Breaking Barriers and Exploiting Heterosis Through Neutral Alleles in Hybrid Rice

The yield plateau in intrasubspecific hybrids necessitates the exploitation of heterosis in intersubspecific hybrids, combined with the introgression of novel genes from wild species through interspecific hybridization. However, the utilization of this advantage is constrained by postzygotic barriers, most notably hybrid sterility. These barriers arise from allelic incompatibilities at a limited number of rapidly evolving loci rather than from genome-wide divergence, as described by classical and modern extensions of the Dobzhansky-Muller model. Overcoming the effects of hybrid sterility loci while retaining favorable heterotic effects will facilitate the development of superior parental lines, thereby increasing the efficiency of hybrid rice breeding. Accordingly, this review integrates indica - japonica adaptive differentiation, the mechanisms underlying hybrid sterility, and heterosis-associated QTLs (quantitative trait loci) and their underlying regulatory loci to elucidate the genetic factors governing reproductive compatibility and hybrid performance in rice breeding. On this basis, fertility in intersubspecific hybrids can be restored through various strategies including the development of indica -compatible japonica lines, wide-compatible indica lines carrying neutral alleles, and advanced molecular approaches such as genome editing, thereby enabling the development of fertile, high-yielding rice hybrids. These strategies provide a practical framework to unlock the full potential of intersubspecific heterosis while also facilitating the introgression of novel genes from wild species through interspecific hybridization, thereby contributing to sustainable rice productivity under future food security and climatic challenges.