Efficient culture method for production of plantlets from mechanically cut horseradish hairy roots

Effects of the initial density of roots fragmented by blender cutting and the addition of kinetin on plantlet formation were studied. The number of plantlets increased with an increasing initial density of root fragments (1.7 g-f.w./l to 13.3 g-f.w./l) at 0.1 mg/l of kinetin, but the number of plantlets with elongated roots unavailable for use as artificial seed dramatically increased after kinetin depletion in the medium. The condition at 0.8 mg/l of kinetin in the medium and 13.3 g-f.w./l of initial density of root fragments increased the number of the plantlets without roots (suitable for artificial seed) compared with the condition at 0.1 mg/l of kinetin in the medium and 13.3 g-f.w./l of initial density of roots. To avoid the toxic effect of a high concentration of kinetin at the beginning stage of the culture, 0.1 mg/l of kinetin was periodically supplemented in the medium 8 times (on the initial day and from 4 d to 10 d of the culture). Under this condition, the total number of plantlets increased and reached a maximum on 12 d, and the number of plantlets 2-4 mm in size without roots (6,270 l^-1) was the highest of all other cultures.