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Chien Yi Wang

Chilling injury inhibits the growth and development of tropical plants and shortens the postharvest life of tropical horticultural commodities. This presentation will emphasize the postharvest aspects of chilling injury. While most tropical commodities are sensitive to temperatures below 10 to 15C, specific critical temperatures may vary with the species, stage of development, and type of tissue. Likewise, symptoms of chilling injury also vary with different commodities. Reduction of chilling injury can be achieved either by increasing the tolerance to chilling in sensitive tissues or by delaying the development of chilling injury symptoms. Some methods involve the manipulation and modification of the storage environment, whereas other techniques involve direct treatment to the commodities. Specific examples of the alleviation of chilling injury in various tropical commodities will be discussed.

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Chien Yi Wang

Cucumbers (Cucumis sativus L.) and zucchini squash (Cucurbita pepo L.) were pressure-infiltrated (82.7 kPa for 3 min) with methyl jasmonate (MJ) in aqueous suspension and then stored at a chilling temperature of 5C. Control fruit were infiltrated with distilled water and handled in a similar manner. Treatment with MJ delayed the onset and reduced the severity of chilling injury symptoms in both cucumbers and zucchini squash. Analysis of polyamines in zucchini squash showed that putrescine increased with time in storage at 5C, while spermidine and spermine decreased during the same period. MJ treatment did not have an appreciable effect on putrescine, but the treated fruit maintained higher levels of spermidine and spermine than the control fruit throughout storage at 5C.

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Chien Yi Wang

Temperature conditioning of zucchini squash (Cucurbita pepo L.) at 15°C for 2 days enhanced polyamine levels and delayed the development of chilling injury during storage at 5°C. Direct treatment of zucchini squash with polyamines increased the endogenous levels of polyamines and reduced chilling injury. However, treatment with polyamine inhibitors after harvest but before temperature conditioning suppressed the increase of endogenous polyamines and reduced the benefit obtained from temperature conditioning. These results suggest that the resistance of squash to chilling injury may be related to the endogenous levels of polyamines.

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Chien Yi Wang

Methyl jasmonate (MJ) was applied to zucchini squash (Cucurbita pepo L.) fruit be pressure-infiltration (82.7 kPa for 3 min). Control fruit were similarly treated with distilled water. All fruit were then stored at a chilling temperature of 5C. Chilling injury occurred in the control fruit within 4 days of storage. However, the onset of chilling injury was significantly delayed by the MJ treatment. MJ-treated fruit also maintained higher levels of carbohydrates, while malic acid was the major organic acid. These constituents deteriorated slower in the MJ-treated fruit than in the control fruit.

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Chien Yi Wang

The activities of catalase and superoxide dismutase decreased while peroxidase activity increased in zucchini squash (Cucurbita pepo L., cv. `Elite') during storage at 5°C. Preconditioning of squash at 15°C for 2 days prior to the cold storage reduced the decline of catalase activity and suppressed the increase in peroxidase activity. The superoxide dismutase activity remained higher in temperature conditioned squash than in untreated squash. These results indicate that acclimation to chilling temperature in squash may also involve modifications in the activities of catalase, peroxidase, and superoxide dismutase.

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Chien Yi Wang

The endogenous levels of abscisic acid (ABA) in zucchini squash were increased by temperature conditioning at 10°C for 2 days. This temperature conditioning treatment reduced the severity of chilling injury in the squash during subsequent storage at 2.5°C. The ABA levels remained higher in treated squash than in untreated samples throughout storage. Direct treatments of squash with ABA at 0.5 mM and 1 mM before storage at 2.5°C increased ABA levels in the tissue and were also effective in reducing chilling injury. The involvement of ABA in reducing chilling injury will be discussed.

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Chien Yi Wang and J. George Buta

Freshly harvested unwaxed `Marsh Ruby' grapefruit (Citrus paradisi Macfad.) were obtained from Wabasso, Fla. The fruit were treated with methyl jasmonate by dipping, pressure infiltration (82.7 kPa for 3 minutes), or vapor fumigation. Control fruit were similarly treated with distilled water. All fruit were then stored at 1°C. Samples from all treatments were transferred to 20°C for 3 days after 4 and 10 weeks of storage at 1°C for evaluation of chilling injury. Symptoms of chilling injury were negligible in all treatments after 4 weeks of storage. However, after 10 weeks of storage, moderate to severe pitting occurred in the control fruit but the severity of chilling injury was significantly reduced by methyl jasmonate treatments. The most effective treatments were either pressure infiltration using a 0.1 mm emulsion or fumigation with vapor at saturation.

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Hsin-Shan Lin and Chien Yi Wang

Off-season production of several tropical and subtropical fruits has been successfully practiced commercially in Taiwan. By combining pruning, removal of leaves, and application of growth regulators, it is possible to have two to three crops of grapes per year. By grafting the chilled scions of temperate Asian pear onto the water shoots of low-chilling native pear varieties, it is possible to produce high-quality Asian pears (temperate-origin) in a subtropical environment. By using techniques such as root-pruning, flooding, and application of growth inhibitors, it is possible to induce flower bud formation and hasten the production of wax apples. The production periods of other fruit crops such as jujubes and sugar apples, can also be modified by pruning and other techniques.