Marker-Assisted Backcrossing to Develop an Elite Cytoplasmic Male Sterility Line in Rice

Cytoplasmic male sterility (CMS) is a cornerstone of hybrid production in many crops. In three-line hybrid systems, use of CMS, maintainer, and fertility restorer lines is necessary for production of hybrid seeds. Limited resources of CMS and low variation of CMS lines cause genetic vulnerability to pathogens. Therefore, diversifying the CMS sources is indispensible for a sustainable production system of hybrid seed. In this study, we attempted for the first time to transfer CMS into maintainer line Yosen B in restricted generations using the marker-assisted backcrossing (MABC) method. The resultant F₁ hybrid of IR68897 A/Yosen B cross was backcrossed to Yosen B, and CMS plants in each backcross generation (from BC₁ F₁ to BC₃ F₁ ) were selected based on phenotyping test and MABC. Molecular assessment of backcross progenies was conducted using a mitochondrial CMS-specific marker and 34 polymorphic nuclear simple-sequence repeat (SSR) markers in early generations (from BC₁ F₁ to BC₂ F₁ ) and was continued using 9 additional SSRs and 82 inter-simple sequence repeat (ISSR) markers in BC₃ F₁ . A MABC strategy could successfully recover the recurrent parent genome (RPG) in BC₃ F₁ generation, and decreased heterozygosity of final CMS plants. Restorability test with known wild-abortive restorer lines (viz. IR36 and IR24) showed that combination of Yosen A × IR24 could produce highly fertile F₁ hybrid. Evaluation of some important agronomic traits of the final CMS line (BC₄ F₁ ) at field condition showed that it was comparable to the original maintainer fertile counterpart. Phenotypic and marker-assisted selections could considerably decrease the time needed for full recovery of RPG so that final CMS line could show a high similarity to original fertile counterpart.