The Karyotype of the Ipomoea’s of Assam Including Two Newly Recorded Variants

抄録

Karyotype can be designated as representative of the species, and in some instances even of the genus. As karyotype is subjected to variation it can be used in the identification of the species or variety and to establish relationships amongst the species. Ipomoea L. the largest genus of the family Convolvulaceae has been subjected to modification many times and is constantly under debate. Taking this into consideration, the genus Ipomoea has been taken up for research. Over 500 species are distributed worldwide and in India just over 60 species could be recorded. Karyomorphologically, Ipomoea L. is a very inadequately investigated genus. To study the chromosome morphology, different parameters were considered such as arm ratio, centromeric index, presence or absence of satellites, total chromatin length, and total form percentage. Using the arm ratio of the long arm to short arm, two classes of chromosomes were obtained—metacentric and submetacentric. Thirteen specimens were investigated and it was established that their somatic chromosome counts varied from 2n=28 to 2n=32, indicating that the species of the genus fall under several basic series as x=14, 15, and 16 of which x=15 is the most frequent. In the investigation process, two new variants each of Ipomoea aquatica and Ipomoea cairica could also be recorded for the first time. Besides these, all the examined species possessed a variable number of satellite chromosomes ranging from two to 12, which could be aptly used as chromosomal markers for their proper taxonomical characterization.