A Survey of Hybrid Sterility Relationships in the Asian Forms of <i>Oryza perennis</i> and <i>O. sativa</i>

Abstract

The sterility of F1 hybrids between cultivated rice varieties (Oryza sativa L.) has been regarded as an index of phylogenetic relationships. In this study an extensive survey was made of the sterility relationships in Asian wild rice, O. perennis Moench, which could be the progenitor of cultivated rice. It was found that the wild strains were mostly inter-fertile and gave fertile F1 hybrids with sativa varieties which were partly inter-sterile. The data for F1 pollen fertility obtained with five test-strains were studied by using the technique of principal component analysis, together with similar data for sativa strains previously obtained by the second writer. The results showed that the Asian wild-rice forms have a potentiality to differentiation into Indica and Japonica types, and that differentiation might advance with the approach to the cultivated type. Further observations were made regarding intra-populational variations in sterility factors. The sterility frequently found in the populations of perennis type was considered to be due to genetic factors with diplontic or zygotic effect, possibly of the same kind as the duplicate-fertility genes (Oka and Doida 1962). In addition to this, the populations were found to contain factors responsible for the gametic sterility of F1 hybrids, which Oka (1957a) called gametic-development genes. It was inferred that wild rice carries double-dominant combinations of those duplicate genes, so that it produces fertile F1 hybrids with sativa varieties of different types, which might have become inter-sterile after recessive mutations or deficiencies had taken place at one or the other of those loci. Variations of those genes within populations indicate the potentiality of wild rice to form partly inter-sterile groups.