Chromosome Studies in the Grass Subfamily Chloridoideae. II. An Analysis of Polyploidy

Abstract

Polyploidy is frequent among the grasses. This study indicates that it has a high frequency in the subfamily Chloridoideae, where more than 90% of the studied specimens are polyploids. These levels range from diploid (2n = 20 for x = 10 and 2n = 18 for x = 9) to 16-ploid (2n = 160) for x = 10 in Ctenium concinnum Nees and 20-ploid (2n = 180) for x = 9 in Hilaria mutica Benth. This polyploid trend is seen in southern Africa, as well as worldwide. Analysis indicates that many polyploids are alloploids, suggesting extensive hybridization within this group. This is supported by the presence of apomixis in many mem bers of the subfamily. Both polyploidy and apomixis are thought to be important evolutionary mechanisms in Chloridoideae as well as closely related Panicoideae, and have a high frequency in southern Africa. Due to the stable ecological, geographical and climatological history of Africa, the continent is ideally suited for the stabilization of hybrid complexes by means of apomixis and polyploidization.

Exceptional subgenome stability and functional divergence in allotetraploid teff, the primary cereal crop in Ethiopia

“…Teff belongs to the Chloridoideae subfamily of grasses 27 which includes important drought and heat tolerant C4 species such as the orphan grain crop finger millet and model desiccation tolerant plants in the genera Oropetium, Eragrostis, Tripogon, Sporobolus , and others. Most (∼90%) of surveyed Chloridoideae species are polyploid, including many of the aforementioned taxa, and this likely contributes to their diversity and stress tolerance 16 . We utilized the wealth of genomic resources within Chloridoideae and more generally across Poaceae to identify patterns associated with improved stress tolerance, polyploidy and genome evolution in teff.…”

“…The general stability of the teff subgenomes may be attributed to low rates of homoeologous exchange. An estimated 90% of Chloridoid grasses are polyploid and among the allopolyploid species, multivalent pairing is rarely detected 16 . The twenty chromosome pairs in teff show bivalent pairing in meiosis I 22 , and double reduction has not been observed in segregating populations 42,43 .…”

“…The effect of polyploidy on desirable traits and interactions between the two subgenomes remains untested in teff. Polyploidy is found in more than 90% of species within the grass subfamily containing teff (Chloridoideae), and this has been hypothesized to contribute to the stress tolerance and diversification of these grasses 16 . Here, we report a chromosome-scale assembly of the teff A and B subgenomes and test for patterns of subgenome interactions and divergence.…”

A classification of the Chloridoideae (Poaceae) based on multi-gene phylogenetic trees

“…Within the subfamily Chloridoideae there is a high frequency of polyploids ranging from diploid to 20-ploid (Pleuraphis mutica Buckley, not sampled in our study) and many of these are thought to be alloploids suggesting extensive hybridization (Roodt and Spies, 2003). The common base chromosome number for all chloridoid tribes treated here is x = 10 and this is the predominant number found in the Triraphideae, Eragrostideae, Zoysieae, and Cynodonteae.…”

A molecular phylogenetic study of southern African Apiaceae

“…Other than a chromosome count of N ¼ 12 for A. macrocarpa (Burtt, 1991), the chromosome numbers are not known for any other member of the Annesorhiza clade, and they would be important to know to confirm polyploidy, if it exists. While the extent of hybridization in the southern Africa flora is poorly known, numerous examples of naturally occurring hybrids have been reported (Goldblatt, 1978;Spies et al, 1987;Takatsu et al, 2001;Roodt and Spies, 2003). Although no interspecific hybridization has been reported for the largely sympatric Annesorhiza and Chamarea, hypotheses of relationships based on morphology show considerable incongruence in the data, with many species not very well separated .…”