Electrolyte leakage and regrowth tests were used to estimate cold hardiness levels of field-grown ‘Midiron’ and ‘Tifgreen’ bermudagrass (Cynodon dactylon × C. transvaalensis crowns. The two procedures were in close agreement. ‘Midiron’ was hardier than ‘Tifgreen’ on all sampling dates. Greatest levels of freeze tolerance were –11°C for ‘Midiron’ and –7° for Tifgreen’ during December and January, ‘Midiron’ was killed at –5° in early June while ‘Tifgreen’ had lost all freeze tolerance by this date. Although the electrolyte leakage procedure was rapid and required no greenhouse space, it was relatively difficult to set up and evaluate.
Two-year-old Actinidia vines, grown on their own roots, were subjected to artificial freezing tests in midwinter to determine their relative hardiness. Plant survival, growth recovery, and stem necrosis were used for estimating freezing injury. Actinidia deliciosa (A. Chev.) C.F. Liang & A.R. Ferguson var. deliciosa vines, which included `Abbott', `Bruno', `Greensill', `Hayward', and `Jones' kiwifruit, were all severely damaged by exposure to a temperature of –18C for 4 hours. Actinidia arguta (Sieb. et Zucc.) Planch. ex Miq., A. kolomikta (Maxim. et Rupr.) Maxim., and A. polygama (Sieb. et Zucc.) Maxim. appeared to be more tolerant to winter cold than A. deliciosa, indicating that potential germplasm exists for improvement of cold hardiness through interspecific hybridization.
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.
To examine injuries caused by freezing temperatures, three woody plants were placed under temperatures ranging from 0 to –20C. Control plants were placed at 0 or –2 C, depending on the field sampling period. Freezing tests were done three times during the fall: Sept., Oct. and Nov., 1993. Spiraea × bumalda `Flamingmount', Spiraea callosa `Alba', and Spiraea × bumalda `Crispa' were tested. After freezing tests were complete, all plants were stored at –2C for the remainder of winter. In May, plants were repotted into containers. Effects of freezing temperatures on plant growth were recorded at the end of the summer. Results indicated that the most sensitive species to cold temperatures is Spiraea × bumalda `Crispa'. Moreover, the response of plants to the September freezing test was too variable to give a valid statistical analysis. Regression analysis was used as a tool to determine the temperature at which there is a 25% reduction in growth of the stem and the root dry matter, respectively. Results obtained in October are as follows: Spiraea × bumalda `Crispa', –6 and –7.6C; Spiraea × bumalda `Flamingmount', –10 and –8.7C; and Spiraea callosa `Alba' –10.7 and –11.5C. Results obtained in November are as follows: Spiraea × bumalda `Crispa', –7.1 and –8C; Spiraea × bumalda `Flamingmount', –12.2 and –12.3C; and Spiraea callosa `Alba', –8.5 and –8.7C. The reduction in cold hardiness observed for Spiraea callosa `Alba' is caused by warmer conditions (20C) in which plants were placed 2 days before the freezing test.
thought ( Dirr, 2009 ). Cold-hardiness of the hybrid fortune’s osmanthus appears to be intermediate to that of its parents ( Dirr, 2009 ), indicating that hybrid breeding may be a promising avenue for improving cold-hardiness in the genus. Germplasm
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.
Flower buds of eight ecotypes representing three native North American azalea species being grown in Burlington, Vermont were compared for cold hardiness by laboratory freezing during the cold acclimation period for three years. Species were Rhododendron calendulaceum, R. prinophyllum, and R. viscosum. There was a high variation in the number of florets killed within an inflorescens in response to freezing temperatures. There was little difference in the cold hardiness of florets of R. Pinophyllum and R. calendulaceum florets, but R. viscosum florets were hardier. Some differences were noted in cold hardiness of florets of ecotypes, but these were not necessarily related to latitude of origin. Cold hardiness showed a relationship with the daily mean temperature of the three days preceding freezing tests.
Field and laboratory tests of cold hardiness were conducted on 8 cultivars of bermudagrass (Cynodon spp.) and 2 cultivars of Paspalum vaginatum. The cultivars of bermudagrass were more cold hardy than those of Paspalum. ‘Brookings’ bermudagrass was the hardiest turfgrass.
Twelve seedling blackberry (Rubus spp.) populations were tested over 2 years for cold hardiness of stem and bud tissues. Seedling populations resulted from a partial diallele of crosses made among nine parents representative of three categories of cold hardiness. Viability testing of xylem, phloem, and bud tissues was conducted following exposure to a temperature lethal to 50% of tested tissue. Significant population effects (P < 0.05) occurred for xylem and bud cold hardiness in 1988 and for xylem, phloem, and bud cold hardiness in 1989. Results were similar for the 2 years, although there was a greater discrimination between populations for xylem and phloem cold hardiness in the 2nd year. Seedling populations having `Darrow' as a parent showed less tissue damage than the other eight populations. The populations having `Brison' as one parent showed consistently poor hardiness with the exception of one resulting from a cross of `Brison' × `Darrow'. This population showed consistently good hardiness, indicating that dominance effects may play a role in cold hardiness of blackberries.
Magnolia has graced southern landscapes for many years. However, its northern distribution is limited due to injury at low, freezing temperatures. Laboratory methods are available to assess the cold hardiness of many plants, but specific methods for Southern magnolia have not been established. Effects of exposure time, temperature at which plants were frozen, rate of warming, sample size and methods of injury evaluation were investigated. With exposure to -1.5 and -4C the leaves and stems were not injured when frozen for up to 7h. Stems and leaves that were nucleated with ice at -4C underestimated the cold hardiness as compared to similar plants that were nucleated at -1.5 and -3C. Samples warmed as taken from the temperature bath at 4C or at 4C/hr in the bath exhibited less injury than those taken directly out of the bath and exposed to room temperature. Similar cold hardiness determinations were obtained using whole and half leaf samples, while a quarter of a leaf or a leaf disk exhibited high variability and resulted in unreliable cold hardiness determinations. Visual analysis for injury was compared to electrolyte leakage and similar cold hardiness levels were obtained using the two methods.