Response of Bt cotton (Gossypium hirsutum L.) to spacing and detopping on growth parameters under north Gujarat conditions

Introduction

Cotton is an important cash crop belonging to the Malvaceae family. India has the unique distinction of cultivating all four cultivated Gossypium species, viz., G. arboreum, G. herbaceum (Asian cotton), G. barbadense (Egyptian cotton) and G. hirsutum (American upland cotton), besides hybrid cotton. The first two are diploid (2n=26), while the latter two are tetraploid (2n=52). Among these, Gossypium hirsutum L. is cultivated on more than 90 per cent of the cotton-growing area world-wide. Cotton, known as the "King of Fibres" and "White Gold", is an important cash crop influencing the economic and social affairs of India and the world. During 2023-24, global cotton cultivation covered about 31.8 million hectares with production of nearly 113 million bales. India produced approximately 25.5 million bales, while China, Brazil and the United States produced 27.5, 14.6 and 12.1 million bales, respectively (Anonymous, 2026 b ) [2] . India exported about 2.8 million bales during the same season (Anonymous, 2026 c ) [3] . In India, cotton production during 2023-24 was 325.22 lakh bales from 126.88 lakh hectares, with a productivity of 436 kg/ha (Anonymous, 2026 a ) [1] . Genetically Modified (GM) cotton, popularly known as 'Bt cotton', has emerged as an effective alternative to conventional cotton by reducing bollworm damage and improving yield and income. Cotton production increased more than fourfold, from 86.24 lakh bales in 2002-03 to 359.02 lakh bales in 2013-14 (DCD, 2017) [5] . To make cotton cultivation economically viable, low-cost production practices such as crop geometry, detopping and removal of monopodial branches play an important role. Maximum growth and yield can be achieved when plant population allows individual plants to express their inherent potential (Ghule et al., 2013) [8] . The terminal bud produces auxin, which suppresses the development of lateral or axillary buds. Hall et al. (1957) [11] reported that removal of the terminal bud can encourage lateral bud development. Thus, detopping at the appropriate vegetative stage may promote the growth and development of sympodial branches and fruiting bodies. Similarly, removal of monopodial branches can improve plant architecture, light interception and reduce mutual shading (Shwetha et al., 2009) [21] . Increased sympodial branches, squares and bolls are essential for maximizing seed cotton yield (Dhillion et al., 2006) [6] .

Materials and Methods

A field experiment entitled "Response of Bt Cotton (Gossypium hirsutum L.) to Spacing and Detopping on Growth Parameters under North Gujarat Conditions" was conducted at Agronomy Instructional Farm, Chimanbhai Patel College of Agriculture, Sardarkrushinagar Dantiwada Agricultural University, Sardarkrushinagar, on plot No. C-9 and A-7 during kharif 2024-25 and 2025-26, respectively. The experiment was conducted on Bt cotton variety GTHH-49 with 18 treatment combinations comprising three plant spacings as main plots: S 1: 60 cm × 45 cm, S 2: 90 cm × 30 cm and S 3: 120 cm × 45 cm, and six detopping treatments as sub-plots: D 1: control (no detopping and no monopodial branch removal), D 2: detopping at 80 DAS, D 3: detopping at 95 DAS, D 4: removal of monopodial branches, D 5: removal of monopodial branches + detopping at 80 DAS and D 6: removal of monopodial branches + detopping at 95 DAS. Treatments were replicated four times in a split-plot design. The soil was loamy sand, low in organic carbon and available nitrogen, and medium in available phosphorus and potassium. During 2024-25 and 2025-26, mean maximum temperature ranged from 24.6-40.6 and 24.5-38.8 °C, respectively, while mean minimum temperature ranged from 6.3-26.9 and 9.7-26.7 °C. Morning relative humidity ranged from 70-98 and 73-96 per cent, and evening relative humidity from 23-89 and 22-87 per cent, respectively. Mean bright sunshine hours ranged from 0.5-9.4 and 0.2-9.1 hours/day, while mean evaporation ranged from 2.0-11.2 and 1.2-7.6 mm during the respective years. A common application of 10 t FYM /ha was made before sowing. The crop received the recommended fertilizer dose of 320-00-120 kg N-P₂O₅-K₂O /ha. At sowing, one-fifth of nitrogen (64 kg/ha) as urea and the entire potassium (120 kg/ha) as muriate of potash were applied in furrows. The remaining nitrogen was top-dressed in four equal splits at 30, 60, 75 and 90 DAS through urea, depending on soil moisture. Detopping was performed at 80 and 95 DAS by pinching the apical bud, while monopodial branches were removed by pruning non-fruiting vegetative branches from the basal portion. For dry matter accumulation, five plants were uprooted from the sampling area of each plot at 30, 60 and 90 DAS. Plants were destructively sampled by cutting at the base, shade-dried for 24 hours, cut into pieces, placed in labelled brown paper bags and oven-dried at 65 °C for 72 hours. Oven-dried weight was recorded using an electronic balance and expressed as dry matter accumulation (g/plant). Crop growth rate (CGR) and relative growth rate (RGR) were calculated using the methods of Radford (1967) [20] and Hunt (1990) [13] , respectively: CGR = (W₂ -W₁) / (t₂ -t₁) × 1/P where CGR = crop growth rate (g/m 2 /day), W₁ and W₂ = dry weight of plant (g) at times t₁ and t₂, respectively, t₂ -t₁ = time interval between consecutive stages (days), and P = ground area (m²) per plant.

RGR = [ln W₂ -ln W₁] / (t₂ -t₁)

where RGR = mean relative growth rate (mg/g/day), W₁ and W₂ = dry weight of plant (g) at times t₁ and t₂, respectively, t₂ -t₁ = time interval between consecutive stages, and LN = natural logarithm.

The result of experiments on plant height at 80, 95 DAS and at harvest of Bt cotton is summarized in Table 1 and graphically depicted in Fig. 1. An examination of data revealed that Bt cotton planted at 90 cm × 30 cm (S 2 ) spacing recorded significantly higher plant height at 80 DAS (87.81, 92.91 and 90.36 cm), 95 DAS (110.60, 114.59 and 112.59 cm) and at harvest (120.58, 124.29 and 122.43 cm) during 2024-25, 2025-26 and in pooled data, respectively which was statically at par with spacing at 60 cm × 45 cm during both the years and in pooled analysis except pooled data of plant height at 95 DAS. The more number of plants per unit area produced more height per plant which may be due to the increased competition for sunlight and CO 2 and might be the closer spacing induced vertical growth due to congestion of plant per unit area. In contrast, significantly lowest plant height at 80 DAS (80.64, 85.27 and 82.96 cm), 95 DAS (98.88, 102.34 and 100.61 cm) and at harvest (106.11, 110.18 and 108.14 cm) were observed under wider spacing of 120 cm × 45 cm during both the years and in pooled results, respectively. Similar results were reported Khargkharate et al. (2015) [15] , Yadav et al. (2021) [22] and Hirpara et al. (2023) [12] . For different detopping treatments, the plant height at 80 DAS of Bt cotton was not influence significantly due to detopping treatments. This is because detopping treatments were imposed at 80 DAS after taking of plant height measurement. Significantly higher plant height at 95 DAS (117.76, 119.55 and 118.66 cm) was registered under control treatment (D 1 ) and it was remained at par with treatment D 3 (detopping at 95 DAS), D 4 (removal of monopodial branches) and D 6 (removal of monopodial branches + detopping at 95 DAS) during both the years but for pooled analysis, it was at par with treatment D 3 only. Significantly higher plant height at harvest (130.05, 132.97 and 131.51 cm) was observed under control treatment (no detopping no removal of monopodial branches) during both the year and in pooled analysis, respectively and it was found statistically at par with treatment D 4 (removal of monopodial branches) during both the years but not for pooled mean data. Contrary to this removal of monopodial branches + detopping at 80 DAS (D 5 ) recorded significantly lower plant height at 95 DAS (88.43, 91.47 and 89.95 cm) and at harvest (98.88, 99.42 and 99.15 cm) during both the year and in pooled data, respectively. This was due to the elimination of the apical meristem, which curtailed auxin-mediated stem elongation and apical dominance. The removal of monopodial branches further reduced vegetative growth potential and altered assimilate distribution within the plant. Consequently, photosynthates were preferentially allocated towards reproductive sinks rather than continued stem growth, resulting in reduced plant height at 95 DAS and harvest. Detopping also restricted the production of new nodes and internodes beyond 80 DAS, thereby limiting vertical growth and producing shorter plants compared to untreated plants. The findings are also in agreement with Chaudhari et al. (2021) [4] , Kakade et al. (2023) [14] , Yashashri et al. (2024) [23] and Mundare et al. (2025) [16] .

2) Dry matter accumulation (g/plant) at 30, 60 and 90 DAS Table 2 indicated that different plant spacing showed significant effect on dry matter accumulation (g/plant) of Bt cotton at 60 and 90 DAS except at 30 DAS during both the years and in pooled results. It was increased with broader spacing. Spacing of 120 cm × 45 cm (S 3 ) recorded significantly the highest dry matter at 60 DAS (89.87, 96.94 and 93.41 g/plant) and 90 DAS (149.06, 164.57 and 156.81 g/plant) as compared to narrow spacing during both years and in pooled analysis, respectively, but dry matter accumulation at 60 DAS was at par with plant spacing 60 cm × 45 cm during the year 2025. On contrary, significantly the lower dry matter accumulation at 60 DAS (78.98, 83.27 and 81.13 g/plant) and 90 DAS (130.95, 139.78 and 135.36 g/plant) during both the years and in pooled analysis, respectively was observed under 90 cm × 30 cm (S 2 ). The increase in dry matter accumulation/plant at wider spacing might be mainly due to the larger ground area, maximum moisture and more interception of light by more number of leaves and leaf area resulting in more photosynthetic activity and more biomass accumulation through the process of plant metabolism. Similar observations of higher dry matter accumulation/plant at wider spacing compared to dense spacing was also reported by Nagender et al. (2017) [17] , Parihar et al. (2018) [18] , Patel et al. (2021) [19] and Gouthami et al. (2023) [10] . On the other side, dry matter accumulation at 30, 60 and 90 DAS didn't significantly influence due to various detopping treatments during both the years and in pooled analysis. This might be due to detopping treatments were imposed from 80 DAS which cause no significant changes in dry matter of Bt cotton.

3) Crop growth rate at 30-0, 60-30 and 90-60 DAS (g/m 2 /day) Dry matter production per ground area i.e. CGR increased significantly with increase in age and crop growth period up to 60-90 DAS. It was increased with dense spacing. Scrutiny of crop growth rate data (Table 3) revealed that dense spacing (60 cm × 45 cm) recorded significantly higher crop growth rate of 4.05, 4.20 and 4.13 g/m 2 /day between 30-0 DAS during both the year and in pooled results, respectively which was remain statistically at par with 90 cm × 30 cm spacing (S 2 ). Between 60-30 DAS, crop growth rate also found significantly the highest under dense spacing of 60 cm × 45 cm during both the year and for pooled data, which was 6.22, 7.23 and 6.72 g/m 2 /day, respectively. This spacing found statistically at par with spacing S 2 (90 cm × 30 cm) during the year 2024-25 only. Crop growth rate between 90-60 DAS found significantly higher for spacing of 60 cm × 45 cm during the year 2024-25 and pooled analysis, which remain at par with 90 cm × 30 cm spacing. Whereas crop growth rate between 90-60 DAS during second year found significantly higher under S 2 (90 cm × 30 cm) spacing, which was remain at par with spacing of 60 cm × 45 cm. Significantly the lowest crop growth rate (2.14, 2.12 and 2.13 g/m 2 /day between 30-0 DAS, 3.41, 3.86 and 3.64 g/m 2 /day between 60-30 DAS and 3.65, 4.17 and 3.91 g/m 2 /day between 90-60 DAS) were recorded with wider spacing of 120 cm × 45 cm during both the years and in pooled results, respectively. Crop growth rate (CGR) are derived with biomass over time unit, hence these parameters improved with the corresponding increase in dry matter accumulation per ground area with narrow plant spacing. These results are in conformity with the results reported by Parihar et al. (2018) [18] , Ghetiya et al. (2021) [7] and Gohil et al. (2024) [9] . Crop growth rate (g/m 2 /day) between 30-0, 60-30 and 90-60 DAS didn't significantly influence by various detopping treatments during both the years and in pooled analysis.

4)

Relative growth rate at 30-0, 60-30 and 90-60 DAS (mg/g/day) Different spacing exhibited their non-significant effect on relative growth rate (mg/g/day) between 30-0, 60-30 and 90-60 DAS during both the years as well as in pooled analysis (Table 4). Relative growth rate was numerically increased with wider spacing. Numerically higher relative growth rate (117.80, 33.22 and 17.42 mg/g/day) between 30-0, 60-30 and 90-60 DAS respectively, was registered under wider spacing 120 cm × 45 cm than other spacing for pooled results. Detopping treatments statistically not differed with each other for the relative growth rate (mg/g/day) at 30-0, 60-30 and 90-60 DAS during the year 2024-25, 2025-26 and for pooled data.

5) Interaction effect

Interaction effect of spacing and detopping treatment were found significant with respect to plant height at 95 DAS and at harvest of Bt cotton during second year of 2025-26 and it is presented in Table 5 and Table 6. Results indicated that treatment combinations of 90 cm × 30 cm spacing along with control (no detopping and no removal of monopodial branches) registered significantly higher plant height at 95 DAS (124.80 cm) and at harvest (138.59 cm) during the year 2025-26. The interactions between spacing and detopping was failed to exert significant influence on dry matter accumulation (g/plant) at 30, 60 and 90 DAS, CGR (g/m 2 /day) and RGR (mg/g/day) between 30-0, 60-30 and 90-60 DAS during both the years and in pooled analysis.

Conclusion

The pooled results of the two-year field experiment indicated that plant spacing significantly influenced the growth of Bt cotton, whereas the effect of detopping was comparatively limited. Among the spacing treatments, 90 cm × 30 cm produced significantly greater plant height at 80, 95 DAS and harvest, while 120 cm × 45 cm recorded the highest dry matter accumulation at 60 and 90 DAS. In contrast, 60 cm × 45 cm resulted in the highest crop growth rate during 30-0, 60-60 and 90-60 DAS. Relative growth rate was not significantly affected by spacing. Among detopping treatments, the control (no detopping and no removal of monopodial branches) maintained the highest plant height at 95 DAS and harvest, whereas removal of monopodial branches + detopping at 80 DAS resulted in the shortest plants. However, detopping treatments did not significantly affect plant height at 80 DAS, dry matter accumulation, CGR and RGR.

Acknowledgement

AcknowledgementIt is really highly fortunate that I got the great opportunity to work under the golden hear head personality, Dr. C. K. Patel for most inoperative guidance, constant encouragement and academic carrier. Special thanks to C. P. College of Agriculture, Sardarkrushinagar Dantiwada Agricultural University for promptly providing technical support, field and laboratory facilities throughout the course of investigation.

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