Domestication and Spread of Broomcorn Millet (Panicum miliaceum L.) Revealed by Phylogeography of Cultivated and Weedy Populations

Cultivated broomcorn millet (Panicum miliaceum L.), one of the most ancient crops, has long been an important staple food in the semiarid regions of Eurasia. Weedy broomcorn millet (Panicum ruderale (Kitag.) Chang comb. Nov.), the companion weed of cultivated broomcorn millet, is also widely distributed throughout Eurasia and can produce fertile offspring by crossing with cultivated broomcorn millet. The evolutionary and genetic relationships between weedy and cultivated broomcorn millets, and the explicit domestication areas and detailed spread routes of this cereal are still unclear. The genetic diversity and population structure of 200 accessions of weedy and cultivated broomcorn millets were explored to elucidate the genetic relationship between weedy and cultivated broomcorn millets, and to trace the explicit domestication areas and detailed spread routes of broomcorn millets by using 23 simple sequence repeats (SSR) markers. Our results show that the weedy populations in China may harbor the ancestral variations that gave rise to the domesticated broomcorn millet. The population structure pattern observed in the wild and domesticated broomcorn millets is consistent with the hypothesis that there may be at least two independent domestication areas in China for the cultivated broomcorn millet, the Loess Plateau and the Northeast China, with both following the westward spread routes. These two westward spread routes of cultivated broomcorn millet coincide exactly with the prehistoric Oasis Route and Steppe Route, respectively.