DTA-CIFE modeling for predicting freezing dynamics and frost tolerance in deciduous fruit buds

The fine-scale quantification of frost tolerance in flower buds during deacclimation remains limited, particularly when integrating both lethal temperature and duration into predictive frameworks. In this study, Differential Thermal Analysis (DTA) combined with mathematical modeling was used to investigate frost tolerance in nine deciduous fruit species at the pink bud and full bloom stages. A single exothermic peak was consistently detected and interpreted as the cell death point (CDP). Bud death times (BDTs) ranged from 5.3 min in sour cherry (Prunus cerasus L.) to 25.88 min in pear (Pyrus communis L.), reflecting distinct survival strategies. To better characterize tolerance, the Conic Iso-Damage Frost Envelope (CIFE) model was applied. Species-specific scale parameters were estimated for each species, where T₀ (°C) defines the temperature semi-axis and D₀ (min) defines the duration semi-axis of the iso-damage ellipse; together these parameters enabled calculation of the Geometric Frost Tolerance Index (GFTI) and anisotropy coefficient (κ). Among all species, quince (Cydonia oblonga L.) exhibited the largest tolerance envelope (T₀ = 9.32 °C, D₀ = 23.86 min, GFTI = 699.1), confirming its exceptional resilience to both low temperatures and extended frost exposure. Sweet cherry (Prunus avium L.) and sour cherry also clustered in the tolerant group with GFTI values of 268.2 and 159.1, respectively. Apple (Malus domestica L.), pear, and peach (Prunus persica L.) formed an intermediate group, whereas nectarine (Prunus persica var. nectarina L.), plum (Prunus salicina L.), and wild apricot (Prunus armeniaca L.) were identified as the most sensitive species with narrow envelopes and GFTI values below 365. Anisotropy analysis further distinguished duration-dominant strategies in pear (κ ≈ 4.8) and nectarine (κ ≈ 5.9) from temperature-dominant tolerance in sour cherry (κ ≈ 0.6). These results demonstrate that frost tolerance is not solely determined by lethal temperature but also by the interaction of time and temperature, highlighting the potential of CIFE modeling as a robust tool for predicting frost injury and supporting breeding programs for resilient cultivars.