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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

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directly to ratings from other publications. Ratings of general bud hardiness were based on percentage survival of primary buds across winters and on percentage bud survival during the two coldest winters of the trial. Ratings for bud vulnerability during

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; Warren, 1998 ). WINTER-HARDINESS AND CLIMATE CHANGE: IMPORTANCE OF DEACCLIMATION RESISTANCE AND REACCLIMATION ABILITY For winter survival, woody perennials not only must acclimate to cold, but also must resist premature deacclimation as a result of

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The cold hardiness of seven deciduous hardwoods, red maple (Acer rubrum L.), white oak, (Quercus alba L.), green ash (Fraxinus pennsylvanica Marsh.), sweetgum (Liguidambar stryaciflua L.), sugar maple (Acer saccharum Marsh.), river birch (Betula nigra L.) and black cherry (Prunus serotina Ehrh.) were evaluated weekly during the fall, winter and spring for three consecutive years. All trees evaluated were established (20-40 years old) and locatd on the Georgia Station Griffin, GA. Each species developed a maximum cold hardiness of at least -30 C by mid-January or early February each season. Response to temperature fluctuations varied with species. Red maple, for example, lost less cold hardiness due to warm mid-winter temperatures than the other species tested, while white oak tended to respond more quickly to the temperature fluctuations. Data will be presented comparing the response of cold hardiness to mid-winter temperature fluctuations for each species for the three year period.

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107 ORAL SESSION 23 (Abstr. 203–208) Cross-commodity: Cold Hardiness

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Abstract

Stomate density was determined for 11 cultivars of Ilex opaca which had been subjectively ranked for winter hardiness as either very hardy, hardy, semi-hardy, or not hardy on the basis of field observations recorded over a 5-year period. Variance analysis revealed that the number of stomates for the cultivars rated very hardy was significantly lower than that of the cultivars rated not hardy. Stomate counts for the cultivars in the intermediate hardiness classes all fell within the range delimited by the counts of the very hardy and not hardy cultivars.

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Ethrel sprays were applied at 50 or 100 ppm at approximately 40%, 70% leaf fall (10/16/89 or 10/24/89, respectively) or at both times on `Redhaven' and `Allgold' peaches. Bud hardiness was determined biweekly by differential thermal analysis (DTA). Stage and percentage of bloom open during the bloom period were subjectively estimated.

Spraying trees with 100ppm Ethrel at 50% leaf fall significantly increased bud hardiness at mid-winter compared to other treatments. After a mid-winter freeze (-21.7 C on 12/21/89), there was no significant difference between % bud survival of any treatments. But, trees treated with 50 or 100ppm Ethrel had 10-20% better bud survival than other treatments. Buds of the 2 cultivars had statistically similar hardiness although DTA analysis indicated that Redhaven had a .5-.8 C lower freezing point than Allgold in mid winter. This trend was reversed close to bloom with Allgold having .7 C lower freezing point than Redhaven. The time of full bloom was significantly delayed by treating trees with 100ppm at 40% leaf fall or 50ppm at both 40 and 70% leaf fall the previous autumn.

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Eight characters relating to flowering and maturity, berry yield, and winter hardiness were estimated on the basis of intersubspecific or interprovenance hybrids to determine heterosis, heritability, and genetic and phenotypic correlations in sea buckthorn (Hippophae rhamnoides L.). Two provenances of ssp. rhamnoides, one of Finnish (Fin) and one of Danish (Dan) origin, were dominant to ssp. sinensis and Russian derived provenances (ssp. turkestanica) for most characters related to flowering or maturity. This tendency for dominance or overdominance also extended to berry yield and winter hardiness, except for hybrids between Finnish origins and Siberian (ssp. mongolica) origins. The start of maturity (Ms) and half maturity (Mh) showed the highest heritabilities (h2 = 0.88 and 0.81, respectively). The hybrids were matroclinal, suggesting that Ms and Mh may be sex-linked or cytoplasmically inherited characters. Winter hardiness was the trait with the lowest heritability (h2 = 0.02), suggesting that the climate at the testing site was not severe enough to differentiate variation among half sibs or full sibs derived from Fin x Dan, which on average proved hardier than the native parental provenance Fin. Full maturity (Mf) showed a moderate heritability but was stable across 2 years (rB = 1). High genetic correlations among Mf, Ms, and Mh (rG = 0.94, 0.96, and 1.00, respectively) suggest that these characters were controlled by the same genes. Yield showed a negative genetic correlation with all characters pertaining to flowering and maturity, indicating that selection for early flowering or early maturity should result in a gain in yield.

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Little is known about the biochemical factors responsible for the wide range in flower bud hardiness of Forsythia species. In other genera, a correlation has been reported between soluble sugars, particularly raffinose and stachyose, and hardiness. Total starch and soluble sugars, their relationship to flower bud hardiness and levels of individual sugars were studied in four Forsythia species: F. × intermedia `Spectabilis', F. × intermedia `Lynwood', F. suspensa var. fortunei and F. `Meadowlark'. Hardiness was determined either by sampling flower buds at intervals during controlled freezing tests or by thermal analysis. Total sugars were extracted with water/ethanol and quantified with Anthrone. Individual sugars were separated and quantified with high pressure liquid chromatography. `Lynwood', the least hardy of the four cultivars, was killed by -16C, while `Spectabilis, the most hardy, survived -22C in midwinter. Total sugars accumulated throughout the winter in buds, apparently at the expense of total starch, in F. `Meadowlark' and F. suspensa var fortunei. As total sugars accumulated in `Spectabilis', however, total starch increased slightly. Although fructose, glucose, galactose and melibiose were detected throughout the year, raffinose and stachyose, were detected only in hardy flower buds.

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Abstract

The highbush blueberry cultivars, ߢRancocasߣ and ߢEarliblueߣ, failed to acclimate in time to avoid low temp injury to stems exposed above the snow level during the 1st year seasonal change in hardiness was studied. In the 2nd year, however, they hardened to temp as low as -40°C and survived the winter. Acclimation occurred earlier in a native selection of Vaccinium angustifolium Aiton and in ߢRancocasߣ. Selections of V. angustifolium and natural hybrids of V. angustifolium and V. cormybosum L. were found to be hardier than any of the highbush cultivars. A selection of V. constablaei Gray and V. membranaceum Douglas, respectively, were also hardier than the highbush types. A low temp exotherm was found to be present in blueberry stems, but it was associated only with xylem injury which was not as critical for survival as the bark tissues. The bark was injured at temp higher than the xylem and was not associated with any exotherm.

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