Genetic studies of speciation in cultivated rice. 1. Genic analysis for the F1 sterility between O. sativa L. and O. glaberrima steud.

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Abstract
The F1 plants between Oryza sativa and O. glaberrima are highly pollen-sterile although the chromosomes normally pair in meiosis. They can be backcrossed as some embryo sacs remain functional. Isogenic F1-sterile lines with the genetic background of sativa [S] and glaberrima [G] parents were isolated from B8F2 plants, respectively. They were self-fertile and showed semi-sterility in the F1 when crossed with the parental strains. The F2 plants were fertile. This F1 sterility is explained by a 1 locus sporogametophytic interaction model of sterility genes which assumes that the sativa and glaberrima parents have S1aS1aS2S2 and S1S1 S2aS2a, respectively; if a S gene is present in the maternal tissue, gametes with Sa deteriorate. Then, the F1 plants having S/Sa are 50% sterile and produce S gametes only. Evidence for this hypothesis was that in an S1/S1a hybrid, a gene controlling apiculus coloration was closely linked with S1; then, the F2 produced colored plants only since the gametes carrying S1a and the colorless allele were eliminated. The presence of other genic systems was also suggested. A true-breeding partly sterile line with sativa background was obtained, which seemed homozygous for some complementary or duplicate recessive genes causing sporophytic sterility. The F1 sterility is probably controlled by a complex of genic systems.

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