Ancient cold spurred the evolution and distribution of rice

Scientists have linked the diversification and spread of rice with global cold about four thousand two hundred years ago. Before this event, rice was grown mostly in China, but later appearing species penetrated into Korea, Japan and Southeast Asia. The results of interdisciplinary research based on genetic, archaeological and paleoclimate data, published in the journal Nature Plants.

Rice seed (Oryza sativa) is one of the most important crops. According to some estimates, he is the source of more than 20 percent of calories in the diet of half the world’s population. Most of the modern varieties of rice refers to the subgroups of japonica and indica, which is sometimes given the status of a separate subspecies. Archaeological data indicate that the rice japonica cultivation started about nine thousand years ago in the Yangtze valley, and indica — five thousand years later in the lower reaches of the Ganges.

About distribution of rice in Asia know far less than about its origin. To fill this gap, a team of specialists under the leadership of Michael Purugganan (Michael D. Purugganan) from new York University decided to study the history of this crop from a genetic point of view. The researchers analyzed the results of whole genome sequencing of more than 1400 varieties of rice and compared them with the archaeological and climatic data.

The study showed that during the first four thousand years after the domestication of rice was grown almost exclusively on the territory of modern China. The impetus for the emergence of new varieties and their dissemination in Eastern and southern Asia began abrupt climate change about four thousand two hundred years ago. In the Northern hemisphere they led to a reduction in rainfall and a decrease in the average temperature on zero point six tenths of a degree Celsius.

According to genetic data, at this point, the rice japonica were divided into two evolutionary lines adapted to temperate and tropical climate respectively. First became widespread in Northern China, the Korean Peninsula and in Japan. Second due to the cold snap advanced in Southeast Asia. However, on the Islands of Indonesia and the Philippine archipelago rice only got a two and a half thousand years ago, after the emergence of networks of lively trade relations between them and the mainland.

The domestication of rice indica occurred later, about four thousand years ago. This line was subsequently extended to China and South-East Asia, and due to the constant gene flow some populations are poorly differentiated from each other.

The study authors emphasize that only a multidisciplinary approach has allowed with such precision to reconstruct the history of one of the most popular of cultivated plants. Genetics and archaeology have provided information about the history of the spread rice, and paleoclimatology — about themselves or their environment changes.

The history of other crops may be no less complex than that of Fig. For example, corn, according to a recent study, was domesticated once, but then I did a long independent selection in North and South America. While in South America she fell twice.

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