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, 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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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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Two species of Passiflora, P. edulis f. edulis (purple passion fruit) and P. edulis f. flavicarpa (yellow passion fruit), and P. incarnata (maypop), were evaluated for acclimation and cold hardiness, using differential thermal analysis, electrolyte leakage and the tetrazolium stain test. The two species showed the capacity to acclimate several degrees during the evaluation period and the three tests gave similar lethal temperatures for the two species; –9C to –10C for yellow passion fruit, –10C to –12C for purple passion fruit and –11C to –13C for maypop. Purple and yellow passion fruit were also assayed for survival after a freeze-thaw cycle, using a tissue culture regeneration technique called “feeder plate”. Yellow passion fruit did not show the capacity to regenerate at any of the temperatures used (0, –3, –6C). Purple passion fruit showed callus formation even at the lowest temperature (–6C).

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. Cane samples were collected from the field trial site on the day of analysis. Data for phenology, yield, berry composition, cold injury ratings, and cold hardiness were analyzed using a linear mixed model analysis of variance (SAS version 8.02; SAS

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damage and yield losses when the most vulnerable tissue, floral buds, deacclimate (loss of cold hardiness). Peach plants deacclimate and become susceptible to freezing temperatures at the end of February, but spring freeze risk remains until late March

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An international seminar on Plant Cold Hardiness was held at the Saint Paul campus of the University of Minnesota on November 2-4, 1977. This meeting was jointly sponsored by the National Science Foundation and the Japan Society for the Promotion of Science under the auspices of the U.S.—Japan Cooperative Science Program as well as the College of Agriculture, University of Minnesota. Seventy scientists representing 13 states and Washington, D.C., Canada, Colombia, Iran, Japan, Mexico, New Zealand, Norway and Poland attended the meeting, which was held to review current research, to discuss research priorities, to foster collaborative projects, and to consider how recent research findings might be applied to increasing food production.

The seminar focused on the fundamental biological processes of freezing survival in plants. Six consecutive sessions dealt with freezing stress, membranes, cold acclimation, supercooling, plant survival/breeding for cold resistance, and cryopreservation/cryoprotection. The subject matter encompassed horticultural and agronomic food crops, and forest species. Specific information can be obtained from the list of participants cited

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Stem and bud tissues of promocanes from more than 260 Rubus genotypes were evaluated for mid-winter cold hardiness after laboratory freezing in January 1990. T50 values were calculated for cane samples of red, yellow, black and purple raspberry, and blackberry cultivars, hybrids and species. Red raspberries exhibited the hardiest stem tissue, although several purple raspberries (Rubus sp. cvs. Brandywine, Royalty) survived as low as -33 C. Fall fruiting red raspberries, such as R. idaeus L. cvs. Zeva Remontante, Indian Summer, St. Regis, and Fallred, survived from -23 to -25 C. Summer-bearing cultivars, Canby and Puyallup, survived to -30 C. Stems of several black raspberries (R. occidentalis L. cvs. New Logan, Bristol) survived to -27 C. Stems of the hardiest blackberry cultivars, (R. sp. cvs. Black Satin, Smoothstem) survived to -22 C. In most genotypes the region of the bud at the axis of the stem was less hardy than tissues within the bud scales. Buds tissue was 2 to 10 C less hardy than stem tissue. Field plants were also visually rated for cold injury following record low temperatures occurring in 1989, 1990, and 1991.

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Abstract

To determine the frost hardiness of some important Camellia species and their cultivars, dormant twigs wintering in Tokyo were collected mainly in midwinter and artificially hardened at −3°C for 15 days to induce the maximum hardiness. Camellia japonica which extends north as far as 40°51′ was the most hardy species, resisting freezing from −18 to −20°C. A great difference in the hardiness was observed in the flower buds among many species and cultivars, ranging from −15 to −5° or above; though the leaves, vegetative buds and twig tissues were all hardy to temperatures from −10 to −15°C in the camellias tested. Except for C. japonica and its cultivars, the peduncle was found to be the least hardy tissue of the flower buds in the genus Camellia.

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, particularly when irrigated; this size is impractical for some landscapes and gardens. Little specific information on the cold hardiness of species of ceanothus cultivars is available. An estimation of winter hardiness can be inferred from the native range of

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Leaf freezing point determinations failed to show a seasonal pattern of cold hardiness in avocado (Persea americana Mill.) plants or to correlate with the known range of cold tolerance of 7 cultivar groups. However, plant freezing point based on freeze-chamber testing estimated cold hardiness based on reported field performance.

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