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
Cold hardiness levels of six cultivars of Chinese elm (Ulmus parvifolia Jacq.), `Select 380', `Orange Ribbon 740', `Emerald Isle', `Emerald Vase', `Drake', and `King's Choice', were determined over eight sample dates from 31 Aug. 1988 to 16 May 1989 and for `Emerald Vase' and `Drake', over three dates from 14 Feb. 1988 to 25 Apr. 1988. All cultivars tested achieved a maximum cold hardiness in December and January of – 21 to – 24C, except `King's Choice', which survived exposure to at least – 30C. `Emerald Isle' and `Emerald Vase' acclimated earlier (both – 9C on 31 Aug.) and reacclimated later (– 6 and – 9C, respectively, on 16 May) than other cultivars tested. `Emerald Vase' and `Drake' exhibited similar cold hardiness levels over the two years tested.
composition with minimal decrease in midwinter primary bud cold hardiness ( O’Daniel et al., 2012 ). However, pruning is a rough regulator of yield and does not adequately control crop level or cropload of interspecific hybrids ( Howell et al., 1987 ; Kaps
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
More than 4500 accessions of eight genera including Pyrus at the National Clonal Germplasm Repository, Corvallis, Ore., require testing for cold hardiness. Since pear xylem deep supercools (7), differential thermal analysis (DTA) would be a suitable test if large numbers of samples could be examined simultaneously. The object of this study was to produce a method of multichannel DTA for defining cold hardiness of pear accessions. Visual browning was also examined to confirm cold hardiness values.
Flower buds of two sweet cherry (Prunus avium L.), 12 sour cherry (Prunus cerasus L.) and one ground cherry (P. fruticosa Pall.) were collected monthly from Aug. 1990 to Mar. 1991, and subjected to freeze tests to determine the level of cold hardiness. LT50 values (temperatures at which 50% of the flower buds were killed) summed over all months were significantly correlated (r = 0.6844, P ≤ 0.01) to the flower bud low temperature exotherms (LTEs). Correlation of LTEs to LT50 values was highest, r = 0.85, P ≤ 0.01 for the acclimation and midwinter period, November to February collections. During this period the average LT50 occurred before and within 2.5 °C of the LTE, indicating tissue injury before the LTE occurrence. During deacclimation, represented by the March collection, the LT50 began within 2.0 °C, on average, of the LTE, and in 11 of 12 cultivars and seedlings preceded the LTE. In March, the correlation of LTEs to LT50 values was less, r = 0.69, P ≤ 0.05, indicating possible changes flower bud deep supercooling. LTE values were selected as a measure of flower bud hardiness in sour cherry. Exotherms were not detected in the flower buds of all germplasm tested on all evaluation dates, but were the best means of separating selections. While LTE analyses expressed significant differences in November, December, and March at P ≤ 0.01, the LT50 analyses expressed differences only in December and February at P ≤ 0.05. The relationship between ambient temperatures and floral tissue hardiness indicated that November and March are two critical times for flower bud injury. November injury would occur in years when sudden low temperatures occur without sufficient pre-exposure to freezing temperatures. March injury would occur in years when sudden freezing temperatures follow warm days. This type of injury would be most pronounced in southern genotypes. Spring freeze injury could be significantly reduced by the selection of cultivars and seedlings that have delayed deacclimation. Exotherm occurrence and bud volume were correlated (r = 0.95, P ≤ 0.05). In January, when exotherms were least prevalent, they were generally present only in the five cultivars and seedlings with large bud volumes. The LTEs in midwinter, occurred within 3 °C of the reported average annual minimum temperature for the northern range of Prunus commercial production (Zone 6). The results of the principal component analysis of flower bud LTEs indicated that other selection criteria as flowering time might have played a more significant role in the hardiness range of sour cherry than simply geographic origin. The first principal component (PC1), which accounted for 77% of the total variance was used to separate among cultivars and seedlings. Selections at the positive end of PC1 had flower buds that were more cold susceptible than selections at the negative end of PC. This concurs with other research showing that flower bud hardiness is related more to commercial range (i.e., the range of commercial production) than to geographic distribution.
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
birch ( Betula pubescens Ehrh.), were found to be modulated mainly by temperature and not photoperiod ( Welling et al., 2004 ). Maximum cold-hardiness in midwinter is affected by the plant's growth cycle and fall conditions, including temperatures and
physiological responses of the plants to cool winter temperatures, not necessarily their specific cold hardiness. Various studies have demonstrated changes in chlorophyll content ( Nunez-Olivera et al., 1994 ), pigments and antioxidants ( Garcia-Plazaola et al
, 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