Oryza sativa, having the common name Asian cultivated rice[2], 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.[3][4][5][6]
O. sativa has an erect stalk stem that grows 80–120 cm (30–45 in) tall, with a smooth surface. The leaf is lanceolate, 15–30 cm (5+7⁄8–11+3⁄4 in) long, and grows from a
ligule 10–20 mm (3⁄8–3⁄4 in) long.[8]
The generic name Oryza[9] is a classical Latin word for rice, while the specific epithet sativa means "cultivated".[10][11]
Oryza sativa contains two major subspecies: the sticky, short-grained
japonica or sinica variety, and the nonsticky, long-grained indica[
zh] [
ja] rice variety. Japonica was domesticated in the
Yangtze Valley 9–6,000 years ago,[12] 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 8,500–4,500 years ago,[12] and its varieties are mainly lowland rices, grown mostly submerged, throughout tropical Asia. Rice grain occurs in a variety of colors, including
white,
brown,
black,
purple, and
red rices.[13][14]
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.[15]
Glaszmann (1987) used
isozymes to sort O. sativa into six groups: japonica, aromatic, indica, aus, rayada, and ashina.[16]
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.[17] The Garris scheme has held up against newer analyses as of 2019,[18] though one 2014 article argues that rayada is distinct enough to be its own group under japonica.[19]
Resistance to the rice blast fungus Magnaporthe grisea is provided by various
resistance genes including Pi1, Pi54, and Pita.[24]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.[25][26]
^Civáň, Peter; Ali, Sajid; Batista-Navarro, Riza; Drosou, Konstantina; Ihejieto, Chioma; Chakraborty, Debarati; Ray, Avik; Gladieux, Pierre; Brown, Terence A (March 1, 2019). "Origin of the Aromatic Group of Cultivated Rice ( Oryza sativa L.) Traced to the Indian Subcontinent". Genome Biology and Evolution. 11 (3): 832–843.
doi:
10.1093/gbe/evz039.