2019 ASHS Annual Conference

The chilling requirement necessary for many cold-hardy grape cultivars is poorly understood. The objective of this study was to determine the number of chilling hours necessary for ‘Edelweiss’, ‘Frontenac’ and ‘Norton’ grapevines to reach 50% budburst. Grapevine budburst typically advances as the number of chilling hours accumulates. Generally speaking, the environments where these grape cultivars are grown are not limited by the lack of chilling hours, nevertheless, this information is still useful in understanding the release of bud dormancy. Canes from the three cultivars were collected from a research vineyard near Nebraska City, NE at two week intervals from November to April in 2016/2017 and 2017/2018. The canes were divided into single bud cuttings and bud position was noted – basal, medial and distal. The single bud cuttings were placed in forcing solution (200 mg/l 8-hydroxyquinoline citrate (8-HQC) and 2% sucrose) and buds were inspected bi-daily for budburst. When budburst occurred the Julian date was recorded and the cutting was removed from the experiment. The number of chilling hours differed between the two experiment years. ‘Edelweiss’ required 594 chilling hours to reach 50% budburst in ‘16/’17 but only need 381 hours in ‘17/’18. ‘Norton’ was more similar in the two years requiring 450 hours the first year and 381 hours the second year. The variability of chilling requirements from year to year can be influenced by the rate of dormancy onset and accumulation of chilling hours but requires further research to understand the relationship between these factors.