Plant Molecular Biology 35: 69–77, 1997.
1997 Kluwer Academic Publishers. Printed in Belgium.
Rice genetic resources: history, conservation, investigative characterization
and use in Japan
, Kazutoshi Okuno and Duncan Vaughan
National Institute of Agrobiological Resources (NIAR), Kanrondai 2-1-2, Tsukuba, Ibaraki 305, Japan (
Key words: rice, wild rice, Oryza spp., evolution, conservation, evaluation, utilization, germplasm, genetic
Rice has been grown in Japan for about 3000 years. Although both japonica and indica varieties have been grown
in Japan, now japonica rices are grown. Japanese rice breeding has used an ecological breeding approach. While
emphasis in rice breeding in the 1940’s and 1950’s focussed on yield in recent decades quality has been of major
importance. Consumer preference and name recognition of high quality varieties, such as Koshihikari, has resulted
in slow acceptance of new varieties.
Rice germplasm was systematically collected throughoutJapan between 1962 and 1963. Subsequent acquisition
and collecting, in Japan and other countries, has resulted in 28,000 accessions being conserved in the National
Genebank, based at the National institute of Agrobiological Resources (NIAR).
Research on genetic diversity of rice using a range of techniques, for example esterase isozymes, has revealed
clinal variation in rice radiating from the center of diversity of rice in and around southwest China. Newly found
genesin traditionalrice germplasm, such asgenes for non-elongatingmesocotyl,are nowroutinely identiﬁedon the
rice genome. Pioneering studies on eco-genetic differentiation of species in the genus Oryza in Japan has revealed
much about the complex genepool for which rice evolved.
Pest and disease resistance sources, particularly to blast, bacterial blight and brown plant hopper, from many
countries have been incorporated into Japanese varieties. Cold tolerance at the booting stage was found in the
Indonesian variety Silewah. In the future in characterisation of rice germplasm and interaction between rice
germplasm specialists and rice molecular scientists, both in Japan and internationally, will be corner stones to
securing rice genetic diversity and rice improvement in the next century.
History of rice diversity in Japan
About 2000 years ago there were series of changes
in Japan associated with the beginning of the Yayoi
culture which was an agriculturally based culture .
Prior to the Yayoi era, in the Jomon era, Japan was
populated with people for whom hunting and gather-
ing, as well as sophisticated ﬁshing, were most impor-
tant. However, it is becomingclear that during the later
part of the Jomon era, agriculture was practised. New
ﬁndings suggest that rice and some other crops, such
as chestnut, were cultivated during the Jomon era in
Japan. The early route(s) of introduction of rice has
not been clearly established. One hypothesis is that
rice was introducedvia the Korean peninsulato Japan.
Jomon era rice found in Hokuriku would support this
(M. Takahashi, personal communication). However,
the earliest evidence of irrigated culture of rice, from
the Yayoi era, has been found on Kyushu, and this
supports the hypothesis that rice was introduced from
the Yangtze river basin  (Figure 1). It is likely that
rice was introducedto Japan several timesvia different
The ﬁrst rices introduced into Japan are thought to
have been japonica rices based on the pottery impres-
sions of rice seeds. However, ceramic pictures of rice