Apple-Tree Resistance to Abiotic Factors in Winter

Data on the reaction of apple cultivars to unfavorable autumn-winter conditions were analysed and summarised. New scab resistant apple cultivars (gene Vf) obtained from the hybridisation of local adapted varieties with a donor of scab immunity also displayed hardiness to unfavourable winter conditions. As a result of artificial freezing, the cultivars resistant to spring frost (-3.5 oC) during flowering were identified. The mechanism of adaptation to unfavourable winter conditions, and the possibility of preliminary prediction of winter hardiness according to some indicators of the physiological state of tissues in wintering trees were found. In all apple cultivars, increase of the concentrations of sucrose, anthocyanin and cyanidin was noted during the autumn-winter period, but in winter-hardy cultivars this process was more intensive; the amount of cyanidin in the bark of shoots was 6-8 times higher in comparison with non-winter-hardy cultivars. Higher water loss in non-winter-hardy cultivars was observed under conditions of extreme temperatures, which can lead to significant freezing and sunburns late in winter. In winter-hardy cultivars, peroxidase activity decreased in winter, while in the non-winter-hardy cultivars it remains high, due to incomplete hardening of tissues.