Identification and transfer of a new cytoplasmic male sterility source from Oryza perennis into indica rice (O. sativa)

Most of the commercial hybrids of indica rice are based on wild abortive (WA) source of cytoplasmic-genetic male sterility (CMS). Such cytoplasmic uniformity may lead to genetic vulnerability to disease and insect pests. To overcome this problem, diversification of CMS sources is essential. Crosses of 46 accessions of O. perennis and two accessions of O. rufipogon as female parents were made with two restorers (IR54, IR64) of WA cytosterility. Sterile hybrids were backcrossed with the respective recurrent parents. Of all the backcross derivatives, one line having the cytoplasm of O. perennis Acc 104823 and the nuclear background of IR64 was found to be stable for male sterility. The newly developed CMS line has been designated as IR66707A. This line is completely sterile (0% seed set) under selfed conditions. Crosses of IR66707A with 10 restorers of WA cytoplasm showed almost complete (93-100%) pollen sterility, indicating that the male sterility source of IR66707A is different from WA sterility. Southern hybridization of IR66707A, O. perennis (cytoplasmic donor), IR66707B (maintainer) and V20A (WA cytoplasm) using mitochondrial DNA specific probes (5 endonucleases × 8 probes) showed identical banding patterns between IR66707A and O. perennis. However, in more than half of the combinations, different banding patterns were observed between IR66707A and IR66707B and between IR66707A and V20A. The results suggest that IR66707A has the same cytoplasm as the donor (O. perennis), and CMS may not be caused by any major rearrangement or modification of mtDNA. The new CMS source identified will be useful in cytoplasmic diversification in hybrid rice breeding