2. Genome analysis of Oryza officinalis complex

K.K. Jena and G.S. Khush

International Rice Research Institute, P.O. Box 933, Manila, Philippines

Oryza officinalis with CC genome is widely distributed in Asia. Its occurrence has been reported from India, Bangladesh, Burma, Thailand, Vietnam, China, Philippines, Malaysia, Indonesia and Sri Lanka. Its Sri Lanka form was considered as a distinct species and named O. collina by Sharma and Shastry (1965). Recently we obtained seed of O. officinalis from China. Second (1983) speculated that O. officinalis from China may have DD genome.

We crossed O. officinalis from China (Acc. No. 104314) and O. collina (Acc. 103410) from Sri Lanka with O. officinalis from Philippines (Acc. 101117) and examined the chromosome pairing and pollen fertility of the F1 hybrids. The F1 hybrids were easily obtained and no crossability barriers were encountered. They were intermediate between the two parents.

Regular chromosome pairing was observed in all the F1 hybrids and only 12 pairs were noted at diakinesis and metaphase I of meiosis (Table 1). The pollen fertility in the hybrid of O. collina and O. officinalis and the reciprocal was 31.1% and 12.4% respectively. The hybrid between O. officinalis from China and O. officinalis from Philippines was completely sterile. No seed set was observed in any of the hybrids. These results suggest that O. officinalis from China and O. collina from Sri Lanka have CC genomes. However, considerable genetic differentiation between these populations of O. officinalis has occurred as shown by high degree of F1 sterility. We are now studying the different accession of O. officinalis from other countries to determine the degree of differentiation within this species complex.

Table 1. Pollen and spikelet fertility and chromosome pairing in O. officinalis and some intra-specific hybrids.

Species/Hybrids             Country     Fertility (%)   Pairing at Metaphase I
                            of origin   -------------   ----------------------
                                       Pollen  Spikelet  PMCs obs.   Bivalents
O. officinalis(Acc.101117) Philippines  67.3      85        65           12
O. officinalis(Acc.104314)   China      77.4      90        65           12
O. collina(Acc.103410)     Sri Lanka    78.5      90        65           12
O. officinalis x O.collina              31.1       0        65           12
O. collina x O.officinalis              12.4       0        60           12
O. officinalis (China) x
O. officinalis (Phil.)                   0.0       0        65           12

Second, G. 1983. The study of isoenzyme in relation to the distribution of the genus Oryza in the palaeo-environment and the subsequent origin of cultivated rice. In Proc. of the Conf. on the palaeo-environment of East Africa from mid tertiary. Hongkong.

Sharma, S.D. and S.V.S. Shastry. 1965. Taxonomic studies in the genus Oryza L. IV. The Ceylonese Oryza spp. Affin. O. officinalis Wall. Ex Watt. Ind. J. Genet. Plant Breed. 25:168-172.