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Wook Oh*, In Hye Cheon, and Ki Sun Kim

This research was conducted to investigate the growth and flowering responses of Cyclamen persicum Mill. `Piccolo' to temperature and photosynthetic photon fluxes (PPF), and to obtain fundamental data for production of good quality pot plant. Cyclamen plants with 10 fully unfolded leaves were grown in growth chambers maintained at three day/night temperatures [20/10 (LT), 25/15 (MT), and 30/20 °C (HT)] combined with three PPF [250 (LF), 350 (MF), and 650 (HF) μmol·m-2·s-1] under 14 h-photoperiod. After 3 months, the higher the temperature was, the greater plant width was. It was the greatest under MT/MF and HT/MF. The number of leaves was greater with increasing temperature and PPF. Petiole length, leaf size, and fresh weight were higher with increase in temperature but decrease in PPF. Days to flowering were lower in MT/MF and MT/HF, but higher under LT regardless of PPF. The number of flowers was the highest under MT/MF and MT/HF, and higher under MF in each temperature treatment. Flowering period was longer in LT and MT compared with HT. Most leaves of plants grown under HT curled upward because of boron deficiency induced by higher temperature and lower humidity. Chlorophyll content was higher in medium and low temperature, except LT/HF. The lower side of leaf in low temperature was more reddish compared to that in higher temperature due to some pigments considered as anthocyanin. Photosynthesis was the highest in MT/MF, but low in MT/HF and LT/HF in accordance with the chlorophyll fluorescence (Fv/Fm) which was lower under the same environment. These results indicate that 25/15°C and 350 μmol·m-2·s-1 yielded the best pot cyclamen in this study.

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Wook Oh, Erik S. Runkle, and Ryan M. Warner

Increasing the photosynthetic daily light integral (DLI) during the seedling stage promotes seedling growth and flowering in many bedding plants. Our objective was to determine the impact of increased DLI for different periods during the seedling stage on young plant quality and subsequent growth and development. Seeds of petunia (Petunia ×hybrida Vilm.-Andr. ‘Madness Red’) and pansy (Viola ×wittrockiana Gams. ‘Delta Premium Yellow’) were sown into 288-cell plug trays and placed under a 16-h photoperiod provided by sunlight plus 90 μmol·m−2·s−1 [supplemental lighting (SL)] or 3 μmol·m−2·s−1 [photoperiodic lighting (PL)] from high-pressure sodium lamps when the ambient greenhouse photosynthetic photon flux was less than 400 μmol·m−2·s−1 from 0600 to 2200 hr. Plants were grown at 20 °C under PL or SL for the entire seedling stage or were exposed to SL for one-third or two-thirds of the seedling stage. Seedlings were then transplanted into 10-cm pots and grown until flowering with SL at 20 °C. Shoot dry mass of transplants increased linearly with increasing DLI provided to seedlings in petunia (y = −4.75 + 1.86x, R 2 = 0.76) and pansy (y = −3.94 + 3.47x, R 2 = 0.78) in which y = dry mass (g) and x = DLI (mol·m−2·d−1). SL during the last two-thirds or the entire plug stage increased shoot dry mass and the number of leaves in both species compared with SL during the earlier stage or PL. SL during the last two-thirds or the entire plug stage accelerated flowering, but plants had a lower shoot dry mass and flower bud number at first flowering compared with that in SL during the first third or two-thirds or that in PL. Therefore, SL generally had greater effects on transplant quality and subsequent flowering when provided later in the plug stage than if provided earlier in production.

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Wook Oh, In Hye Cheon, Ki Sun Kim, and Erik S. Runkle

This study was carried out to examine the effect of photosynthetic daily light integral (DLI) on the growth and flowering of cyclamen (Cyclamen persicum Mill. ‘Metis Scarlet Red’). Plants with six fully unfolded leaves were grown at 24/16 °C (12 h/12 h) under an 8- or 16-h photoperiod at a photosynthetic photon flux of 50, 100, 150, 200, and 300 μmol·m−2·s−1, which provided seven DLIs: 1.4, 2.9, 4.3, 5.8, 8.6, 11.5, and 17.3 mol·m−2·d−1. Days to first flower decreased from 133 to 75 as DLI increased from 1.4 to 17.3 mol·m−2·d−1, although the acceleration of flowering was less pronounced when the DLI was greater than 5.8 mol·m−2·d−1. Mean leaf and flower number increased from 8.7 to 28.0 and from 0 to 14.7, respectively, as DLI increased from 1.4 to 11.5 mol·m−2·d−1, but there was no further increase under a DLI of 17.3 mol·m−2·d−1. Total dry weight and net photosynthetic rate showed a similar trend as leaf and flower number. We conclude that supplemental lighting can accelerate greenhouse production of potted cyclamen under a low ambient DLI (i.e., less than 12 mol·m−2·d−1).