An overview of the red-fleshed apple: History and its importance for horticulturists, gardeners, nurserymen, and consumers

The present review summarizes the information on the botany, breeding, genetic features, cultivation, and nutraceutical values of red-fleshed apples. Malus sieversii var. niedzwetzkyana or Niedzwetzky’s apple became widely known after the publication of Georg Dieck in the last XIX century. It is characterized by anthocyanin coloration of all organs. Another source of red flesh is the ancient variety ‘Surprise’, which differs from the Niedzwetzky’s apple by a mutation in another gene. These two mutated genes, MYB10 and MYB110a, are located on chromosomes 9 and 17, respectively. Their expression correlated with the anthocyanin accumulation. In type 1 red-fleshed apples, which belong to the Niedzwetzky’s apple progeny, the transcription factor MYB10 confers extensive anthocyanin accumulation in fruit flesh and skin, flowers, leaves, and stems. In type 2 red-fleshed apples, the ‘Surprise’ progeny, only the flesh is red, determined by the transcription factor MYB110а. A new combination Malus domestica f. niedzwetzkyana comb. nov. has been proposed for orchard apples, originated from Niedzwetzky’s apple. The apple cultivars which are progeny of Niedzwetzky’s apple and ‘Surprise’ apple can be placed to Malus Niedzwetzkyana Group and Malus Surprise Group, respectively. All red-fleshed cultivars of orchard apple can be grouped together into Malus domestica Red Flesh Group. Many dozens of new ornamental apple trees have been developed for of European and North American conditions, including the most famous red-flowered centennial apple varieties such ‘Aldenhamensis’, ‘Lemoinei’, ‘Makamik’, and ‘Oekonomierat Echtermeyer’. Rootstocks ‘MB’, ‘PB9’, ‘54-118’, ‘62-396’ and others have become popular in nurseries for the propagation of dwarf and semi-dwarf apple trees thanks to their red leaves, which are useful when removing scion shoots from budded plants. In the F3-F4 and next generation, the new high-quality red-fleshed cultivars have been developed by crossing both Niedzwetzky’s apple and ‘Surprise’ apple with the best orchard apple varieties. Marker-assisted breeding shows great promise for accelerating the development of new red-fleshed cultivars with outstanding traits. The use of the Redlove®, Red Moon®, Kissabel®, and Lucy™ apples brands will ensure the red-fleshed apples’ best path to the consumer as well as the fruit quality and production volume of these novelties. Increasing the consumption of red-fleshed apples is essential for a healthy diet.