Influence of time of pruning, bahar treatment followed by chemical defoliation on Jasminum sambac (L.)

Introduction

Jasminum sambac is one of the traditional flowers of India, commonly known as Arabian jasmine, Tuscan jasmine, Gundu mulligan, Mogra, etc. (Navya et al., 2024) [14] . It belongs to the family Oleaceae. It is used in floral decorations, religious festivals, cosmetics, perfumes, oils, attars, etc. Its unique scent is due to the presence of synthetic aroma chemicals or natural isolates, hence it is considered as the queen of fragrance. In South India, jasmine flowers are widely used by women to decorate their hair, benefiting from the region's plentiful supply of these fragrant blossoms. The flowers grow in clusters called cymes. Arabian jasmine blooms continuously throughout the year, especially in tropical and subtropical regions. However, its peak blooming season occurs during the warmer months of late spring, summer and early autumn. Jasmine flowers from both terminal and axillary buds, which means boosting its yield is linked to an increase in the number of branches (Kalimanai et al., 2017) [8] . Pruning is an essential method for revitalizing older plants. By selectively removing excess or undesirable shoots, it not only helps in shaping the plant's growth pattern but also improves energy efficiency (Lokhande et al., 2015) [9] . This process encourages the development of new, robust shoots that yield more flowers than older ones. Eliminating weak, aging or overcrowded branches allows healthier and more productive shoots to emerge, enabling the jasmine plant to focus its energy on producing more blooms. In addition to increasing flower yield, pruning supports the plant's overall health and Vigor, ensuring consistent flowering year after year. Defoliation plays a significant role in determining the quality and quantity of harvested buds. However, despite its benefits, manual defoliation is labor-intensive and time-consuming (Chiamolera et al., 2023) [5] . Using chemical defoliants can be a more efficient alternative. These substances or mixtures promote leaf shedding, which aids in harvesting and improves the quality of the crop. Common chemical defoliants include Potassium nitrate, Sodium chloride, Paraquat dichloride, Ethephon, Tribufos and Thidiazuron. Due to rising labor costs and shortages, it is important to select defoliants that are effective at low concentrations, safe for both plants and the environment and leave no harmful chemical residues.

Material and Methods

The experiment was carried out at Floriculture block, Dr. Y.S.R. Horticultural University, College of Horticulture, Anantharajupeta during 2023-24.

The existing Jasmine plants are 8 years old. The experiment was laid out in two factorial randomized block design with 10 treatments in 3 replications. T 1: Pruning+ Bahar treatment + NaCl @ 1% (December), T 2: Pruning+ Bahar treatment + KNO 3 @ 5% (December), T 3: Pruning+ Bahar treatment + Paraquat dichloride @ 1000 ppm (December), T 4: Pruning+ Bahar treatment + Ethephon @ 1440 ppm (December), T 5: Pruning+ Bahar treatment + Manual defoliation (December), T 6: Pruning+ Bahar treatment + NaCl @ 1% (January), T 7: Pruning+ Bahar treatment + KNO 3 @ 5% (January), T 8: Pruning+ Bahar treatment + Paraquat dichloride @ 1000 ppm (January), T 9: Pruning+ Bahar treatment + Ethephon @ 1440 ppm (January), T 10: Pruning+ Bahar treatment + Manual defoliation (January). Pruning was done to a height of 45cm above ground level in all the plants. Basins were made around the plants by digging 15-20 cm of soil and exposing the roots partially to impose stress in accordance with the treatments planned during December, 2023 and January, 2024. Observations were recorded for three plants per each treatment. The collected data was statistically analysed to determine the mean values of the following characteristics i.e., days taken for complete defoliation, leaf area (cm 2 ), canopy spread (m 2 ), stomatal conductance (m mol H 2 O m -² s -¹), transpiration rate (m mol H 2 O m -² s -¹), shelf life of flower (hours), Blooming period (days).

Results and Discussion

Days taken for defoliation

Early defoliation (7.33) days was observed in C 3 (Paraquat dichloride @ 1000 ppm), M 1 (Treatment application in December) 9.96 days, and M 1 C 3 (Pruning + Bahar treatment followed by application of Paraquat dichloride @ 1000 ppm in January) 6.89 days, significantly superior to other treatments. More days were taken in C 1 (KNO 3 @ 5%) 16.28 days, M 2 (Treatment application in January) 11.67 days, M 2 C 4 (Pruning + Bahar treatment followed by application of Ethephon @ 1440 ppm in January) 18.89 days (Table 1). Paraquat dichloride acts swiftly due to its redox characteristics (Michaelis et al., 1933) [11] . It disrupts plant photosynthesis, leading to plant tissue burning when exposed to light, which causes defoliation (Aguiar et al., 2023) [1] . Similar results were reported by Chaitanya et al. (2016) [4] . [16] in roses and Hossain et al. (2007) [6] in Bougainvillea.

Maximum Canopy spread was recorded in C 3 (Paraquat dichloride @ 1000 ppm) 0.42, 0.61 and 0.64, M 1 (Treatment application in December) 0.35, 0.49 and 0.52, M 1 C 3 (Pruning + Bahar treatment followed by application of Paraquat dichloride @ 1000 ppm in January) 0.47, 0.67 and 0.71 at 30, 60 and 90 days after treatment application respectively (Table 3). The timing of pruning significantly influences plant growth. The observed results can be attributed to favorable climatic conditions. Enhanced light intensity, better aeration and sap flow towards lateral buds contributed to increased plant spread in both north-south and east-west directions. Ratikanth et al. (2005) [15] and Makwana et al. (2024) [10] reported similar findings in Jasminum sambac.

Maximum stomatal conductance was observed in C 3 (Paraquat dichloride @ 1000 ppm) 0.17, 0.19 and 0.20, M 1 (Treatment application in December) 0.15, 0.17, 0.19, M 1 C 3 (Pruning + Bahar treatment followed by application of Paraquat dichloride @ 1000 ppm in January) 0.18, 0.20 and 0.20 at 30, 60 and 90 days after treatment application respectively (Table 4). Newly emerged leaves following defoliation are typically young, tender, and actively growing. These leaves generally exhibit higher stomatal density and increased stomatal activity. Sharma et al. (2004) [17] observed similar results in Peach. 30 60 90 M1 M2 Mean M1 M2 Mean M1 M2 Mean C1 0.14 0.15 0.15 0.17 0.18 0.17 0.18 0.19 0.19 C2 0.15 0.15 0.15 0.18 0.15 0.16 0.20 0.17 0.18 C3 0.18 0.17 0.17 0.20 0.18 0.19 0.20 0.19 0.20 C4 0.15 0.13 0.14 0.17 0.13 0.15 0.17 0.16 0.16 C5 0.13 0.16 0.14 0.16 0.17 0.17 0.19 0.18 0.18 Mean 0.15 0.15 0.17 The maximum rate of transpiration was recorded in C 3 (Paraquat dichloride @ 1000 ppm) 3.17, 3.54 and 3.68, M 1 (Treatment application in December) 2.93, 3.20 and 3.44, M 1 C 3 (Pruning + Bahar treatment followed by application of Paraquat dichloride @ 1000 ppm in January) 3.27, 3.68 and 3.71 at 30, 60 and 90 days after treatment application respectively (Table 5). The rate of transpiration rises in direct relation to leaf stomatal conductance. These findings align with the research conducted by Islam et al. (2014) [7] and Bernacchi et al. (2007) [3] on Soybean. [13] in Jasminum sambac L.

Blooming period

Maximum Blooming period was recorded in C 3 (Paraquat dichloride @ 1000 ppm) 142.61 days, M 1 (Treatment application in December) 135.60 days, M 1 C 3 (Pruning + Bahar treatment followed by application of Paraquat dichloride @ 1000 ppm in January) 147.22 days at 30, 60 and 90 days after treatment application respectively. The variation in flowering duration can be linked to the higher maximum and minimum temperatures and the shorter days from December to March. Flowering stopped in July, likely due to increased temperatures and longer daylight hours. Nair et al. (2009) [12] and Chaitanya et al. (2016) [4] observed similar results in Jasminum sambac.

Conclusion

The present study showed that pruning, bahar treatment followed by Paraquat dichloride @ 1000 ppm as a defoliant in the month of December has shown quick defoliation, maximum leaf area, canopy, transpiration, stomatal conductance, shelf life of flower and blooming period in Jasminum sambac.

Acknowledgement

AcknowledgementMy heartfelt thanks to the advisory committee for their invaluable mentorship and continued support during the course of this research. Iam also thankful to Department of Floriculture and Landscaping, college of Horticulture, Anantharajupeta-Dr. YSRHU, for providing necessary resources and facilities for the completion of this project. Special thanks to my Family and Colleagues for their continuous encouragement throughout this work.

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