15 intersubspecific hybrids from Ory-za sativa were employed to investigate the cytological factors causing poor spikelet fertility and the characterization of female abortion. The results present as following: (1) The factors affecting the seed-set rate of intersubspecific hybrids included embryo sac sterility, pollen sterility, anther indehiscence and non-synchronization of male and female sexual organ development in the same spikelet. Embryo sac sterility is the most important factor causing the low seed...