Understanding the genetic resources and diversity is very important for the breeding programs and improvement of several economically important orchids like Cymbidium. Karyomorphological studies have been carried out on seven Cymbidium species, Cymbidium aloifolium (Linnaeus, 1753), Cymbidium devonianum Paxton,1843, Cymbidium elegans Lindley, 1828, Cymbidium iridioides D. Don, 1825, Cymbidium lowianum Rchb. f.,1877, Cymbidium tigrinum Parish ex Hook. f., 1864, and Cymbidium tracyanum L. Castle,1890, most of them endangered/threatened in their natural habitat. As reported earlier, the somatic chromosome number (2n = 40) has been observed in all the seven species. Distinct inter-specific variation was recorded in the arm ratio of few homologous pairs in the complements. Symmetrical or almost symmetrical karyotypes were prevalent; however significant asymmetry was reported in Cymbidium iridioides and Cymbidium tracyanum. The significance of karyotypic variation in speciation of the genus Cymbidium has been discussed. This study provides useful chromosome landmarks and evidence about genome evolution, heteromorphic chromosomes based heterozygosity, basic chromosome number and ploidy level in the genus Cymbidium.
Keywords: Orchidaceae; heteromorphism; karyotype; mitosis; symmetry.