Effects of day/night temperature differential and irradiance on the flower stem quality of Sandersonia aurantiaca

Abstract

Sandersonia aurantiaca was grown in a controlled-environment (CE) experiment to determine the responses of flower stem quality attributes to day/night temperature differential (DIF) and irradiance. Other objectives were to determine if DIF could be used to manipulate flower stem quality and if irradiance modified plant responses to DIF. Five day/night temperature combinations 18/24, 21/21, 24/18, 27/15 or 30/12 °C with respective DIFs of −6, 0, +6, +12 or +18 at a common 21 °C mean daily temperature, 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, were used. At flower harvest 16 vegetative and floral characteristics were measured. Stem length increased by 55% as DIF increased from −6 to +12, but a further increase in DIF to +18 resulted in markedly shorter stems. Stem shortening at +18 DIF (30/12 °C day/night) was attributed to the adverse effects of the 30 °C day temperature on stem growth. Stem strength was inversely related to stem length. Under high PPF, stem strength was highest in DIF treatments with the shortest stems (−6 and +18) and lower in DIF treatments with longer stems (0, +6 and +12). Under the low and intermediate PPFs, stem strength was low irrespective of DIF. Flower numbers on the main stem, and the number of days from shoot emergence to flower harvest, exhibited only small responses to DIF. Significant flower abortion was recorded only at negative to low positive DIF combined with low PPF. Interactions between DIF and PPF were significant for only 4 of the 16 parameters measured, with stem strength and flower abortion being the most important parameters affected. It was concluded that DIF (−6 to +18) could be used to manipulate flower stem quality in Sandersonia through its effects on stem length, provided the irradiance was high enough (>460 μmol m −2 s −1 PPF) to avoid stem strength problems. Stem length would be maximized at +12 DIF. Either negative DIF or high positive DIF (above +12) could be used to shorten stems, although small reductions in flower numbers on the stem would also occur.