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  • Author or Editor: E.N. Ashworth x
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Abstract

The freezing of water within the young trees of peach [Prunus persica (L.) Batsch] was monitored using differential thermal analysis (DTA). Ice formation was initiated near −2°C. A logarithmic relationship between ice nucleation temperature and tissue sample size was observed. This suggested that the use of small tissue samples to estimate ice nucleation temperature may overestimate the extent of supercooling which would be observed in intact plants. The ice-nucleating agent associated with peach shoots active at − 2° was: 1) present in both field- and greenhouse-grown plants; 2) associated with overwintering dormant tissue and throughout blossom development; 3) resistant to surface disinfestants; 4) resistant to bacterial nucleation inhibitors; and 5) inactivated by autoclaving.

Open Access

Abstract

Deep supercooling in Prunus flower buds was related to vascular development. The continuity of the xylem was monitored by following the movement of a water-soluble dye. Dye was translocated into the primordia of 3 Prunus species which do not supercool, but it was not observed to move into the primordia of 11 species which avoid freezing injury by deep supercooling. Dye uptake may provide a simple and inexpensive technique to screen for bud supercooling.

Open Access

Abstract

Research on the role of ice nucleation active bacteria in frost injury in plants has led to renewed interest in determining the temperature that ice formation is initiated in plant tissues (1, 3-6). We recently determined the temperature at which water froze in mature nectarine trees (Prunus persica L. Batsch) under field conditions (4). Trees supercooled very little prior to freezing. Ice formation was initiated between −0.6° and −2.6°C. We noted that ice formation was initiated at several locations within the tree and subsequently spread throughout. The speed at which ice propagated throughout the tree depended on the prevailing weather conditions.

Open Access

Abstract

Tomato plants (Lycopersicon esculentum Mill. ‘US 28’) and plant parts ranging in fresh weight from 6 mg to 180 g were frozen in the presence and absence of epiphytic ice nucleation active (INA) bacteria. As weight increased, freezing temperatures rose from —10.5° to — 2°C in the absence of INA bacteria but varied from —3° to —2° in inoculated samples. The freezing behavior of entire plants could only be estimated using small plant parts when INA bacteria were present. INA bacteria were detected by a plate harvesting method. The fraction of tomato stem sections frozen increased with increasing exposure duration at constant temperature.

Open Access

Abstract

A method for large scale evaluation of flower bud hardiness in apricots using a thermal analysis system interfaced to a computer is described. The technique measures the heat released during the lethal freezing of supercooled water within the bud primordia. Nine thermoelectric junctions wired in series were used to monitor the temperature of 10 individual buds. Bud temperature was scanned every 30 seconds and the data recorded on magnetic tape. The data were subsequently transferred to a minicomputer which analyzed and stored data and produced graphics. Computer assisted thermal analysis can accommodate a large number of samples and simplifies handling and storage of data. This technique has applications as a research tool, for determining critical bud temperatures and in screening selections from a breeding program.

Open Access

Abstract

In the article “ ‘Ice Formation in Woody Plants Under Field Conditions” by E.N. Ashworth and G.A. Davis (HortScience 21:1233-1234, Oct. 1986) literature citations 1 and 4 were printed incorrectly.

Open Access

Abstract

No relationship was observed between the population of ice nucleation active (INA) bacteria and the temperature at which ice formed in peach [Prunus persica (L.) Batsch] shoots. The ice nucleation temperature remained stable throughout the year, even during periods when INA bacteria were not detected. An intrinsic ice nucleating substance seemed to be responsible for initiating ice formation and limited supercooling to about —2°C. The ice nucleating agent seemed to be a constitutive component of mature wood and was stable under a range of chemical treatments. Ice nucleation was influenced by sample mass, temperature, and length of exposure. The freezing behavior of peach shoots was best described using a stochastic model of ice nucleation.

Open Access

Abstract

Experiments were conducted to determine the relative contributions of bacterial and nonbacterial ice nuclei to freezing of peach [Prunus persica (L.) Batsch] shoots. Exposure to 33°C for 3 hr eliminated bacterial ice nuclei active at −3° on inoculated shoot pieces, but controls were not affected. In another experiment, ice nucleation temperatures and ice nucleation-active (INA) bacterial populations of field-collected shoots were determined. Mean freezing temperatures of 20 g (fresh weight) shoots were not significantly different in the presence or absence of INA bacteria (detection limit of 10 cells/g fresh weight). INA bacteria were detected on 19% of the shoots with a maximum natural population of 180 cells/g fresh weight. Inoculation studies indicated that 20 g fresh weight peach shoots contained a mean of 1.0 nonbacterial (−3°) ice nuclei, while shoots with 180 INA cells/g fresh weight averaged 1.4 (−3°) ice nuclei per 20 g. Most ice nuclei active at −3° were of nonbacterial origin.

Open Access

Abstract

The freezing of water within the woody tissues of apricot (Prunus armeniaca L.) and peach [Prunus persica (L.) Batsch] was characterized and the relationship to freezing injury established. Bark and xylem tissues exhibited contrasting freezing patterns and mechanisms of freezing resistance. Water in xylem parenchyma cells deep-supercooled. Tissue injury appeared to result from the freezing of this supercooled water. In contrast, water within bark tissues underwent equilibrium freezing. Bark injury resulted from the stresses which accompany extracellular ice formation and cellular dehydration.

Open Access