Oryza sativa, Photo: Michael Lahanas
Oryza sativa L.
* Species Plantarum 1:333. 1753
Oryza sativa (*)
Oryza sativa (common names include Asian Rice) is the plant species known in English as rice. Oryza sativa has the smallest cereal genome consisting of just 430Mb across 12 chromosomes. It is renowned for being easy to genetically modify and is a model organism for cereal biology.
Oryza sativa contains two major subspecies: the sticky, short grained japonica or sinica variety, and the non-sticky, long-grained indica variety. Japonica are usually cultivated in dry fields, in temperate East Asia, upland areas of Southeast Asia and high elevations in South Asia, while indica are mainly lowland rices, grown mostly submerged, throughout tropical Asia. Rice is known to come in a variety of colors, including: white, brown, black, purple, and red.
A third subspecies, which is broad-grained and thrives under tropical conditions, was identified based on morphology and initially called javanica, but is now known as tropical japonica. Examples of this variety include the medium grain 'Tinawon' and 'Unoy' cultivars, which are grown in the high-elevation rice terraces of the Cordillera Mountains of northern Luzon, Philippines.
Glaszmann (1987) used isozymes to sort Oryza sativa into six groups: japonica, aromatic, indica, aus, rayada, and ashina.
Garris et al. (2004) used SSRs to sort Oryza sativa into five groups; temperate japonica, tropical japonica and aromatic comprise the japonica varieties, while indica and aus comprise the indica varieties.
Nomenclature and taxonomy
* Indica 
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History of domestication and cultivation
Based on one chloroplast and two nuclear gene regions, Londo et al. (2006) conclude that Oryza sativa rice was domesticated at least twice—indica in eastern India, Myanmar and Thailand; and japonica in southern China and Vietnam—though they concede that there is archaeological and genetic evidence for a single domestication of rice in the lowlands of China.
Because the functional allele for non-shattering—the critical indicator of domestication in grains—as well as five other single nucleotide polymorphisms, is identical in both indica and japonica, Vaughan et al. (2008) determined that there was a single domestication event for Oryza sativa in the region of the Yangtze river valley.
Continental East Asia
Rice appears to have been used by the early Neolithic populations of Lijiacun and Yunchanyan. Evidence of possible rice cultivation in China from c. 11,500 BP has been found, however it is still questioned whether the rice was indeed being cultivated, or instead being gathered as wild rice. Bruce Smith, an archaeologist at the Smithsonian Institution in Washington, D.C., who has written on the origins of agriculture, says that evidence has been mounting that the Yangtze was probably the site of the earliest rice cultivation.
Zhao (1998) argues that collection of wild rice in the Late Pleistocene had, by 6400 BC, led to the use of primarily domesticated rice. Morphological studies of rice phytoliths from the Diaotonghuan archaeological site clearly show the transition from the collection of wild rice to the cultivation of domesticated rice. The large number of wild rice phytoliths at the Diaotonghuan level dating from 12,000–11,000 BP indicates that wild rice collection was part of the local means of subsistence. Changes in the morphology of Diaotonghuan phytoliths dating from 10,000–8,000 BP show that rice had by this time been domesticated. Analysis of Chinese rice residues from Pengtoushan, which were carbon 14 dated to 8200–7800 BCE, show that rice had been domesticated by this time.
In 1998, Crawford & Shen reported that the earliest of 14 AMS or radiocarbon dates on rice from at least nine Early to Middle Neolithic sites is no older than 7000 BC, that rice from the Hemudu and Luojiajiao sites indicates that rice domestication likely began before 5000 BC, but that most sites in China from which rice remains have been recovered are younger than 5000 BC.
Wild Oryza rice appeared in the Belan and Ganges valley regions of northern India as early as 4530 BC and 5440 BC respectively, although many believe it may have appeared earlier. The Encyclopedia Britannica—on the subject of the first certain cultivated rice—holds that:
Denis J. Murphy (2007) further details the spread of cultivated rice from India into South-east Asia:
Chopani-Mando and Mahagara are located on the upper reaches of the Ganges drainage system and it is likely that migrants from this area spread rice farming down the Ganges valley into the fertile plains of Bengal, and beyond into south-east Asia.
Rice was cultivated in the Indus Valley Civilization. Agricultural activity during the second millennium BC included rice cultivation in the Kashmir and Harrappan regions. Mixed farming was the basis of Indus valley economy.
Punjab is the largest producer and consumer of rice in India.
In 2003, Korean archaeologists alleged that they discovered burnt grains of domesticated rice in Soro-ri, Korea, which dated to 13,000 BC. These predate the oldest grains in China, which were dated to 10,000 BC, and potentially challenge the mainstream explanation that domesticated rice originated in China. The findings were received by academia with strong skepticism, and the results and their publicizing has been cited as being driven by a combination of nationalist and regional interests.
Rice is the staple for all classes in contemporary South East Asia, from Myanmar to Indonesia. In Indonesia, evidence of wild Oryza rice on the island of Sulawesi dates from 3000 BCE. The evidence for the earliest cultivation, however, comes from eighth century stone inscriptions from Java, which show kings levied taxes in rice. Divisions of labor between men, women, and animals that are still in place in Indonesian rice cultivation, can be seen carved into the ninth-century Prambanan temples in Central Java. In the sixteenth century, Europeans visiting the Indonesian islands saw rice as a new prestige food served to the aristocracy during ceremonies and feasts. Rice production in Indonesian history is linked to the development of iron tools and the domestication of water buffalo for cultivation of fields and manure for fertilizer. Once covered in dense forest, much of the Indonesian landscape has been gradually cleared for permanent fields and settlements as rice cultivation developed over the last fifteen hundred years.
Evidence of wet rice cultivation as early as 2200 BC has been discovered at both Ban Chiang and Ban Prasat in Thailand.
By the 19th Century, encroaching European expansionism in the area increased rice production in much of South East Asia, and Thailand, then known as Siam. British Burma became the world's largest exporter of rice, from the turn of the 20th century up till the 1970s, when neighbouring Thailand exceeded Burma.
1. ^ Oka (1988)
Source: Wikipedia, Wikispecies: All text is available under the terms of the GNU Free Documentation License