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Fruit from eight Plant Introduction (PI) lines, 12 F 1 hybrids of crosses between chilling-sensitive and chilling-resistant lines and two commercial cultivars of cucumber ( Cucumis sativus L.) were stored for 7 days at 1 or 4°C followed by 2 days at 24°C and evaluated for chilling injury. The chilling-induced symptoms and physiological dysfunctions compared included visible pitting, decay, weight loss during storage at low temperature, electrolyte leakage, chlorophyll fluorescence ratios, respiration rates and pyruvate accumulation in the mesocarp tissue. Severity of chilling-induced injury among the lines, hybrids and cultivars depended on the particular symptom or physiological dysfunction examined. Fruit from all lines, crosses and cultivars exhibited greater injuries after storage at 1°C than after storage at 4°C. Other than visible pitting and decay, only small, sometimes indistinguishable, differences were observed among the various lines as to their sensitivity to low temperatures. In this study, chlorophyll fluorescence ratios proved to be of little value in distinguishing between chilling-sensitive and chilling-resistant lines of cucumber. Decay and weight loss were the only measurements that were significantly correlated with chilling-induced visible pitting. Respiration rates were correlated with weight loss, but not with visible pitting and decay, during storage at 1 and 4°C. It is concluded that low temperatures do not affect all biochemical and physiological processes of cucumber to the same extent. Furthermore, there is a continuum of sensitivity of each process to low temperature, and whether a cultivar is deemed to be chilling-sensitive or chilling-resistant depends on which particular biochemical or physiological process is evaluated. |
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