Interspecific hybrid grapevine cultivars have been developed to expand grape cultivation into cold-climate areas. Cold weather events can lead to bud death and trunk injury which reduce yields and can result in plant death. Phenotyping cold hardiness is challenging, and developing a standardized phenotypic protocol would enable efficient evaluation of University of Minnesota grape breeding germplasm. The objective of this study is to utilize differential thermal analysis as an assay to quantify the low temperature exotherm response of grapevine buds. We phenotyped 28 varieties and advanced breeding selections from October 10th, 2023 through March 20th, 2024. Commercial cultivars (e.g. Marquette, Itasca, Frontenac) and breeding selections (wine grape, table grape, and rootstocks) were sampled weekly or bi-weekly based on availability of plant material. Differences in acclimation and deacclimation patterns between time points were observed in the low temperature exotherm readings, indicating that there may be differences in the genetic mechanisms for cold hardy responses. After the coldest day of the season, January 14, 2024, which had a low of -23°C, the temperature at which 50% of the buds would die, or LT50, for ‘Marquette’, ‘Itasca’, and ‘Frontenac’ were -29.7 °C, -30.9 °C, and -30.5 °C, which is consistent with field observations. The LT50s were rated at lower temperatures than the ambient air temperature, thus all genotypes were able to survive the weather conditions for this cold event. Future analysis aims to utilize K-means cluster analysis to determine groups that differ in responses to winter fluctuations in temperature and to determine the genetic controls for these responses.
