Studies on cytoplasmic sterility of hybrids in distantly related: varieties of rice, Oryza sativa L. I . Fertility of the F<SUB>1</SUB> hybrids between strains derived. from certain Philippine x Japanese variety crosses and Japanese varieties

Abstract

l. Strains were developed, which involved rather wide range of sterility, from an original cross between Tadukan, donor Philippine variety, and Norin 8, recurrent Japanese variety, by backcrosses repeated 3 times, in which hybrid plants were aiways used as fcmale and the recurrent variety as male parent. Several strains, referred to as Tastrains in the following, were finally obtained by selection on fertility from the subsequent pedigree generation ; however, they had a slightly lower fertility than the average Japanese varieties, although their pollen and embryo sacs were function-ally normal. 2. The F1 hybrids of these Ta-strains with Japanese varieties revealed a contrasted difference in fcrtility in reciprocal crosses : F1 hybrids with Japanese varieties used as the male parents revealed a wide range of sterility, while all F1 hybrids from the reciprocal crosses were normal in fcrtility. These results indicate that the sterility might be due to an interaction between the cytoplasm and nuclear genes. 3. The degree of the sterility of the F1 hybrids from Ta-strains × Japanese varieties seemed to indicate two groups involved in Japanese varieties, i.e. the one giving rather low sterility, and the other the higher sterility in F1 hybrids. 4. The sterility above stated was considered ta be intimately connected with the difficulty in anther dehiscence, the sterility range showing a close correlation with pollen dispersal. 5. The cytoplasm connected with this particular sterility in these Ta-strains was considered to have originated from the one in Tadukan, retaining the reaction norm over many backcross generations by the Japanese varieties.