Effect of Ga3, Nano zinc and Nano boron on seed germination, plant growth and establishment of Papaya cv. Red lady

Introduction

Papaya (Carica papaya L.), often called the "wonder fruit of the tropics," is native to tropical America (Hafmer, 1990) [11] . It was introduced to India via Malacca from the Philippines in the early sixteenth century (Singh, 1990). It belongs to the family Caricaceae, consisting of six genera and about 35 species, and its closest relative is Vasconellea with 21 species. Initially grown in home gardens, papaya's adaptability to diverse soils and climates with year-round fruiting helped transform it into a major commercial crop (Drew et al., 1998). India currently leads global papaya production, though annual yields fluctuate due to its short lifespan. Key producing states include Andhra Pradesh, Gujarat, Karnataka, Madhya Pradesh, Maharashtra, West Bengal, Chhattisgarh, Tamil Nadu, Assam, Kerala and Uttar Pradesh (Sharma et al., 2023). In 2023, papaya cultivation in India covered approximately 146,000 ha with an output of 5.54 million t (NHB, 2023), and around 5.95 million t were estimated in the fiscal year 2020-21 (Anonymous, 3rd estimate). Its low input requirements, rapid growth and high profitability have made it a widely cultivated fruit crop. Papaya is valued for its nutritional and therapeutic properties. It contains the digestive enzyme papain, antioxidants such as lycopene, and carotenoid pigments like caricaxanthin. These compounds exhibit anticancer potential, with papaya juice showing et al activity against liver cancer cells (Meena et al., 2017) [14] . Regular consumption may reduce the risk of cardiovascular diseases, diabetes and cancer. A small papaya (150 g) contains 59 kcal, 157% of the RDI for vitamin C, 33% for vitamin A, 14% folate, 11% potassium, trace minerals including calcium and magnesium, vitamins B₁, B₃, B₅, E and K, 3 g fiber, 1 g protein and 15 g carbohydrates (Hardisson et al., 2001) [12] . Papain is used in food processing and pharmaceuticals for protein digestion, meat tenderization and therapeutic applications (Dayeswari et al., 2017;Quenum, 2001) [7, 19] . Papaya is a semi-woody, usually unbranched evergreen tree reaching 5-10 m in height, with large palmately lobed leaves (120-125 cm petioles) clustered at the apex. It is a polygamous species with male, female and hermaphrodite flowers. Hermaphrodite flowers, which bear both stamens and pistils, produce the edible fruits. Fruits range from cylindrical to pyriform (12-45 cm long, 10-30 cm diameter) and change colour from green to yellow-orange when ripe. Seeds are black and located in a central cavity, while the orange flesh owes its colour to carotenoids like caricaxanthin. Propagation is mainly by seed, though germination is often slow and irregular due to the gelatinous sar. Removing this layer, rinsing seeds, and pre-soaking them in plant growth regulators improve germination and seedling vigour. Gibberellic acid (GA₃) is particularly effective at breaking dormancy and enhancing germination by mobilizing seed reserves (Bharadwaj, 2014;Mishra et al., 2017; Zanotti & Barros, 2014) [3, 15, 24] .

Micronutrients like zinc and boron play a vital role in papaya growth and reproductive success. Zinc (Zn²⁺) is essential for enzyme activation, auxin synthesis, gene regulation, pollen production and oxidative stress protection (Brown et al., 1993;Hafees et al., 2013) [5, 10] . Boron is involved in sugar translocation, pollen-tube growth, fruit set and quality enhancement (Brady & Weil, 1996; Abd-Allah, 2006) [4, 1] . Foliar boron application reduces fruit cracking and improves yield in many fruit crops. Nanofertilizer application can increase nutrient efficiency and reduce environmental impact.

Methods and Materials

The experiment was conducted in 2024 at Shade Net-2, Department of Horticulture, Sam Higginbottom University of Agriculture, Technology and Sciences (SHUATS), Prayagraj. The site is located at 25.85° N latitude and 81.15° E longitude, at an altitude of 78 m above mean sea level. Prayagraj falls in a subtropical climate, where summer temperatures can exceed 48 °C and winters may drop to around 20 °C, occasionally with light frost. Hot, dry winds are frequent in summer, and the region receives an annual average rainfall of approximately 1013 mm, mainly during July to September. Weather data for the 2024-25 experimental period were obtained from the SHUATS agrometeorological observatory. Seeds of papaya (Carica papaya) cv. Red Lady were procured from Krishi Paramarsh Kendra, Alopi Bagh, Prayagraj. Polybags (4 × 5 cm; 150 gauge) were sourced locally. Pot trays were prepared using a 1:1:1 mixture of soil, farmyard manure (FYM) and cocopeat, treated with copper oxychloride @ 2% as a fungicide. Single seeds were sown per cell, and light irrigation was provided twice daily, avoiding waterlogging. Before sowing, seeds were soaked in GA₃ @ 200 ppm for 24 hours to enhance germination.

Results and Discussion

Days taken for germination in Papaya -The minimum days taken for completion of germination (7.40) was recorded in T7 Nano Boron at 25 mg/L. While maximum days taken for completion of germination (9.70) were recorded in T0 (control). Nano zinc and nano boron treatments significantly improved germination over the control (69.39%), with the highest rate (91.78%) in Nano Boron at 25 mg/L (T7), followed by T6 (20 mg/L) and T3 (Nano Zinc 30 mg/L). Optimal concentrations outperformed higher doses, and statistical validation (CD = 2.10, CV = 1.52%) confirmed the reliability of results. These findings, in line with (An et al. Germination percentage in Papaya -The maximum germination percentage (91.70%) was recorded in T7 Nano Boron at 25 mg/L. While minimum germination percentage (63.39%) was recorded in T0 (control). Nano zinc and nano boron treatments markedly increased germination over the control (69.39%), with the highest value (91.78%) in Nano Boron at 25 mg/L (T7), followed by T6 (20 mg/L) and T3 (Nano Zinc 30 mg/L). Higher doses showed no further benefit, and statistical analysis (CD = 2.10, CV = 1.52%) confirmed the reliability of results. In line with (An et al. 2022) and (Biradar et al. 2023) these findings highlight nanoparticles as effective in enhancing seed viability and crop productivity in Prayagraj. Seedling height (cm) in Papaya -The maximum seedling height recorded at 30 days (7.91 cm), 60 days (14.32 cm) and 90 days (20.88 cm) in T7 (Nano Boron at 25 mg/L). While minimum seedling height was recorded at 30 days (6.13cm), 60days (9.97cm) and 90 days (14.80 cm) in T0 (control). Nano zinc and nano boron markedly increased seedling height at all stages (30, 60, and 90 DAS) over the control (14.80 cm at 90 DAS), with Nano Boron at 25 mg/L (T7) achieving the tallest growth (20.88 cm). The improvements, supported by statistical significance and a low CV (1.4%), are attributed to enhanced nutrient uptake and metabolic activity (An et al., 2022). These results, consistent with (Biradar et al. 2023) demonstrate the potential of nanotreatments for vigorous seedling establishment and better crop performance in regions like Prayagraj. No. of leaves in Papaya -The maximum number of leaves was recorded at 30 days (6.00), 60days (12.00) and 90 days (18.07) in T7 (Nano Boron at 25 mg/L). While minimum number of leaves recorded at 30 days (4.40), 60 days (8.80) and 90 days (12.87) in T0 (control). Nano zinc and nano boron significantly increased leaf number at all stages (30, 60, and 90 DAS) compared to the control (12.87 leaves at 90 DAS), with Nano Boron at 25 mg/L (T7) producing the highest count (18.07 leaves). These gains, confirmed by statistical significance (CD = 1.12) and a low CV (4.11%), are linked to enhanced photosynthesis and plant health (An et al., 2022). Consistent with (Biradar et al. 2023) the results show nano-nutrients as an effective means of promoting vigorous vegetative growth and improving yield potential in regions like Prayagraj. Stem diameter (mm) in Papaya -The maximum stem diameter was recorded at 30 days (1.31 mm), 60 days (7.28 mm) and 90 days (13.22 mm) in T7 (Nano Boron at 25 mg/L). While minimum stem diameter was recorded at 30 days (0.81 mm), 60 days (5.27 mm) and 90 days (9.54 mm) in T0 (control). Nano zinc and nano boron significantly increased stem diameter at all growth stages compared to the control (9.54 mm at 90 DAS), with Nano Boron at 25 mg/L (T7) producing the maximum girth (13.22 mm). These improvements, confirmed by statistical significance (CD = 0.60) and a low CV (2.90%), enhance plant structure and nutrient transport (An et al., 2022). Consistent with (Biradar et al. 2023) the results highlight nano-nutrients as an effective approach for stronger, more productive crops in regions like Prayagraj.

Chlorophyll content (SPAD Value) in Papaya:

The maximum chlorophyll content was recorded at 30 days (31.95), 60 days (28.63) and 90 days (32.18) in T7 (Nano Boron at 25 mg/L). While the minimum chlorophyll content was recorded at 30 days (25.17), 60 days (28.63) and 90 days (32.18) in T0 (control). Nano zinc and nano boron significantly increased chlorophyll content (SPAD value) at all stages compared to the control (32.18 at 90 DAS), with Nano Boron at 25 mg/L (T7) recording the highest value (38.54). These gains, statistically significant (CD = 1.69) with a low CV (2.80%), enhance photosynthetic efficiency and plant health (An et al., 2022). In agreement with (Biradar et al. 2023), the results indicate nano-nutrients as a promising approach to improve crop productivity in regions like Prayagraj.

Leaf Area (cm 2 ) in Papaya: The maximum leaf area was recorded at 60 days (54.34 cm2) and 90 days (71.29 cm2) in T7 (Nano Boron at 25 mg/L). While the minimum leaf area was recorded at 60 days (32.19 cm2) and 90 days (57.83 cm2). Nano zinc and nano boron significantly increased chlorophyll content (SPAD value) at all stages compared to the control (32.18 at 90 DAS), with Nano Boron at 25 mg/L (T7) recording the highest value (38.54). These gains, statistically significant (CD = 1.69) with a low CV (2.80%), enhance photosynthetic efficiency and plant health (An et al., 2022). In agreement with (Biradar et al. 2023), the results indicate nano-nutrients as a promising approach to improve crop productivity in regions like Prayagraj. Leaf Area Index in Papaya -The maximum leaf area index was recorded at 60days (13.78) and 90 days (17.46) in T7 (Nano Boron at 25 mg/L). While the minimum leaf area index at 60 days (9.51) and 90 days (15.09) in T0 (control). Nano zinc and nano boron significantly increased Leaf Area Index (LAI) at 60 and 90 DAS compared to the control (15.09 at 90 DAS), with Nano Boron at 25 mg/L (T7) recording the highest value (17.46). These statistically significant improvements (CD = 1.21) with a low CV (3.50%) enhance light interception and photosynthesis (An et al., 2022). In line with (Biradar et al. 2023), the results confirm nano-nutrients as an effective approach for optimizing canopy development and boosting crop productivity in regions like Prayagraj.

Specific Leaf Area in Papaya:

The maximum specific leaf area was recorded at 60 days (1.04 cm 2 mg-1) and 90 days (1.15 cm 2 mg-1) in T7 (Nano Boron at 25 mg/L). While minimum specific leaf area was recorded at 60 days (0.83 cm 2 mg-1) and 90 days (0.93 cm 2 mg-1) in T0 (control). Nano zinc and nano boron significantly increased Specific Leaf Area (SLA) at 60 and 90 DAS, with treated plants developing thinner, more expansive leaves for improved light absorption. Nano Boron at 25 mg/L (T7) recorded the highest SLA (1.15 cm² mg⁻¹ at 90 DAS). These statistically significant gains, supported by a low CV (1.80%), enhance photosynthetic efficiency and plant productivity (An et al., 2022). Consistent with (Biradar et al. 2023), the findings show nano-nutrients as an effective means to optimize plant structure and boost crop performance in regions like Prayagraj.

Shoot: Root ratio in Papaya:

The maximum shoot: root ratio was recorded at 60days (3.78) and 90 days (4.19) in T7 (Nano Boron at 25 mg/L). While minimum shoot: root ratio was recorded at 60 days (2.75) and 90 days (3.80) in T0 (control). Nano zinc and nano boron significantly increased the shoot: root ratio at 60 and 90 DAS compared to the control (3.80 at 90 DAS), with Nano Boron at 25 mg/L (T7) recording the highest value (4.19), followed by Nano Zinc at 40 mg/L (T4) with 4.04. These statistically significant gains (CD = 0.08) and the very low CV (1.2%) indicate enhanced biomass allocation to shoots, boosting photosynthesis and productivity (An et al., 2022). In agreement with (Biradar et al. 2023), the results confirm nano-nutrients as a reliable strategy for balanced growth and higher yields in regions like Prayagraj. Absolute Growth rate in Papaya -The maximum absolute growth rate was recorded at 90 days (0.21 cm day-1) in T7 (Nano Boron at 25 mg/L). While minimum absolute rate was recorded at 90 days (0.15 cm day-1) in T0 (control). Nano zinc and nano boron significantly increased the Absolute Growth Rate (AGR) by 90 DAS compared to the control, with Nano Boron at 25 mg/L (T7) recording the highest value (0.21 cm day⁻¹). This improvement, confirmed by statistical significance (CD = 0.02) and a low CV (6.3%), supports faster biomass accumulation and potential for earlier harvests (An et al., 2022). In line with (Biradar et al. 2023), the results highlight nano-nutrients as an effective strategy to enhance growth dynamics and agricultural productivity in regions like Prayagraj. Survival percentage in Papaya -The maximum survival percentage was 84.83% recorded in T7 (Nano Boron at 25 mg/L). While minimum survival percentage was 59.17% recorded in T0 (control). Nano zinc and nano boron significantly improved plant survival over the control (59.17%), with Nano Boron at 25 mg/L (T7) recording the highest rate (84.83%), followed by T6 (20 mg/L) and T2 (Nano Zinc 20 mg/L). These statistically significant gains (CD = 1.41) with a very low CV (1.1%) enhance crop establishment and yield potential (An et al., 2022). Consistent with (Biradar et al. 2023), the findings confirm nano-nutrients as an effective approach to boost plant resilience in regions like Prayagraj. Economic evaluation revealed that T₇ generated net returns of ₹25,178.60 per 1000 plants with a benefit-cost ratio of 1.94, highlighting its commercial viability. The superior performance of nano boron is attributed to its higher bioavailability, efficient nutrient delivery, and its role in cell wall synthesis, sugar transport, and metabolic activities. This integrated approach provides a sustainable and profitable solution to the challenges of poor germination and weak seedling vigour in papaya. It establishes a practical protocol for nurseries and supports the adoption of nanotechnology in tropical fruit crop production systems.

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