Penetration of calcium chloride into apple fruits as affected by stage of fruit development

Using a fruit disc method penetration of (CaCl2)-Ca-45 across apple fruit surfaces (Malus x domestica cv. Golden Delicious) was studied during fruit development in 1999. The donor solutions contained 5 g L-1 CaCl2 and 0.2 g L-1 Glucopon 215 CSUP as wetter. A small droplet (5 mul) was applied to each fruit disc and allowed to dry within 1 h. Penetration was followed from the hydrated salt residue on the fruit discs for 24 111 at 20 degreesC and 100% humidity in light. Rates of penetration were greatly affected by the stage of fruit development. The highest rates were measured during the early stages of fruit development before June drop (90% to 100% penetration). After June drop, when trichomes had vanished and stomata developed into lenticels, the penetration rates declined rapidly (mean 40% - 60% penetration) but large variability (20% - 80%) among the samples developed. Evidence is presented showing that during this later stage of fruit development lenticels represent a preferential site for penetration of calcium chloride across the apple cuticles.