Influence of Monochromatic Light Irradiation as Pre-rooting Treatment on Rooting of Cuttings in Spray-type Chrysanthemums

The influences of monochromatic light irradiation as pre-rooting treatment on the rooting of cuttings in spray-type chrysanthemum cultivars ‘Sei Prince’ and ‘Remidas’ examined using light-emitting diodes. The unrooted cuttings were irradiated with red (660 nm), green (520 nm), and blue (450 nm) light and fluorescent light at around 60 mmol m-2 s-1 of photosynthetic photon flux density (PPFD) for 24 h continuously at 20℃ for 7 days. In ‘Remidas,’ the rooting percentages of cuttings were high above 85% irrespective of light wavelength. In ‘Sei Prince,’ red light irradiation promoted the rooting of cuttings compared to the other light irradiation. When the cuttings were irradiated with red light at 59.4, 37.4, and 12.4 mmol m-2 s-1 of PPFD, a decrease in rooting percentage was not observed even at a low PPFD in ‘Remidas.’ On the other hand, in ‘Sei Prince,’ the rooting percentage of cuttings decreased at the lowest PPFD. Thus, it was shown that monochromatic light irradiation for 7 d before rooting could promote the rooting of spray-type chrysanthemum cuttings, however, not only light wavelength but also light intensity that could promote rooting differed between two cultivars.