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(supercooling). For example, Francko and Wilson (2004) demonstrated that although cold-hardy palms (Palmae) exhibit a significant constitutive foliar cold-resistance capability, enhanced cold tolerance (an additional 5 to 10 °F) can rapidly be induced by

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; Warren, 1998 ). WINTER-HARDINESS AND CLIMATE CHANGE: IMPORTANCE OF DEACCLIMATION RESISTANCE AND REACCLIMATION ABILITY For winter survival, woody perennials not only must acclimate to cold, but also must resist premature deacclimation as a result of

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107 POSTER SESSION (Abstr. 465–478) Stress–Cold Temperatures

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Abstract

Although the tomato is a warmth-loving plant that is adversely affected by low temperatures, some of its wild relatives are more resistant to cold. The genes for cold resistance present in these wild plants could perhaps be used to overcome some of the limitations that low temperatures impose on the tomato, both before and after harvest. Because the different species of Lycopersicon can be crossed, this could be done by conventional plant breeding. However, if the gene products that allow cold tolerance could be identified, there is the additional possibility that homologous genes from even more cold-resistant species could be isolated and transferred using genetic engineering. The cover photograph shows a green-fruited tomato (Lycopersicon hirsutum LA 1363) that was originally collected in Peru at an altitude of ≈3000 m (7). At such altitudes, night temperatures are generally <10°C (17). This article summarizes the progress that has been made towards understanding and using the cold resistance of this and other wild species.

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. Therefore, the main objective of this study was to thoroughly assess ornamental camellia cultivars for their growth, flowering characteristics, cold-hardiness, and disease resistance in McMinnville, TN, USA. Materials and Methods Camellia cultivars and

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The freezing resistance of leaf, crown, and root tissues was determined for nonhardened and cold-hardened cultivars of perennial rye (Lolium perenne L.), Kentucky bluegrass (Poa pratensis L.), and red and chewings fescues (Festuca rubra L. and F. rubra var. commutata Gaud.). The nonhardened leaf and crown tissues of all the cultivars studied survived temperatures below –9.8°C. After acclimating at 5° under short days for 6 weeks or longer, the maximum increase in hardiness was in ‘Wintergreen’ (chewings fescue) which survived –27°. The cold-acclimation behavior of ‘Wintergreen’ was studied at acclimating temperatures of 0° and 5°. Both the leaf and crown tissues had at least 2 stages of acclimation, in which an acclimating temperature of 5° was conducive to the initial stage, followed by a lower acclimating temperature (0°) for the second stage.

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Solanum lycopersicoides is a valuable genetic resource for tomato (Lycopersicon esculentum) genetic improvement. However, there are few reports on its agronomic traits such as disease resistance and cold tolerance. In this paper, the resistance to cucumber mosaic virus (CMV) and leaf mold (Cladosporium fulvum Cooke) and cold tolerance of five lines of S. lycopersicoides were studied through investigation of disease inoculation and electrolyte leakage analysis. The results showed that S. lycopersicoides was highly resistant or immune to CMV and leaf mold and more tolerant to low temperature than L. esculentum. This study is helpful for the genetic improvement of tomato by using S. lycopersicoides as breeding materials.

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The relationship of environmental temperature to the cold resistance of apple bark tissue was studied on mature orchard trees in the field during natural spring dehardening and on 3 and 4 year old trees in the containers which were dehardened under controlled conditions. Field studies showed day to day fluctuations in dehardening and rehardening during the spring in each of 2 years. These short term changes in cold resistance were closely related to the air temperatures of the preceding day. In controlled studies, hardy plants during the winter dehardened as much as 15°C in one day in a warm greenhouse, and rehardened 15° in 3 days when they were held at −15°. The dehardening process was only partially reversible. Once dehardening began, the bark did not reharden beyond a certain base level. This base level raised with each successive day of dehardening. The base level usually corresponded to the minimum killing temperature on the day preceding the final day of dehardening.

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Abstract

Low temperature injury to flower buds of peach [Prunus persica (L.) Batsch.] and sweet cherry [Prunus avium L.] and to one-year-old shoots of peach and apricot (Prunus armeniaca L.) during fall and winter was more severe on trees treated with paclobutrazol (PP 333) than on those not treated. Paclobutrazol had no measurable effect on cold resistance of apricot buds or cherry shoots. The average date of 1st bloom was advanced by one to 2 days in all 3 species by paclobutrazol.

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Peel samples of ‘Marsh’ grapefruit (Citrus paradisi Macf.) from 2 separate chilling injury (CI) experiments conducted during the 1979–80 season were analyzed for proline. Proline levels were highest in the peel of grapefruit after the seasonal night temperatures reached their minimum and levels declined after night temperatures increased in the spring. The greatest resistance of grapefruit peel to CI during postharvest cold storage coincided with high proline concentrations. Peels of unexposed interior canopy fruit had higher proline contents and were also more resistant to CI than peels of exposed exterior canopy fruit. Proline accumulation may be a consequence of an environmental stress rather than a cause of hardening to the stress or a mechanism of resistance.

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