Research On The Origin, Domestication And Dissemination Of Rice In China

Rice(Oryza sativa L.)is an important crop in the world and serves as a staple food source for more than half of the world’s population,it is also one of the most important cereal grains in China.Despite of its essential role in the agricultural history of China,but its domestication history remains unclear.The research of the origin and domestication of rice is of great significance to protect genetic resources,improve breeds and guarantee food security of the world.The domestication and dissemination of rice is also a cultural accumulation process,so the research on this problem also do help to the development of rice culture,especially the rice culture of ethnic minorities.The domestication of rice has been closely accompanied by the whole history of agricultural development,the study of rice’s domestication and dissemination is very complicated,involving archaeology,ecology,ethnology,genetics,paleontology and many other different subjects.We used a variety of highly representative cultivated rice and wild relatives with wide distribution as research materials by many methods,such as literature research,field investigation,the whole genome re-sequencing and model simulation in this study to make a comprehensive research on the domestication and dissemination of rice based on existing evidence from different aspects of archaeology,palaeoclimate and rice culture.The main results are as follows:1.The spatial and temporal distribution of rice sites and the evolution tendency of ancient rice in China.By statistics for current rice sites,the middle and lower of Yangtze river are two regions with largest number of rice sites among the seven regions.The distribution curves of the numbers of rice sites in China are similar to parabola,there is an increasing trend in number of rice sites about 4000 years ago,but there is an obvious decreasing trend after 4000 a B.P.,reflecting the close relationship between the infant rice farming and climate condition.Besides,the overall trend of grain size and shape of ancient rice found in different regions were analyzed,results showed that human beings began to choose this domestication trait consciously after 7000 year before present,and the grain width might be more likely to attract people’s attention compared to grain length.And so beyond that,the general trend of ancient rice evolution in China was japonica type according to the analysis of attributes grain shape of ancient rice,and early japonica formed about 6000 years ago,but the length-width ratio of ancient rice across our country was not reduced gradually,on the opposite the length-width ratio of ancient rice had a growth trend in south China with ancient rice of the type of indica.2.The domesticated mode of genes associated with grain width and the domestication of rice.The process of origin and domestication of cultivated rice in China was explored at the genetic level using the whole genome sequencing data and the grain width of 397 cultivated rice and 175 wild rice,seven candidate genes associated with grain width were identified across the rice whole genome,combined the analysis of genome-wide association and population evolution.The gene polymorphism of wild relatives was significantly greater than cultivated rice at this seven loci,reflecting that a strong genetic bottleneck had occurred during domestication.At the same time combined with the analysis of phylogeny and neutrality test,five of the seven candidate genes were under artificial selection in indica or japonica groups,the other two genes were under neutral evolution,only affected by genetic bottleneck.By the analysis of phylogeny and phenotype variation on indica and japonica,the grain with of indica was changed from broad to narrow,and that of japonica was changed from narrow to broad,reflecting the important influence on the differentiation of indica and japonica from cultural choice and climate environment.And the different domesticated mode of domestication gene in indica and japonica also supported for the dependent origin of indica and japonica in grain width trait.Besides,by the analysis of haplotype,we found that the population of wild rice in middle Yangtze was most likely the ancestor of japonica in the existing population of wild rice,consistenting with the overall evolution direction of ancient cultivated rice in China.The important time nodes of rice domestication was estimated by the relaxed molecular clock model,the forming time of japonica could be earlier than indica more than 1000 years.3.Rice culture and the domestication and disseminate of riceBy the analysis of prehistoric rice culture in each region,the sequence of rice culture in the Han-jiang area of middle Yangtze,the lower Yangtze and the Haidai areas of Huang-huai valleys was relatively complete,among them,the cultural sequence in middle and lower Yangtze was longest,reflecting the continuous domestication on rice by ancestor.Based on the literature research and the analysis of cultural sequence in different regions,the development of rice culture in Huang-huai valleys,Yunan province and South China was all effected by that of Yangtze valleys.In order to explore whether the South China was the origin place of rice,the rice culture of Zhuang nationality who has lived in South China since the ancient time was studied.The rice culture of Zhuang is rich,and not only is linked with the culture of Yangtze valley closely,but also is in common with rice culture of ethnic groups in South Asia and India,forming the cultural circle of "Na culture" represented by place name of "Na",providing evidence for the spread of rice.The earliest rice culture in South China could trace back to Xiao-jin culture,almost only 6000 years ago,the superior natural environment and rich animal and plant resources caused the ancient human be lack of driving force of rice domestication,may leading to the late development of rice cultivation in South China.By the comprehensive analysis of the above several analysis,we suggest that the origin of rice was in the middle and lower of Yangtze river valleys in China,The domestication of rice in China began almost 9000-7800 years ago,the early japonica was formed almost 6000 years ago,then it spreaded to the north and south separately.When the early japonica spreaded to the north,it would form the typical japonica gradually.And during the process of spread southward,the heat-tolerant indica was formed under the hybridization between japonica and wild rice more than once,the forming time was 5000-4200 years ago by preliminary analysis.