Origin of Cultivated Rice

260 Pages·1988·5.172 MB·1-254\260

by  H.I. Oka (Eds.)

Developments in Crop Science
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Volume 14 Origin of Cultivated Rice, by H.I. Oka
Developments in Crop Science 14
Origin of
Cultivated Rice
H.I.Oka
Honorary Fellow, National Institute of Genetics,
Misima, 411 Japan
JAPAN SCIENTIFIC SOCIETIES PRESS Tokyo
ELSEVIER Amsterdam—Oxford—New York—Tokyo
1988
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Flowers of the common wild rice, Oryza rufipogon.
An Indian perennial type with long anthers and extruding black stigmas.
Gathering the grain of wild rice, Oryza breviligulata, by two methods, one
bundling the panicles to keep grain from shedding (above), and the other
sweeping the panicles with a basket (below). At Tom Marefinn, Chad,
late October 1977.
Preface
There was no crop plant when man lived on gathering and hunting.
The manner in which the food crops we now rely on were created has long
been a question to us. A food crop like rice must be a product of evolution-
ary processes which took place in ancestral wild plants many thousands of
years ago when man came into contact with the plants. The origin of culti-
vated rice is a subject of integrated study involving different disciplines of
biology and the social sciences. Cause-effect relationships that are predict-
able and past events that cannot be repeated are both involved in this subject.
My intention in drafting this book is to review the present status of our
knowledge on the origin of cultivated rice, but it is beyond my ability to
cover the whole range of sciences related to this subject. I place emphasis
on the review of findings in the genetics and ecology of wild and cultivated
rices, particularly on those recently reported by my colleagues. I also attempt
to briefly review archaeological literature relative to the subject. A part of
the text includes information given in my lecture on evolutionary genetics
in rice which I gave at the Wuhan University, China, in 1984. In retrospect,
it was 30 years ago that I was engaged in a research project on "the origin of
cultivated rice" under a grant from the Rockefeller Foundation. I now
realize that our knowledge on this subject has increased greatly during the
ensuing period, but many new questions have also arisen.
I have been working with Dr. Hiroko Morishima for these years. Much
of her new and still unpublished data are included in this book with her
approval. She has also helped me by critically reading the manuscript. It
was under her auspice that I started writing the book early this year, and its
completion would not have been possible without her cooperation. I am
also grateful to my colleagues in Japan and Taiwan whose names appear in
the text for their cooperation. I want to mention particularly the cooperation
of the late Dr. Wen-Tsai Chang, who died following a traffic accident in
northern Cameroon on 14 December 1963 while we were travelling together.
I express my sincere thanks to Dr. Robert F. Chandler of the Rocke-
feller Foundation for his generous support of our work and encouragment.
VI
The late Dr. Sterling Wortman was also very supportive, as was the late Dr.
Hitoshi Kihara who provided ingenious leadership in the early days of our
work. I am indebted to the Ministry of Education, Science and Culture of
Japan for the offer of a grant-in-aid for this publication.
September 1987 Hiko-Ichi Oka
Misima, Japan
Synopsis
Among various findings relative to the origin of cultivated rice and questions
remaining unanswered as presented in this book, the major ones are briefly
summarized for special consideration by the reader.
1. There are two cultivated rice species, Oryza sativa and O. glaberrima.
There is sufficient circumstantial evidence for the origin of O. sativa from O.
rufipogon in Asia and that of O. glaberrima from O. breviligulata in Africa.
The Asian common wild rice, O. rufipogon, shows a perennial-annual con-
tinuum. Its intermediate perennial-annual populations seem most likely to
be the progenitor of O. sativa (Chapters 1 and 2).
2. The variation between perennial and annual types of O. rufipogon
concerns the so-called K vs. r strategy and is related to variations in many
life-history traits. The perennial types grow in deep swamps which remain
moist throughout the year, but the annual types occur in temporary swamps
which are parched in the dry season. The perennial types have higher out-
crossing rate than the annual types. Perenniality is correlated negatively with
reproductive effort and positively with pollinating effort. The negative cor-
relation found between pollinating effort and selfing rate suggests that the
allocation of resources to male function and to female function is adjusted by
selfing rate which is selected toward an optimum under a given habitat con-
dition (Chapter 3).
3. When introduced into a semi-natural habitat, the persistence of
perennial populations largely depended on their competitive interaction with
a perennial grass, Leersia hexandra, which had a largely overlapping niche.
Annual populations seemed to require a more specialized niche as their
seeds did not germinate unless a vacant site was offered. This was probably
•due to an allelopathic effect of covering plants (Chapter 3).
4. The Asian common wild rice, O. rufipogon, possesses more alleles
at different isozyme loci and is more polymorphic than O. sativa cultivars.
Annual types generally showed less gene diversity within populations but
.greater gene differentiation among populations than perennial types, as
influenced presumably by their different breeding systems (Chapter 4).
vii
viii
5. In wild-rice populations composed of patches or demes, the sub-
populations showed differential gene frequencies. When they were under
different water regimes or different degrees of habitat disturbance, they tended
to differentiate in adaptive strategy (Chapter 4).
6. Isozyme alleles and fitness characters tended to be associated in a
certain manner, not only among naturally occurring genotypes, but in hybrid
populations also. There might be an internal mechanism causing so-called
gametic disequilibrium (Chapter 4).
7. Domesticated plants differ from wild ones in many life-history traits.
The process of domestication may be considered to have depended on differ-
entiation-hybridization cycles, as suggested by studies of hybrid swarms
(Chapter 5).
8. Harvesting and seeding by man has caused selection for domesticated
types. A low seed-shedding rate and other characters of domesticates were
associated with high selfing rate in hybrid populations (Chapter 5).
9. Weed rices are of two categories, one with both wild and cultivated
rices, and the other occurring in areas where no wild rice is found. These
weed rices receive pollen flow from cultivars and vary widely in life-history
traits (Chapter 5).
10. The genetic diversity of O. sativa cultivars is most prevalent in the
area extending over Assam, Bangladesh, Burma, Thailand, Laos, and
Yunnan, China. Land race populations with great gene diversity are also
found (Chapter 5).
11. Whether the actual site of rice domestication was one or many is
questioned. Archaeological evidence suggests that rice culture occurred in
northern India, Thailand and eastern China around 7,000 B.P. Rice domes-
tication was probably a diffused process in both space and time, although
opinions remain divided (Chapter 6).
12. The earliest rice grains excavated in China are regarded as mixtures
of Hsien (Indica) and Keng (Japonica) types when judged by their outward
appearance. Such early domesticates were probably not completely differ-
entiated into the two types (Chapter 6).
13. Cultivars of O. sativa are divisible into these two types called Indica
and Japonica or Hsien and Keng, which differ in many characters and some
isozyme alleles. The two types can be classified by association patterns of
certain diagnostic characters but not by any single character or gene. Various
atypical or intermediate cultivars are found in the hilly areas of tropical Asia
(Chapter 7).
14. Fi-sterility relationships are too complicated to allow classification
of the parental varieties into two types. Many O. rufipogon strains produce
Synopsis ix
fertile F hybrids with cultivars which are inter-sterile. This trend is also
1
found in some of the land races of tropical Asia (Chapter 7).
15. The dynamics of Indica-Japonica differentiation remain largely
unknown. The wild progenitors, populations of O. rufipogon, are not differ-
entiated into the Indica and Japonica types, but show a latent tendency to
be differentiated, particularly in Chinese genotypes. The perennial and annual
types tended to be related to the Japonica-like and Indica-like genotypes,
respectively, although what this means remains unknown. Weed rices are
differentiated incompletely into the two types. Crossing experiments with
cultivars of typically Indica and Japonica types showed that an Indian wild-
rice strain was potentially capable of evolving both types. The intermediate
wild-cultivated strains collected from Jeypore Tract, India, suggested that the
differentiation occurred gradually with domestication (Chapter 7).
16. Among land races of tropical Asia, those grown on upland fields
were similar in some respects to the Japonica type. Plants of some upland
land-race populations showed a tendency to be differentiated into the two
types (Chapter 7).
17. In the progeny of Indica-Japonica hybrids, genes derived from the
Indica parent tended to increase more than those from the Japonica parent.
The tendency of hybrid-derived plants to restore the parental Indica and
Japonica gene combinations was also detected in independent genes and
some diagnostic characters. In hybrids, genes tend to be associated in a cer-
tain manner across independent loci. This can be partly elucidated by the
presence of many sets of duplicate or complementary genes for gametophytic
and sporophytic sterilities, and seems to suggest an internal mechanism of
genetic differentiation, which could be a complementary system of adaptive
gene blocks (Chapter 7).
18. The two cultivated rice species and their wild relatives have the A
genome in common and their hybrids show no significant disturbances in
chromosome pairing. But they possess almost all kinds of reproductive
barriers known among flowering plants, i.e., crossing barrier due to inviability
of young F zygotes, F weakness, ¥ sterility, and hybrid breakdown in-
x x x
cluding F sterility and F weakness. None of these barriers is absolute in
2 2
effect and they often overlap in the same cross-combination (Chapter 8).
19. For F sterility, four different models of gene action were set up
x
and were compared with the results of experiments, in part of which isogenic
lines each carrying a sterility gene were used. The data for F sterility between
x
O. sativa cultivars largely fitted the first model, which assumes that gametes
with a double-recessive combination of duplicate gametophytic sterility genes
are aborted during development. Pollen grains with a double dominant com-