Molecular Microbiology Research 2024, Vol.14, No.6, 277-289 http://microbescipublisher.com/index.php/mmr 284 Advanced backcross populations and recurrent selection are other methodologies used to enhance blast resistance. For example, recurrent selection in the CNA-IRAT 5 upland rice population has been shown to improve partial blast resistance over multiple generations (Veillet et al., 1996). Transgenic approaches, such as the introduction of chitinase and beta-1,3-glucanase genes into Dian-type hybrid rice, have also been employed to enhance resistance (Xu et al., 2003). 5.2 Key findings from comparative studies Comparative studies have yielded several key findings regarding blast resistance in rice. The identification of a major QTL on chromosome 11 in upland rice highlights the potential for fine-mapping and functional annotation of candidate genes involved in resistance (Tan et al., 2022). Meta-analyses have mapped 85 blast resistance genes and approximately 350 QTLs, providing valuable insights into the genetic basis of both partial and complete resistance (Ballini et al., 2008). Studies on Indian rice landraces have revealed significant genetic diversity at blast resistance loci, with landraces harboring between five to nineteen resistance genes. This diversity is crucial for breeding programs aimed at developing resistant varieties (Yadav et al., 2019). In the CNA-IRAT 5 population, recurrent selection has been shown to efficiently improve partial blast resistance, with hybrid breeding appearing slightly more advantageous than pure line breeding (Veillet et al., 1996). Additionally, fine-mapping of QTLs, such as Pikahei-1(t) from upland rice Kahei, has identified candidate resistance genes that can be targeted in breeding programs (Xu et al., 2008). 5.3 Implications for breeding programs The findings from comparative genetic studies have significant implications for rice breeding programs. The identification and fine-mapping of major QTLs and resistance genes provide valuable genetic resources that can be introgressed into elite cultivars to enhance blast resistance. For instance, the QTL identified on chromosome 11 in upland rice can be used to develop new resistant varieties through marker-assisted selection (Tan et al., 2022). The genetic diversity observed in Indian rice landraces suggests that these landraces can serve as a reservoir of resistance genes for breeding programs. By incorporating diverse resistance genes, breeders can develop varieties with broad-spectrum and durable resistance to blast (Yadav et al., 2019). The success of recurrent selection in improving partial blast resistance in the CNA-IRAT 5 population indicates that this approach can be applied to other rice populations to enhance resistance (Veillet et al., 1996). Transgenic approaches offer another avenue for improving blast resistance. The successful introduction of chitinase and beta-1,3-glucanase genes into Dian-type hybrid rice demonstrates the potential of genetic engineering in developing resistant varieties (Xu et al., 2003). Fine-mapping of QTLs, such as Pikahei-1(t), provides specific targets for breeding programs, enabling the development of varieties with strong field resistance (Xu et al., 2008). 6 Breeding Strategies for Enhanced Blast Resistance 6.1 Marker-assisted selection (MAS) in breeding MAS has become a pivotal tool in rice breeding programs aimed at enhancing blast resistance. MAS involves the use of molecular markers that are closely linked to resistance genes, allowing for the precise selection of desirable traits. For instance, the use of RFLP markers for genes such as Pi1, Piz-5, and Pita has been instrumental in developing blast-resistant rice varieties (Hittalmani et al., 2000). Similarly, the integration of genes Pi-d(t)1, Pi-b, and Pi-ta2 through MAS has demonstrated significant improvements in blast resistance in hybrid rice lines. The application of MAS not only accelerates the breeding process but also ensures the incorporation of multiple resistance genes, thereby enhancing the overall resistance profile of the rice cultivars (Narayanan et al., 2004; Dahu et al., 2015).
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