Improving the performance of calcium-containing spray formulations to limit the incidence of bitter pit in apple (Malus x domestica Bork)

Laboratory and field experiments were carried out with apples (Malus x domestica Bork) cv. ‘Golden Reinders’, to assess the efficacy of sodium salt of carboxymethyl ether of cellulose (0.5%, CMC) as an adjuvant for Ca spray formulations containing either Cachloride or Ca-propionate as active ingredient (120 or 250 mM Ca). This additive significantly increased the retention of Ca-containing solutions by the apple skin and prolonged the process of drying of the solution at room temperature. Four days after immersion of apples in 0.5% CMC plus CaCl2 or Ca-propionate solutions (120 and 250 mM Ca) significant Ca increases were recorded in the peel and cortex of treated fruits. Application to apple trees of in-season sprays containing 250 mM CaCl2 plus 0.05% Tween 20, Ca-propionate (120 and 250 mM Ca) plus 0.5% CMC or 250 mM CaCl2 plus 0.5% CMC had no impact on fruit yield and quality, but significantly limited the rate of bitter pit incidence during the following 3-month cold-storage period. Evidence is provided that addition of appropriate adjuvants to Ca sprays can favour the distribution of Ca into the apple fruit and help to reduce the incidence of Ca-related disorders over the postharvest cold-storage period.