Physiological and genetic control of red skin colouration in apples grown under warm and cool conditions

Red coloration of apple skin is a key factor for consumer acceptance of fruit within the marketplace and is used as a grading standard in the main producing countries. Red colour intensity results from the accumulation of anthocyanin pigments, which is dependent on the cultivar, fruit maturity and environmental conditions, in particular light and temperature. Many red skin apple cultivars grown under warm summer conditions do not redden as much when they are grown in locations with cool summer; however, some strains of 'GalaR' (e.g., 'Brookfield GalaTM') and other red skin cultivars (e.g. 'ModiTM'), are capable of reddening under warm conditions, which indicates genetic variability exists for response to temperature. To unravel the role of temperature on the regulation of the expression of key genes involved in the biosynthesis of anthocyanin a combined approach was used, on fruits of the same cultivar, grown in two different environments, that were exposed to warm (Spain) and cool (New Zealand) controlled temperatures. Genetic markers linked to high intensity colouration have been developed for use in marker-assisted breeding, which will enable the development of red skin apples adapted to these conditions.