Abstract:
Leaf, petiole, and root explants from in vitro maintained triploid purple coneflower plantlets were treated with120
mg·L-1
colchicine for the induction of hexaploid plants. Best result for induction of hexaploid was obtained by
treating the triploid root explants with 120 mg·L-1
colchicine for 25 days. Regeneration of adventitious buds from
the triploid root explants on Murashige and Skoog (MS) medium with 6-Benzyladenine (BA) and Naphthalene
acetic acid (NAA) after the colchicine treatment persisted for a time longer than from those untreated. Only slow growing plantlets in a same genotype-and-treated population were selected and detected to increase the screening
efficiency as well as save time and efforts. Chromosome counting confirmed that most early-regenerating and fast growing buds were triploid, while most late-regenerating and slow-growing buds were hexaploid, screening only
those slow-growing regenerated plantlets could increase effectively the hexaploid. In the present study, screening
efficiency increased from 21% (detected all plantlets) to 53% (detected only the slow-growing plantlets). On the
other hand, hexaploid plants had much larger stomata and more stomatal guard cell chloroplasts. The stomatal
guard cell chloroplast number in hexaploid plants has a good linear relationship with those in the diploid, triploid,
and the tetraploid progenitors. Results indicate that the colchicine-induced hexaploid could be induced and
screened out with high efficiency, making this process worth further exploring in other species as well.