Genetic studies in four interspecific hybrids of the genus oryza

The paper reports the results of genetic studies made in four interspecific hybrids of the genus Oryza, and the data are employed to discuss the inter-relationships between the different species. The characters of wild parents were found to be dominant in the F₁ hybrids.In O. sativa (variety Fukoku) × O. perennis subsp. balunga, the inheritance of the eight characters studied was found to be of the same nature as that of complementary, modifying, duplicating and polygenic types involving two or three genes. In O. perennis (Cuban type) × O. perennis subsp. balunga, the interesting feature was the occurrence of recessive characters (typical of cultivated rices) in the F₂ population, even though the two parents carried the dominant wild characters. This should be possible only by the operation of duplicate genes and such a mode of inheritance was observed for three characters. No definite Mendelian ratios could be got for the remaining five characters studied. The appearance of characters of cultivated rices has been suggested to point to the ability of O. perennis to give rise to O. sativa through natural crossing and selection. In O. glaberrima × O. perennis subsp. balunga, the ten characters studied segregated in monogenic or digenic fashion. When digenic, these characters exhibited complementary or inhibitory factor interactions. In O. glaberrima × O. breviligulata, the simple mode of inheritance in the F₂ generation has been suggested to indicate the close relationship of the two species.Some of the general features of the hybrids and segregating populations studied were the vigorous and fertile F₁s followed by the appearance of weak and unthrifty plants in the F₂ generation and the tendency for the parental characters to inherit together. The appearance of plants looking similar to O. sativa var. fatua in the F₂ populations of O. sativa × O. perennis, and of O. stapfii in the F₂s of O. glaberrima × O. perennis has been supposed to provide further evidence on the hybrid origin of these two forms.