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determination of winter-hardiness under natural conditions. The use of freeze chambers can help determine winter-hardiness in a more timely fashion. The objectives of this research were to determine the LT 50 of zoysiagrass cultivars that were naturally cold

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concentration in the rhizome ( Landry and Wolyn, 2011 ). For a seedling experiment in controlled environments, where cold acclimation induced early senescence of GM as observed in the field, this cultivar had lower LT 50 values (increased freezing tolerance

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length differences between rootstocks. Tree mortality was considered as relative shoot dry weight of 20% or less. Tree mortality data were analyzed using the PROC PROBIT procedure and inverse confidence limits to estimate the LT 50 . Results Expt. 1

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determined for each bud. In total, data from 90 dissected buds were collected for use in each LT 50 determination for subsequent statistical analyses. Controls were similarly handled shoots that were kept at 4 °C with no exposure to the glycol freezing bath

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. Moreover, the relationship between green period, calculated using predicted sigmoid curves, and foliar cold tolerance, measured using LT 50 , was studied to provide a theoretical basis for molecular marker-assisted breeding of new cultivars that combine the

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the R-program ( R Development Core Team, 2009 ). A sigmoidal curve was fit to injury scores versus temperature for each of the 3000 sets of bootstrapped data and interpolated at 50% injury to give LT 50 temperatures ( Ehlenfeldt et al., 2006 ). Stem

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indication for low-temperature damage. From the rate of injury, the freezing temperature that causes damage to 50% of the sample is known as lethal temperature 50 (LT 50 ) ( Bigras and Colombo, 2013 ; Levitt, 1980 ; Stergios and Howell, 1973 ). Peach floral

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Abstract

Field grown onion plants (Allium cepa L. cvs. New Mexico Yellow Grano and Yellow Granex) harvested in December were frozen in a laboratory freezer were removed from the freezer at about 1°C intervals and replanted in sand in a warm greenhouse. Criterion for survival was root regeneration within 3 weeks. The LT50 value as determined by probit analysis for 58-day-old plants (−8.8°C) was significantly higher (0.5% level) than for the 74- or 90-day-old plants (−10.5 or−10.8°C) indicating less cold hardiness for the youngest plants.

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This study aims to determine the relationship between laboratory frost-resistance data for the leaves of eight olive cultivars and observed field resistance in the same genotypes undergoing natural frost damage. The lethal freezing temperature (LT50) for each cultivar was established by measuring the electrical conductivity (EC) of the medium into which solutes from damaged leaf tissue were leaked. The value obtained was then correlated with percentage frost shoot for the same eight cultivars damaged by natural frosts in a field test. A negative correlation was observed between the percentage frost shoot and leaf LT50 for all the cultivars under study. The most frost-hardy cultivars (`Cornicabra', `Arbequina', and `Picual') were those presenting the lowest percentage frost shoot and lowest LT50. Conversely, the most frost-susceptible cultivar (`Empeltre') displayed 100% frost shoot, together with one of the highest LT50 values (–9.5 °C). According to these results, lethal freezing temperature (LT50) calculated from leaf ion leakage at a range of freezing temperatures, seem to be a valid parameter for evaluating frost tolerance in olive cultivars.

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No information is available regarding endogenous soluble carbohydrate accumulation in buffalograss [Buchloe dactyloides (Nutt.) Engelm.] during cold acclimation. The objective of this study was to determine composition of soluble carbohydrates and their relationship to freezing tolerance in two buffalograss cultivars, 609 and NE 91-118, with different freezing tolerances. The experiment was conducted under natural cold acclimation conditions in two consecutive years in Fort Collins, Colo. Based upon average LT50 (subfreezing temperature resulting in 50% mortality) from seven sampling intervals in 1998-99 and six sampling intervals in 1999-2000, `NE 91-118' survived 4.5 °C and 4.9 °C colder temperatures than `609', during the 1998-1999 and 1999-2000 winter seasons, respectively. Glucose, fructose, sucrose, and raffinose were found in both cultivars in both years, and were generally higher in acclimated than pre- and post-acclimated stolons. Stachyose was not present in sufficient quantities for quantification. Cultivar NE 91-118 contained 63% to 77% more glucose and 41% to 51% more raffinose than `609' in the 1998-99 and 1999-2000 winter seasons, respectively. In 1999-2000, fructose content in `NE 91-118' was significantly higher than that of `609'. A significant negative correlation was found between LT50 vs. all carbohydrates in 1999-2000, and LT50 vs. sucrose and raffinose in 1998-99. Results suggest that soluble carbohydrates are important in freezing tolerance of buffalograss.

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