Cultivated rice (Oryza sativa L.) was domesticated from the Asian wild species, Oryza rufipogon Griff. Among morphological differences between them, one of the striking traits specific to cultivated rice is loss of seed shattering. In the early stage of rice domestication, the related traits of this character have been desirable for the ancient seed gatherers because it enhances the efficiency of seed collection. In this chapter, we propose that three morphological traits, closed panicle shape, non-seed shattering, and seed awning, played important roles in controlling the degree of seed dispersal. First, we reviewed domestication loci controlling the three traits. We then evaluated allele effects at these loci using reciprocal backcross populations between O. sativa Nipponbare and our standard wild accession of O. rufipogon W630. In the genetic background of cultivated rice, all the wild functional alleles were responsible for these domestication traits. On the other hand, cultivated non-functional alleles were not always associated with the drastic morphological changes in the genetic background of wild rice. Since ancient humans have selected cultivated-type mutants in natural wild populations, possible domestication process for the emergence of cultivated rice is discussed based on the effects of cultivated non-functional alleles.
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We thank Dr. Cristina Castillo, University College London, UK, for her critical reading and editing of the manuscript. The seeds of wild rice accession, O. rufipogon W630, were kindly provided by the National Institute of Genetics (National Bioresource Project), Japan. This work was supported in part by a Grant-in-Aid from Japanese Society for Promotion of Science (nos. 26292004 and 26450003).
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