BUD HARDINESS AND DEACCLIMATION IN BLUEBERRY CULTIVARS WITH VARYING SPECIES ANCESTRY: FLOWERING TIME MAY NOT BE A GOOD INDICATOR OF DEACCLIMATION
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 °C to 28 °C, followed by visual evaluation after a 24h incubation at 23 °C. Similar shoots were deacclimated at a constant temperature of 20 °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 °C) than northern highbush cultivars (LT50 = 24 °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 °C) than did northern adapted cultivars (Weymouth and Bluecrop) (LT50 = 15 °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. Ozarkblue, an extremely late flowering cultivar, would seem to be adaptable to northern climates, yet the data from this study suggest bud swell and flowering time may be poor measures of rates of deacclimation. Deacclimation under fluctuating field conditions is currently being evaluated.
Ehlenfeldt, M.K., Rowland, L.J. and Arora, R. (2003). BUD HARDINESS AND DEACCLIMATION IN BLUEBERRY CULTIVARS WITH VARYING SPECIES ANCESTRY: FLOWERING TIME MAY NOT BE A GOOD INDICATOR OF DEACCLIMATION. Acta Hortic. 626, 39-44
V. corymbosum, V. darrowi, V. ashei, V. angustifolium