Evaluating growth stimulants for improving different morpho-physiological and seed quality parameters in American cotton

Introduction

Cotton is one of the most important fiber crops globally, contributing significantly to the textile industry and the livelihoods of millions of farmers (Beniwal et al., 2024) [4] . It is an important cash crop which is grown in arid and semi-arid areas of our country (Cetin and Basbag, 2010) [7] . Cotton is also known as "White Gold" and "King of Fibre" (Jogender et al., 2023a) [10] . Cotton plant is a member of family "Malvaceae" and genus "Gossypium" (Jogender et al., 2023b) [11] . More than 50 species belonging to the genus Gossypium. Out of which, four are cultivated due to their spinnable lint, while 44 are wild diploids and remaining are wild tetraploids (Percival and Kohel, 1990) [17] . The cultivated species of cotton are G. hirsutum and G. barbadense which are tetraploids (2n=4x=52; AADD genome); and G. arboreum and G. herbaceum are diploid (2n=2x=26; AA genome) which are also known as new world and old-world species respectively (Ulloa et al., 2006) [22] . In North India, only G. hirsutum and G. arboreum are cultivated commercially (Kumar et al., 2023) [12] . Although G. hirsutum cultivars generate superior quality fibre with greater lint yield and contributed over 95% of the current global production, yet these are vulnerable to several biotic and abiotic stresses including pest infestations, water availability, and nutrient management. Enhancing the yield and quality of cotton seeds through agronomic interventions, such as growth stimulants, has become a critical focus for researchers to optimize cotton production (Ghaffar et al., 2020) [8] . In this context, the American cotton variety H 1098i is widely grown in India, known for its fiber quality and adaptability, making it an ideal candidate for evaluating the effects of different growth stimulants on seed development and overall plant performance. The use of growth stimulants, including plant growth regulators (PGRs), fungicides and fertilizers, is a well-known agronomic practice to enhance plant growth, stress tolerance and yield attributes. Growth regulators like spermidine, a polyamine involved in various physiological processes such as cell division, differentiation and stress response, have shown promise in improving photosynthetic efficiency and plant vigor (Bibi, 2008; Alobaidy, 2013, Noreen et al., 2020) [1,5,16] . Similarly, potassium nitrate (KNO 3 ), a balanced source of potassium and nitrogen, plays a crucial role in enhancing plant metabolism, photosynthesis and yield (Sawan et al., 2007; Sawan, 2013) [19,20] . Additionally, Bavistin, a fungicide widely used to control fungal pathogens, may also contribute to plant health by reducing stress caused by diseases (Metwally et al., 2022) [15] . Keeping in mind above facts, the present experiment was planned to evaluate different growth stimulants and their impact on various morpho-physiological and seed quality traits of the American cotton variety H 1098i. This study could provide a foundation for future research aimed at optimizing growth stimulant applications to enhance cotton yield and quality under varying environmental conditions.

Materials and Methods

The present experiment was conducted at Research Area of Cotton Section, Department of Genetics and Plant Breeding, CCS Haryana Agricultural University, Hisar, Haryana during Kharif 2018. American cotton variety, namely, H 1098i was used as experimental material which was sown in two rows of row length 6.0 m in Randomized Block Design with three replications. Row to row spacing was 67.5 cm and plant to plant spacing was maintained about 30 cm. The treatments included the application of spermidine, Bavistin, potassium nitrate (KNO 3 ), a combination of potassium nitrate and Bavistin, water spray and a control (no spray). These treatments were applied at critical growth stages, i.e., 90 and 120 days after sowing (DAS) to assess their effects on key physiological traits such as photosynthetic rate, chlorophyll content, chlorophyll fluorescence, transpiration rate, stomatal conductance and yield attributes like number of bolls per plant, biomass per plant, lint weight per plant, seed weight per plant. After ginning, seeds were tested for germination in laboratory conditions by taking different observations like seed germination, seedling length, seedling dry weight, seedling vigor and root: shoot ratio.

Results and Discussion

Effect of different spray treatments on various physiological parameters

The table 2 presents the effects of six different treatments on physiological traits, viz., chlorophyll content, chlorophyll fluorescence, photosynthetic rate, transpiration rate and stomatal conductance in the American cotton variety H 1098i. • Chlorophyll Content (SPAD Units): Chlorophyll content was significantly influenced by the treatments. The highest chlorophyll content (45.3 SPAD units) was observed in the plants treated with 13:0:45 (KNO 3 ), followed by the combination treatment of KNO 3 =13:0:45 + Bavistin (44.1 SPAD units). Spermidine-treated plants showed lower chlorophyll content (38.9 SPAD units), similar to the water spray and control treatments. • Chlorophyll Fluorescence (Fv/Fm): Bavistin and water spray treatments had the highest CFL values (0.772), indicating optimal photochemical efficiency of photosystem II. The lowest value was observed in the control treatment (0.742). However, chlorophyll fluorescence did not show significant differences between treatments. • Photosynthetic Rate (µmol m -2 s -1 ): The photosynthetic rate was highest in spermidine-treated and KNO 3 =13:0:45treated plants (15.2 µmol m -2 s -1 ). The control plants had the lowest rate (13.2 µmol m -2 s -1 ). Despite these numerical differences, the photosynthetic rate was not significantly affected by the treatments.

• Transpiration Rate (mmol m -2 s -1 ): The water spray treatment resulted in the highest transpiration rate (6.13 mmol m -2 s -1 ), closely followed by the spermidine treatment (6.09 mmol m -2 s -1 ). The control plants exhibited the lowest transpiration rate (5.27 mmol m -2 s -1 ). Result indicated that there was a significant difference in transpiration rates between treatments. • Stomatal Conductance (mol m -2 s -1 ): The highest stomatal conductance was observed in spermidine-treated plants (0.250 mol m -2 s -1 ), followed by 13:0:45-treated plants (0.223 mol m -2 s -1 ). The control treatment had the lowest stomatal conductance (0.191 mol m -2 s -1 ).

Chlorophyll content, transpiration rate, and stomatal conductance showed significant variation across treatments, indicating that specific treatments, such as KNO 3 and its combination with Bavistin, improved plant physiological traits.

In particular, the KNO 3 treatment led to the highest chlorophyll content, while spermidine enhanced photosynthetic rate and stomatal conductance. The lack of significant variation in CFL and photosynthetic rate across treatments suggests that these parameters were relatively stable, with only minor treatmentrelated differences. On the other hand, transpiration rate and stomatal conductance, both related to water-use efficiency, were significantly affected by growth stimulants, highlighting the role of these treatments in modulating plant water relations and gas exchange processes. Similar findings were observed by Aslam et al., 2021 [2] , Waraich et al., 2011 [23] , Loka et al., 2013 [14] and Yousefi et al., 2021 [25] . Overall, these results suggest that treatments like KNO 3 and spermidine can improve physiological traits in cotton, which may contribute to better growth and yield outcomes under field conditions.

Effect of different spray treatments on various morphological parameters

The table 3 presents the effects of six different spray treatments on various yield-related traits in the American cotton variety H 1098i. Despite the variation in biomass, the results were statistically non-significant, indicating that no treatment had a significant effect on biomass. • Lint weight per plant (g): Lint weight was highest in spermidine-treated plants (79.6 g) and lowest in the control plants (74.6 g). However, the variation in lint weight among the treatments was not significant. • Seed weight per plant (g): Spermidine-treated plants had the highest seed weight (136.8 g), significantly higher than the control treatment (119.6 g). Bavistin-treated plants had the second-highest seed weight (125.0 g), while 13:0:45 alone and its combination with Bavistin showed intermediate seed weights. Results indicated that there was a significant difference in seed weight across the treatments.

• Number of bolls per plant:

The number of bolls per plant was highest in the 13:0:45-treated plants (79.0), followed by Bavistin-treated plants (70.0). The lowest number of bolls was recorded in control plants (64.3). The variation in the number of bolls was significant showing that the treatments significantly influenced boll production.

Spermidine treatment led to the highest biomass and seed weight, suggesting that it enhances overall plant growth and seed development. While the difference in lint weight across treatments was not statistically significant, spermidine-treated plants also had the highest lint weight, indicating its positive but not substantial influence on lint production. Potassium nitrate (13:0:45) treatments, particularly when combined with Bavistin, showed significant improvements in the number of bolls per plant, with the KNO 3 = 13:0:45 treatment alone resulting in the highest number of bolls. This suggests that potassium nitrate can positively impact fruiting, potentially contributing to higher cotton yields. The control plants consistently showed the lowest values across most traits, underscoring the beneficial effects of growth stimulants. The significant differences in seed weight and the number of bolls indicate that certain treatments, especially spermidine and KNO 3 , play a critical role in improving seed yield and boll production, both of which are key indicators of cotton crop performance. Our results coincide with results of Basavanneppa et al., 2015 [3] , Kumar et al., 2011 [13] , Pothiraj et al., 1995 [18] , Sharma and Singh, 2007 [21] , Weir, 1999 [24] , Waraich et al., 2011 [23] , Brar and Brar, 2004 [6] and Yousefi et al., 2021 [25] .

Effect of different spray treatments on various seedling quality traits

The table 4 provides data on seedling quality traits in harvested seeds collected from different spray treated American cotton variety H 1098i. • Germination (%): The highest germination percentage (48.0%) was observed in the 13:0:45 (KNO₃)-treated plants, followed by 13:0:45 + Bavistin (47.8%). The lowest germination was in the control plants (43.3%). However, germination differences were statistically non-significant, indicating that the treatments did not have a significant impact on seed germination. • Seedling length (cm): The longest seedlings were recorded in the KNO 3 =13:0:45 treatment (32.0 cm), with a close second being spermidine-treated plants (31.7 cm). Control plants had shorter seedlings (29.5 cm). Seedling length was also not significantly affected by the treatments. • Seedling dry weight (g): The highest seedling dry weight was observed in the 13:0:45-treated plants (0.496 g), followed by the combination treatment of KNO 3 = 13:0:45 + Bavistin (0.449 g). The control treatment had the lowest seedling dry weight (0.334 g). There was a significant difference in seedling dry weight between treatments. This suggests that KNO 3 , especially in its pure form, significantly increases seedling biomass. • Root: shoot ratio: The water spray treatment had the highest root: shoot ratio (0.252), while spermidine-treated plants had a lower ratio (0.236). The control plants showed an intermediate value (0.215). Despite these differences, the root: shoot ratio did not show significant variation across treatments.

• Seedling vigour: The highest seedling vigour (2.4) was recorded in the 13:0:45-treated plants, indicating better overall seedling quality and robustness. The control plants had the lowest seedling vigour (1.5). Similar to germination and seedling length, seedling vigour differences were not statistically significant across treatments. • While germination percentage, seedling length, root: shoot ratio, and seedling vigour did not show significant differences across treatments, seedling dry weight was significantly influenced, with the highest dry weights observed in plants treated with KNO 3 . This suggests that KNO 3 enhances seedling biomass, which is a crucial factor for early plant establishment and growth. The KNO 3 = 13:0:45 treatment emerged as the most beneficial across several traits, including germination percentage, seedling length, seedling dry weight, and seedling vigour, suggesting that potassium nitrate positively influences early seedling development. The combination of KNO 3 = 13:0:45 with Bavistin also produced good results but was slightly inferior to 13:0:45 alone in terms of seedling vigour and dry weight. Control plants consistently showed lower values across all parameters, reinforcing the importance of growth stimulant treatments in enhancing seedling traits. The non-significant differences for many parameters suggest that while treatments may have visible effects, these differences were not strong enough to be statistically conclusive for germination, length, or vigour. Our results were similar as reported by Ghurde et al., 2021 [9] , Kumar et al., 2011 [13] and Sharma and Singh, 2007 [21] . Overall, the results suggest that potassium nitrate (13:0:45), either alone or in combination with Bavistin, can improve seedling quality and vigour, making it a valuable treatment for improving early growth in cotton crops.

Conclusion

The present study on the American cotton variety H 1098i revealed that growth stimulants such as spermidine, potassium nitrate (KNO 3 ), and Bavistin have impact on enhancing key physiological traits, yield components, and seed development.

The treatments led to improvements in chlorophyll content, photosynthetic rate, and seed weight, with potassium nitrate showing a notable increase in the number of bolls and seedling vigour, while spermidine enhanced biomass and photosynthetic efficiency. The combination treatment of KNO 3 and Bavistin also showed promising results, particularly in germination percentage and boll number. The use of KNO 3 , either alone or in combination with Bavistin, was particularly effective in promoting seedling vigour and enhancing seed development. This study highlights the potential of growth stimulants to boost cotton yield, offering a promising agronomic intervention for enhancing crop performance under both optimal and stressed conditions. In conclusion, this study of plant hormones and their effects on seed germination in cotton offers a promising avenue for enhancing agricultural productivity and sustainability. By delving into the intricate hormonal regulation of germination, this research aims to provide practical solutions for improving cotton crop yields and resilience. The knowledge gained from this study has the potential to benefit farmers, the agricultural industry, and society at large by contributing to food security, economic growth, and environmental conservation.

Future prospects

Further studies can refine the concentration and application timing of growth stimulants like spermidine and potassium nitrate to maximize their benefits in improving cotton yield and quality. Investigating the molecular mechanisms by which these stimulants influence cotton growth and stress tolerance could lead to the development of cotton varieties with enhanced responsiveness to growth regulators. Combining growth stimulant treatments with other agronomic practices such as drip irrigation, nutrient management, and pest control could provide a holistic approach to improving cotton production sustainably. By exploring these future directions, the potential of growth stimulants in optimizing cotton production and resilience to stresses can be further unlocked, contributing to sustainable cotton cultivation globally.

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