Rice Genomics and Genetics 2024, Vol.15, No.2, 83-93 http://cropscipublisher.com/index.php/rgg 85 was not linear; instead, it involved a pre-domestication cultivation phase where wild and domesticated forms coexisted and were cultivated simultaneously (Fuller and Weisskopf, 2011). Rice (Oryza sativa) domestication is a crucial event in agricultural history with significant implications for human civilization. Recent archaeological and genetic studies have provided a clearer picture of the timeline and process of rice domestication. Archaeological evidence indicates that rice cultivation began around 8 000 years ago in the Yangtze River basin in southern China. However, the critical domestication trait of non-shattering was not fixed until around 7 000 years ago, suggesting a prolonged early cultivation phase before achieving full domestication (Choi et al., 2017). This timeline is supported by phytolith evidence from Hainan Island, indicating the presence of domesticated rice as early as 5 600 years ago, implying the spread of rice agriculture from the Yangtze River basin. Genetic studies have further elucidated the domestication process. The genetic differentiation between the two major subspecies of Asian rice, indica and japonica, has been a topic of debate. Recent findings support the single-origin hypothesis of rice domestication, with japonica being the first variety to diverge from its wild ancestor O. rufipogon, approximately 13 100 to 24 100 years ago. This predates the earliest archaeological evidence of domestication, suggesting that early management practices of wild rice may have preceded full domestication (Choi et al., 2017). Additionally, genetic evidence indicates significant gene flow from japonica to indica, facilitating the transfer of domestication alleles and leading to the development of indica rice. The integration of archaeological and genetic data provides a comprehensive understanding of rice domestication. For example, ancient DNA recovered from prehistoric rice remains in Thailand and India reveals the presence of early japonica in these regions, supporting the hypothesis of hybridization between japonica and proto-indica populations (Li et al., 2017). This gene exchange likely played a crucial role in the spread and diversification of domesticated rice. Moreover, the early Holocene climate conditions characterized by an active East Asian summer monsoon may have facilitated the natural expansion of wild rice's distribution range, aligning with the earliest known domestication sites in the middle and lower Yangtze River. This climatic backdrop supports the hypothesis that initial domestication occurred in areas where wild ancestors were naturally abundant (Figure 1) (Dodson et al., 2021). Figure 1 Natural distribution of Oryza rufipogon. Inset shows full natural distribution (Adopted from Dodson et al., 2021) Image caption: On the mainland, the distribution includes Yunnan, Guangxi, Guangdong, Hunan, and Jiangxi provinces, as well as the offshore islands of Hainan and Taiwan, natural populations in Jiangxi and Taiwan have become extinct due to habitat destruction (Adopted from Dodson et al., 2021)
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