Rice Genomics and Genetics 2024, Vol.15, No.4, 178-189 http://cropscipublisher.com/index.php/rgg 184 6.2 Differentiation of cultivated varieties The differentiation of cultivated rice varieties is a complex process influenced by both natural and artificial selection. The genomic analysis of 13 domesticated and wild rice relatives highlighted the rapid species diversification and the emergence of novel genetic elements, including transposons, which contribute to the differentiation of rice varieties (Stein et al., 2018). Furthermore, the study of evolutionary relationships among Oryza species has provided insights into the phylogenetic and evolutionary dynamics that underlie the differentiation of cultivated rice (Wambugu et al., 2018). Interspecific hybridization and introgression have also played a crucial role in the origin and diversification of Asian cultivated rice, leading to the development of various subgroups such as indica, aus, and basmati, which are adapted to different ecological and climatic conditions (Zhou et al., 2022). 6.3 Hybridization and gene flow Hybridization and gene flow have been significant driving forces in the evolution and domestication of Oryza species. Natural hybridization-introgression events have contributed to the genetic diversity and adaptation of Oryza sativa, facilitating the development of subgroups that are well-suited to diverse environments. The complex patterns of introgression observed in domestication genes suggest multiple independent domestication events, further highlighting the role of hybridization in the evolution of cultivated rice (Wang et al., 2018). Additionally, artificial interspecific hybridization has led to significant breakthroughs in rice breeding, such as the development of three-line hybrid rice and the introduction of important pest and disease resistance genes (Zhou et al., 2022). These efforts have been instrumental in enhancing rice production and ensuring food security. 7 Impact of Human Activity onOryza Migration and Domestication 7.1 Agricultural practices and expansion Human agricultural practices have significantly influenced the migration and domestication of Oryza species. The domestication of rice (Oryza sativa) from its wild progenitor, O. rufipogon, in tropical and subtropical regions of Asia, required adaptations to various local environments, including changes in daylight sensitivity, thermal tolerance, and resistance to biotic stresses (Zheng et al., 2021). The introduction of rice cultivation to new regions, such as Madagascar, involved migration bottlenecks and genetic recombination, which resulted in unique genetic diversity patterns among local rice populations (Ahmadi et al., 2020). The selection for traits such as non-shattering seeds and erect plant architecture facilitated dense planting and high yield, which were crucial for the success of rice as a staple crop (Huang et al., 2020). 7.2 Trade routes and cultural exchange Trade routes and cultural exchanges have played a pivotal role in the spread of Oryza species. The movement of rice along trade routes facilitated the exchange of genetic material and the introduction of rice to new regions. For instance, the genetic diversity of African rice (Oryza glaberrima) suggests a non-centric domestication origin, with multiple regions contributing key alleles for different domestication traits (Choi et al., 2019; Veltman et al., 2019). The spread of rice cultivation to Madagascar was associated with the arrival of Austronesians, who introduced new rice varieties and cultivation practices, leading to the emergence of unique rice groups specific to the island (Ahmadi et al., 2020). These exchanges not only expanded the geographical range of rice but also contributed to the genetic diversity and adaptation of rice to different environments. 7.3 Modern breeding and genetic modification Modern breeding and genetic modification have further shaped the domestication and migration of Oryza species. Advances in genomics have enabled the identification of genome-wide signatures of rice domestication and the unlocking of genetic diversity among Oryza species. The development of hybrid rice varieties has leveraged heterotic loci to enhance yield and stress resistance, contributing to the global spread and success of rice cultivation (Chen et al., 2019). The release of complete genome assemblies, such as that of IR 8 ‘Miracle Rice’, has provided valuable resources for future crop protection and breeding efforts (Stein et al., 2018). These modern techniques have not only improved rice productivity but also facilitated the conservation and utilization of genetic resources from wild and domesticated rice relatives (Labroo et al., 2023).
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