Influence of gibberellic acid and bio-inoculants on germination, growth and root development of Aonla (Emblica officinalis Gaertn.) seedlings

Introduction

Aonla (Emblica officinalis Gaertn.), commonly known as Indian gooseberry, is an important indigenous fruit crop valued for its nutritional, medicinal and therapeutic properties. The fruit is a rich source of vitamin C, polyphenols, tannins, phenolic compounds, minerals and antioxidants, contributing substantially to its high nutraceutical value. Its hardiness, wide adaptability and tolerance to adverse soil and climatic conditions make it suitable for diverse agro-ecological regions (Singh and Pathak, 1987) [17] . However, the production of uniform and vigorous planting material is constrained by slow and erratic seed germination associated with the hard stony endocarp and physiological dormancy (Khan and Srivastava, 2013) [7] . Pre-sowing treatment with gibberellic acid (GA₃) helps overcome seed dormancy by stimulating hydrolytic enzyme activity, mobilizing stored reserves and promoting embryo growth, thereby improving germination and seedling vigour (Yamaguchi, 2008) [20] . Its beneficial effects on aonla seed germination and seedling development have also been reported by Chiranjeevi et al. (2017) [4] . Likewise, bio-inoculants such as Azospirillum, Azotobacter and phosphate-solubilizing bacteria (PSB) promote seedling growth through nitrogen fixation, phosphorus solubilization, improved nutrient availability and phytohormone production (Vessey, 2003) [18] . Therefore, the present investigation was undertaken to evaluate the influence of GA₃ and bio-inoculants on germination, growth, root development and seedling vigour of aonla under nursery conditions.

The treatments were T₀ = Control, T₁ = Water soaking for 24 hours, T₂ = Cow urine @ 5 ml/kg rooting media, T₃ = Cow urine @ 10 ml/kg rooting media, T₄ = GA₃ @ 200 ppm for 24 hours soaking, T₅ = GA₃ @ 500 ppm for 24 hours soaking, T₆ = Azospirillum @ 5 ml/kg rooting media, T₇ = Azospirillum @ 10 ml/kg rooting media, T₈ = Azotobacter @ 5 ml/kg rooting media, T₉ = Azotobacter @ 10 ml/kg rooting media, T₁₀ = PSB @ 5 ml/kg rooting media, T₁₁ = PSB @ 10 ml/kg rooting media, T₁₂ = bio-inoculant consortium @ 5 ml/kg rooting media and T₁₃ = bio-inoculant consortium @ 10 ml/kg rooting media. Healthy and uniform aonla seeds were sown in 15 × 20 cm polybags filled with soil, sand and welldecomposed FYM in a 2:1:1 ratio. Seeds under GA₃ and water-soaking treatments were soaked for 24 hours, while cow urine and bio-inoculants were mixed with the rooting media as per the respective treatments. One seed was sown per polybag and uniform cultural practices were followed throughout the experimental period. Observations were recorded on days taken to initiate germination, days taken to 50% germination, germination percentage, seedling height, number of leaves per seedling, collar diameter, root length, number of primary roots and number of secondary roots. Seedling height, number of leaves and collar diameter were recorded at 30, 60, 90 and 120 days, while root parameters were recorded at 120 days. The experimental data were subjected to analysis of variance (ANOVA) for CRD and treatment differences were tested for significance at the 5 per cent level.

Results and Discussion

Germination parameters Days taken to initiate germination

As per the data presented in Table 1, the different treatments significantly influenced the time required for initiation of germination in aonla. The earliest germination (6.16 days) was recorded under T₅ (GA₃ @ 500 ppm for 24 hours soaking), which was statistically at par with T₄ (GA₃ @ 200 ppm for 24 hours soaking), recording 6.20 days, whereas the maximum time (10.27 days) was observed under T₀ (control). The reduction in germination time under GA₃ treatments might be attributed to enhanced enzymatic activity and rapid mobilization of stored food reserves, promoting embryo growth and seedling emergence. These findings are in close agreement with Lalitha et al. (2020) [10] , Singh and Kaur (2021) [16] and Baby et al. (2022) [1] , who also reported earlier germination and seedling emergence in aonla with GA₃ treatments.

Days taken to 50 per cent germination

Among the different treatments, T₅ (GA₃ @ 500 ppm with 24 hours soaking) recorded the shortest duration to attain 50 per cent germination (16.62 days) and was statistically at par with T₄ (GA₃ @ 200 ppm with 24 hours soaking), which recorded 16.91 days. In contrast, the longest duration (23.29 days) was observed under T₀ (control). The faster attainment of 50 per cent germination under GA₃ treatments might be attributed to enhanced enzymatic activity and efficient mobilization of stored food reserves, which stimulated embryo growth and promoted rapid and uniform germination. These findings are in close conformity with those of Dhankhar and Singh (1996) [5] , Gholap et al. (2000) [6] and Chiranjeevi et al. (2017) [4] , who also reported improved germination behaviour and earlier germination in aonla following GA₃ application.

Among the different treatments evaluated, T₅ (GA₃ @ 500 ppm with 24 hours soaking) exhibited the highest germination percentage (91.11%), followed by T₄ (GA₃ @ 200 ppm with 24 hours soaking) (88.89%), while T₀ (control) recorded the lowest germination (55.56%). The superior germination observed with GA₃ application could be associated with its ability to overcome seed dormancy and activate hydrolytic enzymes, resulting in efficient utilization of stored food reserves and enhanced embryo development also documented by Kumari et al. (2007) [8] , Laishramlilabati and Sahoo (2015) [9] and Lalitha et al. (2020) [10] .

Seedling height increased progressively across the growth period and varied among the treatments. T₅ (GA₃ @ 500 ppm) recorded the maximum seedling height of 8.35, 10.26, 12.68 and 15.24 cm at 30, 60, 90 and 120 DAS, respectively. At 120 DAS, it was followed by T₇ (Azospirillum @ 10 ml/kg rooting media) with 14.96 cm and T₄ (GA₃ @ 200 ppm) with 14.83 cm, while the minimum (9.86 cm) was recorded under T₀ (control). The enhanced growth may be attributed to GA₃induced cell division and elongation and improved nutrient availability and growth-promoting activity of Azospirillum. Similar findings were reported by Bhadauria et al. (2000) [2] and Rajamanickam and Anbu (2001) [14] .

Number of leaves per seedling

The number of leaves per seedling increased progressively with seedling age and varied significantly among the treatments. T₅ (GA₃ @ 500 ppm with 24 hours soaking) recorded 4.60, 5.03, 8.00 and 10.20 leaves at 30, 60, 90 and 120 DAS, respectively, followed by T₄ (GA₃ @ 200 ppm) with 4.00, 5.01, 7.11 and 9.40 leaves, respectively. At 120 DAS, the minimum number of leaves (5.80) was recorded under T₀ (control). The increased leaf production under GA₃ treatment might be attributed to enhanced cell division, elongation and vigorous shoot development, resulting in greater leaf formation and expansion. Similar favourable effects of GA₃ on leaf production in aonla seedlings were reported by Bhujbal (1975) [3] and Wagh et al. (1998) [19] .

Collar diameter increased progressively with seedling growth and varied among the treatments. T₅ (GA₃ @ 500 ppm with 24 hours soaking) recorded the maximum collar diameter of 1.32, 1.75, 3.00 and 3.38 mm at 30, 60, 90 and 120 DAS, respectively, followed by T₄ (GA₃ @ 200 ppm) with 1.30, 1.73, 2.91 and 3.21 mm, respectively, while the minimum collar diameter (2.54 mm at 120 DAS) was observed under T₀ (control). The improvement under GA₃ treatments may be attributed to enhanced cell division, expansion and nutrient mobilization, promoting better stem development and biomass accumulation. Similar findings were reported by Mane et al. (2018) [11] and Manekar et al. (2011) [12] .

Root development varied considerably among the treatments, with the maximum root length (14.39 cm) recorded under T₀ (control) at 120 DAS, followed by T₇ (Azospirillum @ 10 ml/kg rooting media) with 14.02 cm and T₅ (GA₃ @ 500 ppm with 24 hours soaking) with 13.80 cm. The greater root elongation observed in untreated seedlings might be associated with relatively greater allocation of assimilates towards root extension, whereas the favourable response under Azospirillum treatment could be attributed to improved nutrient availability and the production of growth-promoting substances in the rhizosphere. Similar beneficial effects of bio-inoculants on root development and seedling growth were reported by Meena et al. (2018) and Raut et al. (2015) [13, 15] .

Number of primary roots

The number of primary roots varied significantly among treatments, with the maximum (38.18) recorded under T₅ (GA₃ @ 500 ppm), followed by T₄ (GA₃ @ 200 ppm) with 34.82 roots. Among bio-inoculants, T₉ (Azotobacter @ 10 ml/kg rooting media) recorded 28.78 roots, while the minimum (13.78) was observed in the control. The improved root development under GA₃ may be attributed to enhanced cell division, elongation and mobilization of stored reserves, whereas bio-inoculants promoted root growth through improved nutrient availability and rhizospheric activity. These favourable physiological and nutritional effects might have stimulated greater root initiation and proliferation, resulting in a more developed root system. Similar findings were reported by Meena et al. (2018) and Raut et al. (2015) [13, 15] .

Number of secondary roots

The maximum number of secondary roots (49.77) was recorded under T₅ (GA₃ @ 500 ppm), followed by T₄ (GA₃ @ 200 ppm) with 47.62, while T₉ (Azotobacter @ 10 ml/kg rooting media) recorded 41.57. The increase in secondary roots may be attributed to enhanced cell division, root initiation and nutrient availability, promoting better root branching. Moreover, the favourable response to Azotobacter could be associated with improved nutrient mobilization and rhizospheric activity, supporting root proliferation. Similar improvement in secondary root development of aonla was reported by Wagh et al. (1998) [19] .

Conclusion

The present study demonstrated that pre-sowing treatments with GA₃ and bioinoculants significantly improved germination and seedling growth of aonla. Among the treatments, GA₃ @ 500 ppm with 24 hours soaking (T₅) showed superior performance for most germination and growth parameters. It promoted faster germination, higher germination percentage, greater seedling height, leaf production, collar diameter and enhanced root development.

The improved response under GA₃ treatment may be attributed to enhanced physiological activity, efficient mobilization of stored reserves and stimulation of cell division and elongation. Bio-inoculants also improved seedling establishment and root development through better nutrient availability and rhizospheric activity. GA₃ @ 200 ppm (T₄) also exhibited consistently favourable results. Overall, GA₃ @ 500 ppm with 24 hours seed soaking proved to be the most effective pre-sowing treatment for producing vigorous and well-established aonla seedlings under nursery conditions.

References

1. Baby G, Reddy PVK, Harshavardhan A, Suneetha DRS. Effect of seed priming and different growing conditions on germination and seedling vigour of aonla (Emblica officinalis Gaertn.). The Pharma Innovation Journal. 2022;11(8):1294-1297.
2. Bhadauria S, Pahari GK, Kumar S. Effect of Azospirillum biofertilizer on seedling growth and seed germination of Emblica officinalis. Indian Journal of Plant Physiology. 2000;5(2):177-179.
3. Bhujbal BG. Improvement in seed propagation of aonla (Phyllanthus emblica L.). Research Journal of Mahatma Phule Krishi Vidyapeeth. 1975;6(1):73-75.
4. Chiranjeevi MR, Muralidhara BM, Sneha MK, Shivanand H. Effect of growth regulators and biofertilizers on germination and seedling growth of aonla (Emblica officinalis Gaertn.). International Journal of Current Microbiology and Applied Sciences. 2017;6(12):1320-1326.
5. Dhankhar DS, Singh M. Seed germination and seedling growth in aonla (Phyllanthus emblica Linn.) as influenced by gibberellic acid and thiourea. Crop Research. 1996;12(3):363-366.
6. Gholap SV, Dod VN, Bhuyar SA, Bharad SG. Effect of plant growth regulators on seed germination and seedling growth in aonla (Phyllanthus emblica L.) under climatic condition of Akola. Crop Research. 2000;20(3):546-548.
7. Khan M, Srivastava R. Studies on seed germination and seedling growth in aonla (Emblica officinalis Gaertn.). 2013.
8. Kumari R, Sindhu SS, Sehrawat SK, Dudi OP. Germination studies in aonla (Emblica officinalis Gaertn.). Haryana Journal of Horticultural Sciences. 2007;36(1-2):9-11.
9. Laishramlilabati, Sahoo UK. Effect of pre-treatments on seed germination and seedling vigor of Emblica officinalis Gaertn. Global Journal of Advanced Research. 2015;2(10):1520-1526.
10. Lalitha KR, Tank RV, Chawla SL, Jena S. Effect of chemicals on seed germination and seedling growth of aonla (Emblica officinalis Gaertn.). The Pharma Innovation Journal. 2020;9(12):239-243.
11. Mane SB, Naglot UM, Parse R. Effect of different presowing treatments on shoot growth of custard apple (Annona squamosa L.). Journal of Pharmacognosy and Phytochemistry. 2018;5(5):1945-1947.
12. Manekar RS, Sable TB, Rane MM. Influence of different plant growth regulators on seed germination and subsequent seedling growth of aonla (Emblica officinalis Gaertn.). Green Farming. 2011;2(4):477-478.
13. Meena RK, Sharma N, Yadav P. Effect of biofertilizers on root development and seedling growth of aonla (Emblica officinalis Gaertn.). Journal of Pharmacognosy and Phytochemistry. 2018;7(6):1100-1104.
14. Rajamanickam C, Anbu S. Effect of biofertilizers and growth regulators on germination and seedling vigour of aonla (Emblica officinalis Gaertn.). South Indian Horticulture. 2001;49(1-6):45-47.
15. Raut UA, Patil MB, Deshmukh PP. Effect of microbial inoculants on growth and vigour of aonla seedlings. Asian Journal of Horticulture. 2015;10(1):65-69.
16. Singh S, Kaur A. Effect of various treatments on seed germination and seedling vigour of aonla cv. Chakaiya. Indian Journal of Agricultural Research. 2021;55(5):614-618.
17. Singh IS, Pathak RK. Evaluation of aonla (Emblica officinalis Gaertn.) varieties for processing. Acta Horticulturae. 1987;208:173-177.
18. Vessey JK. Plant growth promoting rhizobacteria as biofertilizers. Plant and Soil. 2003;255(2):571-586.
19. Wagh AP, Choudhari MH, Kulwal LW, Jadhav BJ, Joshi PS. Effect of seed treatment on germination of seed and initial growth of aonla seedling in polybag. PKV Research Journal. 1998;22(2):176-177.
20. Yamaguchi S. Gibberellin metabolism and its regulation. Annual Review of Plant Biology. 2008;59:225-251.