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Scott R. Kalberer, Rajeev Arora, Norma Leyva-Estrada and Stephen L. Krebs

induction, kinetics, and magnitude of cold hardiness transitions [i.e., hardening (acclimation), dehardening (deacclimation), and rehardening (reacclimation)]. Although “hardening” and “dehardening,” respectively, are an increase in freezing tolerance over

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Lixin Xu, Mili Zhang, Xunzhong Zhang and Lie-Bao Han

dehydration. Patton et al. (2007a , 2007b ) reported that proline content increased in response to cold acclimation in zoysiagrasses. Bermudagrass ( Cynodon L.C. Rich) cultivars with higher stolon proline content exhibited greater freezing tolerance than

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Ali Akbar Ghasemi Soloklui, Ahmad Ershadi and Esmaeil Fallahi

deacclimation as well as their relationships with freezing tolerance. Materials and Methods Plant material. Seven pomegranate cultivars including ‘Mahabadi’, ‘Malas Saveh’, ‘Naderi’, ‘Post Sefid Bafgh’, ‘Robab Neyriz’, ‘Shishe Kap’, and ‘Yusef Khani’ were used

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Peter Havard, Leonard J. Eaton and Peter R. Hicklenton

Two commercial freezers were modified to provide an inexpensive chamber system to investigate frost effects on wild, lowbush blueberries (Vaccinium angustifolium) under field conditions. A computer control system was developed with software written in Visual Basic 6.0 for MSWindows, which precisely controlled temperature in the plant canopy when the chambers were placed over blueberry plants in the field. Frost events (with temperatures ranging from -2 to -15 °C (28.4 to 5.0 °F)) were simulated by user input to control the cooling and warming rates, and minimum temperatures. The system records temperature set points, and current temperature in the plant canopy, or elsewhere in the plant environment, and provides a graphical display of key parameters. Trials have verified the reproducability of temperature profiles and the chambers have been used to provide preliminary information on the effects of frost at bloom on fruit set and development.

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Rajeev Arora, Lisa J. Rowland, Elizabeth L. Ogden, Anik L. Dhanaraj, Calin O. Marian, Mark K. Ehlenfeldt and Bryan Vinyard

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 (Vaccinium L.) 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.

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Mark K. Ehlenfeldt, Elizabeth L. Ogden, Lisa J. Rowland and Bryan Vinyard

The midwinter cold hardiness of 25 rabbiteye (V. ashei) blueberry cultivars was assayed across 2 years using a shoot freezing assay. LT50values (i.e. temperature at which 50% of buds are damaged) for the cultivars ranged from –24.9 °C for `Pearl River' (a 50% V. ashei derivative) to –13.7 °C for `Chaucer'. Under New Jersey conditions, numerous cultivars were observed to exhibit dimorphism for dormant floral bud size. Comparisons of bud dimorphism with LT50 values, found dimorphism more common in cultivars with lower floral bud hardiness. LT50 values generally supported empirical observations of winter hardiness, but exceptions suggest that additional factors contribute to observed winter hardiness under field conditions.

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Joyce C. Pennycooke, Ramarao Vepachedu, Cecil Stushnoff and Michelle L. Jones

Previous studies of plant tolerance to low temperature have focused primarily on the cold acclimation response, the process by which plants increase their tolerance to freezing in response to low nonfreezing temperatures, while studies on the deacclimation process have been largely neglected. In some plants, cold acclimation is accompanied by an increase in raffinose family oligosaccharides (RFO). The enzyme α-galactosidase (EC 3.2.1.22) breaks down RFO during deacclimation by hydrolyzing the terminal galactose moieties. Here we describe the isolation of PhGAL, an α-galactosidase cDNA clone from Petunia (Petunia ×hybrida `Mitchell'). The putative α-galactosidase cDNA has high nucleotide sequence homology (>80%) to other known plant α-galactosidases. PhGAL expression increased in response to increased temperature and there was no evidence of developmental regulation or tissue specific expression. Increases in α-galactosidase transcript 1 hour into deacclimation corresponded with increases in α-galactosidase activity and a concomitant decrease in raffinose content, suggesting that warm temperature may regulate RFO catabolism by increasing the transcription of the α-galactosidase gene. This information has potential practical applications whereby α-galactosidase may be targeted to modify endogenous raffinose accumulation in tissues needed for freezing stress tolerance.

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María A. Equiza and David A. Francko

and varieties. Comparative data on freezing tolerance of diverse palm species obtained under controlled laboratory conditions are scarce with the report of Larcher and Winter (1981) appearing to be the only one available. Several methods have been

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Joëlle Chat

Two-year-old Actinidia vines, grown on their own roots, were subjected to artificial freezing tests in midwinter to determine their relative hardiness. Plant survival, growth recovery, and stem necrosis were used for estimating freezing injury. Actinidia deliciosa (A. Chev.) C.F. Liang & A.R. Ferguson var. deliciosa vines, which included `Abbott', `Bruno', `Greensill', `Hayward', and `Jones' kiwifruit, were all severely damaged by exposure to a temperature of –18C for 4 hours. Actinidia arguta (Sieb. et Zucc.) Planch. ex Miq., A. kolomikta (Maxim. et Rupr.) Maxim., and A. polygama (Sieb. et Zucc.) Maxim. appeared to be more tolerant to winter cold than A. deliciosa, indicating that potential germplasm exists for improvement of cold hardiness through interspecific hybridization.

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Yongjian Chang and Barbara M. Reed

Cold hardiness and cryogenic survival of micropropagated pear (Pyrus cordata Desv.) shoots were evaluated after pretreatments with ABA and sucrose. Shoot cold hardiness increased by 3 °C, and cryopreserved shoot tip growth increased by 17% after a 4-week 150 μm ABA pretreatment. Low temperature (LT) pretreatments improved the recovery of cryopreserved P. cordata shoot tips. Six to 10 weeks of LT were required for reaching high cryopreservation recovery. ABA and LT treatments produced significant synergistic effects on both cold hardiness and cryopreservation recovery. ABA shortened the LT requirement for high cryopreservation growth from 10 to 2 weeks. The optimal treatment for recovery of cryopreserved shoot tips was a 3 week culture on 50 μm ABA followed by 2 weeks of LT, while the maximum cold hardiness (-22.5 °C) was obtained with 150 μm ABA and 2-week LT. A 4 week culture on 150 μm ABA at 25 °C induced dormancy in 74% of shoot tips, but had little effect on cryopreservation growth unless combined with LT. Control and ABA-treated shoot tips, lateral buds, and leaves had similar cold hardiness (-10 to -12 °C), but LT and LT+ABA-treated shoot tips survived the lowest temperatures (-17 to -23 °C), lateral buds next (-15 to -20 °C), and finally leaves (-14 to -18 °C). An increase in the preculture-medium sucrose concentration from 2% to 7% combined with 2-week LT significantly increased cryopreserved shoot tip growth (0% to 75%) and decreased the LT50 from -7.8 to -12.4 °C. The optimal shoot pretreatment for successful recovery of cryopreserved P. cordata shoot tips was a 3 week culture on either 50 μm ABA or 5% to 7% sucrose medium followed by 2 weeks of LT, and increased shoot tip growth from zero to >70%. Chemical name used: abscisic acid (ABA).