Working collection formation of apple-tree (Malus domestica Mill.) gene pool for priority breeding trends

Aim. To define the priority trends of apple breeding in the southern steppe of Ukraine and to identify varieties – sources of high valuable-for-breeding indices for building up a working collection. Results and Discussion. Spring frosts and wet weather in May-June contributing to development of the scab pathogen (Venturia inaequalis), high temperature and water deficit in the 2nd half of the growing period, when fruits grow and ripen, are the major stress weather/climatic factors for apple trees in the southern steppe of Ukraine. Therefore, the priority in breeding is given to developing varieties that would be resistant to several unfavorable factors. At the same time, commercial use of new varieties is possible provided high commercial quality indicators of fruits. High resistance of buds to spring frosts was observed in varieties Vechirnia Zoria, Moldavskoye Krasnoye, and Prima. Oligogenic varieties (genes Vm and Vf), including Harant, Skifske Zoloto, and Liberty, showed no signs of scab development. Varieties with polygenic resistance to this disease were identified; they included Vechirnia Zoria, Ornament, Carola. Drought-tolerant varieties with high water-holding capacity of leaves and their turgor restoration after wilting, including Carola, Florina, and Prima, were selected by a laboratory method. Assessment of drought tolerance in the field made it possible to enrich this group with numerous varieties. Varieties giving fruits with high commercial qualities on insufficient water availability, such as Vechirnia Zoria, Harant, Moldavskoye Krasnoye, Ornament and others, were distinguished. Varieties combining resistance to several unfavorable abiotic and biotic factors with high marketability traits of fruits were singled out. Among them. Harant, Delicious Spur, Liberty, and Prima should be mentioned. Conclusions. The development of varieties with complex tolerance to spring frosts, drought, scab pathogen and high qualities of fruits is the priority trend in the breeding of apple trees in the southern steppe of Ukraine. Varieties - sources of individual valuable traits and their various combinations were identified. Varieties Vechirnia Zoria, Moldavskoye Krasnoye, Ornament, and Golden Resistant combine the maximum number of valuable-for-breeding features. It is varieties-sources of several traits that should make up a working collection of apple trees to increase the breeding efficiency.