The winter hardiness of woody perennials is dependent on a variety of factors, including overall health and vigor, dormancy status, maximal cold hardiness, and resistance to additional nontemperature stressors. Of particular concern are the
A bell shaped, rest-intensity curve as a function of time was obtained for ‘Elberta’ peach and ‘Chinese’ apricot leaf buds growing in the field. Rest was not closely associated with fluctuating environmental temperatures, cold hardiness, or rate of respiration.
Apricot leaf buds reached the peak of their rest before peach leaf buds, and it was not as intense or as deep as it was with the peach buds. Rest was completed by both species at the same time in early January.
Effects of fall fertilization programs on cold hardiness if young Cornus alba `Argenteo-Marginata' and Weigela florida `Rumba' plants, were examined. In August 1992, four fertilization programs were applied to one year old woody plants, propagated by cuttings in 1991. Fertilization treatments were as follows: 1. discontinuation of fertigation treatments on August 30; 2. gradual decreasing nitrogen concentration (100 to 0 mg/l of 20-20-20) from August 15 to September 30; 3. constant nitrogen concentration (100 mg/l of 20-20-20) from August 15 to September 30; and 4. high potassium concentration (110 mg/l of 7-11-27) from August 15 to September 30. Whole plants were the” removed from pots and roots cleaned. They were placed under freezing temperatures ranging from 0 to -20°C at 2°C intervals. Sampling were taken at the end of September, October and November. After the freezing test, the plants were stored at -2°C. re-potted in May 1993, and evaluated for winter injury in August 1993. Results indicate that none of the four fertilization programs induced positive or negative effects on cold hardiness in both species. However, the signs of cold hardiness are observable in October at different degrees in each species. Plants of Weigela died at -12°C, while all plants of Cornus survived down to -20°C. Furthermore, a 25% loss of growth of stems and roots was found at -9°C for Weigela, while for Cornus it was -17 and -15°C stems and roots respectively.
Total protein increases were observed in both Albizzia julibrissin epicotyl and hypocotyl tissues with advancing stage of cold hardiness, while no changes were detected in total nucleic acid quantities. Heavy ribosomal RNA decreased and soluble RNA increased, as percentages of total nucleic acid, during induction of cold hardiness in epicotyl tissues, but they remained unchanged in hypocotyl tissues. The data suggest either different mechanisms of control during induction of cold hardiness between epicotyl and hypocotyl tissues or a lack of relationship quantitatively between nucleic acid fractions and total protein concn or induction of cold hardiness in Albizzia julibrissin tissues.
Deciduous fruit trees undergo endo-dormancy during fall at which time they also attain maximum cold hardiness (CH). Because these two processes occur simultaneously it is difficult to study them independently. We have been able to overcome this limitation with the use of genetically related (sibling) deciduous and evergreen peach trees. Using this system we conducted a time course study to characterize the seasonal fluctuations in CH and proteins in bark and xylem tissues. Cold hardiness (LT50) was assessed using electrolyte leakage method. Polypeptides were separated using SDS-PAGE. The data indicated that 1) CH of bark increased from -5°C (in August) to -49°C (in January) and from -3°C to -22°C for deciduous and evergreen trees, respectively. In January, under favorable conditions, evergreen trees were actively growing. 2) CH of xylem successively increased from -11°C to -36°C in deciduous trees and from -7°C to -16°C (in November) in evergreen trees and then plateaued. 3) LT50 of xylem in both genotypes closely approximated the mid-point of low temperature exotherms determined by differential thermal analysis. 4) As CH increased several qualitative and quantitative differences in polypeptides were noted between two genotypes. These changes during cold acclimation will be compared with those during de-acclimation.
Three cultivars (early, midseason, late), two ground covers (clean cultivation followed by temporary cover vs. permanent sod strips), and trickle vs. no irrigation were studied in a high-density (633 trees/ha) experimental peach orchard established in 1980 on Fox sand. Growth rate in the first 5 years was similar for all three cultivars. It was retarded up to 12% by permanent sod relative to temporary cover and enhanced up to 30% by trickle irrigation vs. no irrigation. Total marketable yields and that of large-sized fruit (>6.3 cm) were significantly influenced by cultivars in the first and second, but not the third year of production. Ground cover treatments did not influence total marketable yields, but did affect the yield of large fruit in one year. Irrigation increased total marketable yields each year and also increased the yield of large fruit. Yields were up to 30.7% higher in trickle vs. non-irrigated plots. Cold hardiness of flower buds and shoot xylem in 1982 was significantly influenced by cultivar and irrigation treatments, but not by ground cover treatments; In 1984, each of these factors affected cold hardiness. Foliation in 1984 was affected by ground cover and irrigation treatments but not by cultivars. The best treatment combination across cultivars for management of the orchard floor consisted of permanent sod strips of creeping red fescue (Festuca rubra L.) in the row middles combined with trickle irrigation in the tree row.
Canes of three field-grown cultivars of red raspberry (Rubus idaeus L. `Maurin Makea', `Ottawa', and `Muskoka') were sampled from October to April. Carbohydrate contents of canes and flower buds were analyzed, and cold hardiness (LT50) was determined by controlled freezing. Starch, sucrose, glucose, fructose, and minor amounts of raffinose and stachyose were present in both cane and bud tissues. Glucose and fructose were the predominant sugars in buds. In canes, the proportion of sucrose of all sugars was greater than in buds. Seasonal changes in carbohydrates were related to changes in cold hardiness and mean air temperature during a 5-day period preceding sampling. Starch decreased during fall and was barely detectable in midwinter. Soluble carbohydrates accumulated to 73 to 89 mg·g-1 dry weight in canes and 113 to 131 mg·g-1 dry weight in buds in midwinter. The most striking increase occurred in the concentration of sucrose, but glucose, fructose, raffinose, and stachyose also accumulated. There was a positive correlation between LT50 and the amount of starch, but a negative correlation between LT50 and the amounts of total soluble carbohydrates, sucrose, glucose, and fructose. High levels of sucrose, total soluble carbohydrates, and a high ratio of sucrose to glucose plus fructose were characteristic of a hardy cultivar. Results are evidence of the importance of carbohydrate reserves, especially sucrose, on winter survival of red raspberry.
Decreasing photoperiods and decreasing temperatures induce cold acclimation and the accumulation of soluble sugars in many plants. Two cultivars of southern magnolia differing in cold hardiness and acclimation patterns, were monitored to determine photoperiod × temperature interaction on cold hardiness and soluble sugar content. Cold hardiness increased with low temperatures and short photoperiods. Total soluble sugars, sucrose, and raffinose consistently increased in the leaves and stems of both cultivars in response primarily to low temperature. `Little Gem' was less responsive to photoperiod than `Claudia Wannamaker'
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.
Biweekly cold hardiness and water content were measured on 1-year-old field cuttings of bearing Concord grapevines at the Horticultural Teaching and Research Center at MSU from Sept. 1998 to Apr. 1999. Cold hardiness index LT50 (temperature at which 50% of the sample was killed) was determined by three viability tests after laboratory controlled sub-freezing treatments. Weather data were obtained from the MSU agricultural weather automatic system. Average maximum and minimum air temperatures of 1, 3, 5, and 7 days prior to each field sampling were regressed against the LT50 of the tissues. Our results suggested that: 1) Tmin1 (minimum air temperature of the preceding 1 day of each sampling) had the most significant correlation with LT50 and cane water content among all air temperatures analyzed. 2) While cane water content was significantly related to its bark water, the water content of periderm and pith did not. 3) When comparing the effects of Tmin1 and bark water content on cane LT50 together, bark water had significant higher coefficient of determination (R 2). This research provided additional information about the mechanisms of plant dormancy and cold hardiness.