Influence of presowing treatments on seed germination, seedling growth, and early development of teak (Tectona grandis)

Introduction

Tectona grandis, commonly known as teak, was first formally described by Carl Linnaeus the Younger in 1782 in his work Supplemental Plantarum (Cardoso, 2015) [7] . This deciduous tree is characterized by its glossy upper leaf surfaces, hairy undersides, and relatively large leaves. In Hindi, it is referred to as "Sagwan," while in Assamese, it is known as "Segun." The first teak plantation was established in Nilambur, Kerala, by Conolly and Chotu Menon. Research indicates that the Sagwan tree is a valuable hardwood species (Choudhari and Prasad, 2018; Palanisamy, 2009) [8,34] recognized for its exceptional physical properties (Venkatesh et al., 2024; Midgley et al., 2015) [46,29] , resilience, and aesthetic appeal, making it suitable for use in the development of degraded lands (Sanwo, 1987) [38] . Teak wood is notable for its moderate specific gravity, remarkable mechanical strength, and outstanding dimensional stability (Freitas, 1958) [11] . It also boasts corrosion resistance (Colbu et al., 2021) [9] and is easy to process, offering good seasoning performance (Adetan, 2019) [1] . Additionally, teak wood is highly regarded for its weathering resistance and durability against decay (Bailleres and Durand, 2000). Even though teak is valued for its high market value and is considered a superior species in many regions due to its quick growth and flexible seedling establishment (Indra and Basha, 1999), private farm teak cultivation is frequently hampered by its naturally low and irregular germination rates, which were identified by Jackson (1994) [18] due to the protected and irregular germination of untreated drupes. The low and inconsistent germination rates (Kollert and Kleine, 2017) [23] of teak not only result in the availability of seedlings and degraded timber quality but also escalate the management costs of teak nurseries. Research conducted by Adhikari et al., (2021) [2] and Sudhakara and Jijeesh (2008) [41] clearly demonstrates that seed size and moisture content are critical factors influencing the germination of teak seeds, and they play a decisive role in causing seed dormancy. Their morphological/physiological dormancy significantly influences teak true seed germination in addition to their mechanical and physical dormancy, as reported by Venkatesan et al., (2024) [45] . Foresters face the challenge of finding a simple and efficient pre-seed treatment method for teak seed germination that reduces seedling failure rates. This is especially crucial because, although pre-sowing hydro-priming facilitates water absorption, activating and mobilizing enzymes, and providing access to stored nutrients, which may improve germination, many researchers have shown that such treatments can significantly increase the germination percentage of teak seeds (Palani et al., 1996; Billah et al., 2015) [33,6] . Therefore, the goal of the study is to determine the best ways to break the dormancy of T. grandis seeds and to determine their germinability parameters and early seedling growth under nursery conditions.

Materials and Methods

The experiment was conducted in the agroforestry nursery, Medicaps University, Indre (M.P.), during the years 2024-2025. The study aimed to evaluate the impact of presowing seed treatments on the germination parameters and seedling initial growth of Tectona grandis. The site is located at 22°37′16.9″N latitude and 75°48′13.8″E longitude, standing 545 meters above mean sea level. The area has a mix of semi-arid and humid subtropical climates, featuring hot summers with temperatures between 25°C and 42°C and mild winters where temperatures range from 8°C to 28°C. The rainfall is approximately 700 mm to 950 mm. The soil in the area varies from medium black soil to shallow black, with a pH range of 7.0 to 8.5. Trees with ideal morphological characteristics, such as vigorous height, optimal crown, and moderate tree age with high seed yield, were selected. Healthy seeds were sourced from healthy trees at Barwaha, Forest Division, Madhya Pradesh. The study involved six pre-sowing treatments, such as seeds submerged in hot water for 48 hours (T1), cold water treatment soaking for 72 hours (T 2 ), seeds were submerged in concentrated H₂SO₄ 80% for 10 minutes (T 3 ), dipping in cow dung slurry for 72 hours (T 4 ), seeds were submerged in GA 3 solution (150 ppm) for 24 hours (T 5 ), control (T 6 ). Each treatment had four replications with 100 seeds per replication. Each seed treatment's five seeds were planted in 5-by-7-inch poly-packets with a 2-cm depth. A combination of equal parts sand, dirt, and vermicompost made up the rooting medium. Urbanization presented problems for the availability of sunshine in the agroforestry nursery regions during the study period. Underground water was used for irrigation every two days. This keeps the soil moist and helps crops grow well. After the germination period ended, the germination percentage was calculated using the formula from Maguire (1962) [25] .

Seedling height and collar diameter were measured five months after sowing. The results were grouped by treatment, using six replications focused on different criteria. One-way analysis of variance (ANOVA) was completed within a complete randomized block design (CRD) and applied Duncan's multiple range tests at a 5% probability level to compare means. This method effectively evaluates the impact of various treatments on seedling growth.

Results and Discussion Effect of different presowing treatments on seed germination

Teak is highly esteemed as a premier timber species, recognized for its exceptional adaptability across a range of soil conditions. Before introducing viable seeds into the germination process, it is essential to employ appropriate mechanical, chemical, or biological treatments to overcome the inherent dormancy that restricts effective germination. The germination percentage of teak seeds is notably low (Ngulube, 1986) [30] . The present study rigorously investigates the effects of various pre-sowing treatments on the germination, seedling growth, and overall development of teak. This research contributes significantly to advancing the understanding and cultivation of this valuable species.

The results indicate that seed germination was significantly improved with 80% H₂SO₄ treatment for 10 minutes, reaching a germination rate of 36.13% (T3), followed by seeds treated with GA 3 at 30.03% (T 5 ), and hot water for 48 hours (T 1 ), 24.99% respectively. Control seeds (T 6 ) had a very list germination rate of only 20.00% which was technically at par with cold water treatment soaking for 72 hours (T 2 ), 20.28%. While seed treated with cow dung slurry for 72 hours (T 4 ) treatment resulted in intermediate responses of 23.49%. Hossain et al. (2002) [15] also concluded that sulfuric acid enhances germination percentages in their research. Numerous studies have shown that various presowing techniques can increase the germination rate and accelerate the germination process (Teketay, 1996 [43,14,36,3,4] . The role of hormones in breaking the dormancy of hard seeds is evident. However, GA 3 treatment did not effectively boost germination in this case, as reported by Seng and Cheong (2020). Generally, the pericarp of teak seeds is impermeable to water, which protects the seeds. It includes the seed or spores along with additional tissues that aid in dispersal. Additionally, the mesocarp and endocarp have thick-walled palisade cells covered by waxy cuticles, contributing to seed dormancy (Diameters et al., 2009). Key limiting factors include the seed's physiological immaturity and the presence of chemical inhibitors within the pericarp (Georgin et al., 2014) [12] . These inhibitors can be broken down and the seed coat softened by soaking the seeds in concentrated sulfuric acid or other chemicals. The positive effect of sulfuric acid on seed germination observed in this study is supported by Imani et al. (2014) [16] , and similar improvements in teak drupe germination have also been documented by Manonmani (2003) [28] . The use of H₂SO₄ can enhance seed germination percentages, as stated by Khader and Chacko (2000) [20] and Nourmohammadi et al., (2019) [32] . While gibberellic acid (GA 3 ) is commonly used to break physiological dormancy (Uarrota, 2021) [44] , it may not be the most effective method for increasing the germination rate of teak seeds, which exhibit physical dormancy due to their hard seed coat. Consequently, GA 3 treatment produces limited effects when combined with H₂SO₄.

Impact of various presowing treatments on growth parameters of teak

The morphological development of seedlings, including height, collar diameter, and root length, is effectively summarized in Table 1. The research clearly demonstrates that pre-sowing seed treatment has a significant impact on collar diameter. Notably, the largest collar diameter of 1.40 cm is observed in seeds treated with gibberellic acid (GA 3 ) at 150 ppm (T 5 ), followed by the 80% sulfuric acid treatment (T 3 ), which results in a collar diameter of 1.16 cm, and seeds treated with cold-water treatment (T 2 ), 0.99 cm collar diameter. In stark contrast, the control group (T 6 ) displays the smallest collar diameter at 0.50 cm. While hot water for 48 hours (T 1 ), 0.60 cm, and seed treated with cow dung slurry (T 4 ), 0.90 cm diameter, showed intermediate results. Gibberellic acid (GA 3 ) is well-established as an agent that promotes vigorous vegetative growth, leading to marked increases in both the length and width of the collar region and other plant structures. This phenomenon explains the superior collar diameter observed in the GA 3 -treated seedlings. Moreover, the effectiveness of GA 3 in enhancing cell elongation is robustly supported by the findings of Mäkilä et al., (2023) [26] . Furthermore, sulfuric acid treatment unambiguously promotes germination and significantly enhances the development of both the plumule and radicle, which are critical components of the seed embryo. Sulfuric acid treatment helps to break this dormancy by weakening the seed coat and allowing water and oxygen to penetrate more easily (Kher and Nataraj, 2015) [22] . This, in turn, stimulates the growth of the radicle (primary root) and the subsequent development of fasciculate roots, faster than the other treatment. An increase in radicle length after the seed was treated with sulfuric acid was also stated by Imani (2014) [16] , Khaleghe et al. (2009) [21] . The collar is the region where the stem and root of a seedling join. A larger collar diameter signifies a stronger root system, which is essential for anchoring the seedling and absorbing water and nutrients from the soil.

Vijayalakshmi and Jamaludheen (2020) [47] and Hadedy et al.

(2024) [13] also reported a similar diameter. Table 1 illustrates the significant differences in plant height among various treatments. The highest seedling height was observed in seeds treated with gibberellic acid (GA 3 ) solution (T 5 ), measuring 30.06 cm, which was statistically greater than those treated with 80% sulfuric acid (T 3 ), measuring 28.49 cm, and seeds treated with cold water for 72 hours (T 2 ), 24.97 cm. Conversely, the lowest seedling height after five months was recorded for the untreated seeds (T 6 ), at 19.13 cm. Seeds treated with cow dung slurry for 72 hours (T 4 ), 21.02 cm, which was at par with hot water treated seeds for 48 hours (T 1 ), 22.71 cm, both treatments yielded moderate results in height increment.

The increased plant height in seeds treated with gibberellic acid (T 5 ) is likely due to enhanced cell elongation and division in meristematic tissues, as noted by Sheoran et al. (2019) [39] . Gibberellic acid is a plant hormone that regulates various developmental processes, including shoot elongation, by increasing both the number of cells and the length of individual cells. In contrast, the teak seeds treated with H₂SO₄ (T 3 ) exhibited lower seedling heights compared to treatment (T 5 ). While sulfuric acid does not directly promote cell elongation after germination, it effectively breaks down the physical barriers of the seed and ensures nutrient availability to the embryo. This early action resulted in better seedling growth compared to other treatments, except for treatment (T 5 ). Rout et al. (2021) [37] and Sonkamble et al. (2024) [40] reported similar findings in their study on the growth of Saraca asoca (Roxb.) using various concentrations of Gibberellic Acid (GA 3 ). Five months later, the teak seeds treated with GA 3 (T 5 ) had the maximum root length of 30.73 cm, which was significantly longer than the teak seeds treated with hot water (T 1 ), 26.23 cm, and seeds treated with concentrated H₂SO₄ 80% for 10 minutes (T 3 ), 25.43 cm. Similarly, the seeds treated with cow dung slurry for 72 hours (T 4 ) exhibited a root length of 23.20 cm, whereas those subjected to cold-water treatment soaking for 72 hours (T 2 ) achieved 19.88 cm root length. Both treatments promoted moderate root development. The control group (T 6 ) had the shortest root length, 17.68 cm. Results revealed that applying GA 3 to seeds promotes cell division and elongation in a variety of plant tissues, including root meristems, which also promotes lateral root elongation; that's why seeds treated with gibberellic acid showed higher root length. These data revealed that GA₃ treatments were effective at promoting root growth, as they showed that root development was slower under hot water treatment and other circumstances. The presented results were also supported by Placido et al., (2020) [35] , while hot watertreated seeds had a good surrounding environment near the root; the heat also inhibited root growth barriers and a favourable microclimate for root development. Sometimes it may be given to better seed vigor. On the other hand, seeds treated with H 2 SO 4 reported less root length compared to seeds treated with GA 3 (T 5 ) and seeds treated with hot water (T 1 ). It may be attributed to the harsh impact of the concentration of sulfuric acid, which can develop some chemical stress near the root zone.

Conclusion

The findings of this study reveal that pre-sowing treatments for teak seeds remarkably enhance the growth and development of seedlings. Teak (Tectona grandis) is known for its beautiful golden-brown wood. It is highly valued in the industrial sector for its durability and attractive appearance. The research uncovered that after five months, seedlings originating from seeds treated with GA3 flourished, showcasing impressive heights, robust root lengths, and substantial collar diameters.

Furthermore, an extraordinary boost in germination rates was observed when seeds were delicately immersed in 80% sulfuric acid (H₂SO₄) for a brief yet impactful period of 10 minutes posttreatment. This meticulous process set the stage for vibrant and thriving seedlings, ready to embark on their growth journey.

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