Abstract
The effect of short-time far-red (FR) irradiation at the end of light period on stem elongation in Chrysanthemum morifolium Ramat. cv. ‘Jimba’ was investigated. Cuttings were inserted into a 128-cell plug tray filled with propagating medium, and grown in a greenhouse where the minimum temperature was set at 18°C. Night interruptions of 4 hours (from 22:00 to 02:00) were performed using incandescent lights. After 3 weeks, seedlings were transplanted to plastic pots filled with the same medium and grown in the greenhouse for 10 days.
The plants were set into two growth chambers with different FR condition. One chamber was set to irradiate FR of 10 Wm-2 on the canopy for 15 minutes at the end of the light period using a LED panel. The other chamber had no FR irradiation. Both growth chambers were maintained at 20°C during the day and the night and a photosynthetic photon flux (PPF) of 100 μmol s -1m -2 was provided at the canopy level during the 9 hours light period (09:00 to 18:00).
An image processing system was employed to monitor stem elongation in five to six C. morifolium Ramat. cv. ‘Jimba’ plants every 15 minutes for five days. Stem elongation after five days with a 15-minute FR irradiation at the end of light period was 17.5 mm. On the other hand, stem elongation without FR irradiation was 6.7 mm during the same period. The difference in growth was statistically significant with a p-value<0.01. We concluded that 15 minutes FR irradiation had a remarkable positive effect on stem elongation in C. morifolium Ramat. cv. ‘Jimba’.
