Development of a platform for breeding by design of CMS lines based on an SSSL library in rice (Oryza sativa L.)

Cytoplasmic male sterility (CMS) is an important foundation for heterosis utilization and exploited widely to hybrid seed production in rice. However, the traditional experience-driven and labor-cost breeding style left little room for sustainable improvement of hybrid rice. Here, we report a platform for breeding by design of CMS lines based on an SSSL library. A line H121B with rf3 and rf4 genes from XieqingzaoB was first developed in the Huajingxian74 (HJX74) genetic background. Using H121B as maintainer line, three isonuclear alloplasmic CMS lines, W-H121A, D-H121A and Y-H121A, with the wild abortive, dwarf wild abortive, and Yegong abortive types of CMS cytoplasm, respectively, were developed. The H121B maintainer line was then improved by a way of breeding by design. Three target genes, gs3 for long grain, Wxt for low amylose content, and OsMADS50 for early heading date, in the chromosomal substituted segments of single segment substitution lines were selected from the SSSL library in the HJX74 genetic background, and were pyramided together in H121B through marker-assisted selection. The new maintainer line, H131B, showing the phenotypes of longer in grain length, lower in amylose content, and earlier in heading date than those in H121B, achieved the breeding goal designed. Using H131B as maintainer line, three new isonuclear alloplasmic CMS lines, W-H131A, D-H131A and Y-H131A, were developed. Establishment of the platform for breeding by design of CMS lines will be helpful for sustainable improvement of CMS lines in hybrid rice development.