Abstract
Ten cytoplasmic male sterile lines of rice, i.e., RT2S, RT4S, RT5S, RT10S, RT11S, RT18S, RT20S, RT40S, RT41S and RT100S, were crossed with two testers having fertility restoring genes, RT61F and RT98F. All of these lines were isogenic lines of Taichung 65 that were developed through repeated backcrosses of Taichung 65 into wild rice, Oryza rufipogon. Then the cytoplasms of the male sterile lines were classified depending on the pollen and seed fertility of their F1. The fertility restoring gene of RT61F has been identified, and shown to be different from that of the RT98F.
The F1 of RT18S showed pollen semi-fertility characteristic to a gametophytic cytoplasm. While all of the lines except RT 18S showed complete pollen fertility in the hybridization with the two testers. Regarding pollen fertility, no cytoplasmic difference was observed. The resulting F1s between RT4S and two testers showed complete seed sterility. When RT2S, RT10S, RT11S and RT41S was crossed with RT61F, all of the offsprings showed seed sterility. While these four lines showed high seed fertility in the hybridization with RT98F. RT5S and RT100S showed low seed fertility in the hybridization with RT61F but showed high seed fertility in the hybridization with RT98F. In crosses of RT20S and RT40S with RT61F, F1individuals showed low seed fertility, but in crosses of RT20S and RT40S with RT98F, F1individuals showed a substantially wide distribution range.
Accordingly, the cytoplasms of the ten cytoplasmic male sterile lines as tested above were classified into the following five groups: (1) RT18S (2) RT4S (3) RT2S, RT10S, RT11S, RT41S (4) RT20S, RT40S (5) RT5S, RT100S.
