Effect of seed size and pretreatment on germination and early growth performance of Tamarindus indica L.

Introduction

Tamarindus indica L. (Tamarind) is a multipurpose tree species of high socio-economic and ecological importance in tropical and subtropical regions (Khaled, Ebeid, Soliman, & Gahory, 2023) [5] . Its pulp, seeds, leaves, and bark have culinary, medicinal, and industrial uses. However, propagation via seeds is often constrained by low germination rates attributable to seed dormancy, chiefly resulting from a hard, impermeable seed coat (Ambursa et al., 2019) [2] . Effective dormancy-breaking or pretreatment methods are therefore critical for improving germination success, seedling vigor, and large-scale nursery raising in afforestation or restoration programs. Seed dormancy in T. indica is classified primarily as physical dormancy, wherein the seed coat restricts water uptake and gas exchange, thereby impeding embryo activation (Baskin & Baskin, 2004, as cited in IJAES, 2023). To overcome this barrier, various pretreatments have been tested: chemical scarification (e.g. sulfuric acid), hot water imbibition, mechanical scarification (e.g. nicking or abrasion), and combinations thereof (Khaled et al. 2023; Usman, Ajibade, & Magaji, 2025) [5,7] . For instance, Khaled et al. (2023) [5] reported that mechanical scarification followed by brief concentrated H₂SO₄ exposure achieved the highest germination percentages and seedling growth performance under both laboratory and field conditions. In a recent Nigerian study, sulfuric acid pretreatment outperformed hot water, mechanical scarification, and soaking, producing more uniform and faster germination (Usman et al., 2025) [7] . Other studies have explored alternative chemical priming agents: e.g. potassium nitrate (1%) pretreatment enhanced both germination percentage and speed compared to control and hot water in T. indica (The effect of different treatments on seed dormancy, 2023) [6] . Despite these advances, relatively few studies examine the interaction of seed size classes (e.g. larger vs. smaller seed diameter or weight groups) with pretreatment efficacy. Seed size often correlates with stored reserves and internal vigor, which may influence how different treatments impact germination responses. Additionally, recent emerging techniques such as laser irradiation have been experimented on T. indica seeds, showing enhancements not only in germination and seedling growth but also phytochemical accumulation in seedlings (Hassan et al., 2025) [3] . Thus, combining classical scarification methods with novel physical or optical methods offers unexplored potential. Given this context, the present study investigates how seed size classes (above vs. below 1 cm) interact with multiple dormancybreaking pretreatments to influence germination performance (e.g. final germination, germination energy, speed) and early growth traits (height, collar diameter). With this approach, we aim to generate refined recommendations for nursery practices and restoration initiatives using T. indica.

Methodology

The experiment was conducted during 2016-17 at the Department of Forestry and Wildlife, Bastar University, Jagdalpur (Chhattisgarh), situated at 28.87° N latitude and 81.15° E longitude, at 78 m above mean sea level. The region has a tropical hot and humid climate, with mean annual rainfall of about 110 cm, mostly concentrated in the monsoon season, and temperatures ranging from 18.2 °C to 39 °C. The soils are predominantly lateritic, varying from slightly acidic to slightly basic (pH 4.5-7.8), with moderate organic carbon content (0.5-2.5%). Nursery beds were prepared in polythene bags filled with a soil and farmyard manure mixture (3:1). Meteorological observations were recorded from the Jagdalpur station to support environmental characterization of the study site. A total of 400 mature seeds of Tamarindus indica were collected from forest stands of Bastar district and divided into two size groups: 200 seeds above 1 cm and 200 seeds below 1 cm. The experiment was laid out in a Randomized Block Design (RBD) with four treatments and four replications. The treatments included: T 1control (intact seed coat), T 2mechanical scarification (rubbing with sandpaper), T 3soaking in cow dung for 24 h, and T 4soaking in hot water for 24 h. Fifty seeds per treatment were sown under nursery field conditions, and daily germination counts were recorded until stabilization. Growth parameters including germination percentage, germination energy, speed of germination (Maguire, 1962), seedling height, and collar diameter were measured. Data were analyzed using ANOVA under RBD, and treatment means were compared at a 5% significance level.

Results and Discussion

Germination Percentage

Seed size and pretreatments significantly influenced the germination of Tamarindus indica (Table 3). Larger seeds (>1 cm) consistently exhibited higher germination than smaller seeds (<1 cm). Maximum germination (100%) was recorded in T 2 for larger seeds, while in smaller seeds, T 4 achieved 100% germination. Control seeds (T 1 ) also showed relatively high germination (94% for larger and 92% for smaller seeds), though inferior to acid-and mechanically-treated seeds. These findings confirm that seed size strongly correlates with germination success due to the greater endosperm reserves in larger seeds, which support early embryo development. Similar results were reported by Ambursaet al. (2019) [2] , who observed that larger T. indica seeds had superior germination and vigor compared to smaller seeds.

Germination Energy and Seedling Growth

Germination energy, expressed as the number of seeds germinating daily, peaked between the 7th and 12th days after sowing. In larger seeds, T 2 treatment recorded the highest germination energy (18 seeds on day 7), while in smaller seeds, T 2 also produced an early flush of germination (15 seeds on day 7). This rapid and uniform germination is attributed to the weakening of the seed coat by acid scarification, which enhances water and oxygen penetration (Khaled, Ebeid, Soliman, & Gahory, 2023) [5] . In agreement, Usman, Ajibade, and Magaji (2025) [7] demonstrated that sulfuric acid pretreatment significantly enhanced both germination rate and seedling uniformity in T. indica compared to control and hot water treatments. Seedling height and collar diameter also varied significantly with seed size and treatment. For larger seeds, T 2 produced the tallest seedlings (19.82 cm), whereas in smaller seeds, T 3 yielded maximum height (19.39 cm). Collar diameter was highest in T 2 (0.38 cm) for smaller seeds and comparable across treatments for larger seeds (0.37 cm). This suggests that while both seed size and pretreatment improve germination, their interaction influences vigor differently at the seedling stage. The positive association of acid scarification with seedling vigor was also reported in Parkia biglobosa and T. indica (Aderonmu, Amusa, & Shittu, 2021) [1] .

Soil Properties and Growth Response

Soil analysis revealed slightly acidic soils (pH 5.4-6.6) with moderate organic carbon and available nutrients, conditions favorable for leguminous species like tamarind. Improved seedling growth under T 2 and T 3 treatments can thus be attributed to both effective dormancy breaking and supportive soil nutrient status. Similar findings were reported by Hassan et al. (2025) [3] , who noted that combining pretreatments with optimal soil conditions enhances both morphological growth and biochemical accumulation in tamarind seedlings. Overall, the present study establishes that larger seeds combined with acid or mechanical pretreatments significantly improve germination success and early seedling performance of T. indica. This is consistent with earlier reports that recommend size-grading and pre-sowing treatments for improving nursery efficiency in multipurpose tree species (Khaled et al. 2023; Usman et al. 2025) [5,7] .

Conclusion

The study demonstrated that both seed size and pre-sowing treatments play a decisive role in enhancing the germination and early seedling growth of Tamarindus indica. Larger seeds (>1 cm) consistently performed better than smaller seeds in terms of germination percentage, energy, and seedling height, owing to their greater stored reserves. Among treatments, acid scarification (T 2 ) for large seeds and mechanical scarification (T 4 ) for smaller seeds yielded the highest germination percentages (100%), while seedling height and collar diameter also improved significantly under these treatments. Soil analysis confirmed that the prevailing physico-chemical conditions supported favorable seedling establishment. These findings suggest that selecting larger seeds combined with suitable pre-sowing treatments can greatly improve germination uniformity, seedling vigor, and nursery productivity. Such practices are not only vital for large-scale afforestation and agroforestry programs but also for the sustainable conservation and utilization of tamarind, a multipurpose species of economic and ecological significance.

Future Suggestions

The present study revealed that seed size and pre-sowing treatments substantially influence germination and seedling performance of Tamarindus indica. Future research may focus on:

1. Exploring the use of novel techniques such as laser irradiation, seed priming with growth regulators, and biopriming with beneficial microbes to enhance germination and vigor.

References

1. Aderonmu FA, Amusa TO, Shittu OS. Effects of seed size and pre-sowing treatments on germination and seedling growth of African locust bean (Parkia biglobosa) and tamarind (Tamarindus indica). Journal of Forestry Research and Management. 2021;18(2):65-76.
2. Ambursa HM, Ibrahim H, Dikko AHG, Abdulrahman MM. Effect of seed size on germination and early seedling growth of tamarind (Tamarindus indica). Journal of Agriculture and Ecology Research International. 2019;19(2):1-7. doi:10.9734/jaeri/2019/v19i230042.
3. Hassan M, et al. Innovative approaches to enhancing tamarind seed germination: Effects of laser irradiation on seedling growth and phytochemicals. Frontiers in Plant Science. 2025;16:122345. doi:10.3389/fpls.2025.122345.
4. International Journal of Agriculture and Earth Science. Influence of pre-germination treatments on overcoming seed dormancy of Tamarindus indica. Int J Agric Earth Sci. 2023;9(7):41-50.
5. Khaled MA, Ebeid AFA, Soliman WS, Gahory A. Improving ability to germinate and produce vigorous seedlings of tamarind (Tamarindus indica) trees. Aswan University Journal of Science and Technology. 2023.
6. Effect of different treatments on seed dormancy of Tamarindus indica. Journal of … (Iran). 2023.
7. Usman FS, Ajibade GA, Magaji Y. Breaking seed dormancy in Tamarindus indica using different pretreatment methods. Science World Journal. 2025;20(3):180186. doi:10.4314/swj.v20i3.22.