Yu Jin Park

Vegetative growth and flowering of Dianthus, Zinnia, and Pelargonium as affected by night interruption at different timings

Influences of night interruption (NI) application timings were examined on vegetative growth and flowering of Dianthus chinensis (quantitative long-day plant), Zinnia elegans (quantitative short-day plant), and Pelargonium zonale (day-neutral plant). The experiments were conducted both in a greenhouse and in a growth chamber. In both experiments, plants were grown under 9 hours photoperiod [short-day (SD) condition] or 9 hours photoperiod plus 4 hours NI with low light intensity at a photosynthetic photon flux (PPF) of 3–5 μmol m−2 s−1. The NI was employed at 18:00–22:00 HR (NI18), 22:00–02:00 HR (NI22), or 02:00–06:00 HR (NI02). Net photosynthesis of Dianthus during the NI period was determined in the growth chamber experiment. In Dianthus, node number increased more rapidly in all NI treatments regardless of the timing of NI. The height of Zinnia was shorter under NI than under SD, and those grown under NI02 were shorter than those under NI18 or NI22. In Pelargonium, leaves of the plants grown under NI02 were produced more slowly than those of the plants under NI18 and NI22. For these three species, dry weights of the plants under NI were not significantly different from those of the plants under SD. The NI had no effect on net photosynthesis of Dianthus. Flowering of Dianthus was hastened by all NI treatments, more in NI02 than in NI18 or NI22. Zinnia flowered later under NI02 than under NI22 or NI18. Flowering of Pelargonium was not affected by the NI application timing. These results indicate that NI02 was most effective in promoting flowering in Dianthus or inhibiting flowering in Zinnia. However, the NI with low light intensity at 3–5 μmol m−2 s −1 PPF had no significant effect on net photosynthesis and subsequent dry matter accumulation in these three herbaceous plants.

Night interruption improves subsequent cut flower quality in Cymbidium ‘Red Fire’

The influence of night interruption (NI) on cut flower quality was examined during subsequent Cymbidium flowering. Forty-two-month old Cymbidium ‘Red Fire’ plants were subjected to first-flower cutting and were regrown for subsequent flowering in the following year. The plants were exposed to 9 hour natural light (control) or 9 hour natural light plus NI from 22:00–02:00 HR with low light intensity (LNI) at 3–7 µmol·m−2·s−1 or high light intensity (HNI) at 120 µmol·m−2·s−1. NI treatments accelerated subsequent flowering and increased the number of inflorescences, the number of flowers per inflorescence, and the inflorescence length compared with those of control plants. The red coloration of petals increased under both LNI and HNI conditions compared with that of control plants, which was represented by increases in a* and total anthocyanin content. These results indicate that NI lighting enhances the cut flower quality and accelerates the subsequent flowering time of Cymbidium for cut flower production. NI could be an effective method for maintaining long-term productivity of high-quality Cymbidium flowers.