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Open-pollinated progeny from 15 peach (Prunus persica) cultivars, two peach × P. kansuensis hybrids, and one peach almond (P. amygdalus) hybrid were evaluated for their cold hardiness and for tolerance to Cytospora canker following artificial inoculation with Leucostoma persoonii. Winter hardiness was negatively correlated with canker necrotic length (r = −0.26**) and positively correlated with canker rating (r = 0.26**), as indicated by qualitative ratings. The half-sib families differed for canker necrotic length following fall inoculation, indicating that individuals with increased tolerance to L. persoonii canker could be selected from the population. Progeny from the cultivar Yennoh exhibited the shortest canker necrotic length following fall inoculation, and all the inoculated branches were visually healthy. ‘Yennoh’, a plant introduction from Russia, may have a higher tolerance to Leucostoma than has previously been found in U.S. germplasm.

Open Access

Cold hardiness of Fraxinus americana `Autumn Purple', Fraxinus oxycarpa `Raywood' and Fraxinus pennsylvanica `Summit' was measured in laboratory tests. Current season stem growth was collected from trees in Willamette Valley nurseries at 3 to 6 week intervals from November 1994 to February 1995 and from October 1995 to March 1996. Replicated 9-cm stem samples with two buds each were placed in tubes and immersed in an ethylene glycol bath. Samples were nucleated with crushed ice, held overnight at –2°C and then frozen at 3°C/hour. After freezing, samples were thawed overnight, incubated at room temperature and 100% relative humidity for 10 to 14 days, then sample viability was determined by visual browning. A Tk50, the temperature at which 50% tissue injury occurred, was calculated for buds and stems. Buds were generally less hardy than stems. `Raywood' was slower to cold acclimate in the fall and did not become as cold hardy in midwinter as `Summit' and `Autumn Purple'. Cold acclimation and midwinter hardiness of `Summit' and `Autumn Purple' was similar; however, `Summit' deacclimated more rapidly. Between the 11 Dec. 1995 and 9 Jan. 1996 freeze tests, `Summit' stems lost about 9 °C of freeze tolerance. In both the 1995 and 1996 February freeze tests, `Summit' stems were less hardy than `Raywood' stems.

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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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Cold hardiness testing is an important tool used at US Forest Service nurseries for evaluating the physiological quality of conifer stock. Three tests were compared. A whole-plant freeze test without root system insulation permitted evaluation of cold injury without complication by drought symptoms if plants were misted. A cutting freeze test underestimated expected field foliar injury due to high humidity used to maintain the cuttings. An electrolyte leakage test failed to detect economically important bud mortality when buds were less hardy than other tissues.

Data from all three testing methods were analyzed with an original software package consisting of standardized input files and a step-by-step series of fortran programs and command files for use with commercially available non-linear modelling programs. Injury (y) versus temperature (x) data were modelled with the versatile, 4-parameter Weibull sigmoid model. Injury estimates at specific temperatures (Ix) or temperature estimates causing specific injury levels (LTy) were calculated with confidence and calibration intervals, respectively. The statistical significance of differences between Ix or LTy estimates was then determined.

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Few genetic studies have been conducted on the inheritance of cold hardiness (CH) in woody plants. An understanding of the genetic control of CH can greatly assist the breeder in reducing winter injury. This study was initiated to evaluate the distribution of CH phenotypes in segregating populations of evergreen rhododendrons. Naturally acclimated leaves from individual plants (parents, F1 and 47 F2 progeny) were subjected to controlled freeze–thaw regimes. Using slow cooling rates, leaf discs were cooled over a range of treatment temperatures from –10°C to –52°C. Freezing injury of leaf tissue was assessed by measuring ion-leakage and non-linear regression analysis (data fitted to Gompertz functions) was used to estimate Tmax, the temperature causing the maximum rate of injury. Tmax for the parent plants (R. catawbiense & R. fortunei) and the F1 cultivar Ceylon, were estimated to be –51.6°C, –30.1°C, and –40.4°C, respectively. CH estimates among F2 progeny (Ceylon, selfed) were normally distributed from –14.8°C to –41.5°C, with mean of –27.6°C. Most F2 progeny were less cold-hardy than the tender parent, R. fortunei. The apparent reduction in F2 CH may be caused by the differences in age between the parents (20-year-old mature plants) and F2 progenies (3-year-old juvenile seedlings). Currently, we are testing age-dependent CH responses in rhododendrons, and are also characterizing CH distributions in a backcross population.

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states as a result of its moderate cold-hardiness, relative disease resistance, and especially its versatile and desirable wine style and quality. In the northeastern United States and Canada, ‘Vidal blanc’ acreage has particularly expanded in the last

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found throughout the upper midwestern United States. Some grasses have the ability to survive in U.S. Department of Agriculture (USDA) climate zones lower than the zone in which they are listed and some should be reevaluated for cold hardiness. Silver

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Many nurseries within Ohio and northeastern, southeastern, and western United States, and Canada have reported severe bark splitting and scald-type problems in 2005. The amount and severity of damage seen in 2005 has been unlike anything seen before. At Ohio State University, samples from across the state started appearing in 2003–04 and increased in incidence in 2005. Growers' reports of exceeding losses of 5% of their inventory or 3000 to 4000 trees per nursery are not uncommon. At an average cost of $125 per tree and with the number of nurseries reporting problems, the stock losses in Ohio have been staggering, in excess of several million dollars. The trees that we have seen problems on in 2005 have been callery pears, yoshino cherry, kwanzan cherry, crab apples, sycamore, serviceberry, hawthorn, mountain ash, black gum, paper bark maple, japanese maples, norway maple `Emerald Queen', red maples, kousa dogwood, magnolia `Elizabeth' and the yellow magnolias such as `Butterflies', `Sawada's Cream', `Yellow Bird', and `Yellow Lantern'. It has long been observed that the actual cause of a bark crack was “preset” by a wound such as the improper removal of a basal sprout, herbicide, leaving of a branch stub, or lack of cold hardiness. Cold and frost may be contributing to the increase in bark splitting across the United States; however, new research results at Ohio State University regarding the effects of DNA preemergent herbicides in the reduction of root hardiness and regrowth potential, sprout removal and other mechanical injuries, and postemergent herbicide application will reveal these are more the causal agents.

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Knowledge of the level of cold hardiness and how hardiness is inherited in sour cherry is essential to germplasm collection and cultivar development. Twig samples of two sweet cherries (Prunus avium L.), 12 sour cherries (P. cerasus L.), and one ground cherry (P. fruticosa Pall.) of diverse geographic origins were collected in Jan. 1990 and monthly from Aug. 1990 to Mar. 1991, preconditioned to induce maximum cold resistance, and subjected to freeze tests and differential thermal analysis. Low temperature exotherms (LTEs) were detected in all stems of P. cerasus investigated and correlated to xylem incipient injury temperatures (ITs) from December to February (r = 0.84, P ≤ 0.01). March had the best correlation of LTEs to xylem ITs with r = 0.84, P ≤ 0.01. LTEs were strongly correlated to phloem-cambium ITs in November, representing the acclimation period. The correlation coefficient (r) for the phloem-cambium ITs and the twig LTEs during November was 0.68, significant at P ≤ 0.01. Cortical tissue and vegetative bud injuries were not correlated to the stem LTEs. Xylem ITs were selected for evaluating the cold resistance of sour cherry in December to March and phloem-cambium ITs were selected for November. The degree of supercooling and hardiness of the phloem-cambium in late fall and early spring appears significant in determining the stem hardiness and commercial range of P. cerasus. Phloem-cambium tissue, expressed the most rapid deacclimation response. The average decrease in hardiness for the phloem-cambium, xylem, and cortical tissues between February and March was 4 °C, 0.32 °C, and 2.14 °C, respectively. Principal component (PC) analyses of the phloem-cambium and cortical tissues depicted gradations between minimum survival temperatures of the two presumed progenitor species of sour cherry, i.e., sweet cherry and ground cherry. The first principal component (PC1), which accounted for 61% of the total variance, was used to separate among cultivars and seedlings. Cultivars and seedlings at the negative end of PC1 exhibited hardier phloem-cambium tissue at critical injury times, October, December, January, and March than cultivars and seedlings at the positive end of the PC1 axis. Cultivars and progeny of crosses of northern origin parents showed hardiness values more comparable to ground cherry than did selections of less-cold-hardy parents suggesting that cold is a major selective force, contributing to sour cherry population variation.

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To date, few summer and fall flowering azaleas exist. Recently, Rhododendron oldhamii, a summer-flowering species, was hybridized with several commercial hybrids. These crosses produced various sizes and colors of flowers that bloom throughout the summer until frost, and again in the spring. However, the cold hardiness level of these azaleas is unknown. Therefore, we evaluated their cold hardiness during several months of the fall and winter. Laboratory cold hardiness tests revealed that there was a range of cold hardiness levels among the new hybrids. `Fashion' and hybrids 02003 and 4003 tended to acclimate earlier than the others, maintain a good level of midwinter cold hardiness, and retain their hardiness into the early spring. Hybrid 15001 acclimated early and had good midwinter cold hardiness, but lost its cold hardiness in the late winter, while 04003 and 09004 acclimated late in the fall and did not attain a high level of cold hardiness in the winter. `Lee's Select' and hybrid 08002 seemed to fall between the groups previously mentioned showing intermediate cold hardiness throughout the winter season. The laboratory cold hardiness results were similar with field observations.

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