Dissemination and population dynamics of rice in the tropics

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To know the origin of rice in the tropics, we investigated population dynamics and dissemination of natural populations of wild ancestor of rice (Oryza rufipogon). Also, we investigated genetic feature of cultivated rice in various areas in the tropical Asia. Data obtained were as follows.1. Wild rice is separated in annual and perennial types based on the morphological and physiological features. In the present study, we revealed that most population of annual type had high similarity of indica cultivars, while those of perennial type had that of japonica cultivars. Japonica-like populations were frequently seen in Mekong delta area. People in the area calls wild rich "ghost rice', because such type shows low seed fertility in the natural stand.2 I the present survey, we discovered new populations of wild rice in the north western part of Laos. They were seemingly belonging to perennial type. In the previous survey that was performed in 1983, we observed annual populations in north Thailand that is neighbored to north western Laos. It is interesting why perennial type was seen in Laos while annual was seen in Thailand.3 We attempted to set up four permanent observation sites for in situ conservation of wild rice. One of them was set at Prachinburi Rice Research Center, while other three were set up in Laos. We made observations for population size (density and area), flux and dynamics of the populations.4 In China, recent archaeological works reveals a possibility of the birth of rice and rice cultivation. We attempted to gather such works in the field of archaeology and biology in China.We strongly feels a necessity of the continuous survey of the present project for wild rice in Asia in the future, in order to reach comprehensive understanding of the origin of rice.