The genus Oryza consists of several species complexes among which the O. officinalis complex has the most species and greatest number of different genomes (Tateoka, 1962; Vaughan, 1989). Nine species and two distinct chromosome races within two of these species have been described in the O. officinalis complex (Table 1).

Several traits of potential economic importance to rice improvement have been found in this complex, for example, resistance to brown plant hopper which has been incorporated from O. officinalis into varieties of rice released in Vietnam (Brar and Khush, 1997).

The taxonomy of the O. officinalis complex is based mainly on morphological and cytological data. It includes 5 diploid species with the CC, BB and EE genomes and 4 allotetraploid species together with two allotetraploid races of diploid species having BBCC or CCDD genome constitution. The phylogeny within the complex is complicated due to the presence of morphologically similar forms of the same taxa completely isolated from each other such as O. eichingeri that occurs in Africa and Asia.

Genomic DNA was extracted from wild rice accessions that represent the diversity of germplasm in this species complex (from Asia, Africa and America) y one accession from Australia (Table 1).

Genetic relationships among accessions were analysed using RFLP technique using a highly repetitive DNA sequence.

A dendrogram was constructed from RFLP data using NTSYS software in which phylogenetic relationships among species of the complex can be analysed (Figure 1).

The species clustered according to their genome designation (CC, BB, BBCC and CCDD genomes), and previous morphological and molecular data.

The repetitive sequence pOe49 was found very useful to study phylogenetic relationships within Oryza genus.

New information about divergence and differentiation of some species and genomes within Oryza genus arises:

Some species did not appear in the same group, for example, O. eichingeri from Africa and Sri Lanka clustered separately from each other.

The same situation was observed for the accessions from China of O. officinalis which cluster together showing a close relationship with O. rhizomatis, and O. eichingeri (both of CC genome).

The specie O. minuta was found to be clearly differentiated from both tetraploid O. punctata and O. officinalis. This suggests that O. minuta evolved independently from other BBCC species. Morphology, habit and present distribution also clearly separate this specie from other in the complex.

The species with the CCDD genome from Latin America (O. latifolia, O. alta and O. grandiglumis) are distantly related to the other species of the complex. This implies that these species evolved independently over a much longer period than other genomes within the complex did (with the exception of O. australiensis).

A precise molecular characterization of different species within O. Officinalis complex is very useful for the conservation and future use of this wild germplasm.

This germplasm can be used for the introduction of agronomic interesting traits into commercial varieties by means of traditional breeding or genetic engineering.

BRAR, D.S. and KHUSH, G.S. Alien introgression in rice. Plant Molecular Biology, 1997, vol. 35, no. 1-2, p. 35-47.

TATEOKA, T. Taxonomic studies of Oryza II. Several species complexes. Botanical Magazine Tokyo, 1962, no. 76, p. 165-173.

VAUGHAN, Duncan A. The genus Oryza L.: current status of taxonomy. IRRI Research Paper Series, 1989, no. 138.