The development of redskinned apples adapted to the warm climates of South European countries

Many red-skinned apple cultivars grown under warm summer conditions do not redden as much as those grown in locations with cooler summer temperatures. Reflective films and over-tree sprinkler irrigation have been used to mitigate the issue. However, the most efficient strategy is to breed new cultivars that have a high genetic potential for fruit colour development under warmer climates. New cultivars selected for their adaptation to such climates are being bred by a joint Institut de Recerca i Tecnologia Agroalimentàries-Plant & Food Research (IRTA-PFR) breeding programme. Understanding the physiological and genetic control of the response to warm orchard temperature is crucial for developing new tools for more efficient breeding of red-skinned apple cultivars. We manipulated fruit skin temperature by heating and cooling ‘Royal Gala’ fruit in orchards in New Zealand and Spain and measured the expression of the genes regulating red pigmentation. Evidence of down-regulation of the main activator of red pigmentation (MYB10) was demonstrated, and this gene is linked to a locus controlling the red-skinned phenotype. A marker based on MYB10 was developed and is now used for marker-assisted breeding of new apple cultivars suited to warm conditions.