Genome size and cytomolecular diversification in two species of the South African endemic genus Tulbaghia L. (Allioideae, Amaryllidaceae)

Abstract

Tulbaghia L. is a South African genus of Allioideae, Amaryllidaceae, which includes circa 25 species with similar karyotypes, all of them with 2n = 12 large chromosomes, predominantly metacentric to submetacentric. This karyotype stability contrasts with the high variability in chromosome number and morphology reported for its South American sister group, the tribe Gilliesieae. Aiming to understand the chromosome evolution in Tulbaghia, we did a karyotype analysis of T. violacea Harv. and T. simmleri Beauverd, looking for a precise characterization of chromosomal length, distribution of heterochromatin, rDNA sites, telomeric DNA sites, and genome size. The two species displayed similar chromosome morphology and size, but the genome size was smaller in T. simmleri (2C = 38.88 pg) than in T. violacea (2C = 43.48 pg). Both species had the Arabidopsis-type (T3AG3)n and the vertebrate-type (T2AG3)n telomeric motifs in all chromosome termini, a single pair of CMA+ bands colocalized with 35S rDNA sites and one pair of 5S rDNA sites neutrally stained with CMA. Additionally, T. simmleri had 12 large CMA+ bands colocalized with 5S rDNA sites and an extra pair of small CMA+ bands. In spite of the morphological karyotype similarity among Tulbaghia species, our data indicate that small chromosomal and genomic changes are actively acting on the karyotype differentiation of these species. Features such as chromosome size and morphology, genome size, number/distribution of rDNA sites and telomeric DNA resemble Tulbaghia karyotypes to those of other genera of tribes Allieae and Gilliesieae, reinforcing the relationship among the three tribes of the subfamily Allioideae.