Stacking S5-n and f5-n to overcome sterility in indica–japonica hybrid rice
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Pyramiding of S5 - n and f5 - n cumulatively improved seed-setting rate of indica–japonica hybrids, which provided an effective approach for utilization of inter-subspecific heterosis in rice breeding.
Breeding for indica–japonica hybrid rice is an attractive approach to increase rice yield. However, hybrid sterility is a major obstacle in utilization of inter-subspecific heterosis. Wide-compatibility alleles can break the fertility barrier between indica and japonica subspecies, which have the potential to overcome inter-subspecific hybrid sterility. Here, we improved the compatibility of an elite indica restorer line 9311 to a broad spectrum of japonica varieties, by introducing two wide-compatibility alleles, S5-n and f5-n, regulating embryo-sac and pollen fertility, respectively. Through integrated backcross breeding, two near isogenic lines harboring either S5-n or f5-n and a pyramiding line carrying S5-n plus f5-n were obtained, with the recurrent parent genome recovery of 99.95, 99.49, and 99.44 %, respectively. The three lines showed normal fertility when crossed to typical indica testers. When testcrossed to five typical japonica varieties, these lines allowed significant increase of compatibility with constant agronomic performance. The introgressed S5-n could significantly improve 14.7–32.9 % embryo-sac fertility in indica–japonica hybrids. In addition, with the presence of f5-n fragment, S5-n would increase the spikelet fertility from 9.5 to 21.8 %. The introgressed f5-n fragment greatly improved anther dehiscence, embryo-sac and pollen fertility in indica–japonica hybrids, thus leading to improvement of spikelet fertility from 20.4 to 30.9 %. Moreover, the pyramiding line showed 33.6–46.7 % increase of spikelet fertility, suggesting cumulative effect of S5-n and f5-n fragment in seed-set improvement of inter-subspecific hybrids. Our results provided an effective approach for exploiting heterosis between indica and japonica subspecies, which had a profound implication in rice breeding.
KeywordsPollen Fertility Spikelet Fertility Neutral Allele Typical Indica Japonica Subspecies
We are indebted to Dr. Jie Hu from Huazhong Agricultural University for discussion. This research was supported by the Science and Technology Major Projects of Genetically Modified Organisms Breeding of China (High Yield Transgenic Rice Breeding, Grant No. 2011ZX08001-004 and 2014ZX08001-004-001), the National High Technology Research and Development Programs of China (863 Programs, “Breeding of New Varieties of Green Super Rice”, Grant No. 2014AA10A604), and the National Natural Science Foundation of China (Grant No. 31371599).
Author contribution statement
YO, TM and QZ conceived and designed the experiments; JM, GL, JH, HY, FZ and TM performed the experiments, including artificial crossing, genotyping, and selecting for breeding in the field; JM analyzed the data; YO and JM wrote the paper.
Compliance with ethical standards
Conflict of interest
The authors have no conflict of interest associated with this study.
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