Water status is known to have an impact on cold hardiness of plants. Cold hardiness of `Catawbiense Boursault' rhododendron was examined under continuous and periodic water stress. Under continuous stress, water content of growing medium was maintained at 0.6 to 0.75, 0.45 to 0.6, or 0.3 to 0.45 m3·m-3. Under periodic stress, water content was either maintained between 0.6 to 0.8 m3·m-3 or plants were subjected to drought episodes at various times in late summer, autumn, and early winter. During a drought episode, watering was delayed until water content was below 0.4 m3·m-3. Watering then resumed and water content was maintained between 0.3 to 0.4 m3·m-3. Cold hardiness was evaluated on detached leaves and stem sections. The effect of continuous water stress depended on its severity and duration. Moderate stress did not increase cold hardiness compared to well watered plants during the first winter, but it did so when continued into the second winter. More severe stress increased cold hardiness during the first winter, but it decreased cold hardiness during the subsequent winter. The effect of periodic water stress depended on the timing of application. During initial and final stages of acclimation, cold hardiness increased in response to water stress less than during the intermediate stages. Water-stress-induced cold hardiness gradually decreased after rewatering.
Abstract
The freezing point of detached leaves of young, budded, container-grown ‘Hamlin’ orange plants was an acceptable measure of cold hardiness. Controlled freezing established that the mean leaf freezing point (MLFP) of detached leaves estimated cold hardiness within 0.86°C and was useful to predict the degree of damage to plants exposed to subfreezing temperatures.
The cold hardiness of Magnolia grandiflora `Claudia Wannamaker' and `Little Gem' was determined under 8, 12 and 16 hour daylengths. Temperature was maintained at 25C day and 20C night. In addition, specific and total carbohydrates of both cultivars were analyzed. Cold hardiness and carbohydrate content were tested at the beginning (0 week), middle (5 week), and end (9 week) of the study. As expected, both southern magnolia cultivars were more cold hardy after 9 weeks at 8 hour daylengths with -9C cold hardiness estimates, as compared to 12 and 16 hour daylengths. The 12 and 16 hour daylengths resulted in similar cold hardiness estimates of -6C after 9 weeks. Additional cold hardiness and carbohydrate information will be presented.
Abstract
Chemical growth regulators were applied in early fall to 1-year-old ‘Delicious’ apple trees (Malus domestica Borkh.) to evaluate cold hardiness and cold injury during late fall to late winter. Evaluations were made by the conductivity test and expressed as the percentage of electrolytes. Of the 18 chemicals tested, CGA-15281 (500 ppm) showed the most promise for increasing cold hardiness, especially in November. During freeze tests in November or February of 1976, AMO-1618 (1000 ppm), GA3 and GA3 + fluoridamid (500 and 6000 ppm, respectively), and Thidiazuron (100 ppm) induced significantly greater cold hardiness than the controls. When tested separately or in combination with other chemicals, ancymidol, CGA-15281, DEPEG, PP 528, and NIA-10637 produced slightly more cold hardiness relative to the controls in more than 50% of the tests. Daminozide, ethephon, GA3, glyphosine, and UBI-P293 were the least effective chemicals for inducing cold hardiness.
The expansion of urban communities to rural areas is leading to an increase of the problem of deer damage. White-tailed deer (Odocoileus virginianus) damage to landscape plants in commercial nurseries, residential and public areas is very widespread. Thuja occidentalis (Arborvitae) is one of the most common landscape plants. It is widely produced by nurseries and used by homeowners in the landscape. However, it is also highly favored by deer for browsing. Thuja plicata (Arborvitae) the Western Cedars is a highly deer-resistant arborvitae. One of the principal limiting factors for new arborvitae for its success in nursery productionand its use in the landscape is cold hardiness (in northern climates). However, the cold hardiness of different Thuja plicata is not known. Deer-resistant Thuja plicata cultivars: `Atroviren', `Cancan', `Elegantissima', `Excelsa', `Gelderland', `George Washington', `Hilleri', `Sunshine', and `Virescens' planted in Sprintg 1998 at The Morton Arboretum research plot in Lisle, Ill. Branch cold hardiness was tested by artificial freezing in Jan. 1999 and 2000. Ice-nucleated samples were placed in an ultra-low temperature and kept at 2 °C overnight, and the temperature then lowered at 5 °C/h to –40 °C, at which time samples were taken out at each test temperature (at 4 °C intervals). After the freezing test, the samples were thawed at 4 °C for 24 h, then planted in a peat and perlite media and kept at 100% humidity in a greenhouse. Samples were evaluated after 2 weeks for visual browning and lowest survival temperature. There were significant differences in coldhardiness between the nine cultivars tested in Jan. 1999. `Elegantissima', `Excelsa'. and `Cancan' were the most hardy (–34 to 40 °C), followed by `Virescens', `Sunshine', and `Gelderland' (–27 to 32 °C), `Hilleri' and `Atrovirens' (–24 to 25 °C). `George Washington' ` was the least hardy (–20 °C) cultivar.
The change in the cold hardiness of Rhododendron (cv. `English Roseum' following chronic exposure to ultraviolet-B radiation (280-320 nm) was studied. Leaf disks removed from ultraviolet-B exposed plants exhibited a greater tolerance to freezing temperatures than plants which received no ultraviolet-B exposure. Visual browning and percent phenolic leakage indicated that UVB-exposed leaf disks were killed at -11 °C, while control disks were killed at -8°C. The increase in phenolics seen in UV-B exposed plants most likely contributed to their increased resistance to cold temperature through the synthesis of cell-wall associated components such as lignin and suberin.
Abstract
The cambium of both ‘Early Amber’ peach and ‘Sungold’ nectarine, Prunus persica L. Batsch gained cold hardiness from November through January even though day and night temperatures were above 15°C. Cultivars attained the greatest hardiness in January, surviving temperatures of -12°C. ‘Early Amber’ maintained its hardiness until just prior to bud break (February 8) and decreased thereafter. ‘Sungold’ remained somewhat resistant to cold until February 15 and gradually lost hardiness until March 8. Characteristically the low chilling cultivars reached an acclimation base higher than reported for cultivars adapted to higher latitudes.
Abstract
Mature ‘Sunqueen’ peach [Prunus persica (L.) Batsch] trees were dormant pruned, summer pruned, or summer topped for 4 consecutive years. Dormant-pruned trees defoliated slightly earlier than summer-pruned trees, but the onset and duration of terminal vegetative bud rest was not influenced by pruning treatment. Compared to dormant pruning, summer topping slightly reduced cold hardiness of flower buds on 2 of 4 test dates in 1982, but not in 1984. Bloom on vertical shoots in the upper canopy was advanced by summer pruning and by summer topping in both 1982 and 1983. Bloom development at other canopy positions was not influenced by pruning treatment.
Abstract
Field grown onion plants (Allium cepa L. cvs. New Mexico Yellow Grano and Yellow Granex) harvested in December were frozen in a laboratory freezer were removed from the freezer at about 1°C intervals and replanted in sand in a warm greenhouse. Criterion for survival was root regeneration within 3 weeks. The LT50 value as determined by probit analysis for 58-day-old plants (−8.8°C) was significantly higher (0.5% level) than for the 74- or 90-day-old plants (−10.5 or−10.8°C) indicating less cold hardiness for the youngest plants.
Abstract
Flower buds of peach (Prunus persica Batsch) and apple (Malus domestica Borkh.) leached with water for 6 hours were less cold-hardy than nonleached buds. Buds which were leached with water for 16 hours and then dried for 0 to 16 hours were equally damaged by freezing; however, their moisture content decreased as drying time increased. Cold-hardiness was reduced rapidly during the first 3 hours of leaching, then loss of hardiness slowed and remained nearly constant through up to 48 hours of leaching. Loss of hardiness appears to be closely associated with leaching of water-soluble compounds from the flower bud, a loss which reduces the bud's ability to supercool.