National Institute of Genetics, Mishima, 411 Japan
Yabuno (1977) reported that the cytoplasm of Japonica strains of O. sativa gave male-sterile plants when combined with the nucleus of O. glaberrima by recurrent backcrossing, whereas the cytoplasm of O. glaberrima produced no adverse effect on pollen fertility when combined with the nucleus of a Japonica strain. As a follow-up study, a backcrossing program was carried out using an Indica strain of O. sativa (Acc 108 S1=E103) and a strain of O. glaberrima (WO25 S2=E104) in an attempt to reexamine the differential nuclear-cytoplasm interaction between the two species. Sano et al. (1979) reported that strains Acc108 and WO25 had S1aS2 and S2S2a, respectively, and in their hybrid, gametes with S1a and/or S2a deteriorate. The isogenic F1-sterile lines, Acc108 S1 and WO25 S2, were expected to have S1S1S2S2 in common, although they differed in other genes.
Backcrosses were continued successively up to the BC8 generation to obtain cytoplasm substitution lines. The result showed that the cytoplasm of WO25 S2 had no adverse effect on pollen development when combined with the nucleus of Acc108 S1. On the other hand, when the cytoplasm of Acc108 S1 was combined with the nucleus of WO25 S2, the substitution line showed no seed set because of male sterility although the pollen grains were normally stained with I2=KI solution. A dominant gene derived from Acc108 S1 seemed to cause another indehiscence in this substitution line. Furthermore, a fertility restoring gene (Rfj) from Akebono (A Japonica strain used by Yabuno) was effective in restoring pollen fertility in the male sterile line, suggesting that the cytoplasm of Acc108 is the same as those of the Japonica type in terms of the fertility-restoring system.
Sano, Y., Y.E. Chu and H.I. Oka, 1979. Genetic studies of speciation in cultivated rice, 1. Genic analysis for the F1 sterility between O. sativa L. and O. glaberrima Steud. Jpn. J. Genet. 54: 121-132.
Yabuno, T., 1977. Genetic studies on the interspecific cytoplasm substitution lines of Japonica varieties of O. sativa L. and O. glaberrima Steud. Euphytica 26: 451-463.