In vitro induction of octaploid from colchicine-treated tetraploid petiole explants of purple coneflower (echinacea purpurea l.)

Abstract

Petiole explants were obtained from in vitro grown tetraploid (2 x = 44) Echinacea purpurea plantlets. Shoots were regenerated by culturing the explants on MS basal medium containing 0.5mg/L benzyladenine (BA), 0.01mg/L naphthaleneacetic acid (NAA) and four concentrations (30, 60, 120, and 240mg/L) of colchicine for 30 days, or 120mg/L of colchicine for 7, 14, 21 and 28 days. The regenerated shoots were induced to root on MS basal medium with 0.01 mg/L NAA, and then the root-tips of the regenerated shoots were sampled for count of chromosome number. It was found that a treatment duration of >7 days was necessary for induction of octaploids (8 x = 88) shoots, and treatment with 120mg/L colchicine for 28 days was the most efficient for the induction of octaploids, yielding 10% of octaploids among all the regenerated shoots. Chimeras were observed in almost all the treat ments. However, the ratio of octaploid to tetraploid cells in a chimeric plant was usually low. In comparison with tetraploid plants, octaploid plants in vitro had larger stomata and thicker roots and had prominently stunt plant with very short life cycle. Octaploid E. purpurea plantlets can’t survival in the natural environment.