Polymorphism of Cenchrus ciliaris L. a perennial grass of arid zones

This study deals with the phenotypic polymorphism of twenty accessions of Cenchrus ciliaris L. (buffelgrass) collected in various climatic areas of Tunisia. Six seedlings per accession were cultivated according to a common garden experiment design, and 33 phenological or morphological variables were measured during one cycle of growth. The observed differences among accessions were not significant for the seedling stage, but they were significant for all other studied variables of the vegetative and reproductive growth, dry matter and habit type. The principal component analysis provided further support for the important fixed genetic polymorphism of this species. On the other hand, a hierarchical classification was used to classify accessions in four groups, but we did not observe a clear geographical pattern associated with these groups. In conclusion, our study revealed considerable genotypic variation for C. ciliaris across Tunisia, which could be preserved by the agamospermous system of reproduction. Finally, among the groups from hierarchical classification, Mezzouna-08 accession may be a good choice for the restoration of degraded Tunisian ecosystems, thanks to its high aboveground biomass productivity.Resume Ce travail concerne l'etude du polymorphisme phenotypique de 20 accessions de Cenchrus ciliaris L. (buffelgrass) recoltees dans differents sites de la zone aride de la Tunisie. Un total de six individus par accession etaient cultives dans des conditions environnementales communes et un total de 33 variables morphologiques et phenologiques ont ete mesurees durant un cycle de croissance l'espece. Les principaux resultats obtenus revelent des differences non significatives entre les accessions au stade germinatif, alors qu'elles sont significatives pour toutes les autres variables observees (phase vegetative et reproductive, la production en matiere seche et type du port de la plante). L'Analyse en Composantes Principales realisee fournit un autre argument pour un polymorphisme genetique stable de ce taxon. En outre, une classification hierarchique a permis de classer les accessions en 4 groupes, independamment de leur origine geographique. En conclusion, cette etude revele une variabilite genotypique pour C. ciliaris en Tunisie, qui pourrait resulter du mode de reproduction agamospermique. Enfin, la classification hierarchique montre que l'accession Mezzouna-08 peut a priori etre candidate pour la restauration des ecosystemes degrades, en raison de son importante biomasse aerienne produite.