Karyotype of Cuphea lanceolata Ait. and Cuphea viscosissima Jacq.

Abstract

Cuphea lanceolata Alton and C. viscosissima Jacq. are potential germplasm sources of medium‐chain fatty acids. The fertile hybrid between these two species is being used to develop unproved cultivars as a domestic source of these important oils. A total of 1401 Giemsa C‐banded chromosomes from 145 root‐tip cells of these two species are karyotyped with the assistance of computer imaging techniques. Karyotype was defined by measuring individual chromosomes, computing the relative chromosome length and arm ratios, and identifying specific heterochromatic and euchromatic regions of individual chromosomes. The karyotype of these two species (2n = 12) consists of one pair of satellited chromosomes, two pairs of metacentric chromosomes, and two pairs of submetacentric chromosomes. Chromosome 2 is submetacentric in C. viscosissima but metacentric in C. lanceolata. The differences in relative chromosome length between homologous chromosomes of C. viscosissima and C. lanceolata were not significant. Karyotype asymmetry indices are the numerical expression for the general morphology of plant karyotypes. The intrachromosomal asymmetry index is 0.43 and 0.47 and the interchromosomal asymmetry index is 0.25 and 0.26 for C. lanceolata and C. viscosissima, respectively. The similarity of homologous chromosomes and C‐banding patterns indicate a close phylogenetic relationship between C. viscosissima and C. lanceolata.