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Norman E. Pellett, Nancy Rowan, and John Aleong

Florets of eight provenances representing three native North American azalea species [Rhododendron calendulaceum (Michx.) Torr., R. prinophyllum (Small) Millais, and R. viscosum (L.) Torr.] being grown in Burlington, Vt., were compared during three seasons for cold hardiness by laboratory freezing during cold acclimation. There was a large variability in the number of florets killed within an inflorescence in response to freezing temperatures. Cold hardiness of florets of the three species ranked, from most to least hardy, were R. viscosum, R. prinophyllum, and R. calendulaceum. Some differences were noted in cold hardiness of florets of provenances, but these were not necessarily related to latitude or elevation of origin. Cold hardiness of most provenances showed a significant linear relationship with the daily mean temperature of the 3 days preceding freezing tests. Ambient temperatures just before subfreezing test temperatures may affect winter injury more than provenance differences for these species.

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Neil Bell, Heather Stoven, James S. Owen Jr., and James E. Altland

as a commercial ornamental plant in North America is limited, principally because of a lack of cold hardiness. Almost all of Australia corresponds to the U.S. Department of Agriculture (USDA) hardiness zone 9 or higher ( Dawson, 1991 ), and as a

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Olivia M. Lenahan, William R. Graves, and Rajeev Arora

cold tolerance of S. americanus . Therefore, we investigated midwinter-hardiness and deacclimation patterns of populations of S. americanus from northern and southern locations within its natural distribution. Cold acclimation is the accrual of cold-hardiness

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

winter-hardiness and susceptibility to spring frosts have been identified as two of the most important problems of current cultivars ( Moore, 1993 ), and in the northern blueberry production areas, winter damage is considered the major factor limiting

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Neil C. Bell and James Altland

cultivated, but may also be attributed to plants being grown in landscapes that are watered regularly in summer, a common practice in summer-dry areas such as western Oregon. Published studies on hardiness of rockroses are rare and tend to be anecdotal in

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Ali Akbar Ghasemi Soloklui, Ali Gharaghani, Nnadozie Oraguzie, and Armin Saed-Moucheshi

, and high fruit quality ( Galletta and Ballington, 1996 ). Cold hardiness is the result of complex physiological mechanisms involving many cellular and whole plant details. Moreover, winterhardiness is affected not only by tolerance to cold but also by

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Hui-qing Li, Qing-he Li, Lei Xing, Gao-jie Sun, and Xiu-lian Zhao

Cold hardiness is the ability of a plant or plant organ to tolerate freezing or survive freezing conditions ( Fuchigami, 1996 ) without sustaining injury ( Lindén et al., 2002 ; Weiser, 1970 ), which is a major determinant of plant species growth

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M. Ahmedullah and C. R. Rom

Roots of one year old grape cvs. Concord, White Riesling, Grenache and Semillon were frozen to 0, -5, -10, -15 and -20°C in a programmable freezer. The tops were protected from cold by insulating them. For survival test, 4 plants of each cv. were planted in the greenhouse and their growth observed. Differential thermal analysis (DTA), using a computer attached to a programmable freezer was performed on roots. To aid in the interpretation of DTA, triphenyltetrazolium chloride (TTC) was performed. Hardiness determinations were based on DTA, TTC and the survival tests. DTA patterns representing exothermic response showed an exotherm associated with extracellular free water in tissue which appeared at about the same temperature range for all cvs. This is not associated with hardiness. Additional minor exotherms related to hardiness appeared at lower temperatures than the extracellular water exotherm. Their location differed from one cv. to another. Based on these tests, Concord roots appear to be hardier than other cvs. with important but minor differences in the hardiness of other cvs.

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M. Ahmedullah and C. R. Rom

Roots of one year old grape cvs. Concord, White Riesling, Grenache and Semillon were frozen to 0, -5, -10, -15 and -20°C in a programmable freezer. The tops were protected from cold by insulating them. For survival test, 4 plants of each cv. were planted in the greenhouse and their growth observed. Differential thermal analysis (DTA), using a computer attached to a programmable freezer was performed on roots. To aid in the interpretation of DTA, triphenyltetrazolium chloride (TTC) was performed. Hardiness determinations were based on DTA, TTC and the survival tests. DTA patterns representing exothermic response showed an exotherm associated with extracellular free water in tissue which appeared at about the same temperature range for all cvs. This is not associated with hardiness. Additional minor exotherms related to hardiness appeared at lower temperatures than the extracellular water exotherm. Their location differed from one cv. to another. Based on these tests, Concord roots appear to be hardier than other cvs. with important but minor differences in the hardiness of other cvs.

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Ali Akbar Ghasemi Soloklui, Ahmad Ershadi, and Esmaeil Fallahi

study were: 1) to determine cold hardiness of seven commercial Iranian pomegranate cultivars in different stages of the hardening cycle, from fall through winter; and 2) to study changes in carbohydrates and proline contents during acclimation and