8. Cytoplasm substitution between an Indica strain of Oryza sativa and O. glaberrima

Y. Sano
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 S\1\=E103) and a strain of O. glaberrima (WO25 S\2\=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 S\1\aS\2\ and S\2\S\2\a, respectively, and in their hybrid, gametes with S\1\a and/or S\2\a deteriorate. The isogenic F\1\-sterile lines, Acc108 S\1\ and WO25 S\2\, were expected to have S\1\S\1\S\2\S\2\ in common, although they differed in other genes.

Backcrosses were continued successively up to the BC\8\ generation to obtain cytoplasm substitution lines. The result showed that the cytoplasm of WO25 S\2\ had no adverse effect on pollen development when combined with the nucleus of Acc108 S\1\. On the other hand, when the cytoplasm of Acc108 S\1\ was combined with the nucleus of WO25 S\2\, the substitution line showed no seed set because of male sterility although the pollen grains were normally stained with I\2\=KI solution. A dominant gene derived from Acc108 S\1\ seemed to cause another indehiscence in this substitution line. Furthermore, a fertility restoring gene (Rf\j\) from Akebono (A Japonic 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 Japonic type in terms of the fertility-restoring system.

References

Sano, Y., Y.E. Chu and H.I. Oka, 1979. Genetic studies of speciation in cultivated rice, 1. Genic analysis for the F\1\ 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.