Calcium Chloride and Boron Foliar Applications Reduce Fruit Cracking and Improve Antioxidant Activities in “Arisoo” Apples

Fruit cracking negatively affects apple quality and marketability, reducing profitability. Therefore, this study aims to evaluate the effects of foliar applications of 0.5% (w/v) calcium chloride (CaCl2), 0.1% (w/v) boric acid (H3BO3; hereafter referred to as B), and their combination (CaCl2 + B) on fruit cracking, quality, and antioxidant metabolism in “Arisoo” apples. Treatments were applied 45, 30, and 15 days before harvest, while control trees received water sprays. Foliar application increased calcium and B concentrations in the leaves, fruit peel, and flesh tissues. Compared with the control, the CaCl2, B, and CaCl2 + B treatments reduced fruit cracking incidence by 52.6%, 32.4%, and 87.4%, respectively, and cracking severity by 55.6%, 44.4%, and 77.8%, respectively. Among the treatments, the combined CaCl2 + B treatment showing the greatest effect in both cracking incidence and severity. Additionally, the CaCl2 and CaCl2 + B treatments improved flesh firmness by 5.0% and 5.6%, compared with the control. However, foliar applications did not affect fruit weight, soluble solids content, titratable acidity, starch pattern index, and color. Foliar treatments reduced lipid peroxidation, increased antioxidant enzyme activities, including catalase, superoxide dismutase, and peroxidase, and enhanced total phenolics and DPPH radical scavenging activity. Polygalacturonase and pectin methylesterase enzyme activities also decreased, particularly in the fruit peel under combined treatment. These findings suggest that foliar CaCl2 and B treatments can reduce fruit cracking in “Arisoo” apples, with the combined treatment showing greater effects than individual treatments.