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 F-1 hybrid of IR68897 A/Yosen B cross was backcrossed to Yosen B, and CMS plants in each backcross generation (from BC1F1 to BC3F1) 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 BC1F1 to BC2F1) and was continued using 9 additional SSRs and 82 inter-simple sequence repeat (ISSR) markers in BC3F1. A MABC strategy could successfully recover the recurrent parent genome (RPG) in BC3F1 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 x IR24 could produce highly fertile F-1 hybrid. Evaluation of some important agronomic traits of the final CMS line (BC4F1) 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.