Cultivar dependent responses of olive (Olea europaea L.) to foliar fertilization in fruit quality and mineral composition of leaves and fruits

This study examined cultivar-dependent responses to foliar fertilization in olive (Olea europaea L.) by jointly evaluating fruit morphology and skin colour, biochemical quality indicators, and mineral nutrient composition in leaves and fruits. Five cultivars (Arbequina, Frantoio, Ayvalık, Gemlik, and Edincik Su) were tested under five foliar treatments (Control, Bestline, Dermin, UAN-32, and Forceful Amino) in a factorial design. Cultivar, treatment, and their interaction significantly affected fruit size, colour parameters, total phenolic content (TPC), total flavonoid content (TFC), antioxidant activity (AA), and the accumulation of multiple mineral elements (p < 0.05). Across treatments, UAN-32 increased fruit size overall (mean fruit weight 3.30 g). In contrast, Dermin and Bestline were more frequently associated with higher AA in specific cultivar combinations, indicating that increases in TPC and TFC did not necessarily translate into higher AA. Mineral profiling revealed treatment-related differences in element accumulation and partitioning: Bestline was often linked to higher fruit Fe–Mg–Zn concentrations, Dermin promoted Ca enrichment, and UAN-32 increased fruit K. Principal component analysis (PCA) further supported these patterns by separating cultivar × treatment combinations primarily along a fruit-size axis and a coordinated mineral-nutrient axis. Overall, responses to foliar fertilization were strongly cultivar dependent, highlighting the importance of optimizing cultivar-treatment combinations according to targeted production goals.