Effects of red, blue, and white LED irradiation on root and shoot development ofCalibrachoacuttings in comparison to high pressure sodium lamps

Abstract

Both light intensity and spectral quality are known to affect plant growth and development. However, studies dealing with the effect of these light parameters on root and shoot development of ornamental cuttings are limited. The aim of this investigation was to test the effects of light intensity and spectral quality on the root and shoot development of Calibrachoa 'MiniFamous Neo Royal Blue' cuttings. Five spectral treatments at two irradiation levels (40 and 80 µmol m-2 s-1) were used: red (660 nm), blue (440 nm), white (400-700 nm) as well as a mixture of all these spectra and a high pressure sodium lamp (HPS) as control. Experiments were conducted in climate controlled growth chambers to exclude natural sunlight. For each treatment, shoot and root length was determined and their respective dry weight measured. In addition, leaf area was determined. Calibrachoa propagated under blue LEDs had greater shoot elongation and leaf area compared to other lighting treatments. The total root length of the blue and mix LED treatments were similar, while the highest results were achieved under the white LED treatment at 80 µmol m-2 s-1. Root dry weight was the highest under HPS lamps and mix LED treatments. The HPS treatment had a higher dry weight and a higher root length than all treatments. The results support both spectral quality and intensity influence shoot and root development of Calibrachoa cuttings. However, the best cutting quality in terms of visual appearance was obtained in treatments with white LEDs and a mixture of all available wavelengths. In further studies an optimized light recipe could be developed for production in multilayer systems.