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

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.