Rice Genomics and Genetics 2024, Vol.15, No.3, 106-120 http://cropscipublisher.com/index.php/rgg 113 6 Breeding Strategies and Techniques 6.1 Traditional breeding methods Selection and hybridization are foundational techniques in traditional rice breeding. These methods involve selecting parent plants with desirable traits and cross-breeding them to produce offspring that combine these traits. Selection involves choosing plants with desirable traits such as high yield, disease resistance, and stress tolerance, and using them as parents in breeding programs (Xu et al., 2021). Hybridization, or cross-breeding, combines the genetic material from two different parent plants to produce offspring with improved characteristics. This approach has been instrumental in developing high-yielding and disease-resistant rice varieties. For instance, interspecific hybridization has played a significant role in the diversification and improvement of Asian cultivated rice, leading to the development of subgroups like indica and japonica, which are adapted to various environmental conditions (Zhou et al., 2022). Mutation breeding involves inducing genetic mutations to create new genetic variations. This can be achieved using physical agents like radiation or chemical agents such as ethyl methanesulfonate (EMS). These mutations can result in new traits that may be beneficial for rice improvement. This method has been used to develop rice varieties with improved yield, disease resistance, and stress tolerance. For example, mutation breeding has been employed to enhance traits such as drought resistance and grain quality in rice (Zhang et al., 2022). 6.2 Modern breeding techniques Marker-assisted selection (MAS) is a modern breeding technique that uses molecular markers to select plants with desirable traits at the seedling stage, thus speeding up the breeding process. MAS has been effectively used to introduce quantitative trait loci (QTLs) associated with yield, drought tolerance, and other complex traits into rice varieties. For example, MAS has been employed to enhance grain number and yield-related traits in rice by incorporating QTLs such as Gn1a and Dep1 (Gouda et al., 2020). Additionally, MAS has been used to pyramid QTLs for moisture and heat stress tolerance, resulting in rice lines with significantly improved yields under stress conditions (Withanawasam et al., 2022). Genetic engineering and CRISPR-Cas9 are cutting-edge techniques that allow precise modifications of the rice genome. These methods have been used to introduce beneficial genes from wild rice species into cultivated varieties, enhancing traits such as yield, stress tolerance, and disease resistance. For instance, CRISPR has been used to edit genes in wild allotetraploid rice, leading to the rapid improvement of agronomically important traits (Yu et al., 2021). Genetic engineering has also facilitated the development of rice varieties with enhanced resistance to biotic and abiotic stresses by incorporating genes from wild progenitors like Oryza rufipogon (Li et al., 2020). 6.3 Integrating wild genetic resources The genetic diversity found in wild Oryza species offers a valuable reservoir of traits that can be harnessed to improve cultivated rice. Integrating these wild genetic resources into breeding programs is essential for broadening the genetic base and enhancing the resilience of rice varieties. Introgression breeding involves the incorporation of genes from wild rice species into cultivated varieties to enhance genetic diversity and improve traits. This method has been used to develop introgression lines (ILs) that carry valuable alleles from wild species, such as Oryza rufipogon, which contribute to traits like drought resistance and grain quality (Zhang et al., 2022). The development of chromosome segment substitution lines (CSSLs) from wild rice has also facilitated the fine mapping of QTLs and the discovery of new genes for rice improvement (Yuan et al., 2020). Pre-breeding and base broadening involve the initial steps of incorporating genetic diversity from wild species into breeding programs. This process helps to create a broader genetic base for future breeding efforts. For example, the de novo domestication of wild allotetraploid rice has been proposed as a strategy to develop new rice varieties with enhanced genome buffering and environmental robustness (Yu et al., 2021). Additionally, the genomic analysis of wild and cultivated Oryza species has provided insights into the genetic basis of important traits, facilitating the identification of genes for rice improvement (Chen et al., 2019). By integrating traditional
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