ASSESSMENT OF FROST DAMAGE RATES IN APPLE DORMANT BUDS BY CONDUCTOMETRY AND GROWTH TESTS

Two methods, a growth test and conductometry, were used for the assessment of frost tolerance in dormant buds of the apple cultivars ‘Denár’, ‘Melrose’, ‘Rubín’ and ‘Šampion’. The dormant buds were treated with eight frost temperatures ranging from -10 to -35°C. Each treatment included 10 buds for each method and the experiment was replicated three times. For the growth test, frost-treated uni-nodal segments of scions were encouraged to sprout in water with the addition of disinfectant. For conductometry, shoot apices were extracted from 10 buds and put together into 1 ml of distilled water for several hours with shaking to release electrolytes from frost-damaged cells; then the conductivities of these solutions were measured at room temperature. The results of conductivity measurements were compared with values from measurements of the same samples after their boiling and cooling down to room temperature during shaking. LT₅₀ were assessed each for regrowth ability and for rate of frost-damaged cells in tissues of extracted buds and their values were compared and discussed.