Few plant species can have been better studied than rice. There is a wealth of information out there; I’ve picked a few interesting and enlightening extracts- a résumé of rice if you like.
Taxonomy (plus a little bit of history)
Oryza sativa L., commonly known as rice, is in the grass family, Poaceae. This is the most economically important flowering plant family in the world, including as it does wheat, maize, sugarcane, lawn grasses, bamboo- to name a few. The genus Oryza contains 23 species, two of which are cultivated; O. sativa L. (sativa means cultivated in botanical Latin) and O. glaberrima (African rice, grown in parts of West Africa).
There are two major subspecies in O. sativa L. ; O. sativa subsp. japonica producing sticky, short-grained rice and long-grained O. sativa subsp. indica. However, there are tens of thousands of cultivars- the largest collection of which (totaling more than 110,000!) are held in the International Rice Gene Bank in the Philippines.
Archaeological evidence suggesting domestic rice originated in China several thousand years ago has been around for some time, but there has been controversy over exactly how, where and when this happened. Recent phylogenetic studies seem to have proven that the two main subspecies of O. sativa were both domesticated from the wild rice Oryza rufipogon (still found growing in the wild in South and South East Asia) approximately 8,200- 13,500 years ago. O. sativa japonica was first domesticated from a specific population of Oryza rufipogon around the middle area of the Pearl River in Southern China, and O. sativa indica subsequently developed from crosses between japonica and local wild rice as the initial cultivars spread into South East and South Asia.
A very cosmopolitan grass
O. sativa has traveled far. Today it is cultivated pretty much everywhere except the poles: Europe, North and South America, Africa, tropical and temperate Asia, and Australia. Although about 90% is still grown in Asia. The japonica varieties are usually cultivated in dry fields, in temperate east Asia, upland areas of southeast Asia and high elevations in south Asia. The indica varieties are grown mainly in lowland, submerged areas in tropical Asia, which is probably what most people think of when they think of rice being grown- paddy fields.
Why is rice grown in paddy fields? To produce a paddy field the soil is ‘puddled’ (a good descriptive word!), meaning it is flooded and then tilled until the structure is broken down. This process makes the soil impervious, which allows the water to stand and not drain away, thus conserving rain and irrigation water. Although, as water is used in the puddling process, whether you end up saving water in the end depends very much on the type of soil you have. Puddling is also used for weed control. You can read more about this on the IRRI website.
A case of being your own worst enemy?
‘Weedy rice’ is a serious weed of cultivated rice, and is widespread around the world. And what is it? The same species. It is thought to originate from out-crosses to wild species such as O. rufipogon and O. nivara, or within domestic rice. On the other hand, the great genetic diversity of O. sativa also means that different varieties can be used to improve cultivated rice by making it more pest resistant and so on.
Throwing rice at weddings seems to have gone out of fashion. I guess it originated as a tradition because of the central role rice has had to play in the survival of humans since antiquity, and the symbolism which has developed around it; fertility and growth etc. This tradition may have other origins though, does anyone know? Looking around on the Internet, its going out of fashion seems partly due to health and safety; people slipping on rice grains and getting rice in their eyes (churches didn’t want to be sued). Another factor was an urban myth going around that if birds eat raw rice it’ll expand in their stomachs and make them explode. I see as one alternative now you can order live butterflies to release at your wedding, each coming in their own little box!
Rice still forms a major part of the diet of more than 50% of the world’s population. There are more than 200 million rice farmers in Asia, and for many of these rural poor it is the main economic activity. When rice prices tripled in 2008 an extra 100 million people were pushed into poverty as a result.
The rice grain, or caryopsis to give it its proper botanical name, is a central part of the food culture of many countries. This is mainly in the form of white rice, which has the embryo and bran removed during milling leaving only the endosperm. The picture below shows unpolished rice with some of the bran still visible. Oil from rice bran is used in cooking in South East Asia. The oil is high in Vitamin E and minerals, so is also used widely in cosmetic products such as shampoo and face creams (have a look on the back of the bottle).
More recently, rice has been genetically modified to produce beta-caroteine, the precursor of vitamin A, so called ‘Golden rice’. Some people thought it would be an excellent way of getting it into malnourished children in parts of the world where rice is a staple. There is an interesting article in Science about what ensued when the Chinese authorities found out that some researchers were feeding this rice to Chinese children.
Finally, rice is a model organism for plant biology, due to its small and easily manipulated genome.
Heywood, V.H., Brummitt, R. K., Culham, A., and Seberg, O. Flowering Plant Families of the World. Firefly Books: Ontario, Canada (2007). pp. 390-395.
Huang, X., Kurata, N., Wei, X., Wang, Z-X., Wang, A., Zhao, Q., Zhao, Y., Liu, K., et al. (2012). A map of rice genome variation reveals the origin of cultivated rice. Nature 490 (7421): 497–501. doi:10.1038/nature11532.
Hvistendahl, M., and Enserink, M. (2012). Charges Fly, Confusion Reigns Over Golden Rice Study in Chinese Children. Science 337 (6100): 1281. doi:10.1126/science.337.6100.1281
International Rice Research Institute. URL: http://www.irri.org/ [7.11.13]
Molina, J., Sikora, M., Garud, N., Flowers, J. M., Rubinstein, S., Reynolds, A., Huang, P., Jackson, S., Schaal, B. A., Bustamante, C. D., Boyko, A. R., and Purugganan, M. D. (2011). Molecular evidence for a single evolutionary origin of domesticated rice. Proceedings of the National Academy of Sciences 108 (20): 8351-8356 doi:10.1073/pnas.1104686108
Royal Botanic Gardens, Kew. Oryza sativa (Rice). URL: http://www.kew.org/plants-fungi/Oryza-sativa.htm [7.11.13]