Karyo-morphological consistency and heterochromatin distribution pattern in diploid and colchitetraploids of Vigna radiata and V. mungo

A systematic genetic analysis of colchitetraploids of Vigna radiata and V. mungo in three different generations (C-1, C-2 and C-3) was made using karyomorphology of chromosomes and heterochromatin distribution pattern among them. Autotetraploid of both species were produced using aqueous colchicine (0.15 and 0.20%) and maintained through three successive generations (C-1, C-2 and C-3). The karyomorphological studies showed that the chromosome karyotype remain constant with a consistent asymmetry index among the 3 generations of colchitetraploids and putative diploids in both species. The differential staining technique using fluorophore chromomycin A3 (CMA) showed that CMA+ heterochromatin increase significantly ranging between 1.2 and 2 folds in the colchitetraploids with the CMA+ blocks located mainly on the proximal and terminal regions in the both diploids and autotetraploids. Our study reveal that the karyo-morphology of chromosome tend to maintain a consistency between diploid and colchitetraploids, however, the heterochromatin pattern showed a significant heterogeneity as revealed by the CMA+.