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  • Author or Editor: Rita L. Hummel x
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Four film-forming antitranspirants, Vapor Gard, Envy, Wilt-Pruf, and Folicote, and a new metabolic antitranspirant UC86177 were applied to container-grown Ulmus parvifolia Jacq. (Chinese elm), Malus sargentii Rehd. (Sargent's crabapple), Viburnum plicatum tomentosum Thunb. (doubleflle viburnum), Lycopersicon esculentum Mill. `Early Giant' (tomato), Petunia × hybrids Hort. Vilm-Andr. `Royal Pearls' (petunia), and Impatiens wallerana Hook. f. `Blitz Orange' (impatiens) plants. Water status was assessed by the following methods: transpiration as water loss per unit leaf area, wilt by visual evaluation, and xylem pressure potential (XPP) determined with a pressure chamber. Antitranspirant treatment had no beneficial effect on water status of doublefile viburnum. In comparison to control plants, results of wilt ratings, XPP, and transpiration measurements for the elm, crabapple, tomato, petunia, and impatiens plants can be summarized as follows: UC86177-treated plants showed significantly less stress in 11 measures and were not different once; Wilt-Pruf was beneficial 10 times and not different twice; Folicote was beneficial nine times and not different three times; Vapor Gard produced eight beneficial results and four similar results; and Envy was beneficial three times and no different nine times. Species differences in response to antitranspirants as well as differences in product efficacy were demonstrated. UC86177 antitranspirant was shown to be as or more effective in controlling water status than the film-forming antitranspirants and may have potential for protecting various plant species against water stress.

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The index of injury (It) and tissue ionic conductance (gTi) formulas for analyzing electrolyte leakage data from freeze-stressed tissues of cabbage (Brassica oleracea L. Capitata group) were compared. The two formulas produced similar results in calculating the relative freezing responses of stem pith, lamina, and petiole tissues. Disagreement occurred only with lamina tissues when the magnitude of ion leakage was low. Vital staining of pith and petiole tissues with triphenyl tetrazolium chloride indicated that the tissue TK50 (the temperature resulting in 50% injury), derived from It data, was a reliable indicator of the freeze-killing point. These results support the use of the simpler It method for analyzing electrolyte leakage data in studies of cabbage freezing tolerance.

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The roles of freeze avoidance and freeze tolerance in determining strawberry (Fragaria ×ananassa) flower freeze resistance were compared in laboratory freeze tests. Genotype, freezing point depression of expressed cell sap, and flower size were examined as potential sources of variation in freeze resistance. When ice was added as a nucleator to excised flowers, mean freeze damage was 97% at -3.0 °C, but in the absence of ice, flowers appeared to supercool and had only 15% damage at -4.0 °C. Without nucleation, cultivar differences in freeze damage were significant in three of four freezing temperatures, but the relative ranking of cultivar freeze damage was not consistent across temperatures. Cultivars that sustained the least amount of injury at -4 °C, were not necessarily the least injured at -7 °C. With an ice nucleator, damage occurred at warmer temperatures (-1.5 °C), but there was no relationship between percentage damage at -1.5 °C with nucleation and -4 °C without nucleation across cultivars. Freezing-point depression of expressed cell sap did not account for the variation in freeze resistance. In nucleated and nonnucleated treatments, larger flowers were more likely to be freeze damaged. Results of this research suggest that flowers of all cultivars are susceptible to freeze damage and survive spring frosts by freeze avoidance.

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Abstract

Freezing tolerances of 31 evergreen and semi-evergreen Ficus species growing out-doors at Fairchild Tropical Garden, Miami, Fla., were determined in late Dec. 1982. Five species, Ficus hookeriana Corner, F. montana Burm.f., F. rubiginosa Desf. ex Venten., F. tinctoria Forst.f., and F. trigonata L. survived freezing at −2°C whereas the hardiest species, Ficus pumila L., survived −4°. The other 25 species failed to survive freezing at −2°. A tender species, Ficus benjamina L., grown under natural environmental conditions in Gainesville, Fla., failed to survive a Jan. 1983 freeze of −4°. Freezing avoidance via supercooling appeared to be an effective means of survival for F. benjamina, as evidenced by 80% rooting in samples that supercooled to −2° and −4°.

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Seasonal changes in freezing tolerance of stems and buds of Rubus idaeus L. `Chilliwack', `Comox', `Meeker', `Skeena' and `Willamette' clones were measured from November through March of 1988-1989 and 1989-1990. Eight additional clones were tested in 1989-1990. Canes were harvested from the field, cut into two-bud samples and subjected to controlled freezing tests. Samples were seeded with ice, held at -2°C overnight and then frozen at 3°C/hour. Viability was estimated by visual browning. Vascular tissue at the base of the buds was the least freeze tolerant tissue in these samples. Results of both the 1988-1989 and 1989-1990 freezing tests, indicated `Meeker' and `Willamette' cold acclimated more slowly in the fall than `Chilliwack', `Comox' and `Skeena'. However, in the spring, `Willamette' and `Meeker' were slower to lose freeze tolerance than the other three clones.

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Cabbage seed production in western Washington is at risk from freeze damage in the months of November to February. During the 1987-1988, 1988-1989 and 1989-1990 winters, the cold protection efficacy of 5 floating row covers (Agryl P17, Dewitt N-sulate, Reemay 2014, DuPont Typar, VisQueen Porous Row Cover) and straw was tested on field-grown cabbage. Air temperature in the cabbage crown, Tk50 of cabbage leaves, plant winter survival and seed yield were measured. During a severe freeze in February 1989, an average temperature of -11.1 °C was recorded in the uncovered controls while temperatures under the row covers were -6.7°C, -6.8°C and -8.4 °C under the N-sulate, VisQueen and Agryl covers, respectively. When compared to controls in June of 1989, row covers increased the survival of the more cold hardy `Brunswick' plants but did not significantly increase seed yields. The duration and severity of the February 1989 freeze was such that all of the less cold hardy `Golden Acre' plants were killed.

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In Spring 1996, `Meeker' red raspberry root cuttings were planted into a sandy loam soil in 30 cm tall x 27 cm diameter black plastic containers. During Mar. 1997, a second bottomless container was placed over the overwintering canes of half of the plants. The second container was filled with the same sandy loam soil to simulate ridging of the plants. All plants were grown using standard cultural practices on an outdoor, gravel nursery bed. Freeze tolerance of potted whole plants and excised root sections was measured at 5 °C intervals between -5 and -20 °C in a series of laboratory freeze tests conducted during Jan. 1998. Electrolyte leakage data were used to calculate the index of injury for excised roots while whole-plant response to freezing was determined by measuring the subsequent growth of floricane lateral shoots and of primocanes. After 1 month in the greenhouse, results indicated the dry weight of primocanes harvested from plants that were exposed to -20 °C was 56% of the nonfrozen control primocane dry weight. Primocane dry weight from plants exposed to -5, -10 and -15 °C was not different from the controls. Similar results were obtained for the percent of floricanes that were alive and for the dry weight of laterals produced by these floricanes after 3 months in the greenhouse. The whole-plant freeze test results indicated plants at the lowest temperature, -20 °C, were injured but not killed. Root index of injury of single potted plants averaged 5%, 15%, 29%, and 58% at -5, -10, -15, and -20 °C, respectively.

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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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Mefluidide, a synthetic plant growth regulator, has been reported to protect chilling-sensitive plants from chilling damage and enhance the freezing tolerance of certain winter-hardy herbaceous plants. The potential of mefluidide to enhance the freezing tolerance of nonhardened and dehardening cabbage (Brassica oleracea L. Capitata Group) leaf tissue was investigated. Mefluidide at 0 to 60 mg·L–1 was tested on `Brunswick' and `Golden Acre' cabbage in five experiments. Leaf tissue freezing tolerance was measured 3 to 9 days postapplication by electrolyte leakage assay. The interval between application and freeze testing had no effect on leaf freeze tolerance. The effect of mefluidide at low rates on leaf freeze tolerance was small and inconsistent. At 30 and 60 mg·L–1, leaf freeze tolerance was decreased consistently. Chemical name used: N-{2,4-dimethyl-5-[[trifluromethyl)sulfonyl]amino]phenyl}acetamide (mefluidide).

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Freezing resistance of strawberry flowers from `Benton', `Honeoye', `Hood', `Puget Beauty', `Rainier', `Redcrest', `Shuksan', `Sumas', `Totem', and WSU 1988 was measured in laboratory tests. Flowers with approximately 13 mm of pedicel attached were placed in test tubes containing 2 ml DI water. Tubes were immersed in an ethylene glycol bath, the temperature lowered to -1°C, and the flowers inoculated with crushed ice. The temperature was lowered to -1.5°C, held overnight then lowered 0.5°C every 2 hours. Samples were removed at 0.5°C intervals, thawed overnight at approximately 3°C and incubated 24 hours at room temperature and 100% RH. Freeze damage of styles and receptacle was determined by visual browning. Flower survival with no visible damage averaged 27% at -1.5, 13% at -2.0, 7% at -2.5, and 4% at -3.0°C. There was clonal variation in flower survival: 56% of `Hood' flowers survived -1.5 and 45% survived -2.0 while 5% of `Redcrest' and `Sumas' flowers survived these temperatures. Results seem to indicate that strawberry flower freeze resistance was due to freezing avoidance via supercooling.

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