Rice Genomics and Genetics 2024, Vol.15, No.3, 142-152 http://cropscipublisher.com/index.php/rgg 146 For instance, MAS has been successfully employed to pyramid multiple resistance genes into a single rice variety, enhancing its resilience against various biotic and abiotic stresses. A study demonstrated the pyramidization of genes/QTLs for resistance to blast, gall midge, submergence, and salinity in an elite rice cultivar, resulting in lines that showed high levels of resistance to these stresses (Matsubara et al., 2016). Similarly, MAS has been used to introduce QTLs associated with grain number and yield-related traits, such as Gn1a and Dep1, into rice plants, thereby enhancing yield (Rana et al., 2019). The integration of MAS with conventional breeding approaches has also been shown to be effective. For example, marker-assisted backcross breeding has been used to integrate major genes or QTLs with large effects into widely grown varieties, providing opportunities to develop high-yielding, stress-resistant, and better-quality rice cultivars (Zhou et al., 2018). The use of cost-effective DNA markers derived from fine-mapped positions of important agronomic traits further enhances the efficiency of MAS. Genomic selection (GS) is another advanced breeding technology that utilizes genome-wide markers to predict the breeding value of individuals. Unlike MAS, which focuses on specific markers linked to target traits, GS considers the entire genome, making it a more comprehensive approach. GS has the potential to accelerate the breeding process by enabling the selection of superior genotypes at an early stage. This method has been particularly useful in addressing complex traits that are controlled by multiple genes, such as yield and nutritional content. The integration of next-generation sequencing technologies has further enhanced the accuracy and efficiency of GS by providing high-resolution mapping of QTLs and facilitating the identification of causal genes (Rana et al., 2019). CRISPR/Cas9 and other gene-editing technologies have revolutionized plant breeding by allowing precise modifications of the rice genome. These technologies enable the targeted editing of specific genes to enhance desirable traits or eliminate undesirable ones. Gene editing has been successfully applied to improve various traits in rice, including yield, disease resistance, and nutritional content. For example, CRISPR/Cas9 has been used to knock out genes associated with negative traits, thereby enhancing yield and stress tolerance. The ability to make precise edits in the rice genome opens up new possibilities for developing rice varieties with improved nutritional content and yield (Tripathy, 2021). 4.3 Integrated breeding approach An integrated breeding approach combines traditional and modern methods to achieve both high nutritional content and high yields. This approach leverages the strengths of each method to overcome their individual limitations. Traditional breeding can be used to create a diverse genetic base, while MAS and genomic selection can accelerate the identification and propagation of superior genotypes (Huang et al., 2009). Multi-trait selection involves the simultaneous selection for multiple desirable traits, such as yield, nutritional content, and stress resistance. This method requires a comprehensive understanding of the genetic architecture of these traits and their interactions. Studies have shown that it is possible to combine high yield with improved nutritional quality through careful selection and breeding strategies (Inthapanya et al., 2000). The use of advanced molecular markers and genomic tools facilitates the efficient selection of multi-trait genotypes, ensuring that new rice varieties meet the diverse needs of farmers and consumers. The integration of traditional and modern breeding methods offers a robust strategy for improving both the nutritional content and yield of rice. By leveraging the strengths of each approach, breeders can develop rice varieties that are not only high-yielding but also nutritionally superior, addressing the dual challenges of food security and nutritional deficiency. 5 Case Studies In a multi-site study, two rice mapping populations (MTU1010/Suraksha and MTU1010/Jalpriya) were tested at two to three sites, and the results showed that zinc content was significantly affected by the environment. Previous studies have also found significant environmental variation in zinc content in rice germplasm, high-zinc transgenic rice, and mapping populations.
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