Search Results
Abstract
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.
Acclimation and cold hardiness of blueberry buds (Vaccinium ashei cv. Tifblue) were evaluated using differential thermal analysis (DTA) and tissue browning. Buds exhibited a single exotherm at -7C October through December and at -11C January through April. LOW temperature exotherms (LTE) were not detected. Tissue browning test ratings indicated that ovary death occurred at -21C.
Effects of temperature on the deep supercooling characteristics of dormant and deacclimating sweet cherry flower buds J. Amer. Soc. Hort. Sci. 112 334 340 Andrews, P.K. Proebsting, E.L. Jr Gross, D.C. 1983 Differential thermal analysis and freezing injury
The objective of this study was to relate the lethal freezing temperatures of St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] genotypes, as measured by differential thermal analysis (DTA), to winter survival observed in the field. DTA-predicted lethal temperatures of 14 St. Augustinegrass genotypes ranged from –7.7 to –4.7C. Regression of field winter survival vs. DTA-predicted lethal temperatures resulted in an r 2 = 0.57 for one field trial that evaluated cultivars with a relatively narrow range of expected freezing tolerance. In a second study evaluating cultivars with a greater range of freezing tolerance, r 2 was 0.92 when winter survival was regressed on DTA-predicted lethal temperatures. DTA was successful in measuring freezing avoidance of St. Augustinegrass cultivars.
Abstract
Superimposed Amplified Exotherm Differential Thermal Analysis System is presented as a system used for detecting low-temperature exotherms of excised dormant flower buds. This system uses thermistors that do not penetrate the tissue and a liquid freezing medium for more uniform temperatures between the sample and reference. A test chamber is presented that can be used with a nonprogrammable freezer. Tests with Forsythia flower buds indicate 2 exotherms, the second of which is associated with a dramatic loss of tissue viability.
Stem critical temperatures for September showed that `Hughes' was later in acclimating than `Jackson'. Maximum hardiness for all cultivars occurred in January and deacclimation in February. Bud critical temperatures for September and October also showed that `Hughes' acclimated later than the other cultivars. Maximum hardiness for buds occurred in January and deacclimation in March. In December, the LT50 for the tetrazolium test, the electrolyte leakage test, and the tissue browning test were –18, –20, and –20C, respectively, as shown by differential thermal analysis of `Desirable'.
Abstract
Thermal and differential thermal analysis (DTA) are used to detect exotherms that result from the freezing of supercooled tissues (4). They provide a convenient and rapid means of assessing the hardiness of tissues that supercool, such as the floral primordia of Prunus spp. (3) and the compound buds of Vitis spp. (2). The inability to process a large number of tissue samples simultaneously, however, has been a major limitation of DTA. Ashworth et al. (3) described a computer-assisted data-logging system for recording thermal analysis data generated when Prunus flower buds were frozen. Multiple cooper-constantan thermocouples were used to increase the number of buds monitored on a given channel of a multichannel data-logger. Copper-constantan thermocouples, however, were not adequate with our instrumentation to discriminate exotherms generated by the freezing of individual shoot primordia of compound grapevine buds. Furthermore, anatomical barriers to ice propagation may be negated if thermocouples are inserted into buds to increase exotherm detection (5).
Differential thermal analysis (DTA) was used to study the freezing behavior of `Berkeley' blueberry (Vaccinium corymbosum L.) flower buds at cooling rates of 10, 5, and 2C/hour. Experiments were conducted at various stages of hardiness on excised and attached (5 cm of stem) buds. The presence and number of low-temperature exotherms (LTEs) in hardy buds generally increased when analyses were conducted using faster cooling rates with excised buds. The number of LTEs detected in individual buds did not correlate (r 2 = 0.27) with the number of injured florets. The inability to detect LTEs in buds attached to stem segments and cooled at 2C/hour indicates that DTA cannot reliably estimate blueberry flower-bud hardiness in field plantings.
Abstract
The freezing patterns of flower buds in peach [Prunus persica L.) Batsch ‘Redhaven’] and sweet cherry (Prunus avium L. ‘Bing’) changed significantly during spring deacclimation. Nucleation temperature, measured by differential thermal analysis (DTA), and freezing injury were monitored for reproductive organs as affected by the presence and absence of vegetative tissue, surface moisture, and the ice nucleation-active (INA) bacterium Pseudomonas syringae van Hall. The flower buds retained the capacity to deep supercool until early bud swell, when the low temperature (LT) exotherm distribution widened and fewer LT exotherms were produced. Following the disappearance of the LT exotherms until the petals tips first appeared through the calyx, the nucleation temperature of the flower buds increased 1° to 3°C. During this period the presence of stem tissue had no effect on nucleation temperature, whereas surface moisture increased the nucleation temperature several degrees. After full bloom, flowers attached to the stem froze at higher temperatures than excised flowers whether wet or dry. From the time the flower buds lost the capacity to deep supercool until petal tip emergence, freezing injury was reduced significantly by increasing the ice nucleation temperature, either by wetting peach flower buds or by inoculating sweet cherry flower buds with INA P. syringae bacteria. Following petal tip emergence, the higher nucleation temperatures no longer reduced freezing injury. Apparently, the flower buds of these Prunus species avoid freezing during the winter by deep supercooling of the dormant flowers, yet tolerate freezing during the early stages of flower development in the spring.
Abstract
Stems and leaves of Pyracantha coccinea Roem. ‘Lalandii’ Dipp. acclimated to —26°, and mature roots to —17°, when previously exposed to 4° for 5 weeks. Young roots, however were killed at —5° even after exposure to 4° for 16 weeks. Differential thermal analysis was used to determine whether the initial freezing processes were altered following exposure to 4°. A higher percentage of tissue water was frozen during the initial period of ice formation in young roots grown at 18° than those grown at 4°. No difference in the percentage of tissue water frozen in mature roots grown at either 18° or 4° was evident. The rate of ice formation in both young and mature roots was highest in tissues grown at 18°. Thus, after exposure to 4°, the physical stresses in root tissue due to ice formation were decreased in both young and mature tissue. While growing the tissue at 4° alters the physical stresses imposed by ice formation, young roots do not survive below —5° whereas mature root roots do. Therefore, it is suggested that differences in survival of mature and young roots of pyracantha are not solely due to a mitigation of the physical stresses imposed by ice formation.