Preharvest Foliar Spray of Various Potassium Sources and Calcium Chloride Affect Fruit Color, Storability, and Bruise Susceptibility of Apples (Malus × domestica Borkh. cv. “Red Delicious”)

This study was conducted in two consecutive growing seasons to evaluate the effect of pre-harvest sprays of three potassium (K) sources (KNO3, K2SO4, and KCl) and calcium chloride (CaCl2) on the color attributes and changes in fruit quality and bruise susceptibility of “Red Delicious” apples during 4 months of storage. During each season, the trees were sprayed five times with CaCl2 (5 g.l−1) and three times with K sources (2.5 g × l−1). Fruit qualitative traits were measured at harvest time as well as 2 and 4 months after storage at 0 °C. Results showed that all treatments positively affected the red skin color, except CaCl2. During the storage period, KNO3 + CaCl2 treatment significantly increased fruit firmness (FF), total acidity (TA), and decreased water loss compared to the untreated trees, while single treatments of K sources increased titratable acidity (TA) only at harvest time. Total soluble solids (TSS) were increased by spraying trees with KNO3 + CaCl2 only at harvest time. Results also revealed that “Red Delicious” apples are more susceptible to bruise damage immediately after harvest compared to after 2 and 4 months of storage. In general, simultaneous foliar application of KNO3 and CaCl2 effectively improved the fruit quality and storability of the “Red Delicious” apple.