Cytogeography of Cenchrus ciliaris (Poaceae) in Tunisia
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Cytogeography of Cenchrus ciliaris (Poaceae) in Tunisia Amina Kharrat-Souissi & Sonja Siljak-Yakovlev & Spencer C. Brown & Mohamed Chaieb
# Institute of Botany, Academy of Sciences of the Czech Republic 2012
Abstract Belonging to the genus Cenchrus with 16–22 species, Cenchrus ciliaris L. (syn. Pennisetum ciliare (L.) Link, buffelgrass) is a perennial, common in warmer regions of both hemispheres, growing as a C4 grass in a wide range of habitats. In the present study we determined chromosome number and nuclear DNA content (2C DNA) for 28 natural populations collected from northern to southern Tunisia. Three ploidy levels were found: one tetraploid population (2n04x036), three pentaploid (2n05x045), and 24 hexaploid populations (2n06x054). The hexaploid chromosome number has already been reported for Tunisian populations of C. ciliaris but tetraploid and pentaploid (2n045) are new for this area. The tetraploid population was found in the semi-arid north; pentaploids were mostly on the northern side of the arid region, while the hexaploids were located mainly in the arid southern Tunisian and Saharan region. 2C DNA values, assessed using flow cytometry, correlated with chromosome counts. Nuclear DNA content ranged from 2C03.03 to 4.61 pg, revealing three ploidy levels corresponding to 4x, 5x, 6x, and mean 2C DNA amounts were of 3.03, 3.7 and 4.48 pg, respectively. Each cytotype produced viable pollen. Flow cytometric seed screening neither proved nor disproved apomixis. The most frequent hexaploid populations seem best adapted to arid conditions in southern Tunisia. The monoploid value, 1Cx, was constant. The existence of pentaploid cytotype suggests hybridization ability between tetraploids and hexaploids. It appears that polyploidization is the major evolutionary mechanism in the speciation of C. ciliaris.
A. Kharrat-Souissi (*) : M. Chaieb Faculté des Sciences de Sfax, Unité de recherche: Diversité végétale et écosystèmes en milieu aride (UR11ES71), Département de biologie, Route de Soukra, Km 3.5, BP 1171, 3000 Gouvernorat de Sfax, Tunisie e-mail: [email protected] S. Siljak-Yakovlev Univ. Paris-Sud, AgroParisTech, UMR 8079, Ecologie, Systématique, Evolution, Université Paris-Sud, Bâtiment 360, 91405 Orsay Cedex, France S. C. Brown Compartimentation Cellulaire, Institut des Sciences du Végétal, CNRS UPR2355, 91198 Gif-sur-Yvette, France
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Keywords Buffelgrass . Cytogenetics . C-value . Flow cytometry . Monoploid genome size . Polyploidy
Introduction Under arid climates, the disturbance of the natural ecosystem is often assessed by the reduction of perennial grasses; overgrazing leads in particular to the extinction of species of high nutritional value (Le Houérou 1993). In this context, ecological restoration by reintroduction of extinct species should be based on choice of taxa optimal by their large ecological amplitude and phenological plasticity (Aronson et al. 1993; Daehler and Goergen 2005; Visser et al. 2007). Perennial herbaceous plants promote good development of t
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