Assessment of Genetic Diversity and Phylogenetic analysis of ‘Star Cactus’ (Astrophytum) Through Chromosome and RAPD Markers

Interspecific variation and molecular phylogenetic analysis among the four species of Astrophytum i.e. A. asterias, A. capricorne, A. myriostigma and A. ornatum of the family Cactaceae were studied using cytological and molecular markers. In all the four species, the somatic chromosomes found were 2n=22. Though they showed a high level of similarity in the number of chromosomes, karyotype analysis revealed species-specific chromosomal characteristics. The total chromosome length varied from 53.05 μm in A. aterias to 60.12 μm in A. capricorne. The chromosome volume varied from 41.82 μm3 in A. ornatum to 61.65 μm3 in A. myriostigma. The centromeric index (TF %) among the four species varied from 35.93% in A. myriostigma to 45.25% in A. capricorne. The symmetrical karyotype with same number of secondary constricted chromosomes in A. asterias & A. myriostigma suggests their close affinity between them. The 4C DNA contents were varied significantly from 8.95 pg in A. aterias to 10.23 pg in A. capricorne. The amplification products in PCR generated RAPD analysis of the four species, revealed a total of 315 bands with fragment size ranging from 0.21 kb to 3.1 kb that showed high correlation of A. asterias with A. aterias and A. capricorne with A. ornatum that were also confirmed from the karyotype analysis. Analysis of the nuclear DNA content showed significant variation in the amount of 4C DNA between the three species. The correlation coefficients showed the various chromosomal and nuclear parameters were interdependent to some extent suggesting interspecific relationship between structural and molecular changes of the genome architecture during evolution of speciation.