Molecular Plant Breeding 2025, Vol.16, No.3, 165-179 http://genbreedpublisher.com/index.php/mpb 171 metabolic and drought response pathways (Nyasulu et al., 2024). Recently, a study used GWAS and linkage mapping to identify drought tolerance genes in japonica rice. The key SNP, C8_28933410, was located on chromosome 8 within the qLRS-8-1 region, validating its role in drought tolerance (Liu et al., 2024). These findings underscore the potential of GWAS in identifying key genetic determinants of drought resistance, which can be leveraged in breeding programs to develop drought-resistant rice varieties. 5.3 CRISPR/Cas9 and other gene editing techniques CRISPR/Cas9 and other gene editing techniques offer precise and efficient tools for modifying specific genes associated with drought resistance in rice. These techniques allow for targeted modifications, such as gene knockouts or insertions, to improve drought tolerance. The role of the OsPP15 gene in drought resistance was validated through genetic transformation experiments, demonstrating the potential of gene editing in validating candidate genes identified through GWAS (Guo et al., 2018). Additionally, transgenic rice plants with enhanced tolerance to water deficit and osmotic stresses have been developed, highlighting the potential of genetic engineering in improving drought resistance. The application of CRISPR/Cas9 and other gene editing techniques in rice breeding holds great promise for accelerating the development of drought-resistant varieties by enabling precise manipulation of key genes involved in drought response mechanisms. Genomic approaches such as GWAS, QTL mapping, and gene editing techniques provide powerful tools for enhancing drought resistance in rice. These approaches enable the identification and validation of key genetic determinants of drought tolerance, which can be leveraged in breeding programs to develop rice varieties with improved resilience to drought stress. The integration of these genomic approaches with traditional breeding methods holds great potential for addressing the challenges of drought in rice cultivation and ensuring food security in the face of climate change. 6 Case Studies of Successful Breeding for Drought Resistance 6.1 Traditional breeding approaches Traditional breeding approaches for drought resistance in rice have primarily focused on selecting for yield stability across various environments and years. Traditional breeding programs often involved participatory approaches, where farmers’ knowledge and preferences were integrated into the breeding process. This led to the development of varieties better suited to local environmental conditions (Oladosu et al., 2019). This method, although effective, is often slow and expensive due to the low heritability of yield under stress and the inherent variability in field conditions. Oladosu et al. (2019) highlight several successful varieties developed through conventional breeding, including IR64 and Swarna, which have been enhanced for drought tolerance through the incorporation of traits from local landraces. Selecting for traits such as deep root systems and osmotic adjustment has been a key focus, but these traits require extensive field or greenhouse facilities and are prone to environmental variability. Despite these challenges, traditional breeding has laid the groundwork for understanding the complex nature of drought resistance and has provided a baseline for more advanced techniques. 6.2MAS MAS has revolutionized the breeding of drought-resistant rice by allowing for the precise identification and selection of genes associated with drought tolerance. MAS involves the use of molecular markers linked to specific traits, enabling breeders to monitor the presence or absence of these genes in breeding populations (Jena and Mackill, 2008). The successful pyramidization of multiple genes/QTLs for resistance to various stresses, including drought, has been demonstrated in rice varieties such as improved Lalat (Das and Rao, 2015). This approach has significantly accelerated the development of drought-resistant cultivars by reducing the number of generations required and increasing the precision of gene transfer (Figure 3) (Das et al., 2017). Additionally, MAS has been used to integrate major genes or QTLs with large effects into widely grown varieties, providing broad-spectrum resistance to multiple stresses (Jena and Mackill, 2008).
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