THE DEVELOPMENT AND CAUSES OF PETAL BLACKENING AND MALFORMATION OF BACCARA ROSE FLOWERS

Commercial production of roses in greenhouses is a young but fast-developing crop in Israel. Most of the production is intended for export during the winter season, and one of the main varieties is Baccara. Until a few years ago, practically all the roses in Israel were grown outdoors. The quality of most of these flowers was inferior to that of European roses grown in greenhouses. The situation was particularly disastrous with Baccara. Practically all outdoor winter flowers were unsalable, due to their black coloured and malformed flowers, colloquially called "Bullhead" (fig.1).

Since these phenomena occured only in winter, it could have been caused by each of the following environmental factors: short days, low light intensity and low temperatures. All these possibilities were examined. Reducing light intensity in the summer and extending day length in the winter have had no significant effect either on blackening or on malformation. The only factor left was, therefore, the drop in temperatures. The controlled experiments reported here confirm this assumption.

A survey of various fields and greenhouses proved that although under outdoor winter conditions both blackening of petals and malformation occur at one and the same time, this is not the case in greenhouse flowers. Therefore, it was decided to investigate each phenomenon separately.