Interactions of Gibberellin, Vernalization, Photoperiod and Temperature in the Flowering of Endive

Abstract

Stem elongation and concomitant acceleration of flowering are well known responses of some higher plants to treatment with gibberellin (2, 3, 7, 8, 19, 20). It is clear that responsive biennials, such as henbane (Hyoscyamus niger L.) and carrot (Daucus carota L.) must reach a certain stage of development before either cold or gibberellin is effective in promoting seedstalk elongation and flowering (4, 5, 9, 19). Thus, in carrot a minimum root diameter of about 1 cm must be attained before flowering may be induced (4, 19). The flowering behavior of the biennials is in contrast to that of winter annual plants such as head lettuce (Lactuca sativa L.) and endive (Cichoritum endivia L.). The winter annuals, one of which is discussed in this paper, have only a quantitative requirement for cold. Flowering is hastened by a short period of seedling vernalization followed by a regimen of long days and high night temperatures (6, 10, 11, 12, 13, 14, 16, 18, 19). Application of gibberellin at any time after seed germination promotes stem growth and subsequent flowering of endive and of lettuce. The questions which the present experiments were designed to answer are: a) to what extent does gibberellin replace the cold and/or long day requirements for flowering of endive, and b) to what extent does gibberellin overcome temperatures unfavorable for seedstalk elongation.