohydrate metabolism remain obscure. This study aimed to examine whether and how MC and PPD affect the leaf morpho-physiological characteristics, and thus final cotton yield. PPD of three levels (D1: 2.25 plants·m−2, D2: 4.5 plants·m−2, and D3: 6.75 plants·m−2) and MC dosage of two levels (MC0: 0 g·ha−2, MC1: 82.5 g·ha−2) were combined to create six treatments. The dynamics of nonstructual carbohydrate concentration, carbon metabolism-related enzyme activity, and photosynthetic attributes in cotton leaves were examined during reproductive growth in 2019 and 2020. Results: Among six treatments, the high PPD of 6.75 plants·m−2 combined with MC application (MC1D3) exhibited the greatest seed cotton yield and biological yield. The sucrose, hexose, starch, and total nonstructural carbohydrate (TNC) concentrations peaked at the first flowering (FF) stage and then declined to a minimum at the first boll opening (FBO) stage. Compared with other treatments, MC1D3 improved starch and TNC concentration by 5.4% ~ 88.4%, 7.8% ~ 52.0% in 2019, and by 14.6% ~ 55.9%, 13.5% ~ 39.7% in 2020 at the FF stage, respectively. Additionally, MC1D3 produced higher transformation rates of starch and TNC from the FF to FBO stages, indicating greater carbon production and utilization efficiency. MC1D3 displayed the maximal specific leaf weight (SLW) at the FBO stage, and the highest chlorophyll a (Chl a), Chl b, and Chl a + b concentration at the mid-late growth phase in both years. The Rubisco activity with MC1D3 was 2.6% ~ 53.2% higher at the flowering and boll setting stages in both years, and 2.4% ~ 52.7% higher at the FBO stage in 2020 than those in other treatments. These results provided a explanation of higher leaf senescence-resistant ability in MC1D3. Conclusion: Increasing PPD coupled with MC application improves cotton yield by enhancing leaf carbohydrate production and utilization efficiency and delaying leaf senescence. [ABSTRACT FROM AUTHOR]

The balance between vegetative and reproductive growth is the central objective in the cotton production system, which is associated with cotton maturity and yield. In China, manual topping (MT) has been performed many years prior to or during the flowering period to inhibit vegetative growth and enhance reproductive growth. MT is gradually being replaced by chemical topping (CT) with mepiquat chloride (MC, 180 g ha−1, 98% soluble powder) due to labor shortages and increasing labor cost. To determine whether CT influences cotton maturity and yield relative to MT, we carried out field experiments at four locations in the Yellow River Valley of China during 2018–2020. The results showed that CT did not alter the boll age, and although it produced taller and slender spatial boll distribution under several environments, it had little effect on the accumulation of boll fraction (the number of bolls in a given period divided by total boll number) over time at the end of blooming across locations. As a result, there were no significant differences between MT and CT in boll opening percentage in the late season. CT did not influence yield or yield components, except under severe drought. Therefore, CT with MC (180 g/ha, 98% soluble powder) during the flowering period will not compromise the maturity or yield of cotton in the Yellow River Valley of China. Similar outcomes would be achieved in other areas with similar ecological conditions and social conditions that require an alternative to extensive manual labor. [ABSTRACT FROM AUTHOR]

Carbon reserves in cotton roots can be remobilized to support reproductive growth, thus potentially affecting cotton yield. However, the regulation of carbon remobilization in cotton roots and its relationship with cotton yield are still poorly understood. Plant population density (PPD) and mepiquat chloride (MC) have been hypothesized to affect the dynamics of nonstructural carbohydrate content and the resulting carbon remobilization in cotton roots through the regulation of carbohydrate metabolism enzyme activities. A mid-maturation cotton line 4003–6 was field-grown in 2019 and 2020. Three different levels of PPD (D1: 2.25 plants m−2, D2: 4.5 plants m−2, and D3: 6.75 plants m−2) and two levels of MC dosage (M0: 0 g hm−2, M1: 82.5 g hm−2) were combined to create six populations differing in terms of the source–sink relationship. The changes in the hexose, sucrose, and starch contents and the key carbon metabolic enzyme activities in cotton roots were examined during peak squaring (PS) to late boll opening (LB). The combination of the PPD of 6.75 plants m−2 and MC application (M1D3) exhibited the greatest cotton yield and reproductive biomass–to–leaf area ratio from peak flowering (PF) onwards. M1D3 presented the greatest total nonstructural carbohydrate (TNC) remobilization amount of 2.96 and 3.80 g m−2, the highest efficiency of 39.11% and 48.39%, and the largest gross contribution to seed cotton yield of 0.66% and 0.79% in 2019 and 2020, respectively. The three parameters were positively correlated with the seed cotton yield except for the remobilization rate in 2019. Unlike the other treatments, the greater carbohydrate content per unit ground area in M1D3 prior to the PF stage was attributed to the higher sucrose phosphate synthase (SPS) and ADP-glucose pyrophosphorylase (AGPase) activities during the PS to first flowering (FF) stages. Conversely, the greater α-amylase and β-amylase activities in M1D3 at the PF stage accounted for the lower starch content at the EB stage, and the smaller vacuolar invertase (VIN) and cell wall invertase (CWIN) activities at the EB stage could be responsible for the lower hexose concentration at that time. The TNC remobilization amount had a positive association with the AGPase and SPS activities at the FF stage and with β-amylase activity at the PF stage in cotton tap roots in 2019 and 2020. This study provides a cotton yield-improving alternative through the promotion of carbon remobilization in roots using certain agronomic practices. • Carbon remobilization in cotton roots was affected by certain agronomic practices. • Carbon remobilization was positively correlated with seed cotton yield. • Carbon remobilization was regulated by carbon metabolism enzyme activities in roots. • Carbohydrate content of cotton roots was positively correlated with seed cotton yield. [ABSTRACT FROM AUTHOR]

Early maturity, complete defoliation and boll opening are essential for the efficient machine harvesting of cotton. Chemical topping, involving one extra application of mepiquat chloride (MC) in addition to its traditional multiple-application strategy, may be able to replace manual topping. However, it is not known whether this chemical topping technique will influence maturity or cotton responses to harvest aids. In this 2-yr field study, we determined the effects of the timing of chemical topping using various rates of MC on boll opening percentage (BOP) before application of harvest aids (50% thidiazuron·ethephon suspension concentrate, referred to as TE), and the defoliation percentage (DP) and BOP 14 days after TE application. The results indicated that late chemical topping (near the physiological cutout, when the nodes above white flower is equal to 5.0) significantly decreased BOP before TE by 5.9–11.2% compared with early (at peak bloom) or middle (seven days after peak bloom) treatments in 2019, which was a relatively normal year based on crop condition. Also, a high MC rate (270 g ha−1) showed a significantly lower (22.0%) BOP before TE than low (90 g ha−1) or medium (180 g ha−1) rates. In 2020, which was characterized by stronger vegetative growth in the late season, the late chemical topping reduced the number of leaves before TE application relative to early or middle treatments, but had lower DP (23.2–27.2%) 14 days after TE application. The high MC rate showed a leaf count before TE application that was similar to the low and medium rates, but it showed the most leaves after TE and much lower (15.0–21.7%) DP in 2020. These results suggest that late timing of chemical topping and a high MC rate decreased the sensitivity of leaves to harvest aids. Further analysis indicated that the late chemical topping mainly affected the leaf drop from the mainstem and fruiting branches where the late regrowth occurred, and the high MC rate reduced leaf shedding from these parts and also from the vegetative branches. In conclusion, chemical topping with MC during the bloom period affected cotton maturity and responses to harvest aids in different ways according to the crop condition. To avoid the risks of delayed maturity and poor defoliation after the application of harvest aids, chemical topping should not be performed too late (i.e., near the physiological cutout) by using MC at more than 180 g ha−1. The optimum timing of chemical topping probably varies from peak bloom to around seven days later, and the safest MC rates for chemical topping should be less than 180 g ha−1.

Cotton is the most important global cash crop which controls economy of many nations. Global sustainability of cotton yield is one of the major challenges for meeting impending threats under climate change. Though India is one among the leading countries in cotton production, the supply is not enough considering the increasing demand. Scientists across the Globe are indulged in developing new lines and cultures with capacity to produce more yields. In this context, here, we have made an attempt to study the growth, physiology, and yield traits of cotton culture - TCH 1819 before its release (now released in the name of CO 17) by different chemical treatments. Observation on the leaf gas exchange traits, leaf parenchymal cells distinguished the source sink relationship of the culture. Chemical manipulation by growth retardants reduced the gibberellins content and modified the foliage structure. By characterizing the physiological potential through manipulation by growth retardant (Mepiquat chloride (0.015 %)) increased the yield by 30%. The traits identified in this study are potential indicators in breeding programme before releasing the variety. [ABSTRACT FROM AUTHOR]

Copyright of Brazilian Journal of Biology is the property of Instituto Internacional de Ecologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Mepiquat chloride (PIX) is an important management tool to reduce stress damage in cotton plants during germination. In this study, the effects of different drought levels and the amount of mepiquat chloride (PIX) were investigated on growth indices and antioxidant enzymes as well as the malondialdehyde and hydrogen peroxide contents of seedlings in two cotton cultivars under laboratory conditions. The study was laid in a completely randomized design using 0, 5, and 10 g/l Pix and also under different drought levels using 0, -4, and -8 bar polyethylene glycol 6000 in petri dishes on two cultivars of cotton plant, namely Sahel (drought sensitive) and Shayan (drought resistant). Germination indices as well as physiological parameters of seedlings were measured under drought and Pix treatment after 4 days. Results showed that the use of Pix increased the germination percentage, root length, dry and fresh weights of seedlings, and the activity of peroxidase and catalase enzymes of cotton cultivars under drought stress while drought stress alone reduced these parameters. Drought also increased oxidative indices such as malondialdehyde and hydrogen peroxide in seedlings of Sahel and Shayan cultivars while Pix application reduced these indices. In general, the results of this study showed that the use of Pix improved growth responses and antioxidant system of the two cotton cultivars and the response of cultivar Shayan was better than Sahel.

Potassium deficiency causes severe losses in yield and quality in crops. Mepiquat chloride, a plant growth regulator, can increase K+ uptake in cotton (Gossypium hirsutum), but the underlying physiological mechanisms remain unclear. In this study, we used a non-invasive micro-test technique to measure K+ and H+ fluxes in the root apex with or without inhibitors of K+ channels, K+ transporters, non-selective cation channels, and plasma membrane H+-ATPases. We found that soaking seeds in mepiquat chloride solution increased the K+ influx mediated by K+ channels and reduced the K+ efflux mediated by non-selective cation channels in cotton seedlings. Mepiquat chloride also increased negative membrane potential (E m) and the activity of plasma membrane H+-ATPases in roots, due to higher levels of gene expression and protein accumulation of plasma membrane H+-ATPases as well as phosphorylation of H+-ATPase 11 (GhAHA11). Thus, plasma membrane hyperpolarization mediated by H+-ATPases was able to stimulate the activity of K+ channels in roots treated with mepiquat chloride. In addition, reduced K+ efflux under mepiquat chloride treatment was associated with reduced accumulation of H2O2 in roots. Our results provide important insights into the mechanisms of mepiquat chloride-induced K+ uptake in cotton and hence have the potential to help in improving K nutrition for enhancing cotton production. [ABSTRACT FROM AUTHOR]

Plant growth regulators such as mepiquat chloride (MC) and chlormequat chloride (CCC) are used to establish the balance between the vegetative and generative growth in cotton. This study was conducted to compare the different doses and application time of CCC with MC and un-treatment (control). The seven treatments including control (non-treatment), T1 (three sprays of chlormequat chloride), T2 (two sprays of mepiquat chloride), T3 (0.4 L ha-1 CCC), T4 (0.5 L ha-1 CCC), T5 (0.6 L ha-1 CCC) and T6 (0.7 L ha-1 CCC) were laid out in Randomized Complete Block Design with four replications. The differences among treatments were found to be significant for seed cotton yield (SCY), the number of bolls per plant (N/B), boll weight (BW), plant height (PH), earliness, ginning out-turn (GOT), fiber fineness (FF), specific seed weight (SWt/S), the number seeds per boll (S/B), single seed volume (V/S) and lint yield per boll (LY/B). Finally, a single application of CCC @ 0.7 L ha-1 at the stage of DAS 90-110 days recorded optimum yield, earliness and fiber characteristics. The effects of early CCC on seed were more important than fiber characteristics. [ABSTRACT FROM AUTHOR]

Copyright of Xinjiang Agricultural Sciences is the property of Xinjiang Agricultural Sciences Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Mepiquat chloride (MC) is the most important plant growth retardant that is widely used in cotton (Gossypium hirsutum L.) production to suppress excessive vegetative growth and improve plant architecture. MicroRNAs (miRNAs) are important gene expression regulators that control plant growth and development. However, miRNA-mediated post-transcriptional regulation in MC-induced growth inhibition remains unclear. In this study, the dynamic expression profiles of miRNAs responsive to MC in cotton internodes were investigated. A total of 508 known miRNAs belonging to 197 families and five novel miRNAs were identified. Among them, 104 miRNAs were differentially expressed at 48, 72, or 96 h post MC treatment compared with the control (0 h); majority of them were highly conserved miRNAs. The number of differentially expressed miRNAs increased with time after treatment. The expression of 14 known miRNAs was continuously suppressed, whereas 12 known miRNAs and one novel miRNA were continuously induced by MC. The expression patterns of the nine differentially expressed miRNAs were verified using qRT-PCR. The targets of the known and novel miRNAs were predicted. Four conserved and six novel targets were validated using the RLM-5′ RACE assay. This study revealed that miRNAs play crucial regulatory roles in the MC-induced inhibition of internode elongation. It can improve our understanding of post-transcriptional gene regulation in MC-mediated growth inhibition and could potentially facilitate the breeding of dwarf cotton.

Mepiquat chloride (MC) is the most important plant growth retardant that is widely used in cotton (Gossypium hirsutum L.) production to suppress excessive vegetative growth and improve plant architecture. MicroRNAs (miRNAs) are important gene expression regulators that control plant growth and development. However, miRNA-mediated post-transcriptional regulation in MC-induced growth inhibition remains unclear. In this study, the dynamic expression profiles of miRNAs responsive to MC in cotton internodes were investigated. A total of 508 known miRNAs belonging to 197 families and five novel miRNAs were identified. Among them, 104 miRNAs were differentially expressed at 48, 72, or 96 h post MC treatment compared with the control (0 h); majority of them were highly conserved miRNAs. The number of differentially expressed miRNAs increased with time after treatment. The expression of 14 known miRNAs was continuously suppressed, whereas 12 known miRNAs and one novel miRNA were continuously induced by MC. The expression patterns of the nine differentially expressed miRNAs were verified using qRT-PCR. The targets of the known and novel miRNAs were predicted. Four conserved and six novel targets were validated using the RLM-5′ RACE assay. This study revealed that miRNAs play crucial regulatory roles in the MC-induced inhibition of internode elongation. It can improve our understanding of post-transcriptional gene regulation in MC-mediated growth inhibition and could potentially facilitate the breeding of dwarf cotton. [ABSTRACT FROM AUTHOR]

Copyright of Brazilian Journal of Biology is the property of Instituto Internacional de Ecologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Mepiquat chloride, widely used growth regulator in cotton fields to increase crop yield. The present study was performed to investigate the effects of growth regulator (mepiquat chloride) and row spacings on growth and yield attributes of cotton. The experiment was conducted on randomized complete block design (RCBD) with split plot arrangement. Three levels of row spacing (25 cm, 50 cm, and 75 cm) were arranged in main plots, whereas, mepiquat chloride treatments (control, MQC0), mepiquat chloride 0.61 liter ha-1). Vegetative (plant height, number of monopodial and sympodial branches, no. of nodes plant-1) and reproductive growth and yield (no. of flowers plant-1, no. of square plant-1, no. of open and un-open bolls plant-1, seed cotton yield and cotton seed yield) parameters were recorded. The results revealed that exogenous application of mepiquat chloride @ 0.61 L ha-1, significantly reduced plant height as compared to control treatment. However, it did not reduce all other yield attributes of cotton. Among the row spacing treatments, widely spaced cotton plants (RS3, 75 cm) without application of mepiquat chloride produced maximum seed cotton yield as compared to all other spacing levels. Ultra-narrow row spacing (RS1, 25 cm) Combination of narrow row spacing (RS2, 50 cm) and mepiquat chloride application slightly higher seed cotton yield. Ultranarrow row spacing must carefully use to exploit in the cotton production system was appeared to be a viable alternative approach for successful cotton production. [ABSTRACT FROM AUTHOR]

The plant growth retardant mepiquat chloride (MC) has been extensively used to produce compact plant canopies and increase yield in cotton (Gossypium hirsutum L.). Previous studies showed that MC reduced plant height and internode length by inhibiting GA biosynthesis and cell elongation. However, whether there are other molecular mechanisms underlying MC-induced growth retardation has remained largely unknown. In the present study, we conducted histological, transcriptomic, and phytohormone analyses of the second elongating internodes of cotton seedlings treated with MC. Histological analysis revealed that the MC shortened the internodes through suppressing both cell division and cell elongation. Consistent with the observed phenotype, many genes related to cell growth were significantly downregulated by MC. Transcriptome profiling showed that the expression of genes related not only to GA, but also to auxin, brassinosteroid (BR), and ethylene metabolism and signaling was remarkably suppressed, whereas that of genes related to cytokinin (CK) and abscisic acid (ABA) metabolism was induced by MC. Consistent with the expression pattern, significant decrease of endogenous GA, auxin, and BR content, but an increase in CK content was observed after MC treatment. Most of these hormone related genes displayed opposite regulation pattern by exogenous GA3 treatment compared to MC; simultaneous application of MC and GA3 could alleviate the genes expression changes induced by MC treatment, indicating MC does not directly affect other plant hormones, but through the inhibition of the GA biosynthesis. In addition, the expression of genes related to secondary metabolism and many transcription factors (TFs) were differentially regulated by MC. In summary, we confirmed the important role of GA in MC-induced growth inhibition of cotton, and further found that other hormones were also involved in this process in a GA-dependent manner. This study provides novel insights into the molecular mechanism underlying the MC-mediated inhibition of internode elongation in cotton seedlings. [ABSTRACT FROM AUTHOR]

Copyright of Xinjiang Agricultural Sciences is the property of Xinjiang Agricultural Sciences Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The plant growth regulator mepiquat chloride (MC) has been widely used to regulate cotton growth and development worldwide. However, little is known about whether MC application during cotton growing season affects defoliation efficiency of the harvest aids (TE), a novel product with the mixture of 10% thidiazuron and 40% ethephon. Here, a 3-year (2018–2020) field experiment was carried out in Hejian, Hebei province, China, involving six treatments as three different MC rates (MC free, farmers' practice-conventional amount, high MC amount) and two defoliant rates (0 ml ha−1 [CK] and 2250 ml ha−1 [TE]). High MC rate delayed cotton leaf abscission and decreased the defoliation percentage at 7 days after TE treatment, but hardly affected harvest aids efficacy at harvest time. The delay of leaf abscission was due to an increase in auxin and cytokinin concentration of cotton leaves in MC treatment. The MC treatment accelerated the natural maturation of cotton, achieving a higher boll-opening percentage before defoliant spraying, and increased cotton lint yield. Over the 3-year period, compared to CK, the defoliant application TE increased the defoliation percentage by 43.4%, the boll-opening percentage by 10.4%, and the cotton lint yield by 9.1% due to an increase in opened boll number per unit land area. We concluded that the optimal MC dose (about 200 g ha−1) would decrease the risk of reducing defoliation and achieve higher cotton lint yield. • Applying mepiquat chloride (MC) only delayed cotton leaf abscission in the early stage of defoliation. • MC application increased auxin and cytokinin concentration in cotton leaf. • Applying MC accelerated cotton maturation and achieved a higher boll-opening percentage. • The optimal MC dose decreased the risk of decreasing defoliation and enhanced cotton lint yield. [ABSTRACT FROM AUTHOR]

Copyright of Agriculture Faculty Journal, Mustafa Kemay University / Ziraat Fakultesi Dergisi, Mustafa Kemal Universitesi is the property of Mustafa Kemal University, Faculty of Agriculture and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Late planting of short-season cotton under high plant density and single fertilization after rapeseed harvest is a promising alternative to traditional relay intercropping of full-season cotton in the Yangtze River Valley of China. However, it is not clear if mepiquat chloride (MC) application is still necessary in the new system. We hypothesized that MC application might reduce leaf photosynthesis and economic yield and thus not be necessary in the new system. To test the hypothesis, short-season cotton was sown in mid-May at 10 plants m −2 and with 225 kg N ha −1 applied at early flowering, and MC was applied three times at five main-stem leaf intervals initiated from the 6th leaf stage at five dosages (MC0, MC30, MC60, MC90, and MC120 represent 0, 30, 60, 90, and 120 g ha −1 , respectively) in a 2-year experiment. The photosynthesis, chlorophyll contents, carbohydrate contents, carbohydrate metabolic enzyme dynamics, and cotton yield under different MC treatments were determined. Photosynthesis was reduced by 1–28% and lint yield decreased by 6–29% as MC dosage increased. However, chlorophyll a , b , a  +  b , sucrose, glucose, fructose, and starch contents in the 4th leaf from the top were increased by 3–56%, 2–45%, 3–51%, 4–48%, 3–48%, 2–63%, and 2–43%, respectively. The activities of enzymes involved in carbohydrate metabolism decreased by 2–25% for sucrose phosphate synthase, but increased by 2–40%, 2–30%, and 3–52% for sucrose synthase, soluble acid invertase, and neutral invertase, respectively. These findings suggest that increased accumulation of sucrose, hexose, and starch in the leaf with MC application diminished photosynthesis and thus could explain the yield loss. Therefore, MC application is not necessary for late-planted cotton. [ABSTRACT FROM AUTHOR]

Cotton production is challenged by high cost with multiple management and material inputs including mepiquat chloride (MC) application to avoid excess vegetative growth and yield losses. A competitive planting model has been practiced in recent years in Yangtze River Valley, China characterized with late sowing, high density and low fertilization. We hypothesized that MC could also be ignored under this planting model to cut down the cost further. A 2-year field experiment was performed to determine cotton response to MC in allied growth and yield dynamics in 2015 and 2016. MC was applied thrice with 5 leaf intervals initiated from the 6th leaf stage in 5 different dosages i.e. 0 (control), 30, 60, 90, and 120 g ha −1 . The results showed that the lint yield was reduced by 6–29% with increase in MC dosages resulted from the reduced cotton plants biomass (from 1036 gm −2 of MC0 to 841 gm −2 of MC120) especially the reproductive organs biomass (492 gm −2 of MC0 to 376 gm −2 of MC120) averaged across two years. The biomass accumulation for control (MC0) during the fast accumulation period (FAP) had a higher rate (10.1 and 29.8 gm −2 d −1 in 2015 and 2016, respectively) for plant biomass and a longer period (34.5 and 28.0 d in 2015 and 2016, respectively) for reproductive organs biomass. The results suggested that MC application could be omitted in the new cotton planting model, ensuring more economic benefits by waiving off the labor and chemicals cost involved. [ABSTRACT FROM AUTHOR]

Drought can substantially limit yield in cotton, and water loss in any crop is closely associated with plant growth, but studies addressing the effects of growth management on drought sensitivity are limited in cotton. We tested the hypothesis that aggressive plant growth management would decrease cotton sensitivity to drought during flowering and boll development. Cotton was grown at a field site near Tifton, GA during the 2021 and 2022 growing seasons. Treatments included mepiquat chloride (MC) strategies (aggressive and untreated) and two water availability treatments (well-watered and drought-stressed). At approximately 2 weeks after first flower, water was withheld from the drought-stressed treatment for a three-week period, and well-watered plots were kept irrigated using a regionally accepted water balance approach. Measurements throughout the season included heights, nodes, length of the fourth internode below the plant terminal, nodes above white flower (NAWF), and soil moisture. End-of-season measurements included lint yield, fiber quality, and yield component assessments. MC treatment significantly affected plant height, mainstem node number, 4th internode length, and cutout date. Soil moisture was significantly reduced during the drought stress period. Aggressive MC treated plots showed less drought-induced yield reduction than untreated in response to drought, but did not reach the same lint yield, boll density, or uniformity as well-watered, untreated plots. Aggressive MC treatment produced greater seed surface area, seed number boll-1, and boll mass. Aggressive MC management may prevent drought-induced yield reductions but penalize yield under well-watered conditions. Among the potential components driving yield, boll number per unit land area was the most important contributor. Our findings highlight the potential for aggressive MC management to mitigate drought risk, but future efforts should evaluate this possibility in a broader range of cultivars adapted for production in the southeastern United States and with the inclusion of a moderate MC treatment. • Aggressive mepiquat chloride treatment can mitigate drought risk but also penalize yield in a well-watered environment. • Aggressive mepiquat chloride treatment produced greater seed surface area, seed number boll-1, and boll mass. • Boll density was primarily associated with lint yield. • Only fiber uniformity and strength were impacted by aggressive mepiquat chloride treatment. [ABSTRACT FROM AUTHOR]

The effect of plant growth regulator mepiquat chloride (1,1-dimethyl-piperidiniuchloride, DPC) on cotton epidermal wax deposition and photosynthesis were investigated using ‘Xinluzao 55’ as the sample. DPC was respectively sprayed on the foliage at the doses of the active ingredients of 0, 4.5, 7.5, 10.5 and 15.0 g/hm2. The photosynthetic rate and wax content of cotton leaves were measured at 1, 4, 7, 12 days after the treatment. The SPAD value of leaves was also tested within 12 days after the application of DPC. The result showed that after DPC was sprayed to cotton leaves, the photosynthetic rate of the cotton leaves, the wax content and the SPAD value have definite reliance on DPC concentration and the processing time. The photosynthetic rate of cotton could be improved by DPC treatment (4.5 g/hm2 or 7.5 g/hm2) and this effect could last for a long period. With the increase of the treatment time and DPC content, the SPAD value of cotton was increased, which indicated that the chlorophyll content of cotton leaves increased and leaf color deepened. The concentration of 4.5 g/hm2 was more favorable for the wax deposition of cotton leaf epidermis. The correlation analysis of photosynthetic rate, photosynthetic rate and SPAD value showed that the photosynthetic rate had a significant positive correlation with the wax and SPAD values. It illustrated that the deposition of wax and the increase of chlorophyll content were beneficial to the photosynthesis of cotton leaves and enhanced the resistance. [ABSTRACT FROM AUTHOR]

Carbohydrate reserves in cotton stems are a potential contributor to cotton yield. However, the regulation of carbon remobilization during reproductive growth and its relationship to cotton yield remain elusive. The objectives of the study were to i) examine the dynamics of the nonstructural carbohydrate content and carbon metabolism-related enzyme activities in the cotton stems during the peak squaring to late boll opening stages and ii) relate them to carbon remobilization and the final yield. A mid-maturation cotton line 4003–6 was field-grown in 2019 and 2020. Three different levels of plant population density (PPD) (D1: 2.25 plants m−2, D2: 4.5 plants m−2, and D3: 6.75 plants m−2) and two levels of mepiquat chloride dosage (M0: 0 g ha−1, M1: 82.5 g ha−1) were combined to create six populations differing in terms of source-sink relationship. Five samplings were taken at the peak squaring (PS), first flowering (FF), peak flowering (PF), early boll opening (EB), and late boll opening (LB), respectively. Leaf area, stem and reproductive biomasses, carbohydrates, and carbon metabolism-related enzyme activities were examined at each of the sampling dates. Yield and yield components were quantified at the cotton harvest each year. The PPD of 6.75 plants m−2 combined with MC application (M1D3) exhibited 5.7–40.0%, and 11.6–56.1% higher in lint yield and boll density than other combinations, respectively. M1D3 also displayed the greatest carbon remobilization amount of 4.72 and 13.23 g m−2, the highest remobilization efficiency of 36.2% and 59.4%, and the largest gross contribution to seed cotton yield of 1.05% and 2.89% in 2019 and 2020, respectively. M1D3 was characterized by a greater carbohydrate accumulation capacity during FF to PF, as indicated by its higher sucrose phosphate synthase (SPS), sucrose synthase (SuSy), vacuolar invertase (VIN), ADP-glucose pyrophosphorylase (AGPase), and starch synthase (StSy) activities at the FF stage, along with a larger starch degradation ability, as indicated by its higher α-amylase and β- amylase activities at the PF stage. These observations accounted for the greater carbon remobilization in M1D3 compared to the other treatments. Either at the FF stage or PF stage, each of the sucrose, hexose, starch and total nonstructural carbohydrate (TNC) contents per unit ground area were positively correlated with the seed cotton yield both years. Carbon remobilization was also positively related to seed cotton yield both years. The SPS, SuSy and AGPase activities at the FF stage as well as α-amylase and β- amylase activities at the PF stage in the lower stem were positively associated with the carbohydrate remobilization amount. The present study provides a cotton yield-improving alternative in the form of prompt carbon remobilization in stems using certain agronomic practices. • Carbon remobilization in the cotton stem was affected by certain agronomic practices. • Carbon remobilization was positively correlated with seed cotton yield. • Carbon remobilization was regulated by carbon metabolism enzyme activity in stems. • Nonstructural carbohydrate content was positively correlated with seed cotton yield. [ABSTRACT FROM AUTHOR]

The aim of this field experiment was to investigate the effect of nitrogen, potassium and a plant growth retardant (PGR) on seed yield and protein and oil content of an Egyptian cotton cultivar (Gossypium barbadense Giza 86). Treatments consisted of: soil application of N (95 and 143 kg N ha-1 in the form ammonium nitrate), foliar application of potassium (0, 319, 638 or 957 g K ha-1 as potassium sulfate) and foliar application of mepiquat chloride (MC) (0 and 48 + 24 g active ingredient ha-1) on seed, protein and oil yields and oil properties of Egyptian cotton cultivar “Giza 86” (Gossypium barbadense). After applying the higher N-rate, foliar application of potassium and plant growth retardant MC significantly increased seed yield and the content of seed protein and oil, seed oil refractive index, unsaponifiable matter and total unsaturated fatty acids (oleic and linoleic). In contrast, oil acid and saponification value as well as total saturated fatty acids were decreased by foliar application of potassium and MC. The seed oil content was decreased with soil application of N.

Drought negatively affects cotton growth and yield, whereas excessive irrigation can limit yield through excessive vegetative growth and poor fruit retention. Mepiquat chloride (MC) application limits plant height, improves fruit retention and hastens maturity in responsive cultivars. Thus, the objective of this study was to address the effects of cultivar, irrigation, and MC strategy on cotton growth, maturity, yield, and fiber quality. Therefore, a field study was carried out using three cultivars, three different irrigation treatments, and three different MC treatments during the 2020 and 2021 growing seasons. In both years there was an interaction between irrigation and MC management for plant height. In 2020, MC treatments hastened cutout by two to three weeks in irrigated plots but did not affect cutout date in dryland plots. 2020 and 2021 differed substantially in rainfall (347 mm and 735 mm, respectively from planting to harvest). 2020 was a dry year in which yield responded positively to irrigation and 2021 was a wet year in which yield responded negatively to irrigation. There was no effect of MC treatments or interaction between MC and any other effect on lint yield. Fiber length was reduced, whereas strength and micronaire were increased by drought stress in 2020. Increased fiber length, strength, uniformity, and micronaire were observed by MC application in both years. Therefore, we can conclude that aggressive MC management reduces vegetative growth, promotes earlier physiological maturity under well-watered conditions, and affects fiber quality, but does not necessarily interact with irrigation management to affect lint yield. • Growth and maturity responses to mepiquat chloride depend on water availability. • Mepiquat chloride hastens maturity under water replete conditions, but not dryland. • Occasionally, fiber quality was positively impacted by mepiquat chloride application. • Mepiquat chloride did not alter cotton yield response to water excess or drought. [ABSTRACT FROM AUTHOR]

Background and Aims Cotton (Gossypium hirsutum) has indeterminate growth. The growth regulator mepiquat chloride (MC) is used worldwide to restrict vegetative growth and promote boll formation and yield. The effects of MC are modulated by complex interactions with growing conditions (nutrients, weather) and plant population density, and as a result the effects on plant form are not fully understood and are difficult to predict. The use of MC is thus hard to optimize. Methods To explore crop responses to plant density and MC, a functional–structural plant model (FSPM) for cotton (named CottonXL) was designed. The model was calibrated using 1 year's field data, and validated by using two additional years of detailed experimental data on the effects of MC and plant density in stands of pure cotton and in intercrops of cotton with wheat. CottonXL simulates development of leaf and fruits (square, flower and boll), plant height and branching. Crop development is driven by thermal time, population density, MC application, and topping of the main stem and branches. Key Results Validation of the model showed good correspondence between simulated and observed values for leaf area index with an overall root-mean-square error of 0·50 m2 m−2, and with an overall prediction error of less than 10 % for number of bolls, plant height, number of fruit branches and number of phytomers. Canopy structure became more compact with the decrease of leaf area index and internode length due to the application of MC. Moreover, MC did not have a substantial effect on boll density but increased lint yield at higher densities. Conclusions The model satisfactorily represents the effects of agronomic measures on cotton plant structure. It can be used to identify optimal agronomic management of cotton to achieve optimal plant structure for maximum yield under varying environmental conditions. [ABSTRACT FROM AUTHOR]

The growth regulator mepiquat chloride (MC) is globally used in cotton (Gossypium hirsutum L.) canopy manipulation to avoid excess growth and yield loss. However, little information is available as to whether the modification of plant architecture by MC is related to alterations in gibberellic acid (GA) metabolism and signaling. Here, the role of GA metabolism and signaling was investigated in cotton seedlings treated with MC. The MC significantly decreased endogenous GA3 and GA4 levels in the elongating internode, which inhibited cell elongation by downregulating GhEXP and GhXTH2, and then reducing plant height. Biosynthetic and metabolic genes of GA were markedly suppressed within 2-10d of MC treatment, which also downregulated the expression of DELLA-like genes. A remarkable feedback regulation was observed at the early stage of MC treatment when GA biosynthetic and metabolic genes expression was evidently upregulated. Mepiquat chloride action was controlled by temporal translocation and spatial accumulation which regulated GA biosynthesis and signal expression for maintaining GA homeostasis. The results suggested that MC application could reduce endogenous GA levels in cotton through controlled GA biosynthetic and metabolic genes expression, which might inhibit cell elongation, thereby shortening the internode and reducing plant height. [ABSTRACT FROM AUTHOR]

Directly measuring plant transpiration of field crops and determining water use efficiency are difficult but essential to understand plant-water relations. In this study, we aimed to quantify plant transpiration and water use efficiency at diurnal and daily bases using sap flow measurements in cotton growing under plastic film cover and drip irrigation in relation to row configurations and chemical topping. Field experiment was carried out in 2020–2021 in Xinjiang, China. The experiment included two topping treatments: chemical topping using heavy amount of mepiquat chloride and traditional manual topping; and two typical row spacing for machine-harvesting: equal row spacing (76 cm) and narrow-wide row spacing (10 cm + 66 cm). Sap flow was measured using a heat ratio method after cotton first flowering stage and then calculated to transpiration per plant and per unit ground area. Chemical topping increased cotton plant height by 12%, leaf area index by 13%, and stem diameter by 9% but did not affect cotton lint yield compared with manual topping across two years and row configurations. The sap velocity of drip-irrigated cotton ranged overall from 20 to 45 cm hr−1 at the daytime and close to zero at nighttime. Across two years, the daily transpiration in chemical topping after flowering was 5.57 mm d−1 and 14.8% higher than in manual topping. That in narrow-wide row spacing was higher than in equal rows. However, the water use efficiency did not differ between topping and row spacing treatments, being 5.64 kg m−3 on average for aboveground dry matter. This knowledge would be useful to optimize cotton irrigation managements and to improve crop models by knowing exact plant transpiration at both plant and system levels. • Chemical topping increased cotton stem diameter and leaf area index but did not affect lint yield. • Plant in chemical topping transpired 14.8% more water than in manual topping. • The plant transpiration in narrow-wide row spacing was higher than in equal row spacing. • Water use efficiency was 5.64 kg m-3 without any differences between topping and row spacing treatments. [ABSTRACT FROM AUTHOR]

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A simple, accurate and highly sensitive analytical method was developed in this study for determining the residues and dissipation dynamics of mepiquat chloride in soil and cotton crops (including plant and seed). The samples in this method were directly extracted with methanol–ammonium acetate solution and followed by analysis of high performance liquid chromatography tandem mass spectrometry (HPLC–MS/MS). The intra-day and inter-day recoveries of mepiquat chloride were in the range of 76.58–98.87 percent and 73.48–104.7 percent with relative standard deviations (RSDs) of 0.89–5.04 percent and 3.84–10.7 percent, respectively. The limit of quantification (LOQ) was 0.05mgkg−1 for soil and 0.1mgkg−1 for cotton plant and seed. The half-life of mepiquat chloride in cotton plants and in soil was 2.51–3.85 days and 7.56–10.50 days, respectively. The final residues of mepiquat chloride in all cotton seeds were below the MRLs of EU (5mgkg−1), Japan and America (2mgkg−1) over 14 days after the last spraying, and were below 1mgkg−1 (the MRLs set by Argentina and Australia) over 21 days after the last spraying at recommended dosage. The final residues in soil were below the LOD (0.01mgkg−1) over 21 days after the last spraying. [Copyright &y& Elsevier]

Abstract: Improvements in carbohydrate source–sink relations are needed to improve efficiency of yield formation in cotton (Gossypium hirsutum L.). Most source–sink research has focused on leaf–boll relationships, with little study of vegetative storage reserves. Possible ways of altering the source–sink balance include increasing the plant population density (PPD) and using a plant growth regulator, mepiquat chloride (MC). We evaluated effects of PPD and MC on plant growth and development, stem starch reserves and lint yield in a 3-year field experiment at Milan, Tennessee. Row spacings of 25, 51, and 102cm averaged 17.6, 13.2, and 8.3plantsm−2, respectively. Mepiquat chloride rates were 0 and 86gha−1. Higher PPD in narrower rows tended to reduce boll number more than leaf area per plant, reducing the number of bolls per unit leaf area. However, boll distribution was more concentrated, implying more synchronous demand for photosynthate in 25-cm rows than in wider rows. Stem starch concentrations during boll filling were similar to, or slightly lower, in 25-cm rows than in wider rows. Findings are consistent with the hypothesis that availability of photosynthate may limit boll load at higher PPD, despite more leaf area per boll. Application of MC tended to reduce leaf area per plant more than boll load, and to increase the number of bolls per unit leaf area. The MC treatment also concentrated the boll set on lower sympodia, increasing the synchrony of boll maturation and demand for photosynthate. Application of MC increased boll set percentage and decreased stem starch reserves slightly. Lint yields were increased by MC application in finger-stripped 25- and 51-cm rows in 2 of 3 years, by an average of 11%, but not in spindle-picked 51- and 102-cm rows. Findings support the hypothesis that MC benefits boll set and yield formation in narrow-row systems by reducing LAI. Source–sink alteration with PPD and MC may be useful in future research to improve carbohydrate use and yield formation in cotton. [Copyright &y& Elsevier]

Effect of foliar application of mepiquat chloride (1,1- Dimethyl-piperidinium chloride 5% SL (W/V), a plant growth regulator, was assessed on seed cotton yield (cv. CIM-473) at Agronomic Research Station, Bahawalpur, Pakistan during 2005 and 2006 under different nitrogen levels (0, 50, 100, 150, 200 kg/ha). A standard dose of of mepiquat chloride (1 l/ha) was applied at an interval of one week in four equal splits (250 ml/ha) during month of July in both years. The data on seed cotton yield showed significant differences among different nitrogen levels as well as mepiquat chloride treated and untreated plots. On the basis of two years average, mepiquat treated plots gave 3.92 to 18.30 percent increase in seed cotton yield over untreated plots under different N levels. Application of mepiquat chloride increased seed cotton yield during both years and proved as a desirable management tool to control excessive vegetative growth in tall growing cotton cultivars for efficient harvest. [ABSTRACT FROM AUTHOR]

The aim of this field experiment was to investigate the effect of nitrogen, potassium and a plant growth retardant (PGR) on seed yield and protein and oil content of an Egyptian cotton cultivar (Gossypium barbadense Giza 86). Treatments consisted of: soil application of N (95 and 143 kg N ha-1 in the form ammonium nitrate), foliar application of potassium (0, 319, 638 or 957 g K ha-1 as potassium sulfate) and foliar application of mepiquat chloride (MC) (0 and 48 + 24 g active ingredient ha-1) on seed, protein and oil yields and oil properties of Egyptian cotton cultivar "Giza 86" (Gossypium barbadense). After applying the higher N-rate, foliar application of potassium and plant growth retardant MC significantly increased seed yield and the content of seed protein and oil, seed oil refractive index, unsaponifiable matter and total unsaturated fatty acids (oleic and linoleic). In contrast, oil acid and saponification value as well as total saturated fatty acids were decreased by foliar application of potassium and MC. The seed oil content was decreased with soil application of N. [ABSTRACT FROM AUTHOR]

Abstract: Cottonseed (Gossypium hirsutum L.) was treated with mepiquat chloride (MC) to examine its potential for the management of vigorous early growth experienced on cotton grown in the tropical winter season. As there is little published research from the field on this topic, we aimed to determine the effect of seed treatment of cotton with MC grown to maturity. In two field experiments over two seasons the seed surface was treated. Seed surface treatment was compared with pre-sowing priming with MC in experiment 2. Lint yields were high, 2059 and 2270kg/ha averaged over all treatments in experiments 1 and 2. In both experiments, seed surface treatment with 2gMC/kg reduced (P <0.05) plant height for up to 30 days after sowing and there were no significant changes to rate of crop development, time to maturity, lint yield or fibre quality. In experiment 2 treating with MC reduced plant establishment in proportion to the amount of MC applied (P <0.01). Pre-sowing priming caused approximately twice the reduction in plant height per gram of MC than surface treatment and significant differences persisted longer, even until maturity using 8gMC/kg seed. Priming with ≥4gMC/kg seed had additional effects (P <0.05): (1) reduced node development between first square and first flower, (2) delayed the time to first square, first flower and maturity by 4 days, (3) increased production of bolls on monopodial branches, and (4) reduced lint yield compared to the same concentrations applied to the surface. Fewer smaller plants having smaller bolls were implicated in this response. It was concluded that the relative benefit of seed treatment with MC at the concentrations and methods that did not reduce lint yield appears questionable as height reductions per gram of MC/ha were less than measured at this location with the same amount applied as a foliar spray. [Copyright &y& Elsevier]

Little research had been conducted on managing cotton growth using mepiquat chloride (MC) during the tropical winter season. Three experiments were conducted over three seasons. Early season internodes (first nine nodes) were long compared to temperate climates. Consequently the effect of MC applied, as multiple or single doses, from four nodes to first flower was evaluated. MC dramatically reduced height and node number in proportion to a total amount of MC up to 45 g/ha, r2=0.66 and r2=0.81, respectively; this response was independent of the frequency of treatment.Lint yields were high averaging 2143, 2415 and 2312 kg/ha for the three seasons. Despite the number of fruiting branches declining linearly with the amount of MC lint yields were decreased (p<0.05) in only 2 of the 28 treatments. There was a trend to increased yield (106.5%) compared with untreated plants where between 9 and 18 g/ha MC was intercepted. There was no economic effect of MC on lint quality. Yield compensation for reduced fruiting branches due to MC was via a linear increase in boll retention over all fruiting sites and vegetative branch bolls, which peaked with 35 g/ha of MC for each yield component. Where >35 g/ha was intercepted yields were the same or reduced compared to untreated plants. Compensation via boll size, possibly related to position, was implicated in this yield response. Thus treatment with 9–18 g/ha of MC, between 4 and 11 nodes, provided a compromise between suppressing plant height for operational efficiency, and optimising these yield components.Crop monitoring techniques based on the length of internodes could not aid MC treatment decisions because critical lengths, developed for temperate locations, were always exceeded and there was rarely a yield response to MC. An explanation came from the independence to MC of the height-to-nodes ratio prior to flowering. Monitoring techniques based on predicting the height and node number response from the MC concentration within the plant showed promise.MC did not affect time to maturity despite ≤15-day reduction in main-stem flowering period due to MC. This difference was attributed to high and increasing end-of-season temperatures synchronising maturity in bolls from later flowers, and it was possible vegetative branch bolls, increased by MC, matured after main-stem bolls.It was suggested future research consider modelling the MC response, irrigation interactions, the cultivar response, the effect on duration of flowering, and the interaction between MC and yield compensation from insect damage. [Copyright &y& Elsevier]

Em 1977/78 foram conduzidos seis experimentos de campo nos municípios paulistas de Jardinópolis, Leme, Salles Oliveira, Santa Bárbara D'Oeste e São João da Boa Vista, para se conhecer a ação do cloreto de mepiquat como fitorregulador para algodoeiro herbáceo. Os tratamentos constaram da aplicação de 25, 50, 75 e 150 g/ha de cloreto de mepiquat, e de uma testemunha com desenvolvimento vegetativo natural, distribuidos em um delineamento estatístico de blocos ao acaso, com quatro repetições. Foram estudados os parâmetros referentes à altura dos algodoeiros, desenvolvimento dos ramos laterais, queda de folhas, número de capulhos por planta, capulhos sem danos/capulhos com danos, características agronômicas (produção, porcentagem de fibras e peso de 100 sementes), características tecnológicas de fibra (comprimento, uniformidade, índice Micronaire, Pressley e maturidade) e ainda, germinação de sementes. Os dados foram analisados estatisticamente e os resultados das anál ises de variância mostraram que o cloreto de mepiquat reduziu significativamente a altura dos algodoeiros, diminuiu o número de maçãs podres, diminuiu a porcentagem de fibras, não prejudicou a produção de algodão em caroço, a qualidade das fibras e a germinação das sementes.Six field experiments were carr ied out in 1977/78 at several regions of São Paulo State: Jardinópolis, Leme, Salles Oliveira, Santa Bárbara D'Oeste and São João da Boa Vista, to know the mepiquat chloride action as a phytoregulator on cotton plants. A design of randomized blocks, with four replications was used for the experiments. The treatments were four increasing doses of mepi16 quat chloride: 25, 50, 75 and 150 g/ha compared with an untreated check. Results were evaluated by cotton he ight, lateral branches growth, fall of leaves, ball number in each plant, damaged balls/undama - ged balls, agronomic characteristics as yield, fiber rate, seed germination and 100 seeds' weig ht, technological characteristics of fiber, as span lenght, uniformit y ratio, micronaire, strength and maturity. Statistical analysis of data showed that the mepiquat chloride caused a decrease in plant height, number of rotten apples, fiber rate, but it didn't cause damage to cotton yield, fiber quality or seed germination.