Effects of different pre-sowing seed treatments on germination and seedling growth of Terminalia Catappa L

Introduction

Terminalia catappa, a large deciduous tropical tree of the family Combretaceae, is commonly known as the tropical almond or Indian almond. Native to the coastal regions of Asia, Africa, and Australia, this highly adaptable species is widely cultivated throughout the tropics for its edible kernels, shade, and ornamental value (Phulwaria et al., 2012) [18] . The tree typically attains a height of 15-25 m. Global annual production of fruit and seed has been estimated at 700,000 tons, with each tree yielding approximately 5 kg of kernels per year (Ezeokonkwo and Dodson, 2004). T. catappa has a straight bole and tiers of horizontal, whorled branches arranged in a distinctive, symmetrical pagoda-like growth habit. Large, glossy, obovate leaves are clustered at the branch tips; before being shed twice a year, the accumulation of pigments such as violaxanthin and lutein produces a conspicuous seasonal change in leaf colour, from red to copper to gold. The species is monoecious, bearing small, inconspicuous greenish-white flowers on axillary spikes, with bisexual flowers at the base of the spike and male flowers toward the tip. The fruit is a flattened, ellipsoidal drupe that changes colour from green to yellow to reddish-purple as it matures. Its fibrous, spongy pericarp confers buoyancy and facilitates seed dispersal by ocean currents (hydrochory), while a single almond-flavoured kernel is enclosed within the hard, fibrous endocarp. Owing to its exceptional tolerance of salinity and drought, T. catappa serves as an important windbreak and soil stabiliser in coastal environments (Ramanan et al., 2025) [20] . Its senescent leaves are rich in tannins and flavonoids, including punicalagin and catappanin, and are widely used in aquaculture to condition water and reduce pH owing to their antifungal and antibacterial properties (Hossain et al., 2013) [12] . Extracts from the leaves, bark, and fruit exhibit potent antioxidant, hepatoprotective, and anti-inflammatory activity, underscoring the species' importance in ethnomedicine and biochemistry. Wider cultivation of T. catappa has also been proposed as a means of increasing urban greenery in areas where the species remains uncommon (Ramanan et al., 2026) [21] . Hard-seed-coat dormancy, caused by the stony endocarp of Maesopsis eminii and Terminalia catappa, restricts water penetration and, in the absence of pre-germination treatment, results in erratic or delayed germination (Azad et al., 2013) [4] . This form of dormancy is classified as physical dormancy, in which a water-impermeable palisade layer in the seed or fruit coat prevents inhibition until the layer is disrupted (Baskin and Baskin, 2004) [6] . Several approaches have been developed to enhance the germination of hard-coated seeds prone to this form of dormancy (Morpeth and Hall, 2000). Because an intact seed coat restricts water uptake and gaseous exchange, seed-coat scarification is essential for overcoming physical dormancy; the fissures created during mechanical or chemical treatment permit water entry and gas exchange, thereby enabling enzymatic hydrolysis and subsequent development of the embryo into a seedling (Shil and Prajapati, 2026) [23] . Gibberellic acid treatment offers a complementary hormonal route to overcoming dormancy, having been shown to enhance germination value in other hard-seeded species such as oak (Adams et al., 2010) [2] . Pre-sowing treatments are therefore essential for improving germination in species with inherently poor germination, whether arising from hard seed coats or other forms of dormancy. According to Markam et al. (2025) [14] , the objective of nursery operations for any given species is to produce the maximum number of high-quality seedlings with the minimum expenditure of labour, cost, and time. The present study evaluated soaking treatments for improving the germination of a hard-coated indigenous tree species, with the aim of guiding institutions and individuals engaged in tree nursery operations. Seed treatments offer considerable scope for breaking seed dormancy, improving germination rate and uniformity, and reducing the time to emergence (Bargah et al., 2025; Maan and Jain, 2026) [5,13] . Judicious use of industrial by-products such as fly ash also offers promising prospects for improving soil fertility and nursery sustainability (Behera et al., 2020) [7] . Despite persistent challenges such as seed dormancy and environmental stress, advances in seed technology and adaptive nursery management continue to offer opportunities for improving propagation performance (Netam et al., 2025) [15] .

Materials and Methods

Seed collection area

Trees of Terminalia catappa were sampled locally from Barnavapara, and seed lots were collected from the selected trees. From the collected seed, 270 seeds were separated and randomly allocated among six treatments, including the control.

Pre-sowing treatments

Seeds of Terminalia catappa were subjected to six pre-sowing treatments to evaluate their effect on germination behaviour, following standard tree-seed pre-treatment procedures (Food and Agriculture Organization of the United Nations, 1993); details of the treatments are presented in Table 1.

Experimental design

The germination trial was laid out in a Completely Randomized Design (CRD), with three replications per treatment (six treatments including the control). For each replication, 15 seeds were sown individually in polybags (one seed per bag) containing a potting medium of soil, sand, farmyard manure (FYM), and cocopeat in a 5:1:1:1 ratio, giving 45 seeds per treatment. Germination was recorded daily; a seedling was considered to have emerged once it appeared above the soil surface, and both the number of days to emergence and the number of seedlings emerged were recorded. Data were subjected to analysis of variance and treatment means were compared following standard procedures for agricultural experimentation (Panse and Sukhatme, 1967) [17] .

Germination percentage

Results and discussion

The goal of the present study was to see how different pre-sowing treatments affected seed germination of Terminalia catappa.

Number of days to plant emergence

All pre-sowing treatments reduced the number of days to seedling emergence relative to the untreated control (Table 2, Fig. 2). Seedlings emerged earliest under T3 (hot water at 70˚C for 5 minutes; 18.86 DAS), followed by T4 (cold-water soak for 24 hours; 21 DAS) and T5 (cold-water soak for 48 hours; 22.86 DAS). Emergence in T2 (1% H2SO4 for 5-10 minutes) required 40.93 DAS. Emergence under T1 (GA3 at 200 ppm for 24 hours) required 33.80 DAS, while the untreated control (T0) required 60.06 DAS. Odoi et al., (2019) [16] similarly reported that a 12hour cold-water soak markedly accelerated seedling emergence in Terminalia catappa relative to an untreated control, while Sharma et al., (2008) [22] . reported that hot-water treatment reduced the time to seedling emergence in several fast-growing tropical tree species with hard seed coats, consistent with the rapid emergence recorded under T3 in the present study.

Germination percentage

Germination percentage was highest in T4 (88.88%; cold-water soak for 24 hours), followed by T3 (77.77%; hot water at 70˚C for 5 minutes) and T5 (66.66%; cold-water soak for 48 hours) (Table 2, Fig. 3). The hormonal and chemical treatments, GA3 at 200 ppm for 24 hours (T1) and H2SO4 at 1% for 5-10 minutes (T2), produced germination percentages of 53.33% and 46.66%, respectively -higher than the untreated control (35.55%) but lower than the water-based treatments (T3, T4, T5). Purohit et al., (2015) [19] . similarly reported that dilute sulfuric acid scarification markedly improved germination in the hard-coated seeds of Zanthoxylum armatum, underscoring the effectiveness of acid scarification for breaking physical dormancy in woody species, although its relative efficacy in the present study remained lower than that of water-based physical treatments.

Mean daily germination, peak value, germination value

Mean daily germination was highest in T4 (0.98%), followed by T3 (0.86%), T5 (0.74%), T1 (0.59%), and T2 (0.51%); the control recorded the lowest value (0.39%). A similar trend was observed for peak value, which was highest in T4 (4.71) and lowest in the control (0.59), and for germination value, which was highest in T4 (4.65), followed by T3 (3.20), and lowest in the control (0.23).

3, Fig. 5), and increased progressively with seedling age under every treatment. At 30 DAS, plant height was greatest in T4 (10.91 cm), followed by T3 (8.42 cm) and T5 (7.54 cm); seedlings of T0, T1, and T2 had not yet emerged at this stage. At 60 DAS, T4 again recorded the greatest plant height (16.41 cm), followed by T3 (13.92 cm) and T5 (13.04 cm), while the control (T0) recorded the lowest height (3.62 cm). At 90 DAS, T4 produced the tallest seedlings (26.41 cm), followed by T3 (22.92 cm) and T5 (21.04 cm), whereas the control remained shortest (13.62 cm).

Number of leaves per plant

The number of leaves per seedling differed significantly (P < 0.05) among pre-sowing treatments at 30, 60, and 90 DAS (Table 3, Fig. 6), and increased markedly with seedling age under every treatment. At 30 DAS, the highest leaf number was recorded in T4 (3.

Conclusion

This study demonstrates that appropriate pre-sowing treatments can effectively overcome the physical seed dormancy of Terminalia catappa L. arising from its thick, woody endocarp. Among the treatments tested, soaking seeds in cold water for 24 hours (T4) was the most effective, significantly enhancing physiological activation and raising the germination percentage to 88.88%, mean daily germination to 0.98%, and germination value to 4.65, while T3 produced the shortest seedling emergence time (18.86 days). The T4 treatment also produced the greatest plant height (26.41 cm), the highest number of leaves per seedling (15.13), the largest shoot diameter (0.43 cm), and the greatest root length (33.76 cm) at 90 days after sowing, indicating a marked overall improvement in seedling growth. In contrast, the untreated control (T0) exhibited delayed and nonuniform emergence together with prolonged physical dormancy, recording the longest time to germination (60.06 days), the lowest germination percentage (35.55%), and markedly stunted seedling growth. Other interventions, including a 48-hour cold-water soak (T5) and a 5-minute hot-water soak at 70°C (T3), did not match the consistency and effectiveness of the 24-hour cold-water soak. A 24-hour cold-water soak (T4) can therefore be recommended as a cost-effective, practicable, and efficient operating standard for large-scale nursery management of this ecologically and economically important tropical tree species, supporting reliable seedling production and larger-scale reforestation efforts.

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