Differential Thermal Analyses in Peach [Prunus persica (L.) Batsch]

The temperature at which any water freezes inside plant cells can be detected by differential thermal analysis (DTA). The results from DTA are often associated with lethal damage of flower buds. The goal of this study was to determine whether the critical freezing temperature of peach floral buds can be determined through winter by DTA. Traditional freezing tests were conducted and compared to the DTA as a standard test used to determine the lethal bud temperature at 50% mortality (LT₅₀). Floral buds of two peach cultivars, ‘Elberta’ and ‘Flavorich’, were collected during the winter of 2015-2016. DTA and freezing tolerance tests were performed every week using excised floral buds (freezing rate of 4ºC/h, temperatures ranging from -3ºC to -27ºC). High temperature exotherm (HTE) and low temperature exotherm (LTE) were clearly identified using DTA before bud swell on February 23. Peach floral buds gained cold hardiness from November to January, at which time LTE of ‘Elberta’ was -16.3°C and -21.2 °C, and ‘Flavorich’ was -12.6 °C and -16.2 °C, respectively. Cold hardiness was gradually lost afterward. A similar trend was observed with freezing tolerance tests. In November, LT₅₀ of ‘Elberta’ and ‘Flavorich’ was -8.6°C and -7.5°C, respectively, and decreased to -15.0°C and -12.0°C right before bud swell in January. After bud swell, DTA was not able to detect LTE in peach buds. However, setting buds at -2°C overnight before running DTA greatly reduced the HTE and shifted the LTE. After setting buds at -2°C overnight, where extracellular water was frozen before DTA was started, DTA was found to be correlated with LT₅₀ results (R² = 0.4831). This approach may be able to overcome the inability of DTA to detect LTE during deacclimation. Information obtained from this project provides insights to peach cold hardiness and the use of DTA to determine the critical bud temperature of peaches. DTA can provide growers with real time information that could help them in making freeze protection decisions and to estimate potential losses.