STEM ELONGATION IN `CARA MIA' ROSES

Abstract

Stem length of cut flower roses is one of the primary determinants of the sales price. Thus knowledge of the process of shoot elongation is useful in optimization of rose production. In this study shoot elongation was investigated by continuously logging `Cara Mia' rose shoot length using linear displacement position sensors (LDPS). Under natural conditions, elongation was found to occur mainly at night. The objective of this study was to investigate the role of environmental factors on rose stem elongation and to determine whether the process was related to an endogenous circadian rhythm or the absence of light. Measurements were made under various photoperiodic conditions (0, 8, 10, 12 and 24 hours night) and various temperature regimes. Under alternating light/dark regimes, regardless of photoperiod, shoot elongation rates follow a cyclical pattern with maximum values during dark periods and lower rates during periods of light. The elongation rate declined abruptly with the beginning of the light, suggesting that phytochrome activity might be responsible for this cessation of elongation. Under continuous light and constant temperature, the cyclical behavior was also observed, although the amplitude of the rhythm was smaller than under continuous light.