Chinese scientists have found traces of indica rice at an archaeological site in Gyirong county of Shigatse, Tibet autonomous region.
The discovery, made by an academic team of the second comprehensive scientific expedition to the Qinghai-Tibet Plateau at the Kongsangqiao Ruin site, provides the earliest definite evidence of indica rice on the Tibetan Plateau millennia ago.
The details of the survey were reported in a research paper published in Science China Earth Sciences journal in December.
It notes that rice cultivated in Asia have two main subspecies, indica and japonica. Japonica rice was domesticated in the middle and lower reaches of the Yangtze River in China, while indica appeared in South Asia after hybridization between japonica and indigenous proto-indica.
"When and how indica rice spread into China is still barely understood, although it is cultivated widely in southern China today," said Yang Xiaoyan, a professor at Lanzhou University, who was part of the scientific expedition.
The Kongsangqiao site is located at an altitude of 2,676 meters above sea level in a low-altitude area of Tibet. The radiocarbon dating of charred indica rice grains suggests the remains are from the 8th century.
"The dominant identified charcoal fragments are Himalayan pine, from which a rather cold climate is inferred where indica rice could not be grown. This suggests it was likely brought to the site," Yang said.
Literary records suggest that earliest indica rice cultivated in China was originally introduced from Vietnam. The Kongsangqiao site is located along the ancient Tubo-Nepal Road and was an official route to India for ministers of the Tang Dynasty (618-907).
"It implies that the indica rice may have spread to the plains areas of China through the ancient Tubo-Nepal and Tang-Tubo roads by at least the 8th century," Yang said.