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ISHS Acta Horticulturae 264: II International Protea Research Symposium

PROTEA POSTHARVEST BLACK LEAF A PROBLEM IN SEARCH OF A SOLUTION

Authors:   Robert E. Paull, J. Dai
Abstract:
It has been proposed that postharvest blackening of protea (Protea neriifolia) leaves is caused by water stress and/or insufficient carbohydrate supply. The following research was undertaken to determine the relative contribution of each to leaf blackening. The rate of development of leaf blackening varied with clonal source, season, and developed sooner in flowers harvested at the closed bud stage, with the slowest rate occurring in flowers harvested when the flower bracts had just started to unfold. Leaves were slower to blacken if harvested in the afternoon than in early morning. The immediate removal of field heat from flowers was only worthwhile if low temperature was maintained to the wholesale or retail level. High light intensities postharvest, solutions containing sugar, flower girdling and removal, significantly delayed the onset of leaf blackening. Water uptake by flowers rapidly declined after harvest with the commercial preservative solutions delaying the rate of decline in uptake. The decline in water uptake paralleled the loss in flower fresh weight. Preharvest irrigation regime did not significantly influence postharvest leaf blackening rate. The effect of flower carbohydrate supply on leaf blackening was felt to be modified by flower stem water uptake ability.
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