Rooting of ornamental cuttings affected by spectral light quality

Adventitious rooting is a critical process in the vegetative propagation of ornamental plants. A well-rooted cutting is essential for optimal growth and high quality plants. We investigated the use of spectral light quality to improve adventitious rooting of cuttings in three ornamental species: Chrysanthemum × morifolium, Lavandula angustifolia and Rhododendron simsii hybrids (azalea). Different combinations of red (R) and blue (B) LEDs were tested: R:B 100:0, 90:10, 80:20, 50:50, 10:90 and 0:100 at a light intensity of 60 µmol m-2 s-1 for chrysanthemum and lavender and 30 µmol m-2 s-1 for azalea. No natural light was supplied. The rooting quality was assessed by determining the rooting percentage, the amount of roots and the root dry weight. For all three species, rooting was highly efficient under 100% red light. Polar auxin transport was also influenced by the different light spectra as demonstrated by the use of auxin transport inhibitors. For chrysanthemum, rooting was most inhibited under 10:90 R:B, while for azalea the inhibition in rooting was highest under 50:50 R:B. The use of LEDs for rooting of ornamental cuttings is promising if it can be used in a multi-layered system. The controlled environment will lead to a year-round high quality rooted cutting production.