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Status and Project of Studies on the Origin of the Chinese cultivated Rice

Chen Wenhua (Academy of Social Sciences, Jiangxi)

Determination of the locality where the Chinese cultivated rice originated

A place could only be considered as the site of the earliest domestication of the Chinese cultivated rice when it would meet the following prerequisites simultaneously: 1. It should be a site where the remains (or carbonated grains) of the most ancient Chinese cultivated rice and its wild progenitor-common wild rice, were excavated. 2. The discovery should also include the remains of ancient human population who had domesticated the ancient wild rice into cultivated rice, together with the tools they used for rice production. 3. The climate and environment of the region then should be suitable for the growth and propagation of the ancient wild rice. According to these prerequisites, the authors concluded that region containing the middle Yangtze River valley and the upper Huai River region might very possible be the center of the origin of the Chinese cultivated rice.

Primitive cultivated rice is the first product of ancient men who domesticated them from the ancient common wild rice. The Pengtaoshan ancient rice, found in Hunan from 8000 to 7000 years ago, and the Jahu ancient rice, found in the same period in Henan Province belonged already basically to modern cultivated rice, but they had some significant differences from the typical modern cultivated rice; their differentiation of India and Japonica is not as pronounced as the modern cultivated rice, and they also retained some of the characteristics of the wild rice. The size of the grains of the primitive cultivated rice grown 6000 to 5000 years ago became apparently larger, indicating that starting from this time, the selection pressure exerted by the early man became obviously higher. The ancient rice excavated at Yuchanyan, Hunan Province, looked not very much like the primitive cultivated rice.

Comparative studies on crossibility, isozyme and DNA indicated that China and South Asia were two independent centers of origin and evolution of Asian cultivated rice.

Confirmation of the Progenitor of the modern cultivated Rice

It is commonly agreed that common wild rice (Oryza rufipogon Griff.) was the wild ancestor of the Asian cultivated rice. But there are more 6000 entries of common wild rice in China. Which of them was the prototype of the ancestor? Which of them the direct ancestor of cultivated rice?

Results of our studies and investigation suggested that common wild rice whose habitat was isolated from cultivated rice, whose isozyme and DNA revealed specific finger-printing, and which was morphologically typical of the common wild rice, might possibly be the prototype of the ancestor. The sloping common wild rice might be the direct ancestor of cultivated rice evolved directly.

Our studies and investigation also revealed that most of the common wild rice in China are perennial types, but there are also some annual types. Since no natural population of them has been found so far, and since the progenies of the seed samples are heterozygous, it was suggested that most of the annual types of common wild rice found in South China might be weedy rice, derived from natural introgression between the perennial common wild rice and the cultivated rice.

The Origin and Differentiation of Indica and Japonica

Modern cultivated rice differentiated mainly into two subspecies: Indica and Japonica. Therefore, problems concerning the origin of the cultivated rice implies also how did the Indica and Japonica evolve from the common wild rice. As answers of these questions, there are three hypotheses: 1. Common wild rice > Indica > Japonica (Ding Y. 1949) 2. Common wild rice > Japonica; parallel: Common wild rice > Indica (Wang X. K. et al., 1984) 3. Wild Japonica > Japonica; parallel: Wild Indica > Indica (Zhou S. L., 1948; Second G., 1981)

The focus of the contemporary dispute over this issue is whether the differentiation of the Indica and Japonica had already begun before the common wild rice evolved into cultivated rice. Our studies revealed that except a few entries, most of the common wild rice in China and abroad have undergone some Indica-Japonica differentiation, although this differentiation is only negligible and preliminary as compared with that of the true cultivated rice. The nuclear DNA of most of the common wild rice in China was inclined to Japonica. mtDNA was mostly inclined to Indica. The ratio of cpDNA inclined to Indica and to Japonica was about fifty-fifty. The repeated sequences of the DNA of most Chinese common wild rice were inclined Indica. The Indica-Japonica differentiation of the common wild rice from China and Southeast Asia are very complicated and diverse. Therefore, the origin and differentiation of the Chinese cultivated rice there must be multichanelled.

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