Vavilov noted that:
When in Kyoto I had also an opportunity to study the large collection of rice, collected from all over the world by Professor Kato. It was evident that the maximum diversity of forms and varieties were concentrated not in Japan or in China, but in India.
In the Journeys he does not have much more to say about the domestication of rice, but knowing his general outlook I infer that he is suggesting that India, rather than China or Japan, was where rice was first domesticated. The actual situation is quite a bit more complex than that, and almost certainly not finally settled. For a start, there are the two basic rice types: Oryza sativa indica and O. sativa japonica. Indica generally has longer grains and a different kind of starch. Japonica types have rounder grains, and their starch tends to make them sticky. They are associated, not surprisingly, with India and Japan respectively, but each type is also found throughout the rice areas of the world.
A very thorough study of rice DNA concluded that indica and japonica varieties share a common ancestor in O. rufipogon, but that the split between the two occurred maybe 100,000 years ago, long before the start of domestication. Domestication then took place separately in India (and Indochina) and in southeastern China, but the two types interbred to a limited extent soon thereafter. Dates remain a little vague, but there seem to be good evidence of japonica from the Yangzi from about 11,000 years ago. Domestic rice from the Middle Ganges dates to about 9000 years ago. Some of the specific changes to the DNA have been identified too: there is a group of genes that results in fatter genes among japonica varieties.
The story for African rice (O. glaberrima) is much sketchier. The Middle Niger Delta is a favoured site, maybe 4000 years ago.
