Simple Pre-Culture Treatment Significantly Enhances the Colchicine Induced Chromosome Doubling Effects in Purple Coneflower (Echinacea purpurea L.)

A haploid clone recovered from anther cultures and 10 diploid clones prepared from seedlings of purple coneflower (Echinacea purpurea L.) were used to compare chromosome doubling colchicine treatments. It was found that, although routine methods of culturing explants directly on colchicine containing medium could induce chromosome doubling, the efficiencies were generally low. However, by first culturing explants on a colchicine-free medium, followed by culturing the explants on a colchicine medium, the number of chromosome doubled plantlets could be significantly increased. Two pre-culture treatments lasting two and four days, and two treatments cultured in 240 mg colchicine l(-1) for four and eight days, were tested for haploid cells with similar results that a step of pre-culture was conducive to the obtaining of regenerated tetraploid plants. Experiments on diploid clones comparing the durations of pre-culture and the duration of 120 mg colchicine l(-1) treatments indicated that pre-culture for four days was more effective than eight days, and treating with colchicine for 12 days was more effective than 24 days. In addition, the mechanism of pre-culture for enhancing the chromosome doubling efficiency is discussed and a potential application of the present method for more plant species is proposed.