‘Summer King’ (Malus domestica Borkh.) was selected in 2010 through a breeding program conducted by the Apple Research Institute of the National Institute of Horticultural and Herbal Science, under the Rural Development Administration of South Korea. It was obtained by crossing ‘Fuji’ and ‘Golden Delicious’. ‘Summer King’ is early maturing apple that can be harvested in late July, ∼100 d after full bloom in Gunwi. The fruit exhibits a blush at harvest and has a conical shape with smooth skin. With a fresh weight of 265 g, it contains 13.7% soluble solids and has a titratable acidity of 0.43% at maturity. Among the cultivars having a showing similar harvest window, it is highly regarded for its excellent taste. In South Korea, apples available in July are typically stored apples harvested in the previous year or unripe apples harvested in the current year, which often suffer from poor quality. However, ‘Summer King’, which can be harvested in late July, has been developed to provide fresh and delicious apples. The self-incompatibility genotype of ‘Summer King’ is S3S9, and it has cross-pollen compatibility with cultivars such as Fuji, Golden Delicious, Gala, Cripp’s Pink, and Honeycrisp. It demonstrates very low self-compatibility and displays parthenocarpy, enabling the production of seedless fruit. These characteristics are advantageous for fruit set and yield management. When stored at a 0 °C or treated with 1-MCP (1-methylcyclopropene), ‘Summer King’ retains quality for a duration of 2 to 4 months after harvest. It stands out as a promising apple cultivar with high-quality traits and the earliest harvest date among those cultivated in South Korea.
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