Impact of variation in kernel nitrogen content on the growth performance of seedlings in a safflower core germplasm under different nitrogen levels

Introduction

Safflower is a minor oilseed crop belonging to the family Asteraceae and originating from the Middle East. A distinctive feature of safflower is its adaptation to hot, dry regions, supported by a taproot system that requires less water. It is mainly grown for its superior seed oil, which is rich in unsaturated fatty acids. Safflower is also an excellent forage crop due to its high quality (Bar-Tal et al., 2008) [5] , and its petal are used as a natural food colouring agent (Steberl et al., 2020) [18] . Favourable growth conditions for safflower typically occur during the winter season (Rabi), from October/November to March/April. Among the seven edible oils cultivated in India, safflower accounts for less than 3.71% of the production share. Maharashtra leads with the highest output of 0.26 lakh tonnes, followed by Karnataka with 0.14 lakh tonnes and Telangana with 0.03 lakh tonnes, together accounting for more than 90% of India's production. The area, production and productivity of safflower in India are 0.56lakh ha, 0.43 lakh tonnes, and 640kg ha -1 , respectively. Nitrogen is an essential macronutrient that plays an important role in plant growth and development. It is a main component of proteins and enzymes in leaves and acts as a functional system for photosynthesis, thereby influencing crop productivity. Seed nitrogen is a decisive factor during the initial stages of plant development. Proteins stored in the seeds serve as a major source of nitrogen during germination and seedling establishment. Before the root system becomes functional, the developing seedling relies on the nitrogen reserves stored in the seed to support cell division, tissue formation, and early growth. Many studies have reported that higher seed nitrogen is associated with increased seedling vigour when soil nutrients are low (Bulsani and Warner, 1980, Hara and Toriyama, 1998, Nedel et al., 1996; Parrish and Bazzaz, 1985; Ries, 1971, Tungate et al., 2002; Welch, 1999) [6,12,13,15,16,19,20] .

Materials and Methods

Location of the study

The proposed paper towel experiment was conducted at Soil Science Laboratory, in ICAR-Indian Institute of Oilseed Research, Hyderabad, Telangana, India.

Estimation of Seed nitrogen content in 100 safflower germplasm

The seeds were allowed to soak in water overnight, and the hull was carefully removed. After drying at 70 o C until constant weight, the N content was estimated in the Kernels. Kjeldahl digestion and distillation method was adopted as described by Jackson (1974). A 0.5 g of finely powdered kernel sample was weighed into a 250 mL digestion tube. For digestion, a 10 mL of conc. H₂SO₄ and 3-4 g of catalyst mixture (K₂SO₄ + CuSO 4 in a ratio of 5:1) were added to the tubes were placed in a Kelplus digestion unit and heated at 410°C for 3 hours till the digestion was completed by observing clear blue solution in the tubes. The test tubes were removed from the digestion chamber and cooled to room temperature. Each tube with the digested content was placed in the distillation unit. To a 250ml conical flask, 20 ml of 4% boric acid containing mixed indicator was taken in a 250 ml conical flask and placed under the receiver tube (dipped the receiver tube end in the boric acid). Then, 15 mL of 40% NaOH was added to the digestion tube, and the distillation process (running steam) was carried out for 6 minutes. After 6 minutes of distillation, the conical flask was removed and titrated with 0.02 N H₂SO₄ until the colour changed from bluish green to wine red. Nitrogen content was calculated from the titre value and expressed as percent dry weight of the kernel.

Paper towel experiment:

Ten safflower genotypes along with one check were selected for the paper towel experiment based on high kernel nitrogen content CGH-41(0.72%), CGH-85(0.64%), CGH-72 (0.61%) CGH-16(0.60%), CGH-118(0.57%), CGH-128(0.55%), CGH-128, (0.55%), CGH-13(0.52%) CGH-219(0.49%), CGH-104(0.44%) and check CGH-69 (0.25%).

Preparation of Hoagland's solution

The composition of macronutrient stock solution included: calcium nitrate (5.903g), magnesium sulphate (2.46g), and potassium dihydrogen phosphate (1.36g) dissolved in 100ml of double distilled water. The micronutrients stock solution comprised of boric acid (1.43g), manganese chloride (0.915g), zinc sulphate (0.11g), copper sulphate (0.025g), and sodium molybdate (0.06g) dissolved in 500ml of distilled water. The Fe-EDTA stock solution was prepared separately by mixing the required quantity of EDTA (5.2g) and ferrous sulphate (3.9g) in 500ml of distilled water. For the half (N1) and full (N2) strength nitrogen levels 5 mL and 10 mL of calcium nitrate stock solution are mixed in 1 L of water, respectively. Remaining nutrients are mixed constantly in 1 L of water in all the treatments (Arnon, D.I and Hoagland, 1950) [4] .

Paper towel experiment for germination and vigour

For this laboratory experiment, brown germination papers were moistened uniformly with distilled water, and the clean seeds were placed evenly on the top of the paper. Another wet germination paper was placed over the seeds. The double sheet was then folded at 1inch at the base and the sheets with the seeds were rolled carefully from one side to form a compact roll. Then each roll was labelled with the genotype number, treatment, and replication number, and secured with rubber bands at both ends. The rolls were placed with seed position upright in beakers containing Hoagland nutrient solution as per the treatment. The paper towels were maintained under suitable conditions for germination and seedling growth. After 10 days the paper towel was opened and recorded the following Observations such as root and shoot length, germination percentage, dry weight and the seedling vigour.

Statistical analysis

The data generated in the paper towel experiment was statistically analysed by adopting 2-factor CRD. Factor -1: 11 Genotypes and factor-2: 3 Nitrogen levels.

Results and Discussion

A set of 100 genotypes from safflower core was characterized for kernel nitrogen content. From the core, the 10 genotypes having high kernel nitrogen content along with check were selected for further studies to assess the germination and vigour test in a laboratory experiment adopting paper towel experiment.

Effect of different levels of nitrogen on growth parameters of the seedlings 3.1.1 shoot length

Among the genotypes, the shoot length values showed variation at the 10 th day of the germination. The genotype CGH-41 recorded the highest shoot length (11.2 cm) followed by CGH-278 (10.6 cm), CGH-85 (10.4 cm) and the lowest shoot length was recorded in check, CGH-69 (6.2 cm). Genotypes also showed variable response in shoot length with the application of external nitrogen levels. The highest mean shoot length was recorded due to nitrogen level N2 (10.5 cm), followed by N1 (9.6 cm) and N0 (8.3 cm) as shown in Table 1. The interaction effect of genotype and N levels on shoot length was found to be prominent. The genotype CGH-41 recorded the highest shoot length of 11.8cm due to N2 level of N application. This was followed by CGH-72 (11.7cm) with N2 level. However, at N0 level of N, genotype CGH-41 produced the highest shoot length of 10.4cm against check CGH-69 (5.4cm). The improved shoot growth may be due to increased nitrogen availability and genotypic differences in nitrogen utilization, promoting greater cell division and elongation leading to greater shoot growth. Similar findings were recorded by Slot et al (2013) [17] and Erbaş et al (2016) [9] . (2008) [1] , Abdurahman et al. (1999) [2] .

Germination percentage

Among the genotypes, the germination showed variation at the 10th day of observation. The genotype CGH-72 recorded highest germination (95.6%) followed by the genotype CGH-16 (94.8%) whereas the lowest germination was recorded in the check CGH-69 (78.9%) as shown in Table 3. Genotypes also showed variable response in germination to the application of external nitrogen levels. The germination percentage increased from 80.7% in N0 to 97.0% in N2. The interaction effect of genotype and N levels on germination was found to be prominent. The genotypes CGH-85, CGH-128 and CGH-118 were recorded 100% of germination due to N2 level of N application. However at N0 Level of N application the genotype CGH-72 recorded the highest germination 93.3% against the check (63.3%). The variation in germination percentage among the genotypes may be due to their differences in genetic makeup and seed nutrient reserves, which might have influenced seed viability and early seedling establishment. The findings are in agreement with Hara and Toriyama (1998) [12] .

Seedling vigour

The data presented in Table 4 showed that among the genotypes, seedling vigour varied significantly due to kernel N content. The highest vigour was noted in genotype CGH-278 (55.5g) followed by CGH-16 (46.9g) and lowest vigour was recorded in CGH-69 (14.2g). Genotypes also showed variable response in seedling vigour with the application of external nitrogen levels. The mean seedling vigour increased from 18.4 g in N1 to 39.1 g in N2 as presented in Table 4. The interaction effect of genotype and N levels on seedling vigour was found to be prominent. The genotype CGH -278 recorded the highest vigour 72.2cm due to the N2 level of N application. This was followed by the genotype CGH-16(60.1cm) at N2 level. However, at N0 level of N application the genotype CGH-278 was recorded highest vigour 37.5 cm against the check (7.6cm). Higher seed nitrogen improved overall seedling establishment and growth, that leads to greater vigour. The evidence was in support of Welch (1977) [21] , Evans and Bhatt (1977) [10] , Wen (2018) [22] .

seedling dry weight

The results presented in table 4 indicated that among the genotypes, the variation for dry weight was found to be significant and the highest dry weight was recorded for genotype CGH-278 (0.60 g) followed by CGH-16 (0.49 g) and lowest dry weight was recorded for CGH-69 (0.18 g). Genotypes also showed variable response in dry weight with the application of external nitrogen levels. The dry weight ranges from N0 (0.22g) to N2 (0.41g) as reported in Table 5. The interaction effect of genotype and N levels on seedling dry weight was found to be prominent. the genotype CGH-278 was recorded highest dry weight of 0.75g due to N2 level of N application. This was followed by the genotype CGH-16 (0.62g) at N2 level. However, at N0 level of N application the genotype CGH-278 was recorded the highest dry weight 0.43g against the check(0.12g). The increase in dry weight indicates efficient nitrogen utilisation and biomass accumulation. (2013) [7] , and Alves de Anicésio et al. (2015) [3] .

Conclusion

The present study revealed that kernel nitrogen content significantly influenced early seedling growth, dry matter, among the selected safflower genotypes. Genotypes with higher kernel nitrogen exhibited better seedling performance than the check under different external nitrogen levels. The observed variation among the genotypes indicates that kernel nitrogen content as an important parameter that can be used as a criterion for identifying the nitrogen-efficient safflower genotypes. These findings may contribute to future breeding programmes aimed at developing cultivars with improved nitrogen use efficiency.

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