The use of ribosomal ITS to determine phylogenetic relationships within Sorghum

For the first time, a combined analysis of the ITS1 regions of all twenty-five Sorghum species has been undertaken. Parsimony analysis revealed a distinct lineage of Sorghum consisting of the cultivated species and their progenitors plus S. angustum, S. brachypodum, S. ecarinatum, S. macrospermum, S. laxiflorum and Saccharum officinarum. A second unsupported lineage consists of the Parasorghum and Stiposorghum species S. grande, S. leiocladum, S. nitidum, S. purpureosericeum, S. timorense, S. versicolor, S. amplum, S. bulbosum, S. interjectum, S. plumosum, S. stipoideum and the African grass Cleistachne sorghoides. Three Australian endemic species, S. angustum, S. brachypodum and S. ecarinatum, are closely related to S. bicolor, with S. angustum showing no difference to S. bicolor in ITS1 sequence. Sorghum macrospermum and S. laxiflorum form a strong clade within the Eusorghum branch indicating closer relationships to this group than to any of the Parasorghum or Stiposorghum species. Saccharum officinarum has shown closer relationships to Sorghum than to Zea mays, while the close relationship of Cleistachne sorghoides to Sorghum has been confirmed. These relationships between Sorghum species provide an important guide for plant breeders to exploit the wider Sorghum genepool through crosses between wild and cultivated species in an effort to improve sorghum production.