In vivo and in vitro bulb multiplication of Lilium rhodopaeum Delip. and growth acceleration using hydroponic technologies.

Lilium rhodopaeum Delip. (Liliaceae) is a Balkan endemic, with limited distribution in Bulgaria and Greece, in the Rhodopes Mts. The species is included in the Red Data Book of Bulgaria as critically endangered, and protected by the national Biodiversity Act. The present study aimed to multiply L. rhodopaeum by in vivo or in vitro regeneration of bulblets and to accelerate their growth using soilless cultivation. An average of 7.2 ± 2.7 in vitro bulblets per half bulb scale was obtained for 4 mo on the best medium (MS supplemented with 0.5 mg/l α-naphthyl acetic acid (NAA) and 0.1 mg/l kinetin (Kin)). More than 800 bulblets were gradually ex vitro adapted in a phytotron, but only a few survived in the greenhouse. Growth of 72 in vitro bulblets evenly distributed in 3 variants was compared: on a flood and drain hydroponic system (with perlite as substrate); cutting board hydroponic system (deep water culture system, peat cubes as substrate); and control (soil substrate, wick system). Besides, a combination of natural sponges as substrate and rooting agents in the solution was tested on the cutting board hydroponic system. Classification by ABC analysis according to the final bulblet weights resulted in three non-overlapping groups. Statistics revealed a lack of correlation between the initial and the final bulblets' weights. Roots' elongation and bulblets' survival and growth were proved to depend on the hydroponic system type, the substrate type, and the composition of the nutrient solution. Best results were obtained in group A of the flood and drain hydroponic system, where bulblets increased their initial weights more than 21 times for 8 mo. Some hydroponically grown bulblets developed stems and the first 10 plants have been successfully acclimated outdoor in the IBER ex situ collection and have bloomed. [ABSTRACT FROM AUTHOR]