Improvement of the outcrossing ability of CMS lines by pyramiding QTLs for SER.

Unlabelled: The stigma exsertion rate (SER) is a key factor in improving the outcrossing ability of cytoplasmic male sterility (CMS) lines in rice. In previous studies, we identified 18 SER-QTLs and developed some SER-QTL pyramiding lines (PLs). In this study, 4QL-1 and 4QL-2 were selected from these PLs and crossed with CMS maintainer lines H211B and H212B, respectively, to develop two new CMS maintainer lines, H221B and H222B, and their CMS lines H221A and H222A. The SER of H221B and H222B were 74.7% and 73.1%, respectively, reaching a high SER level. Compared with CMS maintainer lines, the CMS lines consistently exhibited higher SER, which may be related to the delayed flowering time of the CMS lines. Filed experiments showed that outcrossing seed-setting rates of H221A and H222A were significantly higher than those of the original CMS lines, which meets the requirements for hybrid rice seed production. These results confirm that SER is a key factor in enhancing rice outcrossing ability. Our findings demonstrate that pyramiding SER-QTLs is an effective strategy for improving rice SER and increasing outcrossing seed-setting rate.

Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-025-01545-5.