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.
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
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.
Stem sections of 31 filbert genotypes were collected, artificially frozen, and evaluated by visual browning of cambium and other tissues to determine cold hardiness during 5 sample dates in 1984 and 1985. Corylus heterophylla Fish. ex. Trau. was the most cold-hardy filbert tested, but it deacclimated sharply before the end of February. The tested filberts were divided into 3 temporal groups of acclimation to maximum cold hardiness—early, midwinter, and late. C. avellana L. ‘Butler’, ‘Tombul’, ‘Barcelona’, ‘Ennis’, and ‘Casina’ acclimated early; ‘Gasaway’, acclimated in midwinter season; ‘Daviana’ and ‘Hall’s Giant’ acclimated late. The genotypes tested also were separated into very hardy, hardy, and least hardy groups for cortex-cambium, pistillate bud, and staminate bud tissues. The general order of tissue hardiness from least to most was pith, xylem, cambium, and cortex. Vegetative buds in midwinter were as hardy or hardier than the cambium. Staminate flowers were hardier than pistillate in October, but most pistillate flowers were hardier than staminate by January. Several filberts had fully blooming pistillate flowers that were uninjured at −30°C in December and −40° in January. Filbert flower buds demonstrated maximum cold hardiness during nondormancy.
Seasonal alteration of the cytosolic and nuclear Ca2+ concentrations of spruce (Picea engelmannii Parry) and brome grass (Bromus inermis Leyss) was investigated by the antimonate precipitation cytochemical technique. Electron microscopic (EM) observations revealed that electron-dense Ca2+ antimonate deposits, an indication of Ca2+ localization, were seen mainly in the vacuole, the cell wall and the intercellular space in samples of both species, collected on 14 July 1997. Few deposits were found in the cytosol and nuclei, showing a low resting level during summer months. On 8 Aug. 1997 following a decrease in daylength of 1 hour and 12 minutes, Ca2+ accumulation was initiated in spruce with increased cytosolic and nuclear Ca2+ deposits, but not in brome grass. On 8 Sept. 1997, Ca2+ accumulation occurred in the cytosol of brome grass. This followed a drop in ambient temperature to 12 °C. Cytosolic and nuclear Ca2+ deposits continued to increase in spruce. Controlled experiments confirmed that it was the low temperature, not shortening daylength, that triggered Ca2+ accumulation in brome grass. High cytosolic and nuclear Ca2+ concentrations lasted about three months in spruce from early August to early November. However, the high cytosolic and nuclear Ca2+ concentrations in brome grass lasted only about 20 days from early September to the end of the month. During winter and spring, both species had low resting cytosolic and nuclear Ca2+ concentrations. The relationship between the duration of the high cytosolic and nuclear Ca2+ concentrations and the status of the developed dormancy/cold hardiness is discussed in light of current findings.
Citrus seedlings sprayed with chemicals which influence the cold hardiness of other plants were hardened in controlled conditions. Maleic hydrazide (MH-30) increased cold hardiness; however, growth retardants (2-chloroethyl)trimethylammoniumchloride (chlormequat) and succinic acid-2,2-dimethylhydrazide (SADH), and growth inhibitor abscisic acid (ABA) did not. ABA at high concns decreased cold hardiness as did gibberellic acid (GA3). Benzyladenine (BA), kinetin (KN), decenylsuccinic acid (DSA), and (2-chloroethyl)phosphonic acid (ethephon) had little or no effect on cold hardiness. These results are consistent with tests on citrus conducted under field conditions.
Open-pollinated progeny from 15 peach (Prunus persica) cultivars, two peach × P. kansuensis hybrids, and one peach almond (P. amygdalus) hybrid were evaluated for their cold hardiness and for tolerance to Cytospora canker following artificial inoculation with Leucostoma persoonii. Winter hardiness was negatively correlated with canker necrotic length (r = −0.26**) and positively correlated with canker rating (r = 0.26**), as indicated by qualitative ratings. The half-sib families differed for canker necrotic length following fall inoculation, indicating that individuals with increased tolerance to L. persoonii canker could be selected from the population. Progeny from the cultivar Yennoh exhibited the shortest canker necrotic length following fall inoculation, and all the inoculated branches were visually healthy. ‘Yennoh’, a plant introduction from Russia, may have a higher tolerance to Leucostoma than has previously been found in U.S. germplasm.
Knowledge of the level of cold hardiness and how hardiness is inherited in sour cherry is essential to germplasm collection and cultivar development. Twig samples of two sweet cherries (Prunus avium L.), 12 sour cherries (P. cerasus L.), and one ground cherry (P. fruticosa Pall.) of diverse geographic origins were collected in Jan. 1990 and monthly from Aug. 1990 to Mar. 1991, preconditioned to induce maximum cold resistance, and subjected to freeze tests and differential thermal analysis. Low temperature exotherms (LTEs) were detected in all stems of P. cerasus investigated and correlated to xylem incipient injury temperatures (ITs) from December to February (r = 0.84, P ≤ 0.01). March had the best correlation of LTEs to xylem ITs with r = 0.84, P ≤ 0.01. LTEs were strongly correlated to phloem-cambium ITs in November, representing the acclimation period. The correlation coefficient (r) for the phloem-cambium ITs and the twig LTEs during November was 0.68, significant at P ≤ 0.01. Cortical tissue and vegetative bud injuries were not correlated to the stem LTEs. Xylem ITs were selected for evaluating the cold resistance of sour cherry in December to March and phloem-cambium ITs were selected for November. The degree of supercooling and hardiness of the phloem-cambium in late fall and early spring appears significant in determining the stem hardiness and commercial range of P. cerasus. Phloem-cambium tissue, expressed the most rapid deacclimation response. The average decrease in hardiness for the phloem-cambium, xylem, and cortical tissues between February and March was 4 °C, 0.32 °C, and 2.14 °C, respectively. Principal component (PC) analyses of the phloem-cambium and cortical tissues depicted gradations between minimum survival temperatures of the two presumed progenitor species of sour cherry, i.e., sweet cherry and ground cherry. The first principal component (PC1), which accounted for 61% of the total variance, was used to separate among cultivars and seedlings. Cultivars and seedlings at the negative end of PC1 exhibited hardier phloem-cambium tissue at critical injury times, October, December, January, and March than cultivars and seedlings at the positive end of the PC1 axis. Cultivars and progeny of crosses of northern origin parents showed hardiness values more comparable to ground cherry than did selections of less-cold-hardy parents suggesting that cold is a major selective force, contributing to sour cherry population variation.
The effect of water stress imposed at three dates in late summer and early fall on cold hardiness was examined in Rhododendron L. `Coral Bell', `Hinodegiri', and `Red Ruffle'. The persistence of the water stress-induced cold hardiness was also examined following plant recovery from the stress. Container-grown plants were exposed to three weeks of reduced water supply starting 8 Aug., 29 Aug., or 19 Sept., while control plants were well watered. Cold hardiness of leaves, lower, middle, and upper stems was evaluated with laboratory freeze tests. Reduced water supply independent of time initiated increased cold hardiness by 1 to 4C in the majority of the tested plant parts in the three cultivars. Cold hardiness of all plant parts tested strongly depended on the current water status of the plants as indicated by the stem water potential. In most cases, 3 weeks after rewatering, the cold hardiness of previously water stressed plants did not differ from that of nonstressed plants.
Cold-hardiness evaluations and soluble and insoluble-nonstructural carbohydrate analysis of dormant Vitis vinifera L. cv. Cabernet Sauvignon buds and cane tissue indicate a positive relationship between soluble carbohydrates and primary bud cold hardiness. Seasonal variations in soluble and insoluble carbohydrates appear to be related to changes in air temperatures and the dormancy status of the tissues. No differences were found in bud cold hardiness and only limited differences in carbohydrate levels of buds or stem tissues collected over 3 years from early harvest, normal harvest, or unharvested vines. These findings contrast with the widely held opinion that delayed harvest or failure to remove fruit results in reduced cold hardiness as a consequence of low storage carbohydrate content of the plants.