Performance study of grafted brinjal (Solanum melongena L.) for quality parameters

Introduction

Use of grafting is a well-established practice in Pomology for tree fruits, its adoption in Olericulture is comparatively recent. Globally, vegetable grafting has become increasingly prevalent in crops like cucurbits, tomato, eggplant, and pepper, where the use of robust, disease-resistant rootstocks helps optimize productivity. Nonetheless, challenges from both biotic and abiotic stresses persist (Buller et al., 2013) [2] . Eggplant, commonly known as brinjal, is a member of the Solanaceae family with a chromosome number of 2n=2x=24 (Choudhary, 2013) [3] . It is believed to have originated in India (Zeven and Zhukovsky, 1975) [18] . Nutritionally, brinjal holds great importance as its fruits contain approximately 6.4% carbohydrates, 1.3% protein, 0.3% fat, and small amounts of essential minerals such as calcium (0.02%), phosphorus (0.02%), and iron (0.0013%). It is also a source of several vitamins including β-carotene (34 mg), riboflavin (0.05 mg), thiamine (0.05 mg), niacin (0.5 mg), and ascorbic acid (0.9 mg) per 100 grams of fruit (Choudhary, 2013) [3] . Brinjal is also noted for its cholesterol-lowering effects, thanks to its high polyunsaturated fatty acid content specifically linoleic and linolenic acids which make up about 65.1% of its pulp and seeds. Glycoalkaloid content in Indian commercial cultivars of brinjal typically measures around 0.37 mg per 100 grams of fruit. Wild brinjal, scientifically known as Solanum torvum, is a versatile member of the Solanaceae family, which also encompasses tomatoes, potatoes, and bell peppers. An important species, Solanum xanthocarpum known as yellow-berried nightshade or kantakari is a perennial herbaceous plant native to South and Southeast Asia. It is characterized by its erect or spreading growth habit, adaptability, and consistent medicinal use across indigenous systems of medicine. Likewise, Solanum incanum, often referred to as thorn apple or bitter apple, is recognized for its natural resistance to pests and diseases, making it an ideal candidate for use as a rootstock in vegetable grafting. Its fruits are a rich source of vitamin C, thiamine, folic acid, and moisture (Patel et al., 2018) [10] , enhancing its nutritional and horticultural significance. Although grafting has historically been associated with woody fruit trees, its extension to vegetable crops has gained considerable commercial momentum in recent decades. The practice entered Western agriculture in the early 1990s through the fusion of local scions with imported, disease-resistant rootstocks (Sakata et al., 2007) [16] . However, its roots trace back to the development of protected cultivation systems in the late 1950s, which provided an ideal environment for the adoption of grafted vegetable plants. In today's context of organic and sustainable farming, grafting plays a pivotal role in minimizing the reliance on synthetic fertilizers and pesticides (Davis et al., 2008) [4] . The continuous use of greenhouse systems often leads to a buildup of soilborne pathogens and nematodes, making vegetable grafting essential for ensuring stable production. Moreover, the strategic selection of compatible and stress-resilient rootstocks offers an effective solution to issues arising from successive cropping and environmental stress, thus enhancing overall productivity and sustainability (Hoyos, 2010) [7] .

Materials and Methods

The experiment was conducted during the 2021-22 and 2022-23 at AICRP on Vegetable crops, OUAT, Bhubaneshwar, Odisha. In the present investigation the design used for analysis of variables were Randomized Block Design (RBD) comprising 3 replications ten graft combinations. Combinations comprised of T 1 (Seedling plants of VNR-212 (Control)); T 2 (Solanum torvum x VNR-212); T 3 (Solanum torvum x Sungro-704); T 4 (Utkal Anushree x VNR-212); T 5 (Utkal Anushree x Sungro-704); T 6 (Utkal Tarini x VNR-212); T 7 (Utkal Tarini x Sungro-704) and T 8 (Seedling plants of Sungro-704 (control)). The successful formation of a compatible graft involves three key processes: adhesion between the rootstock and scion, proliferation of callus cells at the graft junction forming a callus bridge, and vascular differentiation across the graft interface. Consequently, the rootstock and scion were systematically managed in a stepwise manner, as outlined by Mohanta et al. (2015) [9] . Splice grafting was the method used in experiment to join a scion (desired plant part) onto the stem of a rootstock or intact root piece. Quality parameters like Phenolic content in fruit, Anthocyanin pigment of fruit, Vitamin A content of fruit, Vitamin B 2 content of fruit, Vitamin C content of fruit Ranganna (1986) [11] , Vitamin E content of fruit were observed. Analysis of Variance was worked out using Fisher and Yates (1967) [6] . Extraction: Polyphenols were extracted using 80% ethanol (Blois, 1958) [1] . Reagent Addition: 2,2-Diphenyl-1picrylhydrazyl (DPPH) solution was mixed with the extract. Incubation & Measurement: After incubation for 30 min, absorbance was measured at 517 nm. Calculation: Polyphenol activity was quantified using a standard curve of gallic acid. Anthocyanin content was estimated using the pH differential method (Giusti and Wrolstad, 2001) [5] . Extraction: Fresh fruit samples were homogenized in acidified methanol (1% HCl). Filtration & Dilution: The extract was filtered and diluted with two buffer solutions (pH 1.0 and pH 4.5). Measurement: Absorbance was recorded at 520 nm and 700 nm using a UV-Vis spectrophotometer.

The anthocyanin concentration was determined using the molar extinction coefficient of cyanidin-3-glucoside. Vitamin A (β-carotene) was determined using high-performance liquid chromatography (HPLC) (Rodriguez-Amaya, 2001) [15] . Extraction: Carotenoids were extracted using acetonehexane solvent. Filtration & Injection: The extract was filtered and injected into an HPLC system. Detection: Carotenoids were detected at 450 nm, and the results were expressed as mg/100g. Vitamin B 2 content was analyzed using fluorometric detection (Bates, 1987). Extraction: Samples were homogenized in an acidic buffer and incubated. Oxidation: The extract was treated with oxidizing agents. Measurement: Fluorescence was measured at excitation 440 nm and emission 525 nm. Vitamin E (αtocopherol) was analyzed using HPLC with UV detection (Kayden et al. 1973) [8] . Extraction: Samples were homogenized with ethanol-hexane mixture. Filtration & Injection: The extract was filtered and injected into an HPLC system. Detection: Tocopherol content was quantified at 292 nm.

Results and discussion 1. Phenolic content in fruit, and Anthocyanin pigment of fruit

The phenolic content (mg GAE/100 g fresh weight) and anthocyanin content (mg/100 g fresh weight) of grafted brinjal fruits across pooled means of two year 2021-22 and 2023-24 (Table 1 and figure 1) showed highly significant differences among treatments. For total phenolics, T 6 (Utkal Tarini × VNR-212) recorded the highest pooled value (81.99 mg GAE/100 g), clearly outperforming all other combinations. This enrichment can be attributed to the compatibility between the vigorous scion Utkal Tarini and the nutrient-efficient rootstock VNR-212, which likely improved secondary-metabolite biosynthesis and transport. The next most effective combinations were T 4 (Utkal Anushree × VNR-212, 73.95 mg GAE/100 g), T 7 (Utkal Tarini × Sungro-704, 73.17 mg GAE/100 g), and T 5 (Utkal Anushree × Sungro-704, 72.52 mg GAE/100 g), all significantly superior to non-grafted plants. Among controls, T 8 (Sungro-704 seedlings, 69.54 mg GAE/100 g) marginally exceeded T 1 (VNR-212 seedlings, 68.02 mg GAE/100 g), but both lagged far behind the top grafts. The lowest phenolic levels were recorded in Solanum torvum-based grafts T 2 (62.29 mg GAE/100 g) and T 3 (54.88 mg GAE/100 g) suggesting that Solanum torvum is less suitable for enhancing this biochemical trait in commercial brinjal cultivars. Anthocyanin accumulation presented a contrasting pattern. T 4 (Utkal Anushree × VNR-212) displayed the highest pooled value (63.88 mg/100 g), significantly surpassing all other treatments (Table 1 and figure 1). This indicates a strong synergy between the anthocyanin-rich scion Utkal Anushree and the nutrient-acquisitive rootstock VNR-212. T 2 (Solanum torvum × VNR-212, 62.39 mg/100 g) and T 5 (Utkal Anushree × Sungro-704, 62.37 mg/100 g) followed, statistically at par and superior to non-grafted controls. T 7 (Utkal Tarini × Sungro-704) recorded 60.40 mg/100 g, outperforming mid-range combinations such as T3 (57.72 mg/100 g) and T 6 (57.43 mg/100 g). Although T 6 was the best performer for phenolics, its moderate anthocyanin level indicates that biosynthesis of these antioxidant groups may be independently regulated and strongly influenced by specific scion-rootstock interactions. The non-grafted controls T 8 (54.43 mg/100 g) and T 1 (51.99 mg/100 g) consistently recorded the lowest anthocyanin concentrations. Overall, the results demonstrate that grafting significantly enhances phenolic and anthocyanin quality traits in brinjal, and that performance depends on the compatibility between scion genetics and rootstock physiology. Combinations involving Utkal cultivars with VNR-212 or Sungro-704 emerged as the most promising for nutraceutical improvement under field conditions. These findings support the strategic use of grafting for quality-oriented vegetable production. Similar biochemical shifts following grafting have also been reported by Turhan et al. (2011) [17] , who observed changes in vitamin C, total sugar, and soluble solids, indicating linked modifications in antioxidant profiles.

Vitamin A and Vitamin B2 content of fruit

The vitamin A content (mg/100 g fresh weight) and riboflavin (vitamin B2) concentration of brinjal fruits across pooled means of two year 2021-22 and 2023-24 (Table 1 and figure 1)) showed significant treatment variability. For vitamin A, T 7 (Utkal Tarini × Sungro-704) achieved the highest pooled value (0.84 mg/100 g), followed by T 3 (Solanum torvum × Sungro-704) with 0.74 mg/100 g. Although numerically lower, the difference between T 7 and T 3 fell below the critical difference, indicating statistical similarity; both were markedly superior to most other graft combinations and the non-grafted controls. T 5 (Utkal Anushree × Sungro-704) formed the next tier with 0.70 mg/100 g, significantly lower than T 7 yet clearly surpassing mid-range treatments. Intermediate values were observed in T 8 (Sungro-704 seedlings, 0.60 mg/100 g) and T 2 (Solanum torvum × VNR-212, 0.54 mg/100 g), which were statistically comparable and superior to VNR-212-based controls. The non-grafted control T 1 (VNR-212 seedlings) recorded 0.33 mg/100 g, while T 4 (Utkal Anushree × VNR-212) registered 0.27 mg/100 g. The lowest vitamin A concentration was recorded in T 6 (Utkal Tarini × VNR-212) with 0.21 mg/100 g, significantly inferior to the top-ranked grafts. These findings indicate that carotenoid biosynthesis is strongly governed by scion genotype and its compatibility with specific rootstocks. Sungro-704 rootstock, when paired with either Utkal Tarini or Solanum torvum (T 7 and T 3 ), proved most effective in enhancing vitamin A accumulation, highlighting the importance of strategic grafting for improving micronutrient density in brinjal under field conditions. For riboflavin (vitamin B2), T 5 (Utkal Anushree × Sungro-704) recorded the highest pooled content (0.049 mg/100 g), followed by T 6 (Utkal Tarini × VNR-212) and T 7 (Utkal Tarini × Sungro-704), both averaging 0.045 mg/100 g. A mid-range cluster around 0.042 mg/100 g consisted of T 2 (Solanum torvum × VNR-212), T 3 (Solanum torvum × Sungro-704) and T 8 (Sungro-704 seedlings). The lowest riboflavin level was recorded in the non-grafted control T 1 (0.037 mg/100 g), though this difference was not statistically significant. Together, the results emphasize that grafting can effectively enhance micronutrient profiles in brinjal fruits (Table 1 and figure 1). While vitamin A showed strong treatment discrimination with Sungro-704based grafts performing best, riboflavin displayed modest yet positive improvements through scion-rootstock combinations, particularly involving Utkal cultivars. These findings align with Rahmatian et al. (2014) [13] , who also observed higher vitamin A and B2 levels in grafted plant fruits, suggesting improved nutrient translocation and enhanced carotenoid and flavoprotein biosynthesis.

Vitamin C and Vitamin E content of fruit

The ascorbic acid (vitamin C) and tocopherol (vitamin E) contents of brinjal fruits measured across pooled means of two year 2021-22 and 2023-24 (Table 1 and figure 1), showed highly significant variability among treatments. For vitamin C, T 4 (Utkal Anushree × VNR-212) recorded the highest pooled concentration (2.57 mg/100 g), significantly surpassing all other combinations. This substantial enhancement likely results from the strong biochemical compatibility between the metabolically vigorous Utkal Anushree scion and the nutrient-efficient VNR-212 rootstock, which together promote carbon assimilation and antioxidant biosynthesis. T 6 (Utkal Tarini × VNR-212) formed the next tier (2.38 mg/100 g), followed by T 7 (Utkal Tarini × Sungro-704) at 2.19 mg/100 g; both were statistically lower than T 4 yet clearly superior to the nongrafted controls. Mid-range values included T 2 (Solanum torvum × VNR-212) and T 5 (Utkal Anushree × Sungro-704) with 1.96 mg/100 g and 1.95 mg/100 g, respectively, exceeding T 3 (Solanum torvum × Sungro-704) at 1.81 mg/100 g. Among controls, T 8 (Sungro-704 seedlings) averaged 1.79 mg/100 g, slightly higher than T 1 (VNR-212 seedlings) at 1.63 mg/100 g, but both remained significantly below the high-performing grafts. Overall, the findings indicate that strategic grafting, particularly the pairing of Utkal Anushree or Utkal Tarini with VNR-212, can markedly improve vitamin C accumulation in brinjal fruit. For tocopherol (vitamin E), T 4 (Utkal Anushree × VNR-212) again achieved the highest pooled content (0.50 mg/100 g), significantly exceeding all other treatments by a margin greater than the CD (Table 1 and figure 1). The next numerically highest value was recorded in T2 (Solanum torvum × VNR-212) at 0.38 mg/100 g, although the large difference from T 4 confirmed the latter's pronounced superiority. T 5 (Utkal Anushree × Sungro-704) ranked third at 0.35 mg/100 g and was statistically comparable to T 2 . Non-grafted controls (T 1 and T 8 ) and T 3 clustered around similar concentrations (0.30-0.31 mg/100 g) without significant differences. Lower tocopherol content was recorded in T 7 (0.26 mg/100 g) and T 6 (0.23 mg/100 g), both significantly inferior to T 4 . Collectively, the results demonstrate that antioxidant vitamin enrichment in brinjal fruits is strongly governed by scion-rootstock compatibility. T 4 (Utkal Anushree × VNR-212) emerged as the most efficient combination, achieving the highest concentrations of both vitamin C and E across seasons, indicating simultaneous enhancement of water-and lipid-soluble antioxidants. T 6 and T 7 also showed notable vitamin C enrichment, while T 2 contributed substantially to tocopherol levels. These results support the effectiveness of precision grafting for nutraceutical enhancement under field cultivation. Davis et al. (2008) [4] similarly reported increased ascorbic acid in grafted tomato fruits, attributing improvements to enhanced antioxidant metabolism through compatible rootstock-scion interactions. led in riboflavin and dry matter content, while T 7 (Utkal Tarini × Sungro-704) stood out for its elevated vitamin A levels. These results collectively affirm that the choice of compatible, vigorous scions paired with nutrient-efficient and disease-resilient rootstocks can significantly influence the metabolic efficiency and nutrient density of brinjal fruits. Notably, grafting not only enhanced antioxidant capacity (phenolics, anthocyanins, vitamins C and E) but also improved vitamins (A and B 2 ) all of which are critical for human health and market value. Therefore, strategic use of grafting, particularly with combinations like Utkal Anushree × VNR-212 and Utkal Tarini × Sungro-704, offers a sustainable and effective approach for improving the nutraceutical quality of brinjal under field conditions.

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