Effect of different plant growth regulators and chemicals on seed germination and seedling growth of Bael (Aegle marmelos L.) under shade net house

Introduction

Bael (Aegle marmelos L.) is an indigenous fruit tree of India belonging to the Rutaceae family and is well known for its medicinal, nutritional and economic importance. Bael is mainly propagated through seeds for raising rootstocks. However, its seeds exhibit deep dormancy and poor, irregular germination, which results in uneven seedling emergence and difficulty in producing uniform nursery planting material. Pre-sowing application of plant growth regulators and chemicals can help overcome these germination constraints. Gibberellic acid (GA₃) promotes germination by stimulating hydrolytic enzymes involved in mobilization of stored food reserves, while other chemicals such as thiourea, KNO₃ and salicylic acid may also improve germination and seedling establishment (Lawhale et al., 2020; Basra et al., 2007) [1,5] .

Materials and methods

The investigation was carried out during the summer season of 2024-2025 at Pt. Kishori Lal Shukla College of Horticulture and Research Station, Pendri, Rajnandgaon, Chhattisgarh, under shade-net house. The experiment was laid out in a Completely Randomized Design comprising 13 treatments, each replicated three times, with 20 seeds per treatment per replication and 780 seeds in total. The treatments consisted of T₀ -Control, T₁ -IBA @ 100 ppm, T₂ -IBA @ 150 ppm, T₃ -NAA @ 100 ppm, T₄ -NAA @ 150 ppm, T₅ -GA₃ @ 100 ppm, T₆ -GA₃ @ 150 ppm, T₇ -Thiourea @ 100 ppm, T₈ -Thiourea @ 150 ppm, T₉ -KNO₃ @ 100 ppm, T₁₀ -KNO₃ @ 150 ppm, T₁₁ -Salicylic acid @ 100 ppm and T₁₂ -Salicylic acid @ 150 ppm. A potting mixture of soil, sand and well-decomposed farmyard manure (1:1:1, v/v) was filled uniformly into black polyethylene bags provided with drainage holes. Working solutions of GA₃, IBA, NAA and salicylic acid were prepared by dissolving the required quantity initially in ethanol and making the volume up to one litre with distilled Water, whereas thiourea and KNO₃ were dissolved directly in slightly warm distilled water. Fully mature, healthy and uniform seeds were soaked for 24 hours in their respective treatment solutions at room temperature, while control seeds were soaked in distilled water. After treatment, seeds were gently rinsed with distilled water and immediately sown in the shade-net house, one seed per polybag at a depth of 1.5-2.0 cm. The medium was irrigated one day before sowing and seeds were covered with a thin layer of fine soil mixture. Uniform irrigation, weekly manual weeding and need-based plant protection measures were followed throughout the experiment. Observations were recorded on germination parameters viz., days required for first seed germination, days required for 50% germination, germination percentage and survival of plants. The data were statistically analysed using CRD and treatment differences were tested at 5% level of significance.

Results and discussion

Days required for first germination

The analysis of variance revealed significant variation among the different plant growth regulators and chemicals with respect to days required for initiation of germination in bael (Aegle marmelos L.) seeds. The minimum number of days required for first germination was recorded in T₆ (GA₃ @ 150 ppm) with 6.67 days, which was statistically at par with T₅ (GA₃ @ 100 ppm) recording 7.33 days. This was followed by T₈ (Thiourea @ 150 ppm) with 8.37 days and T₁₂ (Salicylic acid @ 150 ppm) with 9.63 days. The maximum number of days required for first germination was recorded in the control (T₀) with 14.33 days. The early germination under GA₃ treatment may be attributed to its role in overcoming physiological seed dormancy and stimulating hydrolytic enzyme activity, particularly αamylase, which facilitates rapid mobilization of stored food reserves for embryo growth. The findings are in accordance with Martinez et al. (2016) [6] , Sabarad et al. (2023) and Sagar et al. (2024) [8,9] , who reported beneficial effects of hormonal and chemical treatments in reducing germination time.

Days required for 50% germination: Significant differences were observed among the treatments for days required to attain 50% germination. T₆ (GA₃ @ 150 ppm) recorded the minimum time of 9.30 days, followed by T₅ (GA₃ @ 100 ppm) with 10.20 days and T₈ (Thiourea @ 150 ppm) with 11.40 days. The maximum period of 18.10 days was recorded in the untreated control (T₀), indicating delayed and non-uniform germination. The reduction in days required for 50% germination under GA₃ treatments may be attributed to its role in breaking seed dormancy and promoting faster germination, whereas the beneficial effect of thiourea may be associated with enhanced metabolic activity. Similar reductions in germination time following application of plant growth regulators have been reported by [4,5,10] .

Germination percentage

Pre-sowing treatments significantly influenced the final germination percentage of bael seeds. The highest germination percentage was recorded in T₆ (GA₃ @ 150 ppm) with 86.70%, followed by T₅ (GA₃ @ 100 ppm) with 84.48% and T₈ (Thiourea @ 150 ppm) with 81.68%. The treatments involving IBA, NAA and salicylic acid also improved germination over the control, with values ranging from 63.02 to 76.33%. The lowest germination percentage was recorded in the control (T₀) with 57.44%. The improvement in germination percentage under GA₃ treatment may be attributed to its role in breaking seed dormancy and enhancing enzymatic activity, thereby promoting faster and more uniform germination. The beneficial response to thiourea may be associated with enhanced metabolic activity and its role in overcoming dormancy. The present findings are in agreement with Lawhale et al. (2020) and Kumar et al. (2020) [4] , while Govind et al. (2024) [3,5] also reported higher germination percentage with GA₃ treatments in bael.

Survival

The survival percentage of bael seedlings under shade net house conditions was significantly influenced by different plant growth regulators and chemicals. Among all the treatments, the highest survival percentage was recorded in T₆ (GA₃ @ 150 ppm) with 91.33 percent, followed by T₅ (GA₃ @ 100 ppm) with 88.70 percent and T₁₂ (Salicylic acid @ 150 ppm) with 87.30 percent. In contrast, the lowest survival percentage (67.83) was observed in the control (T₀). The improved survival under GA₃ treatments may be attributed to its role in enhancing cell division and elongation, leading to vigorous seedling growth with better root and shoot development, which facilitates efficient uptake of water and nutrients. Salicylic acid treatments enhanced survival by improving stress tolerance, antioxidant activity, and membrane stability, thereby reducing seedling mortality. Similar results were also reported by Basra et al (2007) [1] in Melon, Govind et al. (2024) and Mutum et al. (2024) [3,7] in Bael. The present findings are in close agreement with Dhum et al. (2025) [2] , who reported improved survival in acid lime with seed priming treatments.

Conclution

Overall, among the different pre-sowing treatments, GA₃ @ 150 ppm (T₆) was found most effective for improving germination behaviour of bael, as it recorded the earliest first germination (6.67 days), minimum days required for 50% germination (9.30 days), maximum germination percentage (86.70%) and maximum survival of plant (91.33 percent).

References

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