Rice Genetics IV - IRRI books - International Rice Research Institute

Within the geographical range of O. rufipogon spreading in Asia and Oceania,distribution of the truly wild annual populations is restricted to tropical continentalAsia. In this area, perennial and annual populations are allopatric because of theirdifferent habitats. The perennial populations prefer habitats characterized by deeperwater and less disturbance. The annual populations are in temporary swamps that areparched in the dry season. These two types reflect differentiation of adaptive strategyresulting from natural selection of habitat conditions (Sano and Morishima 1982,Morishima et al 1984).Perennial and annual types are phenotypically different but genetically close andno reproductive barrier exists. Life-history traits characterizing the two types varycontinuously in nature and segregate continuously in an F 2 population, suggestingthat those traits are controlled by multiple factors. Few markers tend to distributedifferentially between perennial and annual populations. Polymorphism at someisozyme loci such as Pox1 and others (Morishima 1991), the presence or absence ofthe open reading frame (ORF) 100 region of cpDNA (Chen et al 1993), and the presenceor absence of a locus of miniature inverted-repeat transposable elements—MITE(Kanazawa et al 2000)—were found to associate with perennial versus annual differentiationto some extent.Geographical variation in wild racesIn phenotypic characters, geographical variation is not so distinct in O. rufipogon.Polymorphism at molecular markers, however, revealed a trend of geographical differentiation.Our isozyme study demonstrated (Fig. 3) that the strains collected inFactor 1210–1–2–3ChinaSoutheast AsiaTropical islandsSouth Asia–4–3 –2–1 0 1 2 3Factor 2Fig. 3. Scatter diagram of O. rufipogon accessions plottedby the first and second scores of factor analysis basedon 29 polymorphic isozymes. (Cai and Morishima, unpublished.)68 Morishima