Summer fruitlet thinning enhanced quality attributes of Ambrosia™ apple at harvest and after four months of cold air storage

Abstract

Summer fruitlet thinning is implemented as a routine orchard practice to produce apple fruits with good quality. However, its impacts on the dynamics of fruit quality metrics during the growing season and in the postharvest storage, remain unclear. In this study, summer hand thinning on fruitlets of Ambrosia™ apple (Malus x domestica Borkh.) was conducted on two dwarfing rootstocks, Malling 9 (M.9) and Budagovsky (B.9), in an organic orchard and a conventional orchard under the semi-arid climate in Similkameen Valley, British Columbia, Canada. Adequate thinning (“AT”, in which 70% of fruitlets were removed) and light thinning (“LT”, in which 30% of fruitlets were removed) were implemented in randomized plots in eight weeks after full bloom. Fruit development and dry matter content (DMC) were then monitored during the growing season; fruit quality was subsequently evaluated at harvest and after four-month of air storage at 0.5 °C. Relative to LT, AT enhanced fruit quality attributes in DMC, surface blush coverage and intensity, and soluble solids content at harvest. The apples with higher DMC under AT also possessed higher compositional quality and lower disorders in the postharvest stage, This study suggests that summer fruitlet thinning of Ambrosia™ apples can have significant impacts on fruit composition during subsequent on-tree fruit development, on the onset of ripening and eventually on the retention of quality and minimization of disorders over 4 months of cold air storage. This effect is found for OG and CV production systems and with both dwarfing rootstocks