GENETIC-STUDIES OF SPECIATION IN CULTIVATED RICE .1. GENIC ANALYSIS FOR THE F1 STERILITY BETWEEN O SATIVA L AND O ORYZA-GLABERRIMA STEUD

The F1 plants between Oryza sativa L. and O. glaberrima Steud. are highly pollen-sterile although the chromosomes normally pair in meiosis. They can be backcrossed as some embryosacs remain functional. Isogenic F1-sterile lines having the genetic background of sativa and glaberrima parents were isolated from B8F2 plants, respectively. They were self-fertile and showed semi-sterility in the F1 plants when crossed with the parental strains. But the F2 plants were fully fertile. This F1 sterility was most favorably explained by a “one locus sporo-gametophytic interaction” model of sterility genes which assumes that the sativa and glaberrima parents have Sa1Sa1 S2S2 and S1S1 S2aS2a, respectively, and that if a S gene is present in the maternal tissue, gametes with Sa deteriorate. Then, the F1 plants having S/Sa are 50 percent sterile and produce S gametes only. Evidence for this hypothesis was that in an S1/Sa1 hybrid, a gene controlling apiculus coloration was closely linked with S1; then, the F2 produced colored plants only since the gametes carrying Sa1 and the colorless allele were eliminated. The presence of other genic systems was also suggested. For instance, a true-breeding partly sterile line with sativa background was obtained, which seemed to be homozygous for some complementary or duplicate recessive genes causing sporophytic sterility. Possibly, the F1 sterility is controlled by a complex of genic systems, and the backcrossing to derive isogenic F1-sterile lines in this work resulted in extraction of one of them. © 1979, The Genetics Society of Japan. All rights reserved.