Water stress in mature `Redhaven' / Lovell peach [Prunus persica (L.) Batsch] trees was imposed, during the 1988 growing season. Trickle irrigation was reduced from 100% to 25% of a calculated weekly evaporation amount on 22 June, 11 July, and 8 and 27 Aug. Trees were isolated from rainfall by tents under the canopy and from horizontal water movement between root systems on 4 sides to a depth of 0.5 m by a water-proof barrier. Canopy to air temperature differentials monitored throughout the growing season were developed into 3 stress indexes: crop water stress index (CWSI); cumulative crop water stress index (CCWSI); and postharvest cumulative crop water stress index (PCCWSI). CWSI values varied from 0 to 0.6, while both CCWSI and PCCWSI increased through late Sept. Mean PCCWSI of the 22 June 25% treatment increased at a greater rate than the other treatments. Significant linear regressions were found with some of the indexes and net photosynthesis or stomatal conductance; however, the r-square values were low. In general, no linear relationships were found between either CCWSI of PCCWSI and the Index of Injury for cold hardiness.
A time-course study was conducted to characterize seasonal patterns of cold hardiness (CH) and protein profiles in the leaf tissue of five Rhododendron cultivars (`Grumpy Yellow', `Vulcan's Flame', `Autumn Gold', `Chionoides', and `Roseum Elegans'). Leaf samples were collected monthly (starting in mid September) and leaf discs were subjected to controlled freezing and thawing regimes. CH (LT50 defined as temperature causing 50% injury) was assessed by electrolyte leakage and visual observations. Data indicate that cultivars varied in their CH in nonacclimated state and in their ability to cold acclimate. Results obtained in September showed `Grumpy Yellow' to be least hardy (about –3°C) and `Roseum Elegans' to be most hardy (about –7°C). All cultivars exhibited successive increases in CH during fall and winter. Maximum CH in all cultivars occurred by December/January with `Chionoides' being most hardy (about –31°C) while `Grumpy Yellow' was least hardy (about –20°C). LT50 based on electrolyte leakage was highly correlated with visual rating. Seasonal changes of protein profiles and relationship of specific stress proteins to cultivars' CH and cold acclimation ability are discussed.
Seedlings of several landscape tree species frequently experience cold injury at temperatures that are noninjurious to older specimens of the same species. However, there are few published reports quantifying age-related differences in hardiness. In this study, the stem cold hardiness of a mature, 35-year-old female Sakhalin corktree was compared with that of half-sib seedling progeny of different ages. Ten-, 22-, and 34-month-old seedlings were hardy to -4 °C on 9 Oct., while the 35-year-old parent withstood -12 °C. Ten-month-old seedlings exhibited no further increase in hardiness on 26 Oct., whereas the 34-month-old seedlings and the mature parent were hardy to -16 °C. The 22-month-old seedlings were intermediate in hardiness on this date. The 10- and 22-month-old seedlings had died back to the snowline by late January, but the 34-month-old seedlings and the mature tree were uninjured. The corktree seedlings did not attain midwinter hardiness levels comparable to the adult tree until the winter following their fourth season of growth. The absence of flower buds on cold-tolerant 4- and 5-year-old seedlings suggests that physiological maturation is not a prerequisite for full expression of the cold acclimation capability of this species.
Thermal analysis (TA) was used to evaluate dormant bud cold hardiness of nine Vitis cultivars weekly during the 1993–94 dormant period. TA hardiness estimates were expressed as either mean low-temperature exotherm temperature (MLTE) or temperatures lethal to 10% (LT10), 50% (LT50), or 90% (LT90) of dormant bud sample. A destructive freeze on 19 Jan. 1994 presented an opportunity to compare dormant bud field survival with laboratory estimates of bud hardiness that had been derived from TA. Vineyard air temperatures of –24C caused primary bud kill that ranged from a mean of 15% with `Concord' to 100% with `Viognier'. With the exception of `Viognier' and one of two `Cabernet Sauvignon' clones, field mortality levels were accurately bracketed by TA estimates of LT10, MLTE, and LT90 values, which had been obtained in the week preceding the freeze. `Viognier' bud hardiness was overestimated by ≈1.5C, and the hardiness of `Cabernet Sauvignon clone UCD#6' was underestimated by <1C. The discrepancy with `Viognier' may have been related to prior destruction of primary buds by bud necrosis and the misinterpretation of secondary bud exotherms as due to primary buds.
Tissue survival assessments of red raspberry (Rubus idaeus L.), including cane dieback, bud death, time of cane leaf drop, and growth cessation, were compared to freezing tests of stem portions and buds. Four named cultivars and six Guelph (designated Gu) selections were assessed in the field at two locations in each of two winters and in concurrent controlled freezing tests at one location for one winter. The time of cane leaf drop and of cessation of cane extension growth in the fall were not correlated with field survival. Cane dieback as a percentage of cane length was a better estimate of winter survival than was bud number. Controlled freezing tests of stem portions and buds, and calculation of T40s and T50s indicate that genotypes differed in their relative hardiness throughout the winter. The different methods of field assessment of cold hardiness were well correlated, but not well correlated with controlled freezing tests (4.2% significant correlations). Exclusion of the genotype, Gu 75, which behaved differently in the field than in freezing tests, increased the number of significant correlations to 16.7%.
Leaves, shoots and flower buds of 3 peach cultivars differing in cold hardiness were compared biochemically throughout the year. The analyses included starch, reducing and total sugars, total protein, and total and individual amino acids, (a) Starch in leaves and shoots was low in early spring, but increased to peak concentrations in fall. Flower buds were devoid of starch, (b) Reducing and total sugars in leaves and shoots were high in early spring and decreased to a minimum in fall, but increased to a maximum in the shoots during winter. In flower buds reducing and total sugars were relatively high during winter and increased to peak concentrations in early spring, (c) Protein in leaves was high in spring but decreased to a minimum in summer, then steadily increased to a peak concentration in fall. A similar but less pronounced trend occurred in shoots. In flower buds a steady increase in protein occurred during dormancy and reached a maximum in early spring, (d) Total free amino acids in leaves was high in the spring, but decreased rapidly to a minimum in the fall. In shoots the level was relatively high in the spring, decreased in early summer, but increased to a maximum in late summer, then gradually leveled off during the fall and winter. In flower buds the level was relatively high in winter, but increased rapidly in early spring.
Some correlation existed between the levels of the biochemical constituents and the degree of hardiness in the 3 peach cultivars.
Exotherm characteristics of dormant apple, pear, peach, plum, grape, persimmon, and black walnut buds were investigated from late autumn to early spring. Differential thermal analysis indicated differences in the high-temperature exotherm (HTE) and low-temperature exotherm (LTE) among the fruit species and sampling dates. According to exotherm characteristics and cold hardiness, the species tested could be divided into two groups, those without LTE (apples and pear) and those with LTE (grape, persimmon, black walnut, peach, and plum). The latter group with LTE could be further categorized into two subgroups, those possessing three stages of hardiness development (peach and plum group) and those with five stages of hardiness development (grape, persimmon, and black walnut). In the peach and plum group, HTE and no LTE could be detected in the first and last stages when bud water content was >55%. In the second stage, both HTE and LTE could be detected when bud water content was between 40% and 50%. In the grape, persimmon, and black walnut group, the first stage with only HTE was from bud formation to deep supercooling initiation when bud water content was >52%. The second stage with both HTE and LTE was when bud water content was between 40% and 48%. The third stage when only LTE could be detected and bud water content was usually <40%. The fourth stage was from HTE reappearance to LTE disappearance before bud swell. The fifth stage was from LTE disappearance to when only HTE could be detected. No detection of LTE in the buds of apple and pear and no detection of HTE in the buds of grape, persimmon, and black walnut were both closely associated with water status in the buds.
Exotherm characteristics of dormant apple, pear, peach, plum, grape, persimmon, and black walnut buds were investigated from late autumn to early spring. Differential thermal analysis indicated differences in the high-temperature exotherm (HTE) and low-temperature exotherm (LTE) among the fruit species and sampling dates. According to exotherm characteristics and cold hardiness, the species tested could be divided into two groups, those without LTE (apples and pear) and those with LTE (grape, persimmon, black walnut, peach, and plum). The later group with LTE could be further categorized into two sub-groups those possessing three stages of hardiness development (peach and plum group) and those with five stages of hardiness development (grape, persimmon, and black walnut). In peach and plum group HTE and no LTE could be detected in the first and last stages when bud water content was higher than 55%. The second stage both HTE and LTE could be detected when bud water content was between 40% and 50 %. In the grape, persimmon, and black walnut group the first stage with only HTE was from bud formation to deep supercooling initiation when bud water content was higher than 52%. The second stage with both HTE and LTE was when bud water content was between 40% and 48%. The third stage when only LTE could be detected and bud water content was usually lower than 40%. The fourth stage was from HTE reappearance to LTE disappearance before bud swell. The fifth stage was from LTE disappearance to when only HTE could be detected. No detection of LTE in the buds of apple and pear and no detection of HTE in the buds of grape, persimmon and black walnut were both closely associated with water status in the buds.
Storage temperature and season markedly affected cold acclimation and deacclimation and levels of sorbitol and sugars in 1-and 2-year excised apple (Malus domestica Borkh) shoots. Cold hardiness of shoots increased with a decrease in storage temperature (2 to −18°C) from August to January, then decreased as growth began in March. In most seasons, cold hardiness was significantly related to high levels of sorbitol in the sap, and to high levels of sucrose and total sugars (fructose, glucose, sucrose and sorbitol) in the combined bark and wood samples.
In Spring 1993 and 1994, mature trailing `Marion' blackberries (Rubus L. subgenus Rubus Watson) were pruned to 0, 4, 8, and 12 floricanes/plant. An additional treatment of 0 floricanes with early (30 cm) primocane topping and pruning was included. Primocane length was measured from emergence in April until growth cessation at the end of October on individual canes and for the whole plant. In January 1994 and 1995, cane cold hardiness was evaluated by controlled freezing. In 1993, plants without floricanes produced more primocanes and branches with an increased total length at the end of the season than plants with floricanes. However, there were no significant differences in primocane length among treatments in 1994. In all treatments, the absolute growth rate (AGR), on a length basis, of primocanes occurred in flushes of rapid growth followed by slower growth throughout the season. Plants without floricanes had a significantly greater AGR than plants with floricanes on five dates in 1993. In 1994, there was no effect of floricane number per plant on AGR of primocanes over the season and the growth peaks were not as distinct. When comparing primocane elongation rate at three phenological stages in 1993, plants with no floricanes had a significantly higher total primocane growth per day during fruit production and from harvest to length cessation. The following year, plants with no floricanes had the highest rate of growth before bloom and a trend toward greater growth during fruit production. After fruit production, there were no differences in AGR between the treatments. Plants with floricanes produced a second flush of primocanes, while plants with no floricanes produced only one flush of primocanes. Primocane length of the first flush (averaged for 4-, 8-, and 12-floricane plants) was significantly different from the second flush at all dates during the season except for the final end of season measurement date. Primocanes pruned at 30 cm did not produce significantly more branches than unpruned primocanes on plants without floricanes. Plants without floricanes produced primocanes that were significantly more cold hardy (lower LT50) in 1994 and 1995 than plants with floricanes.