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Chon C. Lim, Rajeev Arora and Edwin C. Townsend

Seasonal patterns in freezing tolerance of five Rhododendron cultivars that vary in feezing tolerance were estimated. Electrolyte leakage was used, and raw leakage data were transformed to percent leakage, percent injury, and percent adjusted injury. These data were compared with visual estimates of injury. Percent adjusted injury was highly correlated (0.753) to visual estimates. Two asymmetric sigmoid functions—Richards and Gompertz—were fitted to the seasonal percent adjusted injury data for all cultivars. Two quantitative measures of leaf freezing tolerance—Lt50 and Tmax (temperature at maximum rate of injury)—were estimated from the fitted sigmoidal curves. When compared to the General Linear Model, the Gompertz function had a better fit (lower mean error sum of squares) than Richards function. Correlation analysis of all freezing tolerance estimates made by Gompertz and Richards functions with visual LT50 revealed similar closeness (0.77 to 0.79). However, the Gompertz function and Tmax were selected as the criteria for comparing relative freezing tolerance among cultivars due to the better data fitting of Gompertz function (than Richards) and more descriptive physiological representation of Tmax (than LT50). Based on the Tmax (°C) values at maximum cold acclimation of respective cultivars, we ranked `Autumn Gold' and `Grumpy Yellow' in the relatively tender group, `Vulcan's Flame' in intermediate group, and `Chionoides' and `Roseum Elegans' in the hardy group. These relative rankings are consistent with midwinter bud hardiness values reported by nurseries.

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R.C. Ebel, P.A. Carter, W.A. Dozier, D.A. Findley, M.L. Nesbitt, B.R. Hockema and J.L. Sibley

The current study was conducted to relate ice formation to the pattern and rate of leaf and stem injury of Satsuma mandarins on trifoliate orange rootstock. Potted trees were unacclimated, moderately acclimated or fully acclimated by exposing trees to 32/21 °C, 15/7 °C or 10/4 °C, respectively. Freezing treatments consisted of decreasing air temperature at 2 °C·h-1 until ice formed as evidenced by exotherms determined using differential thermal analysis of stems. Air temperature was then decreased, held constant, or increased and held constant to simulate severe, moderate and mild freeze conditions, respectively. All treatment exhibited exotherms at -2 to -4 °C, which were smaller with milder freezing treatments. Only the fully acclimated trees exhibited multiple exotherms. Leaf watersoaking, an indication of ice formation, occurred concurrently with stem exotherms except for fully acclimated trees where there was up to a 30-min delay and which corresponded with the second exotherm. Electrolyte leakage of leaves began to increase near the peak of the stem exotherm, but increased more slowly with milder freezing temperature treatments. In some treatments, electrolyte leakage reached a plateau near 50% but leaves survived. Leaves died when whole-leaf electrolyte leakage exceeded 50%. These data are discussed within the framework of a proposed mechanism of injury of Satsuma mandarin leaves by subfreezing temperatures, especially multiple exotherms of fully acclimated trees, and the plateau of electrolyte leakage of leaves at the critical level for survival.

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Chiwon W. Lee, Keun Ho Cho, Larry J. Cihacek and Robert W. Stack

The influence of calcium nitrate fertilization on the storage characteristics of carrot (Daucus carota) roots was investigated. Plants of `Navajo' carrots grown under irrigation were sprayed with a 2% solution of Ca(NO3)2 4H2O at a rate of 50 kg/ha Ca 10 days before harvest. Quality of carrot roots stored at 5 °C was evaluated monthly for sweetness, tissue electrolyte leakage, disease development and visual characteristics. For disease development, the crown portion of the carrot roots was inoculated with an ascospore solution (2 × 109 spores/mL) of white mold (Sclerotinia sclerotiorum) before storage. When determined after 1 month of storage, percent tissue electrolyte leakage in the Ca-treated carrots decreased 52% as compared to that obtained from the control. Sugar contents of the cortex and xylem tissues were not affected by calcium nitrate fertilization. Changes in other quality parameters of carrot roots for an extended storage period, including white mold development, will be presented. Initial findings of this research suggest that foliar calcium feeding at the final stage of plant growth may enhance the quality of carrot roots during storage.

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Geeta K. Nanaiah and Jeffrey A. Anderson

Electrolyte leakage (EL) and ethane:ethylene ratio (EER) responses of pepper (Capsicum annuum L. Early Calwonder) leaf disks to temperature stresses were in close agreement. Midpoints of sigmoidal response curves following freezing stress were -4.6 and -4.4C for EL and EER, and 49.0 and 48.8C following high temperature stress. Evolution of ethane and EL were measured from disks infiltrated with a saturation series of 18-carbon fatty acids ranging from 0 to 3 double bonds. Only linolenic acid (18:3 n-3) stimulated ethane production and EL. In a second fatty acid experiment with 18- and 20-carbon acids with a double bond 3 (n-3) or 6 (n-6) carbons from the nonpolar end of the molecule, n-3 fatty acids stimulated more ethane than n-6 acids with the same number of carbons. Trienoic 18-carbon fatty acids stimulated more ethane than trienoic 20-carbon acids. Both 18-carbon acids yielded significantly greater EL than controls. Propyl gallate, a free radical scavenger, reduced ethane production without decreasing EL or K+ leakage.

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Rita L. Hummel and Peter R. Bristow

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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John R. Stommel, Mary J. Camp, Judith M. Dumm, Kathleen G. Haynes, Yaguang Luo and Anne Marie Schoevaars

of fresh-cut products. Steps involved in production of fresh-cut pepper products include precooling and washing of freshly harvested fruit followed by trimming, coring, slicing, packaging, and storage at 4 °C. Electrolyte leakage is commonly used as a

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Shu Hsien Hung, Chun Chi Wang, Sergei Veselinov Ivanov, Vera Alexieva and Chih Wen Yu

the accuracy of measurements of electrolyte leakage determined after the chilling treatment. Therefore, before a chilling treatment, the CaCl 2 -treated plants were rinsed thoroughly with distilled water to remove the residual Ca 2+ on leaves. Any two

Open access

Renée L. Eriksen, Laban K. Rutto, James E. Dombrowski and John A. Henning

, 400, 400, 500, 600, 800, 1000, and 1200 µmol CO 2 . Measurements were set to record after standard stability settings, with a minimum wait time of 2 min and a maximum wait time of 4 min. Electrolyte leakage and pigment concentrations. In a third trial

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Kemin Su, Justin Q. Moss, Guolong Zhang, Dennis L. Martin and Yanqi Wu

volumetric soil water content (θ v ), visual quality, and electrolyte leakage. These data were analyzed using the MIXED procedure of SAS (Version 9.1; SAS Institute, Cary, NC) and differences between means were separated by the SAS PDIFF option ( P = 0

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Carlos A. Parera and Daniel J. Cantliffe

Seeds of two shrunken-2 (sh2) sweet corn (Zea mays L.) cultivars, Crisp N' Sweet 711 and How Sweet It Is were used to analyze seed quality factor differences between the cultivars. Negative correlations occurred among germination percentage and imbibition, electric conductivity, potassium concentration and total soluble sugars of the seed leachate. Imbibition and total soluble sugar in the leachate significantly increased as imbibition temperature increased from 5°C to 25°C in both cultivars. A significant increase in conductivity of the leachate also occurred in `Crisp N' Sweet 711' when temperature increased. Cracks in the seed coat were more frequent in `How Sweet It Is' than `Crisp N' Sweet 711'. The higher concentrations of soluble sugars in the seed, greater imbibition rate, leakage conductivity, potassium and sugar concentration in the leachate may have been directly related to the poorer seed quality of `How Sweet It Is'. The alteration in cell membrane structure caused by a rapid water uptake in `How Sweet It Is' may have led to the high concentration of electrolytes in the seed leachate. This, in turn, might provide a greater nutritive subtrate for fungi development.