Effects of constant temperature and irradiance on the flower stem quality of Sandersonia aurantiaca

Abstract

Sandersonia aurantiaca was grown in a controlled environment experiment to determine the responses of flower stem quality attributes to light and temperature. Other objectives were to seek explanations for stem quality problems observed under summer and winter greenhouse conditions and to make recommendations on the environmental conditions required for high quality flower stems. There were five constant temperatures of 15, 18, 21, 24 or 27 °C, and three photosynthetic photon fluxes (PPFs) of 700, 460, or 210 μmol m −2 s −1 with respective daily photon receipts (DPRs) of 30.2, 19.4 or 9.1 mol m −2 per day. At flower harvest, 12 vegetative and floral characteristics were measured. The longest flower stems were produced at 21 and 24 °C, and a rise in temperature from 24 to 27 °C resulted in the shortest stems. However, flower numbers on the main stem increased linearly with temperature to 27 °C. Temperature strongly influenced time to flower harvest with the interval between shoot emergence and flower harvest being 52 days at 15 °C and 24.5 days at 27 °C. Irradiance generally had larger effects than temperature on many parameters, with most of the responses to irradiance being additive with temperature. The low and intermediate PPF treatments (210 and 460 μmol m −2 s −1) increased stem length but reduced the ability of the cut stems to stand erect without bending. Low PPF also resulted in reduced flower numbers per stem and increased flower abortion, particularly at the lower temperatures. The results suggest that the problem of excessively short stems in summer is due to high temperature (>27 °C) and high irradiance (>700 μmol m −2 s −1), while stem weakness in winter is due to low irradiance (<460 μmol m −2 s −1). The combination of 24 °C temperature and a PPF of 700 μmol m −2 s −1 was recommended for producing long flower stems of the highest quality. This combination would balance rapid flowering time, adequately long and strong stems, and high flower numbers. In general, high quality flower stem production requires relatively high irradiances (>460 μmol m −2 s −1) and temperatures of 21–27 °C.