Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2004
Publication Date: 2/18/2004
Citation: Arora, R., Rowland, L.J., Ogden, E.L., Dhanaraj, A.J., Marian, C.O., Ehlenfeldt, M.K., Vinyard, B.T. 2004. Dehardening kinetics, bud development, and dehydrin metabolism in blueberry (vaccinium spp.) cultivars during deacclimation. Journal of the American Society for Horticultural Science.129:667-674 Interpretive Summary: The blueberry industry in the United States suffers from a lack of cold hardy cultivars. Cold injury in plants can occur due to early fall freezes prior to hardening (cold acclimation), severe mid-winter freezes that exceed the limits of the plant's tolerance, or hard winter/early spring freezes after loss in cold tolerance following unseasonable warm spells (deacclimation). Ideally, blueberry cultivars for the United States should acclimate to cold quickly in the fall, have a high mid-winter hardiness, and deacclimate slowly during spring or unseasonable warm spells in winter without adversely delaying time of fruiting. Until now, no systematic approach has been undertaken to study the deacclimation process in blueberry, even though it is an integral part of winter survival and reproductive success as untimely winter or early spring thaws followed by hard freezes can cause severe injury to dehardened flower buds. In this study we have measured the rate of deacclimation in five blueberry cultivars with different amounts of southern germplasm in their parentage. In general, the northern cultivars (V. corymbosum) were found to have the highest levels of mid-winter hardiness and to deacclimate the slowest, the southern cultivars (V. ashei) were the least hardy and deacclimated the fastest, and the hybrid cultivars (predominantly V. corymbosum but with small percentages of southern germplasm, either V. ashei or V. darrowi, in their backgrounds), were intermediate in terms of their rates of deacclimation. Because differences in deacclimation rate were clearly evident among the cultivars studied, 'rate of deacclimation' should be an important consideration in blueberry breeding programs aimed at improving winter survival. This information is now available to breeders to use in developing slower deacclimating cultivars that should be more tolerant to late winter or early spring frosts.
Technical Abstract: Loss of freeze tolerance, or deacclimation, is an integral part of winter-survival in woody perennials because untimely mid-winter or spring thaws followed by a hard freeze can cause severe injury to dehardened tissues. This study was undertaken to investigate deacclimation kinetics, particularly the timing and speed, of five blueberry cultivars ('Bluecrop', 'Weymouth', 'Ozarkblue', 'Tifblue', and 'Legacy'), with different germplasm compositions and mid-winter bud hardiness levels, in response to an environmentally controlled temperature regime. Based upon bud cold hardiness evaluations in 2000 and 2001, 'Tifblue', a Vaccinium ashei Reade cultivar, was one of the least hardy and the fastest to deacclimate; 'Bluecrop', a predominantly V. corymbosum L. cultivar, was the most hardy and the slowest to deacclimate; and 'Ozarkblue', a predominantly V. corymbosum cultivar but including southern species V. darrowi Camp and V. ashei, was intermediate in speed of deacclimation. 'Weymouth' (predominantly V. corymbosum) and 'Legacy' (73.4% V. corymbosum and 25% V. darrowi) were slow to intermediate deacclimators. Deacclimation rates did not correlate strictly with mid-winter bud hardiness. Data suggest that the southern germplasm component V. ashei may be responsible for the observed faster deacclimation whereas both southern species, V. darrowi and V. ashei, may contribute genes for cold sensitivity. Strong positive correlations between stage of bud opening and bud cold hardiness existed in both years (r = 0.90 and 0.82 in 2000 and 2001 study, respectively). Previously identified major blueberry dehydrins, 65-, 60-, and 14-kDa, progressively decreased in their abundance during incremental dehardening in 'Bluecrop', 'Weymouth', and 'Tifblue'. However, down-regulation of the 14-kDa dehydrin most closely mirrored the loss in cold hardiness during deacclimation, and, therefore, may be involved in regulation of bud dehardening. Because differences in deacclimation rate were clearly evident among the genotypes studied, rate of deacclimation of the flower buds of blueberry should be an important consideration in breeding to improve winter survival.