Duncan A. VAUGHAN
International Rice Germplasm Center, IRRI, P.O. Box 933, Manila, Philippines
The origin of the genus Oryza has been the subject of intensive debate in recent years (Chang 1985; Second 1991). However, little attention has been paid to the biogeography of Oryza species in the Malay archipelago where the genus is most diverse. The distribution of species in this important floristic region (Takhtajan 1987) are shown (Figs. 1, 2).
A comparison of species found on major islands in this archipelago reveals that New Guinea is richer in Oryza species and genomic diversity than other islands of the archipelago. Other geographic regions have less genomic diversity than New Guinea, the New World has species with 3 genomes, Africa has species with 4 genomes and South Asia has species with 4 genomes. With respect to the origin and evolution of this genus based on existing Oryza species and their current distribution, New Guinea appears to be pivotal.
Fig. 1. Distribution of species with the A, B, C and E genomes across the Malay Archipelago.
Fig. 2. Distribution of the Oryza granulata (____), O. ridleyi (solid line)complexes and O. schlechteri (......) across the Malay Archipelago.
Table 1. Wild Oryza species found on some major islands of the Malay Archipelago
===================================================================== Island Number of species1 Number of genomes2 ===================================================================== Borneo 4 5 Mindanao 4 4 New Guinea 6 6 Sumatra 5 5 =====================================================================1 Borneo (O. meyeriana, O. officinalis, O. ridleyi, O. rufipogon); Mindanao (O. meyeriana, O. minuta, O. officinalis, O. rufipogon); New Guinea (O. longiglumis, O. minuta, O. officinalis, O. rufipogon, O. schlechteri); Sumatra (O. granulata, O. meyeriana, O. officinalis, O. ridleyi, O. rufipogon). Species present based on direct observations by the author of the species in-situ or herbarium specimens seen and identified by the author.
2 Genomes which have not got a designation but are believed to differ from genomes designated to date have been included. Thus, O. ridleyi and O. longiglumis are believed to both have the same 2 genomes which have not been designated and O. granulata and O. meyeriana are believed to have the same single genome yet to be designated.
Chang, T. T., 1985. Crop history and genetic conservation: Rice-A case study. Iowa State Journal of Research 54(4): 425-455.
Second, G.S., 1981. Molecular markers in rice systematics and the evaluation of genetic resources. Pages 468-494 in Y.P.S. Bajaj (ed.) Biotechnology in Agriculture and Forestry, vol. 14. Springer-Verlag, Berlin, Heidelberg.
Takhtajan, A., 1987. Flowering plan origin and dispersal: the cradle of the angiosperms revisited. Pages 26-32 in T. C. Whitmore (ed.) Biogeographical evolution of the Malay Archipelago. Clarendon Press, Oxford.