Abstract
Polyploidy or whole genome duplication is an important mechanism for acquiring new genes and creating genetic novelty in plants. In the present study, successful induction of autotetraploidy has been achieved through seedling treatment of colchicine in Cosmos sulphureus. Young seedlings were treated with different concentrations of aqueous colchicine (0.15, 0.2%, each for different durations) using the cotton-swab method. Polyploidy was confirmed during meiotic behavior of pollen mother cells. Induced tetraploid was cytogenetically distinguished from diploid by the occurrence of 48 chromosomes at diakinesis/metaphase-I with different combinations of univalent, bivalents, trivalents, and multivalent. In addition, different types of chromosomal anomalies such as laggards, micronuclei etc. were also observed at anaphase/telophase-I. Various cytological features like chromosomal associations (quadrivalents, bivalents and univalents) and chiasmata frequency were recorded at diakinesis/metaphase-I. It is expected that the induced colchiploid, if established, could be used in further cytological and breeding programs.
