Night Interruption and Night Temperature Regulate Flower Characteristics in Cymbidium

Abstract

We investigated the influences of night interruption (NI) and night temperature on flowering and flower coloration in Cymbidium. Cymbidium 'Red Fire' and 'Yokihi' were grown under a 9 hours photoperiod (control), a 9 hours photoperiod with NI at a low light intensity (LNI) of 3-7 <TEX>${\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$</TEX>, or a 9 hours photoperiod with NI at a high light intensity (HNI) of 120 <TEX>${\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$</TEX> for four hours (22:00-02:00 HR) for 16 weeks during the reproductive growth stage (Experiment 1). Thirty month-old Cymbidium 'Red Fire' plants with initiated flowering buds were placed in four different growth chamber with night temperature set points of 6, 9, 12, or <TEX>$15^{\circ}C$</TEX> for 16 hours (18:00 to 09:00 HR) and a daytime temperature of <TEX>$25^{\circ}C$</TEX> (Experiment 2). In Experiment 1, the numbers of visible buds and flowers increased, and time to flowering decreased in both the LNI and HNI treatments, as compared to the control in both cultivars. Red color in Cymbidium 'Red Fire' increased by both LNI and HNI, as evidenced by an increased <TEX>$a^*$</TEX> in plants grown under these conditions, relative to those grown under the control condition. Number of days to visible buds at 9-<TEX>$15^{\circ}C$</TEX> ranged from 31-34 days, as compared to 39 days at <TEX>$6^{\circ}C$</TEX> in Experiment 2. Although as the temperature increased days to flowering decreased when the plant was grown at <TEX>$15^{\circ}C$</TEX> as compared to 6, 9, or <TEX>$12^{\circ}C$</TEX>, the red color (<TEX>$a^*$</TEX>) also decreased. The number of flowers and percent flowering increased when the night temperature was maintained higher than <TEX>$9^{\circ}C$</TEX>. Therefore, NI treatment and maintaining the night temperature at approximately 9-<TEX>$12^{\circ}C$</TEX> during the winter season after flower spike initiation in the reproductive developmental growth stage improve flower quality and controls flowering time.