Rice Genetics IV - IRRI books - International Rice Research Institute

Evolution and domestication of riceH. MorishimaThis chapter intends to explore some implications of rice evolution from theviewpoints of genetics and ecology. Core issues are (1) what genetic changesare associated with differentiation among and within species of cultivatedrice and their wild relatives and (2) what factors are responsible for the domesticationprocess. First, genetic diversity among and within AA genomespecies is summarized. Second, four directions of differentiation within theAsian AA genome gene pool are clarified: differentiation from wild to cultivatedtype (domestication), ecotype differentiation from perennials to annualsin wild races, geographical variation in wild races, and indica-japonicadifferentiation in cultivars. Third, the genetic basis of the domestication syndromeis discussed. Our recent study demonstrated that mapped genomiclocations of quantitative trait loci (QTLs) tended to cluster, reflecting the domesticationsyndrome as well as the indica-japonica syndrome. This phenomenonwas explained by “multifactorial linkages.”Domestication might bea process driven by conscious and unconscious selection of adaptive geneblocks distributed over the genome.In the past decade, a wealth of data provided by molecular markers,together with phenotypic, ecological, and archaeological data, significantlyincreased our evolutionary understanding of the genus Oryza. The target speciesdealt with in this chapter are diploid AA genome species—cultivated riceand its wild relatives. Several important problems such as the genetic basisof reproductive isolation are not included, but some new information obtainedfrom our recent studies is discussed.Inter- and intraspecific genetic diversity in the O. sativa complexDelimitation of the related wild taxa of the cultigensThe two cultivated rice species, Oryza sativa L. and O. glaberrima Steud., belongto a species group called Oryza sativa complex together with the five wild taxa,O. rufipogon (sensu lato), O. longistaminata Chev. et Roehr., O. barthii A. Chev.,O. glumaepatula Steud., and O. meridionalis Ng. This species complex was firstEvolution and domestication of rice 63