Modulation of juice quality and nutritional composition of newly developed sweet oranges [Citrus sinensis (L.) Osbeck]: variation from rootstocks

Abstract

Rootstock diversification plays a vital role in citrus orchard systems, as rootstocks significantly influence the overall fruit quality by affecting their pomological characteristics, physico-chemical attributes, and bioactive composition. In the present context, the rootstock ‘Jatti Khatti’ is traditionally favoured for the ‘citriculture’ industry in the subtropics of northern India. However, it is often associated with inconsistent and sub-optimal fruit quality of citrus fruits. Following a long-term evaluation programme, two promising indigenous sweet oranges ( Citrus sinensis (L.) Osbeck), ‘Pusa Sharad’ and ‘Pusa Round’, have been released for the subtropics. However, their performance on diverse, locally-adapted rootstocks is inadequately explored. It is essential, as rootstocks are an indispensable component of citrus orchard systems. Therefore, the present investigation evaluates the influence of four indigenous (‘RLC-6’, ‘RLC-7’, ‘Jatti Khatti’, and ‘Soh Sarkar’) and three exotic (‘C-35’, ‘X-639’, and ‘Yamma Mikan’) rootstocks on the fruit quality of newly developed sweet oranges under the subtropics of northern India. Significant rootstock-mediated variations were observed in the physico-biochemical and nutritional attributes of the newly developed sweet orange cultivars relevant for both fresh consumption and juice processing. Fruit physical characteristics varied significantly, including fruit volume (226.60–288.60 cm³), juice recovery (46.72–54.38%), seed mass (1.07–2.05%), peel thickness index (8.20-13.62), and peel firmness (12.87–17.01 N). Juice quality attributes also differed significantly, including soluble solids (7.94–9.91 °Brix), citric acid (0.67–0.84%), maturity index (9.91–13.94), BrimA (5.55–7.73), juice pH (3.29–4.09), juice conductivity (2.60–3.33 mS/cm), reducing sugars (2.39–5.00%), and non-reducing sugars (1.98–3.00%). Significant variation was also recorded in nutritional and functional quality traits, including ascorbic acid (39.20–54.25 mg/100 mL juice), total phenols (75.44–92.57 mg gallic acid (E)/100 mL juice), total flavonoids (17.26–37.21 mg quercetin (E)/100 mL juice), and CUPRAC antioxidant activity (6.43–12.59 µmol Trolox/mL juice). Rootstock effects were further reflected in the derived indices, including technological index, industrial yield, fresh fruit index, and juice processing index. Multivariate analysis highlighted notable trade-offs among the studied parameters. For ‘Pusa Sharad’, ‘RLC-6’ and ‘X-639’ performed best across most parameters, whereas ‘X-639’ was most suitable for ‘Pusa Round’. In contrast, ‘Jatti Khatti’ and ‘RLC-7’ produced larger fruits, but with reduced fruit quality in both cultivars. Notably, rootstock ‘X-639’ advanced fruit maturity and exhibited the highest technological index and juice processing index values with lower industrial yield requirements, indicating its suitability for the production of fruits for orange juice processing. In our study, the rootstock × cultivar interactions significantly influenced the evaluated fruit morpho-physical, biochemical, and nutritional attributes. The present investigation demonstrated a notable impact of rootstock selection on key juice processing traits of citrus fruits. The findings provide insights for enhancing nutritional quality and improving juice processing suitability of the newly developed sweet oranges. Rootstocks, ‘RLC-6’ and ‘X-639’ emerged as promising alternatives to ‘Jatti Khatti’, offering superior fruit quality and nutraceutical properties for commercial sweet orange cultivation in the subtropics.