Rice Genomics and Genetics 2024, Vol.15, No.6, 277-286 http://cropscipublisher.com/index.php/rgg 282 5.3 Utilizing modern genomic tools to optimize intersubspecific heterosis and high-yield traits Modern genomic tools have been instrumental in optimizing intersubspecific heterosis and high-yield traits in hybrid rice. The exploitation of wide compatibility (WC) systems, such as the S5 locus on chromosome 6, has facilitated successful hybridization between indica and japonica subspecies. Marker-assisted screening has identified several novel WC sources, which have been used to develop high-yielding intersubspecific hybrids with stable performance across different locations (Figure 3) (Kallugudi et al., 2022). Additionally, molecular biotechnology has enabled the identification and introduction of yield-enhancing genes from wild rice and the construction of autoregulated senescence-delaying genes, significantly improving the heterosis of hybrid rice (Wu, 2009). The rational design approach, which combines wide-cross compatibility and intersubspecific heterosis with rapid genome sequencing, has further unlocked the potential for creating high-yielding hybrid rice varieties (Azad et al., 2022). Figure 3 Combined biplots for multilocation performance wide compatible hybrids based on GGE biplot analysis on the most significant NPT related traits (Adopted from Kallugudi et al., 2022) 6 Case Studies 6.1 Successful breeding of specific hybrid varieties and their performance The breeding of hybrid rice varieties has seen significant advancements through the integration of intersubspecific heterosis and high-yield traits. For instance, the development of hybrid varieties such as Guang8A×Giza181 and II-32A×Giza179 has been achieved by crossing cytoplasmic male sterile (CMS) lines with restorer (R) lines. This strategy leverages both additive and non-additive gene actions, with additive variance being the main component of the total genotypic variance (Gaballah et al., 2022). Additionally, the use of wide compatibility (WC) systems, such as the S5n allele, has facilitated successful hybridization between indica and japonica subspecies, leading to the development of high-yielding hybrids like IRG137 and IRG143 (Kallugudi et al., 2022). The agronomic traits contributing to the high yield of these hybrids include large panicle size, reduced tillering capacity, and improved lodging resistance. These traits have been emphasized in the breeding programs to meet the demand for heavy panicles and a large source supply (Peng et al., 2008). The integration of superior alleles through genomic analysis has also played a crucial role, with high-yielding hybrid varieties accumulating numerous rare superior alleles with positive dominance (Figure 4) (Huang et al., 2015). The specific combining ability (SCA) and general combining ability (GCA) analyses have identified the best combiners among the genotypes, further enhancing grain yield (Azad et al., 2022).
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