Oryza sativa

Oryza sativa, commonly known as Asian

rice, is the plant species most commonly
referred to in English as rice. Oryza sativa
is a grass with a genome consisting of
430Mb across 12 chromosomes. It is
renowned for being easy to genetically
modify, and is a model organism for cereal
biology.
 Oryza sativa

Scientific classification

Kingdom: Plantae

Clade: Angiosperms

Clade: Monocots

Clade: Commelinids

Order: Poales

Family: Poaceae

Genus: Oryza

Species: O. sativa
 Binomial name

Oryza sativa
L.

Oryza sativa, inflorescence

Classification
Oryza sativa contains two major
subspecies: the sticky, short-grained
japonica or sinica variety, and the
nonsticky, long-grained indica variety.
Japonica varieties are usually cultivated in
dry fields, in temperate East Asia, upland
areas of Southeast Asia, and high
elevations in South Asia, while indica
varieties are mainly lowland rices, grown
mostly submerged, throughout tropical
Asia. Rice occurs in a variety of colors,
including white, brown, black, purple, and
red rices.[1] Black rice (also known as
purple rice) is a range of rice types, some
of which are glutinous rice. Varieties
include Indonesian black rice and Thai
jasmine black rice.
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.[2]

Glaszmann (1987) used isozymes to sort

O. sativa into six groups: japonica,
aromatic, indica, aus, rayada, and ashina.[3]
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.[4]

Nomenclature and taxonomy

O. sativa
Rice stem cross section magnified 400 times

A: Rice with chaff

B: Brown rice
C: Rice with germ
D: White rice with bran residue
E: Musenmai (Japanese:無洗米), "Polished and ready
to boil rice", literally, non-wash rice
(1): Chaff
(2):Bran
(3): Bran residue
(4): Cereal germ
(4): Cereal germ
(5): Endosperm

Rice has been cultivated since ancient

times and oryza is a classical Latin word
for rice. Sativa means "cultivated".

History of domestication and

cultivation
Origins

Debates on the origins of the

domesticated rice are numerous. In 2011,
genetic evidence showed that all forms of
Asian rice, both indica and japonica,
sprang from a single domestication that
occurred 8,200–13,500 years ago in China
of the wild rice Oryza rufipogon.[5] A 2012
study, through a map of rice genome
variation, indicated that the domestication
of rice occurred in the Pearl River valley
region of China. From East Asia, rice was
spread to South and Southeast Asia.[6]
Before this research, the commonly
accepted view, based on archaeological
evidence, is that rice was first
domesticated in the region of the Yangtze
River valley in China.[7][8][9]

The precise date of the first domestication

is unknown, but depending on the
molecular clock estimate, the date is
estimated to be 8,200 to 13,500 years ago.
This is consistent with known
archaeological data on the subject.[5]

Aerial view of terrace rice fields in Yuanyang, Yunnan

Province, southern China

An older theory, based on one chloroplast

and two nuclear gene regions, Londo et al.
(2006) had proposed that O. 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 archaeological
and genetic evidence exist for a single
domestication of rice in the lowlands of
China.[10]

Because the functional allele for

nonshattering, 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 a single
domestication event for O. sativa
happened in the region of the Yangtze
River valley.[8]
In 2003, Korean archaeologists alleged
they discovered burnt grains of
domesticated rice in Soro-ri, Korea, which
dated to 13,000 BC. These antedate the
oldest grains in China, which were dated to
10,000 BC, and potentially challenge the
mainstream explanation that
domesticated rice originated in China.[11]
The findings were received by academia
with strong skepticism.[12] [13]

Continental East Asia

Rice appears to have been used by the

early Neolithic populations of Lijiacun and
Yunchanyan.[14] Evidence of possible rice
cultivation in China around 11,500 BP has
been found, but whether the rice was
indeed being cultivated, or instead was
being gathered as wild rice is still
questioned.[15]

Zhao (1998) argues that collection of wild

rice in the Late Pleistocene had, by 6400
BC, led to the use of primarily
domesticated rice.[16] 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.[17] Analysis of Chinese rice
residues from Pengtoushan, which were
carbon 14 dated to 8200–7800 BC, show
that rice had been domesticated by this
time.[18]

In 1998, Crawford and Shen reported the

earliest of 14 AMS or radiocarbon dates
on rice from at least nine Early to Middle
Neolithic sites are 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.[14]

South Asia

Paddy field in West Bengal, India

Paddy fields in the Indian state of Tamil Nadu

Wild Oryza rice appeared in the Belan and

Ganges valley regions of northern India as
early as 4530 BC and 5440 BC,
respectively,[19] although many believe it
may have appeared earlier. The
Encyclopædia Britannica—on the subject of
the first certain cultivated rice—holds
that[20]
 Many cultures have evidence of
early rice cultivation, including
China, India, and the civilizations
of Southeast Asia. However, the
earliest archaeological evidence
comes from central and eastern
China and dates to 7000–5000 BC.

Denis J. Murphy (2007) further details the

spread of cultivated rice from India into
Southeast Asia:[21]
Several wild cereals, including
rice, grew in the Vindhyan Hills,
and rice cultivation, at sites such
as Chopani-Mando and
Mahagara, may have been
underway as early as 7000 BP.
The relative isolation of this area
and the early development of rice
farming imply that it was
developed indigenously.

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.[22] Agricultural activity during
the second millennium BC included rice
cultivation in the Kashmir and Harrappan
regions.[19] Mixed farming was the basis of
Indus valley economy.[22]

According to Zohary and Hopf (2000,

p. 91), O. sativa was recovered from a
grave at Susa in Iran (dated to the first
century AD) at one end of the ancient
world, while at the same time rice was
grown in the Po valley in Italy. In northern
Iran, in Gilan province, many indica rice
cultivars including 'Gerdeh', 'Hashemi',
'Hasani', and 'Gharib' have been bred by
farmers.[23]

Korean peninsula and

Japanese archipelago

Mainstream archaeological evidence

derived from palaeoethnobotanical
investigations indicate dry-land rice was
introduced to Korea and Japan sometime
between 3500 and 1200 BC. The
cultivation of rice then occurred on a small
scale, fields were impermanent plots, and
evidence shows that in some cases
domesticated and wild grains were
planted together. The technological,
subsistence, and social impact of rice and
grain cultivation is not evident in
archaeological data until after 1500 BC.
For example, intensive wet-paddy rice
agriculture was introduced into Korea
shortly before or during the Middle Mumun
pottery period (circa 850–550 BC) and
reached Japan by the final Jōmon or initial
Yayoi periods circa 300 BC.[14][24]
Southeast Asia

Rice is the staple for all classes in

contemporary Southeast 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 16th 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 1500 years.[25]

In the Philippines, the greatest evidence of

rice cultivation since ancient times can be
found in the Cordillera Mountain Range of
Luzon in the provinces of Apayao, Benguet,
Mountain Province and Ifugao. The
Banaue Rice Terraces (Tagalog: Hagdan-
hagdang Palayan ng Banaue) are 2,000- to
3,000-year-old terraces that were carved
into the mountains by ancestors of the
Batad indigenous people. The terraces are
commonly thought to have been built with
minimal equipment, largely by hand. The
terraces are located about 1,500 m
(5,000 ft) above sea level and cover
10,360 km2 (about 4,000 mi2) of
mountainside. They are fed by an ancient
irrigation system from the rainforests
above the terraces.
Evidence of wet-rice cultivation as early as
2200 BC has been discovered at both Ban
Chiang and Ban Prasat in Thailand.

By the 18th century, encroaching European

expansionism in the area increased rice
production in much of Southeast Asia, and
Thailand, then known as Siam. British
Burma became the world's largest
exporter of rice, from the turn of the 20th
century to the 1970s, when neighbouring
Thailand exceeded Burma. In recent years,
Vietnam has been a strong exporter, as
well, occasionally eclipsing Thailand.
While China, India, and Indonesia remain
the top rice producers, they are also some
of the top rice consumers.
Using water buffalo to plough rice fields in
Java; Indonesia is the world's third-largest
paddy rice producer, and its cultivation has
transformed much of the country's
landscape.
 Traditional medicinal rice of Niyamgiri
Hills, India

Medicinal rice of Chhattisgarh used as

immune booster

See also
Black rice
International Code of Nomenclature for
Cultivated Plants
 Japonica rice
Maratelli rice
Oryza glaberrima (African rice)
Traceability of genetically modified
organisms

References
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"Highland Rice Production in the Philippine
Cordillera."
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Theoretical and Applied Genetics. 74 (1):
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D.; Boyko, A. R.; Purugganan, M. D. (2011).
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