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item Ehlenfeldt, Mark
item Rowland, Lisa
item Arora, R

Submitted to: Acta Horticulture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/21/2002
Publication Date: 11/20/2003
Citation: Ehlenfeldt, M.K., Rowland, L.J., Arora, R. 2002. Bud hardiness and deacclimation in blueberry cultivars with varying species ancestry : flowering time may not be a good indicator of deacclimation.. Acta Horticulture Proceedings. 626:39-44.

Interpretive Summary: The development of more cold hardy and spring frost resistant blueberry cultivars is an important need to the blueberry industry in the United States. In an effort to better understand deacclimation (the loss of cold hardiness with exposure to warm temperatures) in blueberry, we have measured deacclimation and developed models to describe deacclimation in several blueberry cultivars with different species ancestry and different flowering times. We found that cultivars with any amount of southern species ancestry were less hardy initially than northern cultivars which are composed primarily of V. corymbosum and they deacclimated to a slightly less hardy level than did northern-adapted cultivars. After 6 days, deacclimation was relatively complete for all cultivars. Some southern cultivars such as `Ozarkblue¿ flower later than northern types suggesting they might avoid frost damage; however this study suggests that these cultivars may still be susceptible to damage. This information will be useful to scientists studying deacclimation, and to extension agents and blueberry breeders interested in developing cold-hardy blueberry cultivars.

Technical Abstract: Blueberry cultivars with varying percentages of species ancestry (V. corymbosum L., V. angustifolium Ait., V. ashei Reade, V. darrowi Camp) were assayed in mid-February to determine initial bud hardiness, and rates of deacclimation under constant temperature conditions. The LT50 (the temperature at which 50% lethality occurs) of detached shoots of field-grown plants of Weymouth, Bluecrop, Legacy, Ozarkblue, and Tifblue were evaluated at Day 0 by controlled freezing in a glycol bath at temperatures from -1 to -28 degrees C, followed by visual evaluation after a 24h incubation at 23 degrees C. Similar shoots were deacclimated at a constant temperature of 20 degrees C and a new batch was evaluated daily for 6 days. Cultivars with any amount of southern germplasm (V. ashei or V. darrowi) were less hardy (LT50 = -20 to -21 degrees C) than northern highbush cultivars (LT50 = -24 degrees C) which are composed primarily of V. corymbosum with small percentages of V. angustifolium. Cultivars with greater amounts of southern germplasm (Legacy, Ozarkblue, and Tifblue) started at less hardy levels, and deacclimated to a slightly less hardy level (LT50 = -12 to -14 degrees C) than did northern-adapted cultivars (Weymouth and Bluecrop) (LT50 = -15 degrees C). By Day 6, deacclimation appeared to plateau for all cultivars. Cultivar deacclimation was modeled using a log-linear regression model. Northern and southern cultivars differed in their regression parameters.