The effectiveness of 0.7% oxygen to attenuate scald symptoms in 'Delicious' apples is influenced by harvest maturity and cultivar strain

Abstract

In a 3-year study, the effectiveness of 0.7% and 1.5% O2 to attenuate scald was evaluated on three strains of 'Delicious' apples (Malus xdomestica Borkh.)-'Harrold Red', 'Starking', and 'Starkrimson'-harvested five times at weekly intervals from a wide range of orchards. Scald susceptibility of fruit held in air, 1.5% O2 + 1.0% CO2, and 0.7% O2 + 1.0% CO2 at 0°C decreased sharply as the fruit matured on the tree (starch index 1.0 to 2.5 on a 0 to 9 scale). Later harvests (starch index >2.8) further reduced scald but the fruit had more watercore-induced breakdown and were 3 N softer than fruit picked at a less advanced maturity. Early picked 'Starkrimson' (starch index <2.0) scalded more than 'Starking' and 'Harrold Red' in air, 1.5% O2, and 0.7% O2 storage at 0°C, and 0.7% O2 was less effective than 1.5% O2 in scald control. While 0.7% O2 storage effectively reduced scald (less than 10%) for 8 months in 'Starking' and 'Harrold Red' picked over a wide range of maturity (starch index 0.7 to 4.3), it did not adequately control scald (up to 45%) in early picked 'Starkrimson' (starch index <2.0). Storage in 0.7% also reduced watercore-induced breakdown in 'Starkrimson' (starch index >3.0) and did not result in skin purpling or alcoholic taste in 'Harrold Red', 'Starking', and 'Starkrimson'.