Abstract
Cytological and morphological studies were made on the F1 plants obtained from the crosses between Oryza sativa (AA) and two species with unknown genomes, O. ridleyi and O. meyeriana. As expected from the parental species, 2n=36 and 2n=24 chromosomes in the somatic cells were counted in the F1 plants of O. sativa×O. ridleyi and O. sativa×O. meyeriana, respectively. At meiotic division, almost all the chromosomes failed to make pairing. The results suggest that both species, O. ridleyi and O. meyeriana, have different genomes from O. sativa (AA).
