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Lisa J. Rowland, Elizabeth L. Ogden, Fumiomi Takeda, David Michael Glenn, Mark K. Ehlenfeldt, and Bryan T. Vinyard

, 2008 ). Only a few studies have been carried out on frost tolerance of open flowers of blueberry, primarily on the southern rabbiteye species, V. virgatum Aiton (syn. V. ashei Reade) ( Gupton, 1983 ; NeSmith et al., 1999 ; Spiers, 1978 ). Spiers

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Diego Barranco, Natividad Ruiz, and María Gómez-del Campo

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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Francine Bigras

Spring frosts frequently cause significant damage to conifer seedlings during bud flushing and shoot elongation in forestry nurseries. To ensure adequate protection, levels of frost sensitivity must be known during these stages of development. Eight-month-old, containerized, black spruce seedlings were submitted to freezing temperatures of 0, –4, –6, –8, and –10C for 1, 2, 3, 4, 5, and 6 h at the following stages: 1) nonswollen buds; 2) swollen buds; 3) bud scales bursting, needle tips emerging; and 4) shoot elongation, 1 to 5 cm. After the treatments, seedlings were grown for 90 days in a greenhouse. Seedling survival then was estimated; dead seedlings discarded; and damage to buds, needles, and roots and shoot increment and diameter were measured on the remaining seedlings. Results show that frost sensitivity increases with the developing bud and shoot. A decrease in seedling and bud survival was noted with an increase in time of exposure (stages 2, 3, 4); otherwise, time exposure has no effect. Damage to needles and roots increases and diameter decreases with decreasing temperatures at all stages. Shoot increment was influenced by decreasing temperatures at stages 2 and 3 only.

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E. W. Neuendorff and K. D. Patten

A late spring frost, -2°C on 10 Mar 1989, destroyed all blossoms on `Delite' rabbiteye blueberries. To determine the effect of hedging as a rejuvenation method, six-year-old `Delite' plants were pruned on 26 April 1989. All branches were removed at 46 cm from ground level. Unpruned control plants were approximately 184 cm tall. On 21 Mar 1990 a frost of -2°C occurred. Two days later bud damage was assessed on three wood types: spring-old (SO), spring growth on old, weak wood; spring-new (SN), spring growth on vigorous 1-year-old shoots; and fall (F), postharvest late summer/fall growth. Buds were identified as to their stage of development. Buds formed on both types of spring wood were further developed than those on fall wood. As flower stage advanced frost damage increased. Blossoms on fall growth were most frost tolerant and SN was more hardy than SO. Subsequent yields will be determined and reported.

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E. W. Neuendorff and K. P. Patten

Rabbiteye blueberry flower buds are initiated and differentiated on three distinct wood types - spring growth on old weak growth, spring growth on vigorous 1-year-old shoots, or postharvest late summer/fall growth. Flower buds on spring growth are usually formed and visible by July, while buds formed on postharvest growth flushes appear in late summer and early fall. To evaluate the influence of wood type on cold damage, shoots of `Tifblue' and `Delite' were tagged by season of growth. Following a -10°C freeze in Feb. flower buds on shoots from each growth flush were examined for dead ovaries. Flower buds surviving the freeze were evaluated following a -2° late frost in Mar. Influence of wood type on floral bud and fruit development was determined. All fruit were removed from 5 shoots of each wood type on 2 harvest dates corresponding to early and midseason harvests. Floral buds formed on fall growth were more freeze and frost tolerant than those initiated on spring growth at similar stages of bud development. `Tifblue' was more cold tolerant than `Delite'. Floral buds formed on both spring wood types were earlier to develop than buds formed on fall wood. There were no differences in ripening patterns and quality of fruit removed from spring - new and fall wood. Fruit formed on spring - old wood were later maturing and smaller sized for both harvests than spring-new or fall wood. Postharvest pruning to encourage fall growth may be a cultural means of frost avoidance.

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Yoshihiko Sekozawa, Sumiko Sugaya, Hiroshi Gemma, and Shuichi Iwahori

Effects of n-propyl dihydrojasmonate (PDJ) treatment on flowers of Japanese pear 'Kousui' (Pyrus pyrifolia Nakai cv. Kousui) during spring frost were investigated to study mechanisms for avoiding spring frost injury. PDJ applied during the flowering period resulted in a lower injury index for the ovules and pistils after freezing tests. Average ion leakage in control flowers was 37.9% during the balloon stage at -5 °C, while the flowers treated with PDJ displayed a 16.6% ion leakage. Similarly, at the full bloom stage, PDJ treatment reduced ion leakage at -5 °C from 73.1% to 47.8% in the control. The organs of the flower more sensitive to low temperature stress were the ovule, pistil, and ovary; stamens were more resistant. Sugar content in the flower at the balloon stage was increased by PDJ when treated at the pink stage. Moreover, free amino acids, especially proline, increased similarly with PDJ treatment. These results show that PDJ affects supercooling capacity of a flower by changing solute content and protects organs from freezing.

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László Szalay, Béla Timon, Szilvia Németh, János Papp, and Magdolna Tóth

frost resistance, which also vary greatly over time. The experiments carried out in apricot and peach chiefly examined changes in the frost resistance of the flower buds, but there is information on the frost tolerance of the vegetative buds and the

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Lisa J. Rowland, Elizabeth L. Ogden, Mark K. Ehlenfeldt, and Rajeev Arora

deacclimation, which should translate into greater spring frost tolerance in addition to contributing genes for midwinter hardiness. To determine if the stage of bud opening could be used as an indicator of the level of BCH, we examined bud opening in the

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Yang Yang, Runfang Zhang, Pingsheng Leng, Zenghui Hu, and Man Shen

leaves Cryobiology 81 192 200 Siboza, X.I. Bertling, I. Odindo, A.O. 2014 Salicylic acid and methyl jasmonate improve chilling tolerance in cold-stored lemon fruit ( Citrus limon ) J. Plant Physiol. 171 1722 1731 Suojala, T. Lindén, L. 1997 Frost

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Timothy P. Hartmann, Justin J. Scheiner, Larry A. Stein, Andrew R. King, and Sam E. Feagely

without frost is required ( Norton, 1994 ). Limited cold tolerance is generally considered the greatest barrier to production. Although vines can be severely damaged or killed by temperatures of −12.2 °C or lower ( Norton, 1994 ), kiwifruit also have a