Sorghum laxiflorum and S. macrospermum, the Australian native species most closely related to cultivated S. bicolor

Sorghum is separated into five taxonomic sections: EU-sorghum, Chaetosorghum, Heterosorghum, Para-sorghum and Stiposorghum. Genetic relationships within the EU-sorghum section are well known, however little is known about the genetic relationships and crossabilities outside the primary genepool. A detailed investigation of genetic relationships within Sorghum to identify wild species most closely related to cultivated sorghum was undertaken using independent and combined analyses of ITS1 and ndhF data. The EU-sorghum species were resolved into a strongly supported lineage by all three analyses, and included the Australian natives S. laxiflorum and S. macrospermum. All remaining Sorghum species were resolved into a second well-supported lineage in the combined analyses, although some internal relationships within this second lineage remain unresolved. We identified S. laxiflorum and S. macrospermum as the Australian species most closely related to cultivated sorghum. Our data supports a reduction in the number of subgeneric sections from five to three: EU-sorghum (unchanged); a combined Chaetosorghum/Heterosorghum to reflect the very close relationship between these two species; and a combined Para-sorghum/Stiposorghum section thereby removing the unclear taxonomic and genetic boundaries between these species.