Foliar nutrient applications to 'Wonderful' pomegranate (Punica granatum L.). I. Effects on fruit mineral nutrient concentrations and internal quality

Investigations into putative health benefits of pomegranate fruit have increased interest in its consumption and production but limited evidence exists regarding fruit mineral nutrient concentrations and other internal fruit quality characteristics, especially for Wonderful, an industry standard cultivar, and even less is known about the effects of agricultural practices such as foliar fertilizer applications on these variables. Mature 'Wonderful' pomegranate trees were treated during fruit set with zinc sulfate (ZnSO4), magnesium sulfate (MgSO4), potassium nitrate (KNO3), and with deionized water. Mature fruit were analyzed for mineral nutrient concentrations, antioxidant activity (AA), total phenolics (TP), total soluble solids (TSS), and titratable acidity (TA). Fruit mineral nutrient concentrations were characterized. Zinc-treated trees had greater fruit Zn concentrations. No other significant differences in fruit mineral nutrient concentrations were detected. Antioxidant activity ranged from 67.1 to 87.1 percent inhibition of 2,2′-diphenyl-1-picrylhydrazyl with no treatments resulting in AA that was significantly different from the control. Total phenolics ranged from 2091 to 3735 mg·L−1 gallic acid equivalents, with 2% KNO3 resulting in a statistically significant increase in TP at one site. Fruit TSS and TA were not affected significantly by the treatments. The results suggest that foliar ZnSO4, MgSO4, and KNO3 could be used as part of an efficient, sustainable fertilizer program for 'Wonderful' pomegranate while maintaining or improving fruit mineral nutrient concentrations, bioactivity, and internal quality.