Petal Blackening in ‘Baccara’ Roses1

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Abstract
The causes for petal blackening of ‘Baccara’ rose petals and the differences between normal (red) and black flowers were investigated. Black flowers are frequent in field grown plants and dark red ones in those grown in unheated greenhouses during the winter. Two anthocyanins were isolated and identified: cyanidin 3,5-diglucoside (cyanin) and pelargonidin 3,5-diglucoside. The 2 pigments were found in both red and black petals. The content of both anthocyanin pigments as well as that of tannins, was several times higher in black flowers than in normal flowers. High polyphenolase activity was found in black petals, while no activity could be detected in normal red flowers. The blackening phenomenon is attributed to an increase in anthocyanin content at low temperatures, and to the accumulation of oxidation products of polyphenols.

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