Indian Society of Genetics & Plant Breeding

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ORIGIN OF ASIAN CULTIVATED RICE AND ITS ECOTYPIC DIFFERENTIATION

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Oryza nivara is an annual wild species that grows in small seasonal pools mainly
in the plateau regions of south and southeast Asia. O. rufipogon Griff. is a perennial
wild species adapted to swamps and margins of tanks in the coastal belts and in
the lower valleys of rivers of south and southeast Asia. The cultivated rice,
O. sativa 1., which shares the same ploidy level (2n = 24) and the genome (AA)
with these two wild species, has originated mainly from O. nivara in the same
part of the world. O. Sativa has differentiated into ecospecies (aus, aman, japonica
and javanica) and, within the ecospecies, into ecotypes. When cultivars of different
ecotypes are crossed, the hybrids often express various degrees of sterility. The
authors recognise the hill rices of southeast India (that includes the Jeypore tract
of Orissa), the japonica-like cultivars of the hilly .treas of southwest China (extending
westward upto Nepal) and the hill rices of mainland southeast Asia as the three
basic stocks that have evolved directly from O. nivara in their respective regions.
The Proto-Australoid people who spoke Austric languages were responsible for the
origin of this crop as well as for its initial spread all over south and southeast
Asia before the advent of Indian and Chinese civilizations into this region. The
aus ecotype was developed directly from the southeast Indian hill rices and the
japonica ecotype of northern China from japonica-like types of southwest China.
The spread of cultivation of aus types to the lower Gangetic valley and that of
japonica- like types to the Brahmaputra valley resulted in the introgression of
rufipogon genes into these types and led to evolution of aman and shali ecotypes
respectively. The aman ecotype was successful only after iron was introduced for
plough and oxen as draught animals in the lower Gangetic valley presumably by
the Aryans in the second millenium B.C. Subsequently, the aman types were carried
by. Indian colonisers to Indochina and Indonesia during the ninth century A.D. The
tjereh ecotype was developed from the aman ecotype in Indonesia. Similarly, migration
of hill rices of mainland southeast Asia to Indonesia with introgression of genes
of O. rufipogon into them has resulted in the origin of javanica ecotype.
 

Keywords: Oryza sativa, Oryza nivara, Oryza rufipogon, Origin of cultivated rice, ecotypic differentiation

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Year: 1997
Volume: 57
Issue: 4
Article DOI: NA
Print ISSN: 0019-5200
Online ISSN: 0975-6906

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