Breeding assessment of heteroploid crosses in the development of triploid apple varieties

A 40-year-long study of apple breeding on a polyploid level shows that the most promising crossings for regular development of triploid varieties are 2x × 4x and 4x × 2x. Cytological control shows that the reciprocal combinations are unequal in the output of seedlings with different ploidy. In 2x × 4x crossings, the output of triploid seedlings is higher than in 4x × 2x crossings. The reason is the different degree of autogamy in parental tetraploid forms: when nonemasculated flowers are pollinated, highly autogamous forms are preferably pollinated with their own pollen. In order to obtain a larger number of triploid plants using 4x × 2x crossings, flowers of these forms should be emasculated. The article describes production and biological features of eight triploid apple varieties with a more regular fruit bearing and highly marketable fruits.