PRELIMINARY STUDIES ON TAXONOMY AND BIOSYSTEMATICS OF THE AA GENOME ORYZA SPECIES (POACEAE)

The genus Oryza L (Oryzeae) include$ 22 wild species and two cultivated species-a. sativa L (Asian rice) and O. glaberrima Steud. (African rice). Asian rice is an economically important crop; it is the staple food for half of the world's population. Eight taxa, including the cultivated ones, are classified In the O. sativa complex on the basis of their morphological similarity and their common AA genome. Wild species in this complex are the most accessible and valuable genetic resources for rice breeding. Because of considerable variation in the morphology and habitat preferences of these rice species, taxonomy in this complex has long been a problem in terms of species delimitation and nomenclature. This paper summarizes recent biosystematic studies of the AA genome Oryza species through interspecific hybridization and meiotic analysis of F I hybrids and their P!ir'ental species. It concludes that most of the AA genome species in the O. sativa complex. such as O. rufipogon, O. barth;;, O. g/umaepatula, O. meridiana/is, and O. /ong;staminata, are distinct species with prominent reproductive barriers between them, although differentiation of the AA genome is limited between different species in the complex. A hypothetical biosystematic relationship of the AA genome Oryza species is proposed.