Was Asian Rice (Oryza sativa) Domesticated More Than Once?

Abstract Recently, a dual or multiple origin of domesticated rice has been the prevailing opinion among rice scientists because rice is clearly differentiated into two major varietal groups, indica and japonica, and several minor groups. Molecular clock studies that suggested that divergence in the A-genome wild rice genepool occurred prior to domestication gave further weight to the opinion that rice had a dual origin. However, recent analysis of the major gene that is responsible for the difference in degree of shattering between rice and wild rice has revealed that it is the same mutation in indica and japonica rice, which is not compatible with a dual origin of domesticated rice. Here, we discuss the geographic and genetic reasons why a single origin for domesticated rice is compatible with current data regarding the evolution of rice. The apparently conflicting data regarding the origin of rice can be resolved by the role hybridisation–introgression has played during rice evolution since domestication.