5. Genetic differentiation in Oryza glumaepatula and its phylogenetic relationships with other AA genome species 


1) Fuc. Agr., Hokkaido Univ., Sapporo, 060 Japan
2) National Institute of Genetics. Mishima, 411 Japan

Oryza glumaepatula which is distributed in Central and South America is a diploid wild rice having the same AA genome with cultivated rice, O. sativa, and is considered as one of the important genetic resources. However, its life-history and phylogenetic relationships with other AA genome wild species have not been well investigated. To examine inter- and intra-specific differentiation of O. glumaepatula, we analyzed 44 strains together with related AA genome wild species, O. rufipogon from Asia, O. meridionalis from Australia, and O. longistaminata and O. barthii from Africa. Variability for nine phenotypes (number of days to heading, plant height, stem elongation after heading, panicle length, anther length/spikelet length, kernel length/spikelet length, harvest index, number of reproductive tillers and regenerating ability), 22 isozyme loci of 13 enzymes and 5 regions of mtDNA was examined. In the present study, O. longistaminata was not included in phenotype analysis and O. rufipogon not in mtDNA analysis, because of their incomplete data. Based on the data obtained from each analysis, we performed principal component analysis separately and three scatter diagrams of the strains plotted on the first and second component scores were derived.

Fig. 1. Scatter diagrams generated by principal component analysis at phenotype (A), isozyme (B) and mtDNA (C) variability.

The scatter diagram for phenotype analysis showed that O. glumaepatula strains were divided into three groups (Fig. 1A). hese three are geographically isolated ecotypes distributed in Central America and northern region of South America (ecotype I), the Amazon basin (ecotype II) and central region of South America (ecotype III) (Fig. 2). In the scatter diagram, ecotype I partly overlapped with perennial type of 0. rufipogon and ecotype II and III were independent from other taxa.

On the scatter diagram for isozyme analysis, all species tended to be separated from each other forming respective clusters, indicating that each species has its unique isozyme type (Fig. 1B). Among O. glumaepatula strains, ecotype I and ecotype III were grouped together but were differentiated from ecotype II.

Mitochondrial DNA haplotypes of O. glumaepatula strains were divided into two groups. Similarly as in isozyme analysis, one was composed of ecotype I and ecotype III and another of ecotype II. The former had a similarity to those of O. longistaminata and the latter to those of O. meridionalis (Fig. 1C).

Fig. 2. Distribution area of three ecotypes of O. glumaepatula in Central and South America.

O. glumaepatula proved to be a variable species and genetic differentiation was well recognized. The F1 plants from intraspecific crosses among these three ecotypes are known to be fertile. The origin of heterogeneity in nuclear and mitochondrial genomes found in Latin American wild rices remains to be investigated. It may be supposed that the origin of O. glumaepatula is not monophyletic and there may have been several migrations of wild rices between the New world and other continents.