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Hybrid Swarms Between Wild and Cultivated Rice Species, Oryza perennis and O. sativa

Hiko-Ichi Oka and Wen-Tsai Chang
Evolution
Vol. 15, No. 4 (Dec., 1961), pp. 418-430
DOI: 10.2307/2406310
Stable URL: http://www.jstor.org/stable/2406310
Page Count: 13
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Hybrid Swarms Between Wild and Cultivated Rice Species, Oryza perennis and O. sativa
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Abstract

Several wild rice populations supposedly of hybrid origin between wild and cultivated forms have been analyzed. First, Patna population, found in the suburb of Cuttack, Orissa, India, though it appeared to be a mixture of wild and cultivated plants growing in a paddy field, was shown to be a hybrid swarm. A part of the plants, having many wild characters and a few cultivated ones, were found to be highly heterozygous for genes of cultivated rice. Secondly, Sampatoon population, found in a stream running through a paddy farm of glutinous rice in the suburb of Chiengmai, Thailand, was observed. It consisted of plants of intermediate perennis-spontanea type, and contained many heterozygotes for the glutinous gene. The offspring of the heterozygotes tended in various characters to be intermediate between the wild and the cultivated type. It was also found that though in northern and northeastern parts of Thailand glutinous rice is grown in almost all paddy farms, the majority of wild populations growing in proximity of glutinous rice fields had a low frequency of the glutinous gene, so that hybrid swarms might be regarded to be rather rare. Thirdly, three small populations found in Tao-Yuan Prefecture, Formosa, which were phenotypically of perennis type, were observed. They were found to be highly heterozygous for genes of cultivated rice. Thus, it is pointed out in general that a hybrid swarm could preserve a great amount of genetic variability, which might cover the whole range of variation from the wild to the cultivated type. Based on the results of these observations, emphasis is laid on the significance of hybridization in the evolution of cultivated rice.

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