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Gena R. Hughes and Frank B. Matta

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.

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Jun Liu, Orville M. Lindstrom and Dario J. Chavez

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

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H.W. Philley, C.E. Watson Jr., J.V. Krans, J.M. Goatley Jr. and F.B. Matta

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.

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Frank B. Matta and Amin Kawatin

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'.

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Cindy L. Flinn and Edward N. Ashworth

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.

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A.M. Shirazi and M.V. Thierry

Survival of temperate plants is often dependent upon their resistance or ability to tolerate low temperatures. Differential thermal analysis (DTA) has been employed to explore the freezing characteristics of plants and other organisms. However, there appears to be a need for further studies to better understand the physiology of freezing and its significance as related to supercooling. Methods employing thermocouples, differential wiring, and digital data acquisition boards allow detection of very small exothermic responses (about 0.025 °C). This study reports on techniques and apparatus for using DTA as well as results obtained on various plant tissues. When Fagus grandifolia (American beech) was compared to Fagus sylvatica (European beech), it exhibited both a lower high temperature (HT) and low temperature (LT) exotherm that correlated with lower stem tissue water content during September to May. The DTA on Acer pseudosieboldianum (Korean maple) from a higher elevation showed lower LT exotherm in stem tissues when compared to lower elevation samples. Incubation of Cornus amomum, Cornus obliqua, and Larix gmelinii var. olgensis stem tissue with d-H20 for 20 hours resulted in an induction of LT exotherm at a significantly higher temperature than a normal LT exotherm. This phenomenon was attributed to the bark tissue in Larix gmelinii var. olgensis. Sucrose and glycerol exotherm profiles exhibited lower exotherm temperatures. In a companion study, we used thermal analysis (non-differential) to study supercooling in [Homadaula anisocentra(Mimosa webworm)] and a single exotherm event was detected. New technology provides a great deal of flexibility in the method of evaluation of exothermic responses in plants and other organisms.

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April D. Edwards, Steven E. Newman, Frank B. Matta and Adolph J. Laiche

During recent freezes in the mid-south, crape myrtles have suffered severe freeze damage. Some increased levels of cold hardiness have been observed in the National Arboretum crape myrtle releases, but the degree of tolerance has not been documented. The relative cold hardiness of five hybrid crape myrtle cultivars `Muskogee', `Natchez', `Osage', `Tuskegee' and `Yuma' was determined using differential thermal analysis. Stem samples were collected from established trees at two locations, Poplarville, Zone 8 and Starkville, Zone 7 once per month from October through April. Freezing point suppression was determined from five samples from each cultivar and location. Observed exotherms ranged from -7C to -13C.

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Frank B. Matta and Amin Kawatin

Our objectives were to 1) Determine acclimation and deacclimation patterns of buds and stems of four pecan cultivars in Mississippi and 2) to determine the relationship between cold hardiness, based on DTA, and tissue injury, based or viability tests. Stem critical temperatures for September showed that `Hughes' was slower in acclimating than `Jackson'. Maximum hardiness for all cultivars occurred in January, except for `Desirable', which reached maximum hardiness in December but started deacclimating in January. Deacclimation for the remaining cultivars started in February. Bud critical temperatures for September and October also show that `Hughes' was slower in acclimating compared to the remaining cultivars. Maximum bud hardiness for `Desirable' occurred in December, with the remaining cultivars reaching maximum hardiness in January. Bud deacclimation for all cultivars occurred in March. The LD50 for the tetrazolium and electrolyte leakage tests occurred at about –32 and –30C, respectively. In buds, LT50 for the tetrazolium test was –18C. The LT50 electrolyte leakage and browning test was –20C.

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Michele R. Warmund, Fumiomi Takeda and Glen A. Davis

Abbreviations: DTA, differential thermal analysis; FAA, formalin-acetic acid-alcohol; LTEs, low temperature exotherms. Contribution from the Missouri Agr. Expt. Sta., J. Ser. no. 11577. We gratefully acknowledge the technical assistance of Milon

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D.L. Barney, C.J. Mancuso and T.L. Finnerty

An inexpensive controlled freezing system that allows the temperature regime of eight modular sample chambers to be varied independently was constructed. A microcomputer-based data acquisition and control unit controls the freeze-thaw cycle in each of the chambers, as well as recording sample temperatures at desired time intervals. The computer also controls the freeze-thaw cycles in, and records data from, two differential thermal analysis units and records data from an electrical conductivity meter.