Department of Botany, University of Delhi, Delhi-7
Morphological and cytological characteristics of the naturally occurring diploids (n=12), tetraploids (n=24), and hexaploids (n=36) of S. nigrum were studied.
Karyomorphological studies and studies on the chemical nature of the fruit pigment of the induced autotetraploid, the diploid and the natural tetraploid have indicated that the diploid has not directly contributed to the evolution of the naturally occurring tetraploid S. nigrum. The lack of genetic relationship between the natural diploid and the tetraploid was further shown by the cytological studies of the triploid obtained by crossing the natural tetraploid with the diploid.
Tetraploid nigrum resembled S. luteum (n=24) closely in morphology, cytology and in the chemical nature of fruit pigments, thereby indicating that the former may be a geographical race of the latter.
The synthesized hexaploid obtained from the triploid (4n x 2n) by colchicine technique resembled the natural hexaploid closely in morphological and cytogenetical characters and in the chemical nature of fruit pigment, thereby suggesting that the latter could have arisen through chromosome doubling of the triploid. The present work has shown that the natural diploid and the tetraploid have given rise to the hexaploid S. nigrum. This has been further confirmed from the cytogenetical behaviour of the pentaploid obtained from a cross between a hexaploid and a tetraploid.
The taxonomic status of the three cytotypes of S. nigrum found in India has been considered.
