Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 9, 2005
Publication Date: June 1, 2005
Citation: Rowland, L.J., Ogden, E.L., Ehlenfeldt, M.K., Vinyard, B. 2005. Cold hardiness, deacclimation kinetics, and bud development among 12 diverse blueberry (vaccinium spp.) genotypes under field conditions. Journal of American Society for Horticultural Science. 130:508-514. Interpretive Summary: The blueberry industry in the United States suffers from a lack of cold hardy cultivars. Cold injury in plants can occur with early fall freezes, severe mid-winter freezes, or hard early spring freezes. Flower buds must survive these freezes in order to produce berries the next season. Up until now, no one has studied the blueberry plant's response to some of these freeze conditions systematically. We studied 12 different blueberry varieties to see how they respond to early spring freezes after unseasonably warm spells. We found differences in their responses which lead us to believe that some of the varieties have genes that could be important in breeding for good spring frost tolerance or even mid-winter hardiness. This information will be of value to breeders to use in developing cultivars that should be more tolerant to late winter or early spring frosts.
Technical Abstract: Deacclimation response is an important part of reproductive success in woody perennials because late winter or early spring thaws followed by hard freezes can cause severe injury to dehardened flower buds. There is a need to develop more spring-frost tolerant cultivars for the blueberry industry. The identification of later or slower deacclimating genotypes could be useful in breeding for more spring-frost tolerant cultivars. This study was undertaken to investigate cold hardiness and deacclimation kinetics under field conditions for 12 blueberry genotypes (the cultivars 'Bluecrop', 'Duke', 'Legacy', 'Little Giant', 'Magnolia', 'Northcountry', 'Northsky', 'Ozarkblue', 'Pearl River', 'Tifblue', and 'Weymouth' and a population of V. constablaei Gray) with different germplasm compositions and expected mid-winter bud hardiness levels. Examination of bud cold hardiness (BCH) versus weeks of deacclimation over a seven-week period in two consecutive years (2002 and 2003) revealed clear genotypic differences in cold hardiness and timing and rate of deacclimation. Among cultivars, 'Legacy' was the least cold hardy at initial evaluation, even less so than 'Tifblue'. Regarding deacclimation kinetics, the weekly intervals with the largest losses (i.e. high rates of deacclimation) also varied among genotypes. For 'Duke', the largest losses in BCH were detected at weeks 2 and 3, making it the earliest deacclimator. For 'Bluecrop', 'Ozarkblue', 'Weymouth', 'Tifblue', and 'Legacy', the greatest losses in BCH were observed at weeks 3 and 4. For 'Little Giant', 'Magnolia', 'Northcountry', 'Northsky' and 'Pearl River', losses in BCH were greatest at weeks 4 and 5, while for V. constablaei, losses were greatest at weeks 6 and 7, making it the latest deacclimator. Deacclimation kinetics were not correlated with mid-winter hardiness or chilling requirements in any fixed pattern. On the other hand, a strong positive correlation was found between BCH and stage of bud opening (r = 0.84). A comparison of timing of deacclimation with germplasm composition indicated that V. constablaei was particularly late to deacclimate. 'Little Giant', a 50:50 hybrid of V. constablaei and V. ashei, was nearly as late to deacclimate as the 100% V. constablaei selections. Thus, V. constablaei may be useful in breeding programs to contribute genes for late deacclimation, which should translate into greater spring frost tolerance, in addition to genes for mid-winter hardiness.