Genome size variation in the genus Carthamus (Asteraceae, Cardueae): systematic implications and additive changes during allopolyploidization

Abstract

Background and aims: Plant genome size is an important biological characteristic, with relationships to systematics, ecology and distribution. Currently, there is no information regarding nuclear DNA content for any Carthamus species. In addition to improving the knowledge base, this research focuses on interspecific variation and its implications for the infrageneric classification of this genus. Genome size variation in the process of allopolyploid formation is also addressed.

Methods: Nuclear DNA samples from 34 populations of 16 species of the genus Carthamus were assessed by flow cytometry using propidium iodide.

Key results: The 2C values ranged from 2.26 pg for C. leucocaulos to 7.46 pg for C. turkestanicus, and monoploid genome size (1Cx-value) ranged from 1.13 pg in C. leucocaulos to 1.53 pg in C. alexandrinus. Mean genome sizes differed significantly, based on sectional classification. Both allopolyploid species (C. creticus and C. turkestanicus) exhibited nuclear DNA contents in accordance with the sum of the putative parental C-values (in one case with a slight reduction, frequent in polyploids), supporting their hybrid origin.

Conclusions: Genome size represents a useful tool in elucidating systematic relationships between closely related species. A considerable reduction in monoploid genome size, possibly due to the hybrid formation, is also reported within these taxa.

Fig. 1.

Nearest-neighbour method dendrogram based on Cx values, showing the squared Euclidean distance of the Carthamus taxa analysed.