Xiangkun WANG, Chuanqing SUN, Chinese Agricultural University and

Juzhong ZHANG, Henan Institute of Cultural Relics and Archaeology

(translated by Jiwu Wang; edited by B. Gordon)

        The origin of cultivated rice is a research subject conducted for >50 years, but still leaves many unsolved theoretical questions. China is one of the world’s first rice-planting countries.1,2 Abundant historic records, widely distributed wild rice3 and archaeological rice remains and tools show China is one of the earliest countries to develop rice planting technology. This is particularly true when 6000-7000 year-old rice remains occurred in Hemudu of Zhejiang Province in the 1970’s and 4000-6000 year-old rice sites in the middle and lower Yangtze Valley. 4,5 Indeed, since the 1980’s, China has been recognized as one of the earliest cultivated rice sites in Asia.7,8 However, where did rice cultivation start in China? There are many explanations about the origin of cultivated rice. Ying Ding says that it is in southern China; Dubu Zhongshi thinks Yunnan is the place and Wenming Yan gives us his theory of the middle and lower Yangtze River4,5, none of which agrees with the others.

        Most scholars agree the cultivated rice ancestor is common wild rice (Oryza rufipogon Griff.). However, wild rice can be easily found in regions of eight provinces and now there are nearly 6000 common wild rice species in collections10,11, more than any other country. Among Chinese species, which is the original? Does it have one or different origins? It still remains a question.

        There are two subspecies of Asian cultivated rice, japonica and indica. China has the biggest japonica and indica acreage in the world12. Rice growing also has regional differences; e.g., japonica can be found in much of south China, but in the north, indica is more popular. Moreover, indica is often found at high latitude, japonica at low latitude. How did common wild rice develop into cultivated rice? Is the procedure stepwise from common wild rice to japonica and then to indica?2 Did common wild rice become indica when cultivated in mountain areas, or japonica in lowlands?13 Did common wild indica develop into cultivated indica, and wild japonica into cultivated japonica?14,15

        This article explores Chinese cultivated rice origin, ancient cultivated rice species and reasons why common wild rice developed into japonica and indica subspecies. The project is sponsored by the National Foundation for Natural Science.

        The following three pioneering agricultural archaeology sites attract our attention to research on cultivated rice origin:

(1) 5000 grains of 5-7000 year-old carbonized rice in Longqiu, Jiangsu Province, in 1994.

(2) 7-8000 year-old carbonized rice in Jiahu, Henan Province, in 1994.

(3) ca 10,000 grains of 7-8000 year-old carbonized rice in Bashidang, Li County, Hunan Province, in 1995 & 1997.

        After their reports we began our research project with the cooperation of archaeologists; esp. when we realized Yunnan was not the only cultivated rice origin, although a centre of rice species diversity16,17. We also believed cultivated rice origin could be found if ancient rice was also found. The following are our results:

        There is no agreement on the place of Chinese rice origin because we do not have a standard rule for origin. Based on previous research, we propose the following four requirements to determine a place of cultivated rice origin:

(1) oldest cultivated rice remains;

(2) both wild and cultivated rice;

(3) ancient people and rice cultivating tools;

(4) suitable natural environment, plus pressure on people to develop rice.

        Only with these requirements can we compare our study of cultivated rice origin.

1.2 New Data on the Origin of Cultivated Rice on the Middle Yangtze River

        As Yunnan 4,000 year-old carbonized rice does not satisfy requirements 1 & 2, most scholars at the 1993 Japan and 1994 Zhejiang conferences dropped Yunnan. The oldest cultivated and wild rice do not occur in South China, and there was no pressure to domesticate wild rice because of good climate18; e.g., cultivated rice is only 7,000 years old in the sites of Hemudu and Longqiu Village. In >100 Chinese Neolithic rice sites, only Pengtoushan and Jia Lake satisfy the above four conditions. They are neighbours, only 4 latitudes or 400 km apart. Climate is similar, as was culture. After comparative study of other ancient rice sites, we believe the middle Yangtze and upper Huai Rivers are the two earliest places of cultivated rice origin, where wild rice was cultivated and developed possibly the same time (Fig. 1).

Fig. 1. Central Cultivated Rice Origin on the Middle Yangtze and Upper Huai Rivers

        (1) The earliest Chinese cultivated rice and some wild rice occur in Jia Lake and Pengtoushan sites16,19, both almost contemporaneous (Figs. 2, 3; Table 1) and showing the same developmental stage. Accompanying fishing and gathering tools place this early, their economy transferring to agriculture from gathering and fishing.

        (2) People in both regions had a settled life with similar houses, living style, graves and pottery technology.

        (3) Jia Lake and Pengtoushan climate was similar 7-8,000 years ago, but with minor differences. Their earliest climate was the initial 8,500 year-old Recent warming trend20, when wild rice grew easily. As gathering and fishing resources shrank (they had far less than south China), people felt more pressure on their winter food supply, forcing them to find alternatives. Eventually, wild rice was cultivated into paddy rice, making both regions origins of Chinese cultivated rice.

        Some radical changes occur when comparing Pengtoushan and Jia Lake ancient rice with ancestral common wild rice. They resemble modern cultivated rice in grain length-width ratio, phytoliths and character of the bi-peaked tubercle, but have some differences. The ancient rice still has some wild rice traits like much smaller grain size than modern cultivated rice (Fig. 4), a hazy line in the evolution between indica and japonica. As this rice is at its initial evolutionary stage from wild to cultivated rice, it is called "primitive cultivated rice." It resembles a primate at the stage between ancient ape and modern man; e.g.s, "Peking and Java Man" In this sense, we can call Pengtoushan, Jia Lake and Hemudu rice "Pengtoushan ancient rice", "Jia Lake ancient rice" and "Hemudu ancient rice". Using grain length-width ratio, Jia Lake rice looks more like indica, but its phytoliths resemble japonica19, while Bashidang rice is longer and its bi-peaked tubercle resembles japonica22 (Fig. 5).

A. Maweihsien, Indica

        After a comparative study of rice remains in Pengtoushan, Jia Lake, Hemudu and Longqiu Village and >100 Neolithic sites, we can say modern rice was first cultivated by the middle Yangtze and upper Huai Rivers ca. 8,000 years ago. It was then carried to the lower Yangtze and middle-lower Huai Rivers 6-7,000 years ago. In its first 2,000 years, rice grain length and width did not change much, but 5-6,000 years ago, grain became longer, wider and thicker23 (Table 2), indicating heavier pressure for domestication.

1.4 Multi-Centers of Chinese Cultivated Rice Origins

        Genetic analysis of 9 multi-shape unifunctional enzymes in 700 rice samples from Yunnan, Yangtze-Huai Rivers and Huanan regions show three origins of cultivated rice24 (Fig. 6). But the genetic center need not be the original center, although the middle Yangtze and upper Huai Rivers can be seen as the original center of cultivated rice.

        When we compared affinity of SW and SE Asian species, we found hybridization weak; e.g., some combined F1 has <20% rice bearing grain.25 Moreover, Est, Cat, Amp, Mal, Pox, Pgi and other isodynamic enzymes26,27, core DNA,28 and KClO3 29 results show tremendous differences in both cultivated and wild Chinese and SE Asian species, due to lengthy separation by the Himalayas, which permitted two independent origins.

2 Determination of Ancestral Species

        It is generally believed the ancestor of Asian cultivated rice is common wild rice. By focussing our research on classifying ca. 6,000 common wild rice samples from 8 provinces, we try to find the original, direct and indirect ancestors of cultivated rice. We also hope to find any annual common wild rice species in China.

2.1 Classification of Chinese Common Wild Rice Patterns

        Using 10 traits, we analyzed 571 common wild rice samples from 7 provinces and 27 from foreign countries: growth habits, stem base coleoptile colour, blade leaf length and width, anther length, stigma colour, awnness, shattering, glume colour, and grain size and colour. Results show Chinese common wild rice can be classified into perennial and annual groups and 7 subgroups30,31 (Fig. 7).

Fig. 7. Classification of Chinese Common Wild Rice Patterns

2.2 Determination of the Original Pattern of Common Wild Rice

        Analyzing common wild rice shape29,30, growing mode, isodynamic enzyme31,33 and DNA28,34,35 shows the following traits:

        (1) little similarity to cultivated rice in stolon, purple leaves, shorter thinner flag leaf, longer anther >5mm, purple stigma seen externally; red awn, easily dropped grain, long thin grain (l/w ratio >3.5), dark or brown glume husk and red grain.

        (2) wild and cultivated rice areas are fully separate, esp. in earing and flowering; natural groups are usually large but shape is simple, isodynamic enzyme32,33, core DNA28,34 and shape of DNA grain string35 contain a particular loop and whorl plate. After bagging plant for self-reproduction, the new generation is inseparate from parent. All show this is typical common wild rice.

        (3) rice land is usually marshy or near stable ponds and rivers. Rice depends on its perennial root to survive winter, reproducing by asexual propagation. Ratio of pollination among different flowers is high, but seed-producing ability from a single plant is low, typical of perennial common wild rice. Guilin, Yuanjiang and Dongxiang rice represents original common wild rice.

        The wild rice species most directly resembling cultivated rice is called proximate ancient common wild rice. It evolves from the original species, but some evolutionary changes occur, mainly in sloping shape, thin long blade leaves and large grain tassels with considerable sub-branches. It usually grows in marshland and besides ponds >0.5m deep. Using 30Co-g rays on seven plants of common wild rice30, slope M1 becomes short and their tassels shorter and more like the straight shape of cultivated rice. Common wild rice slope without treatment is crooked, but their M2 has more straight plants. This seems to show that common wild rice slope evolves to cultivated rice.

2.4 Does Annual Type Common Wild Rice exist in China?

        Ying Ding1,2 and other scholars39-42 believe common wild rice is perennial, with appropriate roots to survive winter, recently confirmed by a published report on wild rice resources43. But these scholars and the report do not mention a Chinese annual type of common wild rice. Our study38 makes it clear there are considerable annual types of common wild rice that grow from seed. Where do they originate? After several years of field study, we did not find any natural annual common wild rice, while wild rice seed usually produces rice with more multiple shapes in cultivated rice. Isodynamic enzymatic results show most annual common wild rice erect stem types are from a mixed breed. It can be seen that south China annual common wild rice is possibly a mixed breed of perennial common wild rice and cultivated, from natural hybridizing of both species.

        As cultivated rice is mainly two subspecies, indica and japonica, how these subspecies came from common wild rice falls under three main theories:

1. common wild rice first became indica and then evolved to japonica2
2. common wild rice in mountains became japonica; lowland became indica13
3.  japonica common rice evolved to japonica cultivated rice; likewise indica14,15

        The point is whether common wild rice had japonica and indica subspecies before it evolved to cultivated. Except some species of original common wild rice, our study shows most common wild species had both japonica and indica subspecies28,33-35, but differences between common wild rice subspecies are much fewer than cultivated ones. In fact, difference between wild japonica and indica is tiny or incipient. Common wild rice core DNA has more japonica than indica traits; long grain rice DNA shows mostly indica traits; green leaves show half japonica and half indica39. But repeat DNA arrays of most common wild rice species show indica traits. The split between japonica and indica in SE Asian and Chinese common wild rice is very complex, as seen in Sun Chuanqing's Fig. 8 by analyzing DNA, mtDNA and cpDNA of 34 Chinese common wild rice species.

Fig. 8. DNA Classification in Chinese Common Wild Rice

Obviously, cultivated japonica and indica splits many ways. By analyzing Jia Lake, Pengtoushan and Hemudu rice and the patterns of common wild and cultivated rice, their isodynamic enzyme and DNA, we hypothesize the origin and splitting of Chinese japonica and indica as follows (Fig. 9):

Fig. 9. Origin of Chinese Cultivated Rice Subspecies

Forecast for Future Research

        This study systematically studied three main issues: place of origin of cultivated rice, ancient rice species and the origin and differentiation of japonica and indica. Based on previous research, our project made considerable progress, but deeper research is needed to clarify the issue:

        1. Is there any relationship between Pengtoushan and Jia Lake sites, both with the oldest rice remains in China? Do they belong to the same rice origin centre, or are they independent? As Hunan’s earlier Yuchanyan site has earlier rice remains, does it have an earlier rice centre? These unsolved questions await further survey and research because they may clarify rice origin concepts and establish conditions for the place of origin of rice.

            2. Can the concept of "original cultivated rice" be established? How do we define it? We need more research on Pengtoushan, Jia Lake and Longqiu Village rice to learn more about their relationship. We need to clarify the link between rice and its common wild rice ancestors, their relation and specific evolution to modern cultivated rice.

            3. Common wild rice dates ca. 70 million years in the early division of the grasses in the Tertiary and continuing to the Quaternary Period. What we call "original type" and "proximate relative type" depend only on existing common wild rice analysis, which mostly comes from guessing. Research on the issue must solve the methodology problem. We must modernize our archaeological research methods, and more importantly, develop new techniques in DNA analysis and ancient rice recovery.

        4. Many unsolved questions remain on the origin and split of indica and japonica. New scientific methods and modern technology must be applied to the large amount of analysis on ancient cultivated rice in past years, and the differentiation of common wild rice, indica and japonica.

        We believe multi-disciplinary research on the origin of Chinese rice and fieldwork in agricultural archaeology will contribute much to introduce Chinese culture to other Asian countries and even to the whole world.

22 Wenxu Zhang & Shengxiang Tang, " Study of the Bi-peaked tubercle in Hemudu Rice". Collection of the Research on the Origin and Evolution of Chinese Cultivated Rice (Beijing Agricultural University Press, 1996), pp. 42-46.

37 Chengbin Chen, Jiezhen Lai, Daoxuan Li, etc., "Study of M1 Changes in X-rayed Common Wild Rice". Journal of Guangxi Agriculture College, 1996,3, pp. 8-11.