Abstract: Cytoplasmic male sterility (CMS), which is governed by mitochondrial-nuclear interactions that disrupt pollen development, is a crucial mechanism for hybrid seed production in rice. The wild abortive (WA) CMS system underpins over 95% of commercial hybrid rice, but overreliance on this single cytoplasm increases vulnerability to biotic and abiotic stresses. Limitations such as overreliance on a single cytoplasm, occasional incomplete fertility restoration, and a narrow restorer gene pool further constrain breeding efficiency. Diversifying CMS systems is therefore essential to enhance genetic resilience and hybrid performance. This review discusses strategies for CMS diversification, including the exploration of novel cytoplasmic sources from wild rice, development of new CMS lines through backcrossing, and molecular characterization of mitochondrial and restorer genes. Advances in genomics, proteomics, and CRISPR/Cas9-mediated genome editing have identified key sterility-associated genes such as orf79, orf312, and RMS, enabling precise fertility restoration. Integrating CMS diversification with cropping system innovations can further improve hybrid rice productivity, resource use efficiency, and climate resilience. Genomic insights into adaptive divergence among rice subpopulations provide promising avenues for developing novel CMS types. Coordinated research in mitochondrial biology, molecular breeding, and biosafety policy will be critical to fully harness the potential of diversified CMS systems for sustainable and high-yielding hybrid rice cultivation.

Key words: rice, cytoplasmic male sterility, hybrid rice, fertility restoration, restorer gene, mitochondrial genome, CRISPR/Cas9, genetic diversity