Fruits of many citrus cultivars become injured when exposed to low non-freezing temperatures. The effect of various heat treatments either alone or in combination with calcium on the induction of cold resistance in citrus fruits were examined and also their effects evaluated according to other post harvest quality parameters e.g. ion leakage, decay development, firmness, acid content and total soluble solids. Hot water, hot water plus cold conditioning and hot water with calcium, significantly reduced chilling injury symptoms in the additional 2 days in 2O° at the end of storage at 2° in Thompson Navel orange but in Satsuma mandarin there were no significant differences observed between treated and control fruits. In the additional 2 days in 20 C hot water treatment significantly reduced ion leakage in orange peel but in Satsuma mandarin the lowest ion leakage was achieved throygh cold water with calcium treatment. With increasing temperature, hot water and hot water plus cold conditioning were the most effective treatments for Thompson orange, furthermore, 20 C water with calcium and cold conditioning were the most effective treatments in reducing decay in comparison with the other treatments used in Satsuma mandarin at this stage. With increasing temperature at the end of storage period of orange fruit, hot water and cold water with calcium were the most effective, considering firmness. Satsuma mandarin was similar to Navel orange except that, there were no significant differences between cold and hot calcium solutions. Sugar to acid ratio was influenced by various treatments. The lowest sugar to acid ratio was achieved with increasing temperature through hot water treatment.
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