Rootstock-Mediated Agronomic Biofortification of Citrus Fruits: Evidence from Mineral Nutrient Profiling

The influence of rootstocks on mineral nutrient composition in the edible tissue of citrus fruits has not been explored so far. This study assessed leaf and juice mineral nutrients of sweet orange (Citrus sinensis (L.) Osbeck) cultivars (‘Pusa Sharad’ and ‘Pusa Round’) grafted onto different rootstocks (‘RLC-6’, ‘C-35’, ‘X-639’, ‘Yamma Mikan’, ‘Soh Sarkar’, ‘RLC-7’, and ‘Jatti Khatti’). Deviation from optimum percentage (DOP) index was employed as an integrative measure to assess leaf mineral nutrient balance for specific scion–rootstock combinations. The relative abundance of leaf mineral nutrients was ranked as follows: Ca > K > P > S > Mg > Na > Fe > Mn > Zn > Cu. Overall, rootstock ‘X-639’ demonstrated superior mineral nutrient uptake efficiency across grafted plants of both scion cultivars, as indicated by higher leaf mineral nutrient concentrations. Juice mineral nutrient concentrations followed the order K (930.87–1362.17 mg L−1), Ca (346.40–651.33 mg L−1), P (116.23–236.97 mg L−1), Mg (64.60–102.50 mg L−1), S (49.35–74.34 mg L−1), Na (25.61–47.88 mg L−1), Fe (4.76–7.92 mg L−1), Zn (1.79–4.34 mg L−1), Mn (0.73–1.62 mg L−1), and Cu (0.41–0.71 mg L−1), indicating distinct differences in the accumulation pattern of macro- and micro-mineral nutrients in the edible tissues across the studied scion–rootstock combinations. Multivariate analysis revealed that the rootstocks significantly influenced juice mineral nutrient levels, indicating rootstock-mediated agronomic biofortification. Rootstock ‘RLC-6’ enhanced juice K levels, and ‘Soh Sarkar’ improved juice Mg contents, while ‘X-639’ improved juice micronutrient (Zn, Mn, Cu) accumulation in both cultivars. This study constitutes the first comprehensive investigation that explicitly evaluates the influence of rootstocks on the enhancement of mineral nutrient content in the edible tissues of citrus fruits. It further elucidates how rootstock selection can indirectly affect dietary mineral intake, thereby highlighting its potential role for improved nutrition.