, Volume 249, Issue 3-4, pp 139-149
Date: 20 Oct 2004

Chromosome evolution of Pennisetum species (Poaceae): implications of ITS phylogeny

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Phylogenetic relationships based on internal transcribed spacer (ITS) sequences were used to assess evolutionary trends in genome structure within the genus Pennisetum on the basis of observed variations in genome size, basic chromosome numbers (x=5, 7, 8 and 9) and ploidy level (from 2x to 8x). The evolutionary reconstruction is congruent with the gene pool classification and in agreement with some morphological grouping. Pearl millet, P. glaucum, together with elephant grass, P. purpureum, form a monophyletic group with a basic chromosome number of x=7 but different chromosome sizes. The ancestral characters of the genus are x=9 small chromosomes, an apomictic mode of reproduction and a perennial life cycle. Species with basic chromosome numbers of x=5, 7 and 8 appear in the most recently divergent clades, indicating that the genome structure in Pennisetum might have evolved towards a reduced chromosome number and an increased chromosome size.

We would like to thank Evelyne Besin and Marie-France Jubier from the Institut des Biotechnologies des Plantes, Gif-sur-Yvette, France, for assistance with the DNA sequencing. We are also grateful to M. Branco, S. Hamon and M. Noirot for their critical review of the manuscript. This work was partly supported by a grant from the French Ministère de l’Education et de la Recherche to E. M.