Molecular Plant Breeding 2024, Vol.15, No.6, 362-370 http://genbreedpublisher.com/index.php/mpb 363 markers such as simple sequence repeats (SSR). Studies have shown that genetic distance estimates based on phenotypic and SSR markers can range widely, indicating substantial genetic variation among sorghum genotypes (Amelework et al., 2016; Chauhan and Pandey, 2021). This genetic variation is essential for identifying unique genotypes with desirable traits and for maximizing heterosis, or hybrid vigor, which is the phenomenon where hybrid offspring exhibit superior qualities compared to their parents (Mengistu et al., 2020; Chen et al., 2024a; Chen, 2024b). Heterosis in sorghum has been extensively studied, with findings indicating that hybrids can exhibit significant positive heterosis for traits such as grain yield, plant height, and micronutrient content. For instance, hybrids developed for grain Fe and Zn concentrations showed significant positive mid-parent heterosis, suggesting the potential for improving these nutritional traits through hybrid breeding (Gaddameedi et al., 2020). Additionally, studies have demonstrated that hybrids can outperform local varieties by 20% to 80% in yield under various environmental conditions, highlighting the potential of hybrid breeding to enhance sorghum productivity (Kante et al., 2019). 2.2 Breeding techniques for hybrid sorghum varieties Several breeding techniques are employed to develop hybrid sorghum varieties. One common method is the line × tester mating design, which involves crossing multiple lines with testers to evaluate the combining ability and heterosis of the resulting hybrids. This approach helps in identifying the best parental combinations for producing high-yielding hybrids (Chauhan and Pandey, 2021; Rachman et al., 2022). Another technique involves the use of backcross populations to introduce genetic diversity from unadapted germplasm into elite breeding lines. This method has been effective in retaining genetic variation for key traits while improving the performance of the progeny (Jordan et al., 2011). Genomic selection is another advanced technique used in sorghum breeding. This method involves using genomic information from parental genotypes to predict the performance of hybrids (Sapkota et al., 2022). Studies have shown that genomic prediction can significantly improve the efficiency of hybrid breeding programs by accurately forecasting hybrid performance based on parental genotypes (Maulana et al., 2023). 2.3 Key traits targeted in hybrid sorghum breeding Hybrid sorghum breeding programs target several key traits to develop superior varieties. These traits include grain yield, plant height, days to flowering, and micronutrient content. High grain yield is a primary target, as it directly impacts the economic viability of sorghum cultivation. Studies have shown that hybrids can achieve substantial yield improvements over local varieties, making yield a critical focus in breeding programs (Amelework et al., 2016; Kante et al., 2019). Plant height and days to flowering are also important traits, as they influence the adaptability and harvestability of sorghum. Breeding programs aim to develop hybrids with optimal plant height and early flowering to ensure better adaptation to different growing conditions and to facilitate mechanical harvesting (Ribeiro et al., 2021). Additionally, improving the nutritional quality of sorghum, particularly grain Fe and Zn concentrations, is a key objective. Hybrids with higher micronutrient content can address malnutrition issues in regions where sorghum is a staple food (Gaddameedi et al., 2020). 3 Development of New Hybrid Sorghum Varieties 3.1 Parent line selection and hybrid combination The selection of parent lines and the combination of hybrids are critical steps in the development of new sorghum varieties. Studies have shown that combining ability and heterosis play significant roles in determining the success of hybrid breeding programs. For instance, research conducted on sorghum hybrids in West Africa demonstrated that hybrids developed from Guinea-race parents exhibited substantial yield advantages over local varieties, with heterosis levels ranging from 20% to 80% under different phosphorus conditions (Kante et al., 2017; Kante et al., 2019). Additionally, combining ability studies in tropical sorghum revealed that both general combining ability (GCA) and specific combining ability (SCA) are essential for traits such as grain yield, plant height, and seed mass, indicating the importance of both additive and non-additive gene actions (Kenga et al., 2004). These findings underscore the necessity of selecting parent lines with strong GCA and SCA effects to maximize hybrid performance.
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