Sunlight affects the incidence of internal ring cracking and other physical attributes of 'Gala' apples

Internal ring-cracking (IRC) occurs in apples such as 'Gala', 'Royal Gala', and 'Fuji' which are susceptible to stem-end splitting (SES). This paper examines the effects of fruit exposure to sunlight during growth and development on the incidence of IRC and SES, and changes in physical attributes of 'Gala' apples. Fruit were either well exposed to direct sunlight (outer canopy) or naturally shaded (inner canopy) by leaves, branches, and other fruit. Exposure to direct sunlight significantly increased the incidence of internal ring-cracking but the proportion of fruit with stem-end splitting was not affected. Fruit size, flesh crushing stress, and soluble-solids concentration (SSC) were significantly higher in well-exposed fruit; however, skin bursting stress and starch maturity index were not affected significantly. The nonsignificant effect of fruit exposure to sunlight on the incidence of SES may be related to uniform fruit maturity level (starch index) in both well-exposed and shaded parts of the tree canopy.