Rice Genomics and Genetics 2024, Vol.15, No.4, 178-189 http://cropscipublisher.com/index.php/rgg 181 necessitating conservation efforts to preserve its genetic diversity (Wang et al., 2020). Additionally, the genetic diversity of O. rufipogon in the Mekong Delta is influenced by both nuclear and maternal lineages, suggesting that historical migration and local adaptation have played significant roles in its current distribution (Lam et al., 2019). 4 Migration Pathways of Oryza Species 4.1 historical migration routes The historical migration routes of Oryza species, particularly Oryza sativa and Oryza glaberrima, have been extensively studied to understand their domestication and spread. Oryza sativa, commonly known as Asian rice, is believed to have originated from the wild species Oryza rufipogon. Genetic evidence suggests that the domestication of O. sativa occurred in multiple regions across Asia, with subsequent migration and diversification leading to the widespread cultivation of rice across the continent (Stein et al., 2018; Chen et al., 2019). On the other hand, Oryza glaberrima, or African rice, is thought to have been domesticated independently from its wild progenitor Oryza barthii in West Africa. The domestication and migration of O. glaberrima are characterized by a non-centric or polycentric origin, with multiple regions contributing to its domestication traits (Choi et al., 2019; Veltman et al., 2019). 4.2 Biogeographical barriers and facilitators The migration of Oryza species was influenced by various biogeographical barriers and facilitators. For instance, the geographical isolation of different regions in Africa and Asia played a significant role in the independent domestication events of O. sativa and O. glaberrima. In Asia, the diverse climatic and geographical conditions facilitated the spread and adaptation of O. sativa to different environments, leading to the development of various rice ecotypes (Stein et al., 2018; Chen et al., 2019). In Africa, the presence of distinct genetic clusters and isolation by distance in coastal populations of O. glaberrima suggests that geographical barriers such as rivers and mountains influenced the migration and diversification of this species (Veltman et al., 2019). Additionally, human activities, such as trade and agriculture, acted as facilitators for the spread of domesticated rice species across different regions (Choi et al., 2019). 4.3 Genetic evidence of migration Genetic studies have provided substantial evidence for the migration and domestication pathways of Oryza species. Genome sequencing and analysis of wild and domesticated rice accessions have revealed genome-wide signatures of domestication and migration. For example, the analysis of genome variations in O. sativa and O. rufipogon has identified specific genetic markers associated with domestication traits, supporting the theory of multiple domestication events in Asia (Stein et al., 2018; Chen et al., 2019). Similarly, whole genome sequencing of O. glaberrima and O. barthii has shown genetic structure and phylogeographic patterns that indicate a non-centric domestication origin in Africa (Choi et al., 2019; Veltman et al., 2019). These genetic insights have been crucial in tracing the roots and migration pathways of Oryza species, providing a deeper understanding of their evolutionary history and domestication processes. 5 Domestication Centers and Processes 5.1 Primary domestication centers South Asia is recognized as one of the primary centers for the domestication of Oryza species, particularly Oryza sativa. Genetic and genomic studies have revealed that the domestication of Asian rice involved significant genetic diversity and complex evolutionary processes. The division of Oryza sativa into subgroups such as indica and japonica, and further into aus, tropical japonica, and aromatic, highlights the intricate domestication history in this region. The emergence of these subgroups is believed to have occurred over the last 4-5 millennia, with aus diverging from indica earlier than tropical japonica from japonica (Lu, 2023). East Asia also played a crucial role in the domestication of Oryza species. The genomic analysis of numerous wild and cultivated rice accessions has provided insights into the origin and domestication of Asian rice. The identification of genome-wide signatures of domestication in Oryza sativa underscores the importance of this
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