6. An Oryza sativa X 0. officinalis hybrid obtained by using a male-sterile line as maternal parent

Chengdu Institute of Biology, Academia Sinica, P.O. Box 416, Chengdu, Sichuan 610015, China

Wild species of Oryza have desirable characters such as good quality, resistances to insects and diseases, and tolerance to stress conditions. We found that many strains of 0. officinalis were resistant to all known biotypes of brown plant-hoppers. The transfer of alien genes into 0. sativa cultivars attracts the interest of rice breeders throughout the world. However, it is difficult to obtain species hybrids because of reproductive barriers due to chromosomal differences. The embryo-rescue technique is necessary for satival officinalis crosses (Jena and Khush 1986).

I have attempted to use a cytoplasmic male-sterile line as the maternal parent. An Indica ms line MS297 was pollinated by an 0. officinalis strain from Guangxi, China in September 1988. To let the plants flower simultaneously, the officinalis plants were grown under short days. Pollination without emasculation was repeated for three days. The rate of seed set was 31% one week after pollination. The panicles of the ms line, when. bagged, set no seed. The crossed seeds started abortion two weeks after pollination, but embryo culture was not made. One good seed was obtained, which germinated on moistened filter paper. The plant grown in a pot showed some characters of 0. officinalis such as spreading habit of tillers, awned glumes and high photoperiod sensitivity. Examination of esterase isozymes proved that the plant was really a hybrid. This year, I have obtained many hybrid seeds by the same method. It seems that male-sterile plants are useful as maternal parents in interspecific crosses.

Jena, K. K. and G. S. Khush, 1986. Production of monosomic alien addition lines of 0. sativa having a single chromosome of 0. officinalis. In IRRI (ed.), Rice Genetics, p. 199-208, IRRI, Manila.