Examining the relationship between color, diameter, and cold hardiness in one-year-old suckers of ‘Frontenac’ and ‘Prairie Star’

Increasing numbers of wineries in cool and cold viticultural climates have coincided with the introduction of new cold hardy grapevine (Vitis spp.) cultivars from public and private breeding efforts in the northern United States. Despite their relative hardiness when compared to traditional European wine grapes (Vitis vinifera), producers in Upper Midwest states, such as North Dakota, struggle to achieve consistent production due to occurrence of cold events that kill dormant buds and/or entire vine trunks. Cold damage in the 2018-2019 dormant season resulted in widespread death of grapevines’ above ground plant material in plots at the North Dakota State University Horticulture Research Farm (near Absaraka, ND) providing a rare opportunity to examine trunk reestablishment from suckers. Using research vineyards composed of ‘Frontenac’ and ‘Prairie Star’ grapevines, multiple one-year-old suckers were retrained at each vine position throughout the 2019 growing season to form new trunks. Monthly from October 2019 to February 2020, 65 total individual trunks per cultivar were randomly sampled, removed from the vineyard, and examined for the following traits: total lignified internodes (whole plant), internode length (nodes one to five), caliper (between nodes one and two), CIELAB color coordinates (for internodes one and five), and differential thermal analysis for dormant buds, xylem, and phloem (buds one to six and the five internodes between them). Due to the recurrence of cold damage, sampling of trunks was halted in February when less than 10% of suckers were deemed viable. Linear relationships were examined between traits to assess trends of hardiness. Despite the subsequent death, cold hardiness of sampled trunks for both ‘Frontenac’ and ‘Prairie Star’ were related to CIELAB color characteristics with L* (lightness) and a* (red-to-green) standing out as prominent traits that may inform future pruning and trunk retention methodologies.