Rice Genomics and Genetics 2024, Vol.15, No.4, 178-189 http://cropscipublisher.com/index.php/rgg 180 2.2 Fossil evidence and early records Fossil evidence and early records of rice cultivation provide insights into the ancient origins of Oryza species. The cultivation of African rice (Oryza glaberrima) dates back more than 3 000 years, with evidence suggesting that it was domesticated in a single region along the Niger River (Wang et al., 2014). In contrast, the domestication of Asian rice (Oryza sativa) has been traced back to China, where it is believed to have originated from the wild species Oryza rufipogon (Huang et al., 2012; Wei et al., 2012). The genetic diversity center of O. rufipogon is located in Southern China, particularly around the Pearl River basin, which is also considered the domestication center of O. sativa(Huang et al., 2012; Wei et al., 2012). 2.3 Genetic ancestry and lineage The genetic ancestry and lineage of Oryza species have been extensively studied through population genomics and multilocus analyses. Oryza sativa, the most widely cultivated rice species, has two subspecies: indica and japonica. These subspecies were domesticated independently from different populations of O. rufipogon, with gene flow occurring later from japonica to indica (Wei et al., 2012). The domestication of O. sativa japonica rice is believed to have occurred around the middle area of the Pearl River in southern China, while O. sativa indica rice was subsequently developed from crosses between japonica rice and local wild rice as the initial cultivars spread into South East and South Asia (Huang et al., 2012). The population genetic structure of Oryza rufipogon and Oryza nivara, two closely related wild species, has also been studied to understand their evolutionary history. O. rufipogon exhibits a complex population genetic structure shaped by repeated extinction and colonization events due to glacial-interglacial cycles during the Quaternary period. O. nivara, on the other hand, is believed to have independently originated multiple times from different O. rufipogon populations, highlighting the role of climatic factors in its adaptation and expansion (Liu et al., 2015). 3 Geographical Distribution of WildOryza Species 3.1 Global distribution patterns Wild Oryza species exhibit a broad geographical distribution, spanning various continents and ecological zones. For instance, Oryza rufipogon, a significant wild relative of cultivated rice, is found extensively across Asia, including India, China, and Vietnam (Singh et al., 2018). In India, O. rufipogon populations are distributed across diverse agro-climatic zones, indicating a wide ecological adaptability (Singh et al., 2018). Similarly, in China, O. rufipogon populations are concentrated in regions such as Guangdong, Hainan, and Guangxi, which are identified as centers of genetic diversity (Wang et al., 2020; Zhang et al., 2022). The Mekong Delta in Vietnam also serves as a crucial habitat for O. rufipogon, showcasing significant genetic diversity (Lam et al., 2019). 3.2 Ecological niches and habitats Wild Oryza species occupy a variety of ecological niches, ranging from riverine systems to wetlands and upland areas. In India, O. rufipogon is found in diverse habitats, including marshes, swamps, and riverbanks, reflecting its adaptability to different environmental conditions (Singh et al., 2018). In China, O. meyeriana populations are distributed across various administrative regions, river systems, and climatic zones, each exhibiting different levels of resistance to bacterial blight, which is influenced by their specific habitats (A et al., 2020). The Mekong Delta's channels and rivers provide a unique ecological niche for O. rufipogon, where it thrives in both upstream and downstream areas, showing vigorous vegetative growth in specific channels (Lam et al., 2019). 3.3 Factors influencing distribution Several factors influence the distribution of wild Oryza species, including climatic conditions, geographical barriers, and human activities. In Yunnan, China, the resistance of O. meyeriana to bacterial blight varies significantly with latitude and altitude, indicating that climatic factors such as temperature and humidity play a crucial role in shaping its distribution (Mokodongan et al., 2018). Human activities, such as habitat fragmentation and agricultural expansion, have also impacted the distribution and genetic diversity of wild rice populations. For example, in China, the genetic structure of O. rufipogon populations has been affected by habitat fragmentation,
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