Intervalent Crosses: the Main Way of Creating Triploid Apple Cultivars

Abstract

This paper presents history and ways of creating triploid apple cultivars differing from common diploid ones by less pronounced fruiting periodicity by years, higher marketability and weight of fruits, and self-fertility. In the search for an effective method of mass production of triploid seedlings, crosses of the type 4x × 4x, 4x × 3x, 4x × 2x, 3x × 4x, 3x × 3x, 3x × 2x, 2x × 4x, and 2x × 3x were studied. The most effective way of mass production of triploid seedlings was the 2x × 4x cross (diploid × tetraploid). In the group of 2x × 4x crosses, more than 9000 seedlings from different families were subjected to cytological analysis. The ratio of hybrid progeny in terms of ploidy levels was as follows: 30.3% diploids, 69.5% triploids, 0.2% tetraploids, and 0.04% aneuploids. It was established that triploids can also be obtained in 4x × 2x crosses; however, it is necessary to castrate the flowers in the maternal parent, since all apple tetraploids have high self-fertility. For the first time in the world, a series of triploid cultivars (approximately 20) was obtained from intervalent crosses of the diploid × tetraploid type in the All-Russia Research Institute of Fruit Crop Selection. Particularly interesting are triploid cultivars that have immunity to scab, which include nine cultivars, of which Aleksandr Boiko, Vavilovskoe, Maslovskoe, and Yablochnyi Spas are included in the State Register of breeding achievements allowed for use.