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ISHS Acta Horticulturae 264: II International Protea Research Symposium

CARBOHYDRATE STRESS CAUSES LEAF BLACKENING IN PROTEAS

Authors:   Julie P. Newman, W. Doorn, M. S. Reid
Abstract:
Leaf blackening in cut flowers of Protea eximia was not retarded by modifying the vase solution to ensure adequate water uptake (addition of a biocide), by preventing ethylene action (pulsing with STS), by preventing oxidation of phenolics in the vase solution (use of bisulfite), or by reducing transpiration (covering the cut flowers with polyethylene bags). At moderate concentrations, addition of sucrose to the vase solution substantially delayed the onset of leaf blackening, but higher concentrations accelerated the appearance of the disorder. The symptoms were more rapidly expressed when the flowers were held in the dark at room temperature. Removal of the inflorescence, placing the flowers in high light conditions, or girdling the stem immediately below the inflorescence delayed or eliminated leaf blackening. These data suggest that competition for carbohydrate, rather than water stress, is a major cause of leaf blackening in cut stems of Protea species. Leaves on cut stems of P. cynaroides, P. repens, P. punctata, and Leucodendron sp. similarly blackened much more quickly in the dark than in high-light conditions, indicating that the leaf blackening disorder is a common response of proteaceous plants to carbohydrate stress. Practical measures for reducing the occurrence of leaf blackening in harvested proteas are discussed.
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