Optimizing growth promoters use for improved seed yield and quality in sesamum (Sesamum indicum L.)

Introduction

Oilseeds have long been integral to India's agricultural economy, serving as one of the primary sources of vegetable oils for both domestic consumption and export. Ranking second in demand after cereals, oilseeds contribute significantly to the agricultural sector. In the early 1990s, India's 'Yellow Revolution' briefly propelled the country towards self-sufficiency in oilseeds production (Anon, 2022 (a) [2] . This marked a period of substantial growth, helping India reduce its dependence on imported vegetable oils. However, since that time, India has faced challenges in sustaining such progress. Despite being the fourth-largest oilseed producer globally, behind the USA, Brazil and China-India remains one of the largest importers of vegetable oils, largely due to relatively low domestic productivity. Among many oilseeds cultivated in India, sesamum holds a special place due to its high-quality edible oil. The crop's resilience and ability to grow in marginal environments have contributed to its widespread cultivation. In the modern world India, China, Myanmar and Sudan are the major producers of sesamum. India, in particular, holds the distinction of being the world's largest producer of sesamum, with an output of approximately 8.66 lakh tonnes grown on 19.47 lakh hectares of land. This accounts for roughly one-third of the world's sesamum production. However, despite India's dominant role in sesamum cultivation, the country's average yield is low, at 413 kg/ha, lags behind other nations such as China (535 kg/ha). Factors such as climatic variability, dependent on rainfed agriculture and underdeveloped farming practices contribute to this productivity gap (Angel et al., 2022) [1] . From a nutritional standpoint, sesamum seeds are a rich source of edible oil, containing 45-50% oil. The oil is high in unsaturated fatty acids, particularly oleic and linoleic acids, which are beneficial for heart health. Sesamum seeds also provide a good source of fiber, which helps reduce cholesterol and triglyceride levels, thereby lowering the risk of heart disease. In addition to these benefits, sesamum seeds are rich in protein (20%) and carbohydrates (14.2%) (Angel et al., 2022). [1] Sesamum oil is naturally resistant to rancidity due to the presence of antioxidants like sesamin, sesamolin and sesamol.

India, as one of the largest producers of sesamum, has a significant opportunity to capitalize on global demand by enhancing its sesamum export potential. Despite India's status as a major global producer, the country faces significant challenges in increasing productivity. One of the primary reasons for the low average yield is the fact that 72% of India's oilseed cultivation occurs in rainfed farming systems, which are typically managed by marginal and small-scale farmers. These farmers often operate under input-starved conditions, with limited access to quality seeds, modern farming techniques and appropriate technology. Additionally, oilseed cultivation in India is frequently subjected to both biotic and abiotic stresses, including pests, diseases and unpredictable weather patterns (Anon., 2022(b) [3] . To overcome these challenges, several strategies can be employed, including the use of high-yielding varieties, proper nutrient management and the application of growth promoters. Among this growth promoters have added advantages like accurate action, flexibility, environmental compatibility etc. Plant growth promoters are complex chemicals that, when applied in minute quantities, can significantly influence plant growth and metabolism. Unlike fertilizers and pesticides, which are often used in larger quantities, growth promoters act at much lower concentrations and have a more targeted effect on specific physiological processes. Some of the benefits of growth promoters application include prolonging photosynthesis, reducing respiration and enhancing the partitioning of photoassimilates. These regulators also optimize the uptake of minerals and stimulate nitrogen metabolism, all of which contribute to better plant growth, higher yields and improved seed quality. India, being one of the largest producers, has a significant opportunity to enhance its export potential by using this technology and farmers can enhance their average yield and get more return from foreign exchange. Keeping in view all these points, the study titled "Influence of growth promoters on seed yield and quality in sesamum (Sesamum indicum L.)" was undertaken with the following objectives: 1. To evaluate the effect of growth promoters on plant growth and seed yield. 2. To know the influence of growth promoters on seed quality.

Material and methods

Seeds of sesamum variety GKVK S-1 were collected from AICRP on oil seed scheme, Zonal Agricultural Research Station, Gandhi Krishi Vignana Kendra, Bangalore. The field experiment was conducted by using RCBD design during kharif, 2023 at ZARS, University of Agricultural Sciences, GKVK, Bangalore. Different growth promoters T1-control, T2-Benzyl adenine @ 25 ppm, T3-Benzyl adenine @ 50 ppm, T4-NAA @ 75 ppm, T5-NAA @ 100 ppm, T6-Ascorbic acid @ 75 ppm, T7-Ascorbic acid @ 100 ppm, T8-IAA @ 75 ppm & T9-IAA @ 100 ppm were used as a foliar application at flower initiation stage (45 DAS) and capsule formation stage (60 DAS).

Collection of experimental data Plant growth and seed yield parameters

Five plants were randomly selected and tagged in the net plot for recording observations on plant growth and seed yield parameters at 40, 60, 90 DAS and at harvest. Data were recorded on plant height (cm), number of branches, number of capsules and seed yield.

Seed quality parameters:

The harvested seeds were analysed to examine the effect of growth promoters on seed quality parameters such as seed germination (%), seedling vigour indices I and II, total soluble protein content (%) using Lowry's method (1951), oil content (%) using a pulsed Nuclear Magnetic Resonance (NMR) spectrometer and lipase activity (meq/min/g) by the titrimetric method of Sadasivam and Manickam (1996) [20] .

Results and discussion

In the present study, among different treatments significantly highest (87.32 cm, 112.55 cm and 118.73 cm) plant height was recorded in T5 (NAA @ 100 ppm) at 60, 90 DAS and at harvest respectively which was followed by T4 (NAA @ 75 ppm, 84.23 cm, 108.23 cm and 115.93 cm respectively). While, the lowest (68.28 cm, 94.39 cm and 100.19 cm respectively) was observed in control (T1) is presented in Table 1. The increased plant height might be due to the stimulating action of auxin (NAA) which softens the cell wall by increasing its plasticity or might be the oxidative decarboxylation of synthetic auxins which could not be catalysed by the enzyme peroxidase (Ramesh and Ramprasad, 2013) [18] .These results were consistent with the findings of Angel et al. (2022) [1] and Siddik et al. (2015) [21] in sesamum. [10] .

Number of Capsules per plant:

The number of capsules varied significantly among treatments. The highest (48.50, 93.00 and 94.22) number of capsules per plant at 60, 90 DAS and at harvest respectively was recorded in T5 (NAA @ 100 ppm) which was followed by T4 (NAA @ 75 ppm-44.97, 88.58 and 91.09 respectively) while, the lowest (34.82, 74.58 and 81.67 respectively) was recorded in control (T1) (Table 3). The application of NAA leads to significant increase in number of flower clusters per plant while, reducing the percentage of flower drop. This in turn increased number of capsules per plant in sesamum (Siddik et al., 2015) [21] . These findings are in accordance with the reports of Priya et al., 2023 [17] in Ber and Angel et al. (2022) [1] in sesamum.

Seed Yield Parameters

The variation among treatments showed significant difference in seed yield per plant (g), seed yield per plot (g) and seed yield (kg/ha) due to foliar application of growth promoters (Table 4). The treatment T5 ((NAA @ 100 ppm, 4.01 g, 1278.72 g & 631.47 kg ha -1 ) showed highest seed yield per plant (g), seed yield per plot (g) and seed yield (kg/ha) whereas, lowest result observed in T1 (control, 2.53 g, 1059.15 g & 523.46 kg ha -1 ) respectively. The increase in yield may be attributed to NAA's role in enhancing the translocation of sugars from source to sink, particularly from photosynthesizing tissues to developing seeds in oil crops (Gangadhar and Brar, 2020) [8] . These findings are consistent with the reports of Upadhyay and Ranjan (2015) [23] in soybean and Ema et al. (2020) [7] in sesamum.

The seed germination (%) differed significantly among treatments is presented in Fig. Where, maximum germination percentage was noticed in T5 (NAA @ 100 ppm, 93.67%) which was on par with T4 (NAA @ 75 ppm, 91.33%), while lowest was observed in T1 (Control, 82.00%). The germination percentage is a critical characteristic used to estimate the planting value of seeds. NAA accelerates cell elongation, leading to quicker root and shoot growth, improved nutrient assimilation through a larger root system and enhanced seed vigour, all contributing to the successful establishment of robust seedlings (Patil et al., 2023) [16] . These results align with findings reported by Borkar et al. (1991) [6] in cowpea, Hilli et al. (2010) [9] in ridge gourd, Khan et al. (2013) [12] in okra, Kene et al.

(1992) [11] in safflower and Arvindkumar et al. (2014) in tomato [4] . [15] and in pigeon pea (Sharvani et al., 2022). Which increased efficient nutrient translocation to developing seeds, ensuring that they accumulate more essential nutrients, hormones and energy reserves such as starch and proteins. This results in seeds with higher metabolic activity and better initial energy stores, which leads to faster germination and more vigorous early growth. Additionally, NAA improves hormonal regulation in seeds, particularly by increasing auxin levels, which directly stimulate stronger root and shoot development. Furthermore, the foliar application of NAA may also enhance the seed coat permeability, allowing for quicker water absorption and faster imbibition during germination. Together, these factors contribute to increased seedling vigour. Similar findings were observed by Hilli et al. (2008) [9] revealed that NAA 50 ppm recorded significantly highest vigour index in ridge gourd, Kumbari (2002) [13] revealed that NAA 100 ppm recorded maximum vigour index in tomato, Therakam (2001) [22] recorded that among various concentrations of NAA under his study showed highest vigour index with foliar application of NAA @ 20 ppm in brinjal.

Seedling

There was a significant difference among treatments for total protein content. The highest (21.83%) protein content was observed in treatment T5 (NAA @ 100 ppm) which was on par with T4 (NAA @ 75 ppm, 21.61%). The lowest (18.03%) protein content was observed in T1 (control) is presented in Table 5. Due to foliar application of NAA, there was significant increase in protein content, connected with increased metabolism of nitrogen (Patil et al., 2023) [16] . The results are in line with the findings of Bai et al. (1987) [5] in green gram, Ravikumar and Kulkarni (1988) [19] in soybean and Patel and Saxena (1995) [15] in mung bean.

Oil content (%): The data on oil content is presented in Table 6. Showed significantly the highest (55.04%) oil content observed in treatment T5 (NAA @ 100 ppm) which was on par with T4 (NAA @ 75 ppm, 54.85%). The lowest (46.25%) oil content% was observed in treatment T1 (control) presented in Table 5. Increased oil content is consequence of increased conversion of carbohydrates to oils. Foliar application of NAA increases the uptake and availability of nutrients and its further assimilation for biosynthesis of oil increasing oil content in seed in the present investigation. These results are comparable with Pain and Sarkar (1980) [14] , Vasudevan et al. (1996) [24] observed in sunflower and Kene et al. (1992) [11] in safflower respectively. The data on lipase activity computed as influenced by foliar application of growth regulators are presented in Table 5. The significant difference was observed among treatments. The highest (0.33 meq/min/g) lipase activity was observed in treatment T5 (NAA @ 100 ppm), which was on par (0.31 meq/min/g) with T4 (NAA @ 75 ppm) and lowest (0.20 meq/min/g) was observed in treatment T1 (control). Seed germination increases lipolytic activity in sesamum seeds with lipase primarily hydrolysing saturated fatty acids (Wanasundara et al., 2001). The foliar spray of NAA at 100 ppm further enhanced germination in turn increased lipase activity. NAA stimulates metabolic processes like nutrient mobilization, which boosts enzyme production. This leads to higher lipase activity in seeds, improving fatty acid breakdown during germination. The results are in line with Ravikumar and Kulkarni (1988) [19] in soybean.

Conclusion

The present study demonstrated that the application of growth promoters significantly influenced the growth and yield attributes of sesamum (Sesamum indicum L.) cv. GKVK S 1. Among the treatments evaluated, foliar application of Naphthalene Acetic Acid (NAA) at 100 ppm showed superior performance, resulting in enhanced plant height, number of branches and improved seed yield components The findings indicate that NAA at 100 ppm effectively stimulates vegetative growth and reproductive development, likely by modulating endogenous hormone levels and promoting cell division and elongation. This suggests that NAA can be effectively integrated into sesame cultivation practices to improve productivity. Further research may focus on optimizing the timing and frequency of application to maximize benefits under varied agro-climatic conditions.

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