Rice Genomics and Genetics 2024, Vol.15, No.4, 190-202 http://cropscipublisher.com/index.php/rgg 194 Figure 1 Two candidate genes hd3aandtac1for heterosis for yield traits in type-A hybrids (Adopted from Huang et al., 2016) Image caption: a: Gene structure of Hd3a and hd3a alleles; b: Plots of the advantage of the heterozygous state (Hd3a/hd3a) over Hd3a/Hd3a for grain yield per plant and yield components in nine type-A populations of 3 947 F2 lines; c: Gene structure of TAC1 and tac1 alleles; d, The performances of tiller angle for three genotypes of the TAC1 gene in 438 F2 lines (mean±s.e.); The three genotypes are colour-coded in d and e; e: Computational modelling of the planting number per unit area (mu, equivalent to one-fifteenth of a hectare) for TAC1 gene; f: The allele frequencies of hd3a and tac1 in 1 063 pairs of type-A parents and 254 pairs of type-B parents (Adapted from Huang et al., 2016) The final step in hybrid breeding is the testing and evaluation of hybrid performance. This involves multi-environment trials (METs) to assess the stability and adaptability of hybrids across different locations and conditions. Key traits such as yield, disease resistance, stress tolerance, and grain quality are evaluated to determine the overall performance and suitability of the hybrids for commercial cultivation. Rigorous testing ensures that only the best-performing hybrids are released to farmers. This process includes on-farm trials and farmer participatory breeding programs, where farmers' feedback is incorporated into the selection process. Successful hybrids are then multiplied and distributed as hybrid seeds to farmers, contributing to increased productivity and sustainability in rice production (Virmani, 1996). The exploitation of heterosis in rice through traditional and modern breeding strategies has significantly enhanced rice yields and resilience. By integrating advanced genomic tools and techniques, breeders can develop superior hybrid varieties that meet the growing demands for food security and agricultural sustainability. 4 Case Studies of Successful Hybrid Rice Varieties 4.1 High-yielding hybrids Shanyou 63, developed in China, is one of the most renowned high-yielding hybrid rice varieties. Released in the 1990s, Shanyou 63 quickly gained popularity due to its remarkable yield potential. The hybrid combines the male-sterile line Zhenshan 97A with the restorer line Minghui 63, both of which were carefully selected for their combining ability and superior traits.
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