Studies on cytoplasmic sterility of hybrids in distantly related varieties of rice, Oryza sativa L. II. Analysis of nuclear genes in Japanese varieties controlling cytoplasmic sterility.

Abstract

1. Ta 820 is a strain obtained from the backcross generation of Tadukan x (Norin 8)4 in which the donor parent Tadukan, a Philippine variety, was used as female in the original cross and the recurrent parent Norin 8, Japanese variety always as male. In this strain was observed a slight sterility which was believed to be due to the cytoplasm originated from the donor parent. Tadukan. 2. When Ta 820 was crossed with the pollen of Japanese varieties, F1 hybrids revealed sterility which was considered to be due to the interaction between the cytoplasm and nuclear genes of the hybrids, and according to, the degree of the sterility in F2, the Japanese varieties were classified into two group. The one causes a high sterility in F1 and the other a low sterility in F1' 3. In order to test the above stated reaction of the Japanese varieties, several varieties from each of the groups were chosen, and many intra- and inter-group crosses were made, and these F1 hybrids were again crossed as the male parents with Ta 820 to investigate sterility variation in the offspring. The result indicated that the F1 hybrid plants from the intra-group crosses gave only either high or 10w sterility range corresponding to that of the parent Japanese varieties, while the F1 plants from the inter-group crosses gave the segregation of high and low range in the ratio of 1 : 1. The sterility, as shown above, seemed to result from the interaction between Ta 820 cytoplasin and sensitive allelic genes possessed by Japanese varieties, thus the high sterility being conditioned by the dominant gene and the low sterility by the recessive. Other than these major alleles, modifiers or polygenes were also supposed to affect, to a certain extent, the present cytoplasmic sterility.