Low Temperature Exotherm Ratios (LTER)

Cold damage is a perennial concern for tree fruit growers as they must make timely decisions based on current hardiness levels and forecasted temperatures. Our lab group has been evaluating hardiness levels in sweet cherry (Prunus avium L.) reproductive buds which are comprised of multiple florets that supercool independently. The transition to endodormancy in sweet cherry begins in the fall when florets gain supercooling ability, enabling hardiness evaluations via DTA and exotherm analyses. In contrast, the transition from endo-to ecodormancy in the spring is marked with a loss of supercooling, and the inability to detect exotherms. Our research group is investigating the potential to track transitions in dormancy state of sweet cherry based on the ratio between the number of florets (i.e. expected exotherms) assessed and the number of exotherms observed, which we define here as low temperature exotherm recovery (LTER). Specifically we evaluated the use of LTER to determine: 1) onset of acclimation and deacclimation; 2) rates of acclimation and deacclimation; 3) duration of endodormancy and ecodormancy. LTE data were collected on eight sweet cherry genotypes. Floral buds were collected prior to fall acclimation, throughout winter, and until tight cluster (bud stage 4) in spring. During dormancy, DTA was used to collect LTE data. LTER10, 50 & 90 (days (d) until 10%, 50% and 90% LTER) for acclimation (acc) and deacclimation (deacc) were calculated from September 1 st (d = 0). To determine duration of endodormancy, we calculated total days between LTER10acc to LTER90deacc and for ecodormancy, LTER90deacc to LTER10deacc. We observed significant genotypic variability in LTER. On average 'Santina' had the earliest onset of endodormancy (LTER10acc = 5.9 d), while 'Tieton' (31.1 d) had the latest. However, 'Tieton' reported the fastest average acclimation rate (k = 0.16), while 'Santina' (k = 0.05) had the slowest. 'Napoleon' (161.3 d) exhibited the longest endodormancy, while 'Schmidt' (96.7 d) had the shortest in 2020. Similarly, 'Schmidt' had the earliest average onset of ecodormancy (LTER90deacc = 118.4 d), while 'Napoleon 'had the latest (162.4 d). However, 'Napoleon' reported the fastest average deacclimation rate (k =-0.084), while 'Schmidt' exhibited the slowest (k =-0.051). 'Napoleon' (52.1 d) had the shortest average ecodormancy length, while 'Hedelfingen' (93.8 d) had the longest. Understanding genotypic variation in sweet cherry dormancy control will help growers make better informed decisions on cultivar selections to avoid fall and/or spring frost prone production areas, and guide breeders hybridization decisions. Presented by Jonathan T. Magby at the ASHS Annual Conference, 2022. This is the original author version of the abstract presented at the American Society for Horticultural Science (ASHS) Annual Conference. Original abstract and presentation of methods available via ASHS archive: Shared for academic and non-commercial use under standard fair use guidelines. UPDATES COMING in 2026