Cotton (Gossypium barbadense) is primarily cultivated for lint and fiber, is native to Mexico and India. China and India hold first and second ranks in cotton production. The area under cotton cultivation, production and productivity in India were raised from 44.24 lakh Ha, 33.36 lakh bales and 132 kg Ha^-1 in 1947 to 129.57 lakh Ha, 371 lakh bales and 487 kg Ha^-1 in 2020-21 [10]. Telangana state has cotton cultivation in 17.94 lakh ha, with a total production potential of 53 Lakh bales and productivity of 502.23 kg ha^-1 [9]. Dry matter accumulation under moisture stress is reduced by 50% in Gossypium barbadense [14].  As only 38% of the total cotton cultivation is under irrigation, developing a crop model to withstand drought and heat stress is the need of the hour. Results of several recent studies conclude that the yield potential of Bt cotton is at a level of stagnation. The current experiment explores the physiological basis of phenological changes in cotton under moisture stress conditions. And this study is also oriented towards potential yield improvement in desi cotton, which would replace the Bt Cotton at field level. 

Materials and Methods

        Two field experiments were conducted at the College Farm of College of Agriculture, Hyderabad (17^o19’ 17.44 N & 78^o24’ 35.32 E) at an altitude of 542.6 m above mean sea level. It falls under the Southern Telangana agro- climatic zone of Telangana. The climate of Hyderabad was classified as dry- tropical and semi- arid. Six genotypes viz., ADB- 39, H- 4492859, NDLH- 1938, Anjali, Suraj and WGLV- 48 were grown in the present study, at three different spacings viz., 75×10 cm, 60×10 cm and 45×10 cm, which accommodate 1.33, 1.66 and 2.22 lakh of plants respectively.

        The total number of days from the date of sowing to the date 50 percent of the plants initiated squaring in a plot was recorded as Days to squaring. And the total number of days from the date of sowing to the date on which 50 percent of the plants initiated flowering in a plot was recorded as Days to 50% flowering.  The number of days taken to initiate bolls in a plot was recorded as Days to boll initiation. And the total number of days from the date of sowing to the date on which 50 percent of the plants opened bolls in a plot was recorded as Days to peak boll burst.

            The cumulative yield lint from three pickings in each treatment plot was weighed and expressed as Lint Yield in kg ha^-1. Seeds after separation by delinting of the seed cotton by soaking the kapas in concentrated H₂SO₄, by which the fuzz gets burnt and left over seeds were immediately washed 3- 4 times with fresh water followed by lime water again and with fresh water to neutralize the acid residues and dried under shade. This is noted as 100 seed weight in grams. The results were analyzed statistically in spilt plot design. Data on various traits were statistically analyzed following Panse and Sukhatme (1978) [12].

Table No.1: Number of days required to obtain each growth stage in cotton genotypes under different plant spacings.

Table No. 2: Lint Yield (Kg Ha^-1) and 100 seed weight (g) of cotton genotypes as influenced by different spacings in two seasons of crop growth and pooled.

Table 3: The genotypes and spacings, recorded earliest square initiation, flower initiation and boll formation.

Results and Discussion

Quantification of growth stages viz., square, flowering and boll formation

        Cotton usually require 5, 38, 59, 116, 140 days and 50, 550, 950, 2150, 2600 heat units to seedling emergence, square initiation, flowering initiation, boll bursting and harvest respectively. Days taken by the crop to attain each specific phenological phase was quantified for six cultivars at three plant densities (Table 1 and Fig 1). Days to square formation was observed earliest with WGCV-48 cultivar in 41 and 39 days under 75×10 cm spacing and observed late in ADB-39 and Anjali in 46 days under 45×10 cm spacing. Squares were found early in 75×10 cm at 43.2 days in Kharif, 2015 and 41.2 days in Kharif, 2016. The combination of WGCV-48 planted in 75×10 cm in Kharif, 2016 had recorded squares formation in 39 days.

        Days to flower initiation was observed early in WGCV-48 in 67 and 65.2 days and later flower initiation was recorded in Anjali in 70.3 and 69.3 days in Kharif, 2015-16 and Kharif 2016-17 respectively. Flowers initiated early in 75×10 cm in 67.7 days in Kharif, 2015 and 66.1 days in Kharif,  [5] reported that the days of first flower formation in cotton was recorded in 55.33 days in 75×45 cm spacing and late in 60×45 cm spacing. The mean days taken for square formation is slightly lesser in 67 days in Kharif, 2016 as compared to 69 days in Kharif, 2015. The combination of WGCV-48 planted at 75×10 cm in Kharif, 2016 flowered early in 64 days. During both seasons WGCV-48 showed significantly early boll formation in 93.8 and 91.5 days compared to other genotypes. Anjali was found late in boll formation in 97.4 and 96.7 days. 

        Boll development was early in 75×10 cm spacing in 95.1 days in Kharif, 2015 and 93.7 days in Kharif, 2016, [5] reported that the days of the first boll splitting formation in cotton was found earlier in 75×45 cm spacing than in 60×45 cm spacing.  The combination of WGCV-48 and NDLH-1938 planted in 75×10 cm cropping system in Kharif, 2016 had reported minimum days for boll initiation in 91 days. Cotton grown under cool and moist conditions tend to extend the vegetative cycle favoring more dry matter production, whereas under hot and dry conditions in the second season of study selected shortening of the crop cycle. These results are in close conformity with Adare, (2015) [1].

        The number of days for planting to square formation is decreased by narrow plant spacing due to increased inter plant competition [11]. Delay in the appearance of first flower and first boll splitting and increase in the height of first fruiting branch with the increase in space between rows was reported by [15].

Fig 1: The Phenological parameters of cotton genotypes under different plant spacings.

Fig 2: Lint Yield and 100 seed weight of cotton under different spacings

100 Seed Weight (g)

        It is an important trait that determines yield especially in seed cotton. And with the increase of spacing among high HDPS, 100 seed weight improved. WGCV-48 was found to have a significantly higher 100 seed weight than other genotypes studied (8.3 g) followed by NDLH-1938 (7.9 g) and minimum in Anjali (6.9 g). 75×10 cm spacing which accommodates 1,33,333 plants per hectare, has contributed to a high 100 seed weight (7.8 g), followed by 60×10 cm (7.5 g) and minimum in 45x 10 cm spacing (7.1 g). The combination of genotype WGCV-48 under 75×10 cm spacing had shown the best 100 seed weight (8.7 g) than all other combinations.

        Deho [6] in a study on effects on sowing dates on yield components of cotton, stated that sowing on May 1^st resulted in best boll weight (2.83 g) and 100 seed weight (8.74 g).  Shukla et al., 2013 [18] reported the highest 100 seed weight (8.02 g) in broader spacing. 100 seed weight was improved due to a higher level of fertilization (Dhillon et al., 2006) [7]. Maximum 100 seed weight (8.59 g) under wide plant spacing of 45cm and minimum 100 seed weight under 15 cm plant spacing (8.47 g) was reported by [2]. 

Lint Yield (kg ha^-1)

        The cotton cultivar, WGCV-48 under 75×10 cm spacing exhibited the maximum lint yield during both Kharif, 2015 (736 kg /ha) and Kharif, 2016 (737 kg/ha). Among the genotypes, WGCV-48 (642 kg/ha) has shown maximum and Anjali recorded minimum lint yield (417 kg/ha). High photosynthetic rate, better assimilates translocation and better dry matter partitioning efficiency has contributed to the highest lint yield of WGCV-48.

        75×10 cm spacing that accommodates 1,33,333 plants ha^-1 has shown maximum lint yield during Kharif, 2015 (633 kg/ha) and also during Kharif, 2016 (469 kg/ha). The rate of increment in lint yield under 75×10 cm spacing when compared to 60×10 cm and 45×10 cm recorded was 6% and 20% respectively. [4], reported high heterosis for lint index in cotton cultivar, DHB -105, which recorded maximum lint index (6.47) followed by DCH-32 (6.12).

Conclusion

Cotton requires a minimum growing season of 180-200 frost-free days. Squares, flowers and bolls have appeared earlier in 75×10 cm spacing in 42, 67 and 94 DAS (Table 1). The number of days taken for different phenophases to appear decreased with high- density planting. 43, 68 and 95 days in 60×10 cm and 44, 69 and 96 days taken in 45×10 cm spacing for squares, flowers and bolls initiation respectively. Besides, phenophases appeared also early in Kharif, 2016 compared to Kharif, 2015. The shortening of phenophase is because of the increased inter and intra plant competition. 

100 seed weight is significantly higher in WGCV-48 (8.3 g) among the genotypes studied (Table 2 and Fig 2). In addition, seed weight was higher in 75×10 cm spacing (7.8 g) as compared to other spacings of 60×10 cm (7.5 g) and 45×10 cm (7.1 g). Lint yield recorded was maximum in WGCV-48 (642 kg ha^-1) grown at 75×10 cm spacing (633 kg/ha). WGCV-48 had also recorded maximum individual boll weight (2.9 g) and the number of bolls per plant (6.9). The seed cotton yield was maximum in WGCV -48 (1908 kg ha^-1) in 75×10 cm spacing (1639 kg ha^-1).

Future line of Work

Achieving enhanced earliness without compromising on yield potential could be a boon to breeding programs. Suitable spacing and genotype should be identified to harvest the best in High- Density Planting System [13]. Breeding for ideotype of short (90-100 cm) compact type with early maturity, high sucking pest tolerance with 6-7 bolls per plant is essential. Identifying the physiological and harvestable maturity phases of cotton coinciding with the greatest vigor of plant and yield potential should be on main focus (Santosh et al, 2019) [16 & 17].

Conflict of Interest Statement

        The authors declare no conflict of interest.

Acknowledgment

        The present work was done in the department of crop physiology, college of agriculture, Rajendranagar, with financial and technical support from the Central Institute for Cotton Research (CICR), ICAR, Nagpur, India.

References

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