<Origin of Cultivated Rice> by H.I Oka, 1988
This book aims to up-date our present understanding of the origin of cultivated rice and in doing so involves different disciplines of biology and the archaeological-historical sciences. Various recent discoveries are reviewed and questions posed for further consideration by the reader.
The book covers a wide range of studies on problems relative to the origin of cultivated rice, placing emphasis on ecological and genetical aspects. Comparisons are made between two cultivated rice species, independently evolved in Asia and Africa from respective wild progenitors. Phenomena are observed during mixed planting and hybrids discussed. Detailed information is presented about Asian common wild rice, thought to be the ancestor of common rice. The dynamics of domestication are considered with regard to hybridization, selection, formation of weedy types and the accumulation of genetic diversity.
Also included are recent（1988） archaeological findings in relation to the beginnings of rice culture, leading to the hypothesis of diffused origins. Cultivars of common rice fall into one of two types called Indica and Japonica. The dynamics of differentiation are discussed, giving evidence and different hypotheses. Information on the genetic bases and functions of various reproductive barriers found between the cultivated and wild taxa is presented and discussed. The practical aspects of crop-evolutionary studies concerned with the breeding phylosophy and germplasm （种质， 生物体亲代传递给子代的遗传物质 ）conservation are briefly commented on and arguments for rediversification of crop germplasm and conservation of the environment given.
Senior scientists and post-graduate students interested in rice genetics, crop evolution, and related sciences will find this book invaluable.
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 continuum. Its intermediate perennial-annual populations seem most likely to be the progenitor（先辈） 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（生活史特征）. 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 outcrossing rate（异交结实率） than the annual types. Perenniality is correlated negatively with reproductive effort and positively with pollinating effort.
The negative correlation found between pollinating effort and selfing rate（自交率） 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 condition (Chapter 3).（ 授粉工作量与自交率之间呈负相关关系，这表明资源分配给男性功能和女性功能是通过在给定的生境条件下选择最佳自交率来进行调整的。）
（ Oryza rufipogon ：https://www.wikiwand.com/zh/%E9%87%8E%E7%94%9F%E7%A8%BB）
（ Perennial plants regrow every spring, while annual plants live for only one growing season, then die off. ）
（ 根據生活史理論，生物體的生活史有7個最重要的特徵（trait）：出生時的大小；生長模式；成熟時的年齡和大小；後代的性別比例、大小，以及數量；繁殖投資（按大小和年齡）；死亡時間分佈（按大小和年齡）；壽命。 爲了適應生存的環境，生物體會擁有具獨特特徵的生活史。 ）
3. When introduced into a semi-natural habitat, the persistence of perennial populations（常年 种群数）largely depended on their competitive interaction with a perennial grass（常年草）, Leersia hexandra（李氏禾）, which had a largely overlapping niche(生态位）. Annual populations（年种群数） 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（化学交感作用） effect of covering plants (Chapter 3).
（allelopathic： 化感作用Allelopathy，又称为 异种化感、他感作用、异种克生 或 相剋作用，是指一种生物产生一种或多种生物化学成分向环境释出，以影响其他相邻生物生长、生存与繁殖的生物学现象。 )
（Environmental niche： In ecology, a niche is the match of a species to a specific environmental condition. It describes how an organism or population responds to the distribution of resources and competitors and how it in turn alters those same factors. ）
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).
5. In wild-rice populations composed of patches or demes, the subpopulations 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 differentiation-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 domestication 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 differentiated 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 fertile F1 hybrids with cultivars which are inter-sterile. This trend is also 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 differentiated 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 wildrice 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 certain 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 Fx zygotes, Fx weakness, ¥x sterility, and hybrid breakdown including F2 sterility and F2 weakness. None of these barriers is absolute in effect and they often overlap in the same cross-combination (Chapter 8).
