Rooting response under LED systems in Rosa canina in vitro cultures

The objective of this study was to investigate the composition of monochromatic LED lights as an optional illumination for rooting of rose shoots. Rosa canina axillary shoots were propagated on MS medium with 1 µM BA and 1.5 µM GA₃, pH 5.7. The cultures were incubated under fluorescent light (Philips TL-D 36W/54), PPFD 35 µM m^-2 s^-1 on a 16 h day^-1 photoperiod. For adventitious root formation, rose shoots were transferred to MS medium without plant growth regulators, and growth conditions were maintained as in the shoot multiplication phase, but three different types of LED lights were tested: red 50% and blue 50% (RB); red 40%, blue 40% and white 20% (RBW); red 49%, blue 49% and far red 2% (RBfR). Fluorescent lamps (FL) were used as a control. PPFD in all treatments was 35 µmol m^-2 s^-1. After a 6-week rooting cycle, regardless of the tested light, 83-87% of rose shoots formed adventitious roots. RB LED light treatment stimulated the number of roots (3.9 roots plant^-1). There was no effect of light on the number of leaves and root length, but under RBW LED, shoots were highest. The water content in roots was lowest in control conditions (FL). LED illumination did not reduce chlorophyll a and carotenoid content in leaves, however, it decreased chlorophyll b content in comparison to traditional fluorescent light.