Oryza sativa, having the common name Asian cultivated rice, is the much more common of the two rice species cultivated as a cereal, the other species being O. glaberrima, African rice. It was first domesticated in the Yangtze River basin in China 13,500 to 8,200 years ago.
Oryza sativa belongs to the genus Oryza and the BOP clade in the grass family Poaceae. With a genome consisting of 430Mbp across 12 chromosomes, it is renowned for being easy to genetically modify and is a model organism for the study of the biology of cereals and monocots.
Description
thumb|[[Oryza rufipogon is the scientific name for brownbeard rice. This wild rice was first domesticated into Oryza sativa, and its subsequent divergence into japonica and indica subspecies, occurred through a long process of domestication, artificial selection, and hybridization. Domestication led to artificial selection of rice with a mutation that made seeds non-shattering. This forced grains to stay attached and made harvesting easier. The plant was also bred for vertical architecture in its growth to maximize field density, and the awns were selectively bred away to reduce bulk density. Oryza sativa then led to the creation of two subspecies, japonica and indica. Oryza sativa subsp. japonica was primarily grown in temperate and subtropical regions, the plant was shorter than indica and had darker leaves. Japonica grains are short, round, and plump, and have lower amylose content than indica. Oryza sativa subsp. indica was primarily grown in tropical and humid regions. Indica has a taller growth and lighter leaf color. The grains are thinner, longer, and have higher amylose content. Diagram Legend 1.a - wild rice (Oryza rufipogon) 1.b - grains of wild rice (Oryza rufipogon) 2.a - Japanese rice (Oryza sativa subsp. japonica) 2.b - grains of Japanese rice (Oryza sativa subsp. japonica) 3.a - Indian rice (Oryza sativa subsp. indica) 3.b - grains of Indian rice (Oryza sativa subsp. indica)]]
O. sativa has an erect stalk stem that grows tall, with a smooth surface. The leaf is lanceolate, long, and grows from a ligule long.
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Image:Kerbau Jawa.jpg|Water buffalo ploughing a rice paddyfield, Java
File:Jumli Marshi Oryza sativa Rice.jpg|Jumli Marshi, brown rice from Nepal
File:Niyamgiri rice.jpg|Traditional rice of Niyamgiri Hills, India
File:Medicinal Rice.jpg|From Chhattisgarh
File:Koeh-232.jpg|
File:RiceStemcs400x1.jpg|Stem cross section magnified 400 times
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Taxonomy
Oryza sativa contains two major subspecies: the sticky, short-grained japonica or sinica variety, and the nonsticky, long-grained ' rice variety. Japonica was domesticated in the Yangtze Valley 6,000–9,000 years ago, and its varieties can be cultivated in dry fields (it is cultivated mainly submerged in Japan), in temperate East Asia, upland areas of Southeast Asia, and high elevations in South Asia, while indica was domesticated around the Ganges 4,500–8,500 years ago,
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 Central Cordillera Mountains of northern Luzon, Philippines.
Glaszmann (1987) used isozymes to sort O. sativa into six groups: japonica, aromatic, indica, aus, rayada, and ashina.
Garris et al. (2004) used simple sequence repeats to sort O. sativa into five groups: temperate japonica, tropical japonica and aromatic comprise the japonica varieties, while indica and aus comprise the indica varieties. The Garris scheme has held up against newer analyses as of 2019, though one 2014 article argues that rayada is distinct enough to be its own group under japonica.
Etymology
The generic name Oryza is a classical Greek word for rice, while the specific epithet sativa means "cultivated".
Genetics
/ is a gene that regulates the overall architecture/growth habit of the plant. Some of its epialleles increase rice yield. An accurate and usable simple sequence repeat marker set was developed and used to generate a high-density map. Other molecular breeding tools have produced rice blast resistant cultivars. O. sativa uses the plant hormones abscisic acid and salicylic acid to regulate immune responses. Salicylic acid broadly stimulates, and abscisic acid suppresses, immunity to M. grisea; success depends on the balance between their levels.
O. sativa has a large number of insect resistance genes specifically for the brown planthopper. , 15 R genes have been cloned and characterized.