Genetic diversity and domestication history of African rice (Oryza glaberrima) as inferred from multiple gene sequences

Nucleotide variation in 14 unlinked nuclear genes was investigated in species-wide samples of African rice (Oryza glaberrima) and its wild progenitor (O. barthii). Average estimates of nucleotide diversity were extremely low in both species (theta(sil) = 0.0007 for O. glaberrima; theta(sil) = 0.0024 for O. barthii). About 70% less diversity was found in O. glaberrima than in its progenitor O. barthii. Coalescent simulation indicated that such dramatic reduction of nucleotide diversity in African rice could be explained mainly by a severe bottleneck during its domestication. The progenitor of African rice maintained also low genetic diversity, which may be attributed to small effective population size in O. barthii. Self-pollinating would be another factor leading to the unusually low diversity in both species. Genealogical analyses showed that all O. glaberrima accessions formed a strongly supported cluster with seven O. barthii individuals that were sampled exclusively from the proposed domestication centers of African rice. Population structure and principal component analyses found that the O. glaberrima group was homogeneous with no obvious genetic subdivision, in contrast to the heterogeneous O. barthii cluster. These findings support a single domestication origin of African rice in areas of the Upper Niger and Sahelian Rivers.