Frost Resistance Potential of Hybrid Apple Seedlings of Russian Research Institute of Fruit Crop Breeding after Artificial Thawing

The goal of our work was to assess the ability of hybrid apple seedlings and their parent forms to maintain frost resistance during the thaw period, by using artificial freezing methods. Apple resistance was studied in the laboratory by modelling the damage factors of the frost resistance component III with the use of a climatic chamber. All of the studied hybrid apple seedlings from all used crossing combinations showed a sufficient level of frost resistance under modelling of a three-day artificial thaw (+2 °C) with subsequent temperature lowering to –25 °C. The damage of bark, cambium and wood in all of the studied hybrid seedlings was reversible and did not exceed a 2.0 point rating on a 5-point scale. The temperature rise up to +2 °C during three days in February did not cause the activation of growth processes in buds and bark and did not dramatically affect hybrid apple seedlings. According to the results of the artificial freezing, hybrid apple seedlings of the 6026 family (‘Imrus’ × ‘Krasa Sverdlovska’) and hybrids of the 6030 family (‘Svezhest’ × ‘Pepin Orlovsky’) showed the largest potential frost resistance after a thaw in winter.