Studies on Tetraploid Rice

VI. Fertility variation and segregation ratios for several characters in tetraploid hybrids of rice, Oryza saliva, L

Abstract

1. In tetraploid hybrids between distantly related varieties of cultivated rice, such as between the Continental and Insular groups, the F₁ plants generally showed relatively high fertility. However, plants with different fertilities were produced after the F₂ due to segregation and the mean fertilities tended to go down with the repetition of generations. Plants showing vigorous growth tended to have high fertility.
2. In the tetraploid hybrids between distant varieties, F₂ segregation ratios so far observed for several monogenic characters (phenol reaction, apiculus pigmentation, glutinous endosperm and seed coat coloration) all agreed with the autotetraploid ratios 35:1 or 20.8:1, based on the assumption of random pairing of homologous chromosomes or chromatids.
3. The F₂ genotypic ratio for glutinous endosperm showed a significant deviation from the expected ratio: glutinous homozygotes and simplex heterozygotes were deficient. This deviation was found to be due, not to selective pairing of chromosomes, but to a certation in favor of non-glutinous pollen, in the same manner as in diploid hybrids.
4. It was concluded that tetraploid hybrids between distant varieties of cultivated rice have no amphidiploid-like nature, and that the variation in cultivated rice is mainly due to genic changes.