Study of Karyotype Variability and Genome Size in 13 Species of Cassia L. in Interpreting Interspecific Genetic Diversity

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Somatic chromosome number, karyotype and 4C DNA content was studied in 13 species of Cassia of the family Leguminosae obtained from Royal Botanic Gardens, Kew. Somatic chromosome number 2n=28 was observed in all the species except C. lindheimariana and C. versicolor with 2n=26 chromosomes. In addition, polyploid chromosomes were observed in C. atomaria and C. hirsuta (2n=56). Variations among the species were observed in their minute structural details of the karyotype. On the basis of centromeric index, 4 types (Type A, B, C and D) of chromosomes were found in different species. Significant variations in the chromosome length were observed among different species from 13.25 μm in C. wislizenii to 24.73 μm in C. polyantha. Total chromosome volume varied significantly from 6.93 μm³ in C. hirsuta to 11.10 μm³ in C. lindheimariana. Highest centromeric index percentage (43.69%) was noted in C. italica and that of lowest (34.12%) was found in C. polyantha. Significant variation in 4C nuclear DNA content was observed among the species that varied from 6.45 pg in C. italica to 15.77 pg in C. spectabilis. The correlation coefficients showed various chromosomal and nuclear parameters interdependent suggesting a interspecific relationship between structural and genetic changes of the genome architecture during evolution of speciation.