Abstract
To determine whether cold hardiness of peach [Prunus persica (L.) Batsch] is affected by cultural practices, 2-year-old ‘Coronet’ trees growing in a peach tree short-life site were treated by soil fumigation with 1,2-dibromo-3-chloropropane (DBCP) late fall application of nitrogen, combination of fumigation and fall applied nitrogen, fall pruning (November), or usual grower practices (control). Cold hardiness was measured by determining the leakage of electrolytes from dormant terminal twig sections exposed to low temperatures, and visually by oxidative browning and ease of phloem-xylem separation. Fall-pruned trees were lower in cold hardiness and survival than controls. Nitrogen applied alone or in combination with fumigation reduced cold hardiness in early winter but increased vigor and survival. Trees grown in fumigated soil and winter-pruned were hardier than control trees and fall-pruned trees in nonfumigated soil. Differences in hardiness were greatest near bloom time. Cultural practices strongly affected cold hardiness of xylem, phloem, and cambium of treated trees, and cold hardiness was associated with tree longevity.
Seasonal, stem and leaf cold hardiness levels of male and female plants of Ilex purpurea Hassk. and Ilex rotunda var. microcarpa (Lindl. ex Paxton) were determined over two winter seasons. The samples for the cold hardiness studies were taken from established plants growing at the Univ. of Georgia Bamboo Farm and Coastal Gardens in Savannah. Each month, 40 stem cuttings (4 to 5 inches long) were sent by overnight mail for evaluation. The plants were prepared for laboratory freezing exposure tests within 2 h of receiving. The samples were visually evaluated after freezing exposure to estimate their cold hardiness. In general, Ilex purpurea was more cold-hardy than I. rotunda var. microcarpa over both seasons tested, except in midwinter (Jan. 1998 and Feb. 1999) where I. rotunda var. microcarpa was more cold-hardy than I. purpurea. Ilex purpurea attained cold hardiness earlier in the fall and lost its hardiness later in the spring. In general, few consistent differences were observed between the cold hardiness of male and female plants within species.
Abstract
Growth regulators were applied in early autumn to evaluate their effects on induction of cold hardiness in 2-year-old apple shoots, as determined by the conductivity test. Mid-October applications of 500 ppm (2-chloroethyl)phosphonic acid (ethephon), followed 11 days later by 100 ppm of naphthaleneacetic acid (NAA), increased cold hardiness up to 5°C by early November in 1974 and to a lesser extent in 1976. Two annual sprays of succinic acid-2,2-dimethylhydrazide (daminozide, SADH) in June increased cold hardiness slightly (2 to 3°C) in late fall of 1974, 1975, and 1976. However, in 1974 treated trees were no hardier than the controls later in the winter and fruit set on ethephon-treated trees was severely reduced. In most cases, the combined content of fructose, glucose, sucrose, and sorbitol in the 2-year-old wood was slightly higher in treatments that induced cold hardiness in November or December, 1974 than in the controls. Techniques are described for screening growth regulators for induction of cold hardiness and estimating relative cold protection.
Abstract
Normalized electrical impedance and cold hardiness were measured for internodal sections of ‘Delicious’ apple (Malus domestica Borkh.) during fall and winter for 2 years. Each year, the normalized impedance for the August date was significantly higher than on later dates. The relationship between normalized impedance and cold hardiness was inconsistent; r2=0.03 and P>5%, first year and r2=0.4 and P<1%, second year. The relationship between cold hardiness and the mean temperature for the 7 days before the sample date was consistent; r2=0.85 and P<1%, first year and r2=0.81 and P<1%, second year. The slope of the line relating sample diameter and normalized impedance changed from plus to minus each year.
Abstract
Two-year-old ‘Redhaven’ peach (Prunus persica (L.) Batsch) trees on 7 different peach seedling rootstocks growing on short-life and on non-short-life sites were examined for cold hardiness of trunks using trunk cambial browning (TCB), and cold hardiness of twigs using tests for electrolytic conductivity (EC), triphenyl tetrazolium chloride (TTC), and ninhydrin-reactive compounds (NRC). It was found that Lovell, Halford, and NA 8 rootstocks invariably imparted more cold hardiness to ‘Redhaven’ budded onto them than other rootstocks tested, whereas maximum cold injury was sustained by trees on NRL 4 rootstock. Tree mortality was higher and cold injury was more severe on the short-life site than on the non-short-life site.
Dormant, intact crowns were used to determine the cold hardiness of the herbaceous perennial Heuchera sanguinea `Chatterbox'. Crowns were placed in moist cheesecloth, wrapped in aluminum foil, and subjected to -4,-6,-8,-10,-12,-14, -16, or -18C in a programmable freezer. Regrowth quality ratings and dry-mass measurement decreased linearly with temperature. No regrowth was evident from any crown exposed to -12C or lower temperatures. Freezing dormant plant crowns proved an efficient and reliable technique for estimating cold hardiness of Heuchera `Chatterbox'.
Cold hardiness and carbohydrate content of 4 cultivars of field-grown southern magnolia (Magnolia grandiflora L.) were determined monthly during the 1992-1993 winter. Initially, `Claudia Wannamaker', `Little Gem', `Timeless Beauty', and `Victoria' had similar stem and leaf cold hardiness estimates of -6C in October. However, by February `Claudia Wannamaker' and `Victoria' stems were 6 and 3C more cold hardy than `Little Gem' and `Timeless Beauty' stems. `Claudia Wannamaker' leaves were also 6C more cold hardy than `Little Gem' and `Timeless Beauty' leaves in February. Carbohydrate analysis indicates increases in oligosaccharides during cold acclimation in fall.
Abstract
Fall applications of K and
Abstract
Levels of soluble sugars in bark, leaves, leaf buds and flower buds of 2 cultivars of peach (Prunus persica (L.) Batsch) differing in cold hardiness were compared throughout the year. Thirteen sugars — galactose, glucose, fructose, xylose, stachyose, sucrose, raffinose, rhamnose, maltose, trehalose, arabinose, ribose and mannose — were present in measurable and variable concentrations. In general, oligosaccharides accumulated, particularly in the bark, during fall and winter, whereas monosaccharides accumulated during periods of active growth. These data do not show significant differences between the 2 cultivars regarding the accumulation of these sugars and cold hardiness.
The effect of water stress on cold hardiness was examined in evergreen azaleas, `Coral Bell' (CB), `Hinodegiri' (HD), and `Red Ruffle' (RR). Plants were well-watered between 8 Aug. and 1 Nov. (wet) or were subjected to 3 weeks of reduced water supply starting on one of three dates, 1 Aug. (dry 1), 29 Aug. (dry 2), and 19 Sept. (dry 3). Cold hardiness of leaves and lower, middle, and upper stems was tested on 29 Aug., 19 Sept., 10 Oct., 1 Nov. By the end of each 3-week period, water potential of water stressed plants reached –1.5 to –1.8 MPa compared to around –0.8 MPa of well-watered plants. Reducing the water supply significantly increased cold hardiness of all tested plant parts in all cultivars regardless of timing of watering reduction, with two exceptions, CB middle stems on 29 Aug. and HD leaves on 19 Oct. Three weeks after rewatering cold hardiness of water-stressed plants did not differ significantly from well-watered plants, except for HD plants under dry three treatment, which continued to be 1.0 (middle stems) to 4.3 (upper stems) more cold hardy.