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{{Short description|Cereal grain and staple food}}
[[File:20201102.Hengnan.Hybrid rice Sanyou-1.6.jpg|thumb|upright=1.35|Rice plant (''[[Oryza sativa]]'') with branched [[panicle]]s containing many grains on each stem]]
[[File:Rice grains (IRRI).jpg|thumb|upright=1.35|Rice grains of different [[Variety (botany)|varieties]] at the [[International Rice Research Institute]]]]
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'''Rice''' is a [[cereal grain]] and in its [[Domestication|domesticated]] form is the [[staple food]] of over half of the [[world's population]], particularly in [[Asia]] and [[Africa]]. Rice is the seed of the grass species ''[[Oryza sativa]]'' (Asian rice)—or, much less commonly, ''[[Oryza glaberrima]]'' (African rice). Asian rice was domesticated in [[China]] some 13,500 to 8,200 years ago; African rice was domesticated in Africa about 3,000 years ago. Rice has become commonplace in many cultures worldwide; in 2023, 800 million tons were produced, placing it third after [[sugarcane]] and [[maize]]. Only some 8% of rice is traded internationally. China, India, and Indonesia are the largest consumers of rice. A substantial amount of the rice produced in developing nations is lost after harvest through factors such as poor transport and storage. Rice yields can be reduced by pests including [[insect]]s, [[rodent]]s, and [[bird]]s, as well as by [[weed]]s, and by [[List of rice diseases|diseases]] such as [[rice blast]]. Traditional [[rice polyculture]]s such as [[rice-duck farming]], and modern [[integrated pest management]] seek to control damage from pests in a [[Sustainable agriculture|sustainable]] way.
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Dry rice grain is milled to remove the outer layers; depending on how much is removed, products range from brown rice to rice with germ and white rice. Some is [[parboiled rice|parboiled]] to make it easy to cook. Rice contains no [[gluten]]; it provides [[protein]] but not all the [[essential amino acids]] needed for good health. Rice of different types is eaten around the world. The composition of starch components within the grain, [[amylose]] and [[amylopectin]], gives it different texture properties. Long-grain rice, from the ''Indica'' cultivar, tends to stay intact on cooking, and is dry and fluffy. The [[aromatic rice]] varieties such as [[basmati rice|basmati]] and [[jasmine rice|jasmine]], are widely used in Asian cooking, and distinguished by their bold and nutty flavor profile. Its varieties include [[calrose rice|Calrose]], which founded the [[Rice production in the United States|Californian rice industry]], [[Carnaroli]], attributed as the ''king of Italian rice'' due to its excellent cooking properties, and [[black rice]], which looks dark purple due to high levels of [[Anthocyanin|anthocyanins]], and is also known as ''forbidden rice'' as it was reserved for the consumption of the royal family in ancient China. Short-grain rice, primarily from the ''Japonica'' cultivar, has an oval appearance and sticky texture. It is featured heavily in Japanese cooking such as sushi (with rice such as ''[[Koshihikari]]'', ''Hatsushimo'', and ''[[Sasanishiki]]'', unique to different regions of climate and geography in Japan), as it keeps its shape when cooked. It is also used for sweet dishes such as [[mochi]] (with [[glutinous rice]]), and in [[European cuisine]] such as [[risotto]] (with [[arborio rice]]) and [[paella]] (with [[bomba rice]], which is actually an ''Indica'' variety). Cooked white rice contains 29% [[carbohydrate]] and 2% protein, with some [[manganese]]. [[Golden rice]] is a variety produced by [[genetic engineering]] to contain [[vitamin A]].
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Production of rice is estimated to have caused over 1% of global [[greenhouse gas emissions]] in 2022. Predictions of how rice yields will be affected by climate change vary across geographies and socioeconomic contexts. In human culture, rice plays a role in various religions and traditions, such as in [[wedding]]s.
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== Description ==
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The rice plant can grow to over {{cvt|1|m|ft|0}} tall; if in deep water, it can reach a length of {{cvt|5|m|ft|0}}. From seed to harvest, it takes about six months. A single plant may have several leafy stems or [[Tiller (botany)|tillers]]. The upright stem is jointed with [[Node (botany)|nodes]] along its length; a long slender leaf arises from each node. The [[Autogamy|self-fertile]] flowers are produced in a [[panicle]], a branched [[inflorescence]] which arises from the last internode on the stem. There can be up to 350 [[spikelet]]s in a panicle, each containing male and female flower parts ([[anther]]s and [[ovule]]). A fertilised ovule develops into the edible grain or [[caryopsis]].
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Rice is a cereal belonging to the family [[Poaceae]]. As a [[Tropics|tropical]] crop, it can be grown during the two distinct seasons (dry and wet) of the year provided that sufficient water is made available. It is normally an annual, but in the tropics it can survive as a [[perennial]], producing a [[ratoon]] crop.
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File:Koeh-232.jpg|Anatomy of rice flowers: [[spikelet]] (left), plant with [[Tiller (botany)|tillers]] (centre), [[caryopsis]] (top right), [[panicle]] (right)
File:Oryza sativa of Kadavoor.jpg|Detail of rice plant showing flowers grouped in panicle. Male [[anther]]s protrude into the air where they can disperse their [[pollen]].
</gallery>
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== Agronomy ==
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=== Growing ===
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Like all crops, rice depends for its growth on both biotic and abiotic environmental factors. The principal biotic factors are crop variety, [[Pest (organism)|pests]], and [[plant disease]]s. Abiotic factors include the soil type, whether lowland or upland, amount of rain or irrigation water, temperature, [[Photoperiodism|day length]], and intensity of sunlight.
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Rice grains can be planted directly into the field where they will grow, or seedlings can be grown in a seedbed and transplanted into the field. Direct seeding needs some 60 to 80&nbsp;kg of grain per hectare, while transplanting needs less, around 40&nbsp;kg per hectare, but requires far more labour. Most rice in Asia is transplanted by hand. Mechanical transplanting takes less time but requires a carefully-prepared field and seedlings raised on mats or in trays to fit the machine. Rice does not thrive if continuously submerged. Rice can be grown in different environments, depending upon water availability. The usual arrangement is for lowland fields to be surrounded by [[Bunding|bunds]] and flooded to a depth of a few centimetres until around a week before harvest time; this requires a large amount of water. The "alternate wetting and drying" technique uses less water. One form of this is to flood the field to a depth of 5&nbsp;cm (2&nbsp;in), then to let the water level drop to 15&nbsp;cm (6&nbsp;in) below surface level, as measured by looking into a perforated field water tube sunk into the soil, and then repeating the cycle.[[Deepwater rice]] varieties tolerate flooding to a depth of over 50 centimetres for at least a month. [[Upland rice]] is grown without flooding, in hilly or mountainous regions; it is [[rainfed]] like wheat or maize.
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{{multiple image |align=center |caption_align=center |total_width=840 |image_gap=10 |image_style=border:none;
|image1=Kerbau Jawa.jpg |caption1=Ploughing a rice terrace with [[Domestic buffalo|water buffaloes]] in [[Java]]
|image2=Cambodian farmers planting rice.jpg |caption2=Farmers planting rice by hand in [[Cambodia]]
|image3=Rice-planting-machine 2,katori-city,japan.JPG |caption3=Mechanised rice planting in Japan
|image4=Pana Banaue Rice Terraces (Cropped).jpg |caption4=Ancient mountainside [[Banaue Rice Terraces|rice terraces at Banaue]], Philippines
}}
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=== Harvesting ===
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Across Asia, unmilled rice or "paddy" (Indonesian and Malay {{lang|id|padi}}), was traditionally the product of [[smallholder]] agriculture, with manual [[harvest]]ing. Larger farms make use of machines such as [[combine harvester]]s to reduce the input of labour. The grain is ready to harvest when the moisture content is 20–25%. Harvesting involves [[reaping]], stacking the cut stalks, [[threshing]] to separate the grain, and cleaning by [[winnowing]] or [[sieve|screening]].
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{{multiple image |align=center |caption_align=center |total_width=840 |image_gap=10 |image_style=border:none; 
|image1=Rice-combine-harvester, Katori-city, Japan.jpg |caption1=Rice [[combine harvester]] in [[Chiba Prefecture]], Japan 
|image2=Rice farmers Mae Wang Chiang Mai Province.jpg |caption2=After the harvest, rice straw is gathered in the traditional way from small paddy fields in [[Mae Wang]], Thailand
|image3=NP India burning 48 (6315309342).jpg |caption3=Burning of rice residues to prepare the land for [[wheat]] planting in [[Sangrur]], India
|image4=Nellu.JPG |caption4=Drying rice in [[Peravoor]], India
}}
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== Evolution ==
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=== Phylogeny ===
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{{further|Oryza sativa}}
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The edible rice species are members of the [[BOP clade]] within the grass family, the [[Poaceae]]. The rice subfamily, [[Oryzoideae]], is sister to the bamboos, [[Bambusoideae]], and the cereal subfamily [[Pooideae]]. The rice genus ''Oryza'' is one of eleven in the Oryzeae; it is sister to the [[Phyllorachideae]]. The edible rice species ''O. sativa'' and ''O. glaberrima'' are among some 300 species or subspecies in the genus.
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{{clade
|label1=[[Poaceae]]
|1={{clade
   |1=other grasses
   |2={{clade
      |label1=[[PACMAD clade]]
      |1=(inc. the [[C4 carbon fixation|C4 grasses]], [[maize]], [[sorghum]])
      |label2=[[BOP clade]]
      |2={{clade
         |label1=[[Oryzoideae]]
         |1={{clade
            |1=[[Streptogyneae]]
            |2={{clade
               |1=[[Ehrharteae]]
               |2={{clade
                  |1=[[Phyllorachideae]]
                  |label2=[[Oryzeae]]
                  |2={{clade
                     |1=Wild rices inc. ''[[Zizania]]''
                     |label2=''[[Oryza]]''
                     |2={{clade
                        |1=other rice species and subspecies
                        |2='''''[[Oryza sativa|O. sativa]]''''' (Asian rice)
                        |3='''''[[Oryza glaberrima|O. glaberrima]]''''' (African rice)
                        }}
                     }}
                  }}
               }}
            }}
         |2={{clade
            |1=[[Bambusoideae]] (bamboos)
               |2=[[Pooideae]] (grasses and cereals inc. [[wheat]], [[barley]])
            }}
         }}
      }}
   }}
}}
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{{Anchor|Domestication}}
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=== History ===
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{{main |History of rice cultivation}}
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[[File:KITLV_40091_-_Kassian_Céphas_-_Relief_of_the_hidden_base_of_Borobudur_-_1890-1891.jpg|thumb|upright=1.5|Bas-relief of 9th century [[Borobudur]] in Indonesia describes [[rice barn]]s and rice plants infested by mice.]]
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''[[Oryza sativa]]'' rice was first [[Domestication|domesticated]] in [[Neolithic China|China]] 9,000 years ago, by people of [[Neolithic]] cultures in the [[Upper Yangtze|Upper]] and [[Lower Yangtze]], associated with [[Hmong-Mien]]-speakers and [[pre-Austronesians]], respectively. The functional [[allele]] for [[Shattering (agriculture)|nonshattering]], the critical indicator of domestication in grains, as well as five other [[single-nucleotide polymorphism]]s, is identical in both ''indica'' and ''[[Japonica rice|japonica]]''. This implies a single domestication event for ''O. sativa''. Both ''indica'' and ''[[Japonica rice|japonica]]'' forms of Asian rice sprang from a single domestication event in China from the wild rice ''[[Oryza rufipogon]]''. Despite this evidence, it appears that ''indica'' rice arose when ''japonica'' arrived in India about 4,500 years ago and hybridised with another rice, whether an undomesticated proto-''indica'' or wild ''[[Oryza nivara|O. nivara]]''.
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Rice was introduced early into [[Sino-Tibetan]] cultures in northern China by around 6000 to 5600 years ago, and to the [[Korea]]n peninsula and [[Japan]] by around 5500 to 3200 years ago. It was also carried into [[Taiwan]] by the [[Dapenkeng]] culture by 5500 to 4000 years ago, before spreading southwards via the [[Austronesian expansion|Austronesian migrations]] to [[Island Southeast Asia]], [[Madagascar]], and [[Guam]], but did not survive the voyage to the rest of the Pacific. It reached [[Austroasiatic]] and [[Kra-Dai]]-speakers in [[Mainland Southeast Asia]] and southern China by 5000 years ago.
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Rice spread around the rest of the world through cultivation, migration and trade, eventually to the Americas as part of the [[Columbian exchange]] after 1492. The now less common ''[[Oryza glaberrima]]'' (African rice) was independently domesticated in Africa around 3,000 years ago, and introduced to the Americas by the Spanish. In [[British North America]] by the time of the start of the [[American War of Independence]], rice had become the fourth most valuable export commodity behind only tobacco, wheat, and fish.
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== Commerce ==
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{| class="wikitable" style="float:right; clear:right; width:14em; text-align:center; margin-right:1em;"
! colspan=2|Rice production – 2023
|-
! style="background:#ddf; width:50%;"|Country
! style="background:#ddf; width:50%;"|<small> Millions of [[tonne]]s </small>
|-
|{{IND}}||[[Rice production in China|207]]
|-
|{{CHN}}||[[Rice production in India|207]]
|-
|{{BGD}} ||[[Rice production in Bangladesh|59]]
|-
|{{IDN}} ||[[Rice production in Indonesia|54]]
|-
|{{VNM}} ||[[Rice production in Vietnam|43]]
|-
|{{THA}} ||[[Rice production in Thailand|33]]
|-
|'''World''' ||'''800'''
|}
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=== Production ===
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{{ See also |List of countries by rice production }}
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In 2023, world production of rice was 800 million [[tonne]]s, led by China and India with a combined 52% of the total. This placed rice third in the list of crops by production, after [[sugarcane]] and [[maize]]. Other major producers were [[Bangladesh]], [[Indonesia]] and [[Vietnam]]. 90% of world production is from Asia.
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<gallery class="center" mode="nolines" heights="300" widths="450">
File:Production of rice (2019).svg|Production of rice (2021)
File:World Production Of Primary Crops, Main Commodities.svg|Since 2000, rice production (orange) has increased,<br/>but its share of total crop production has fallen.
</gallery>
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=== Yield records ===
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The average world yield for rice was {{convert|4.7|MT/ha|ST/acre|abbr=off}}, in 2022. [[Yuan Longping]] of China's National Hybrid Rice Research and Development Center set a world record for rice yield in 1999 at {{convert|17.1|MT/ha|ST/acre|abbr=off}} on a demonstration plot. This employed specially developed hybrid rice and the [[System of Rice Intensification]] (SRI), an innovation in rice farming.
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=== Food security ===
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Rice is a major food staple in Asia, Latin America, and some parts of Africa, feeding over half the world's population. However, a substantial part of the crop can be lost post-harvest through inefficient transportation, storage, and milling. A quarter of the crop in Nigeria is lost after harvest. Storage losses include damage by [[Mold|mould]] fungi if the rice is not dried sufficiently. In China, losses in modern metal [[silo]]s were just 0.2%, compared to 7–13% when rice was stored by rural households.
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=== Processing ===
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{|class="wikitable floatright" style="font-size:85%;text-align:left;width:25em;"
|-style="text-align:center;"
| colspan=2 | [[File:Rice Animation.gif|frameless|upright=1.15|alt=Five-step animation showing the removal of successive layers from raw rice grains, starting with the grain with its inedible hull and ending with polished white rice.]]<br/>[[#Processing|Rice processing]] removes one or more layers to create marketable products. 
|-
|<ol style="list-style-type:upper-alpha;">
<li>Rice with [[chaff]]</li>
<li>[[Brown rice]]</li>
<li>Rice with [[Cereal germ|germ]]</li>
<li>[[White rice]] with [[bran]] [[Crop residue|residue]]</li>
<li>Polished</li>
</ol>
|<ol>
<li>[[Chaff]]</li>
<li>[[Bran]]</li>
<li>Bran [[Crop residue|residue]]</li>
<li>[[Cereal germ]]</li>
<li>[[Endosperm]]</li>
</ol>
|}
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The dry grain is milled to remove the outer layers, namely the [[husk]] and [[bran]]. These can be removed in a single step, in two steps, or as in commercial milling in a multi-step process of cleaning, dehusking, separation, polishing, grading, and weighing. Brown rice only has the inedible husk removed. Further milling removes bran and the germ to create successively whiter products. [[Parboiled rice]] is subjected to a steaming process before it is milled. This makes the grain harder, and moves some of the grain's [[vitamin]]s and [[Mineral (nutrient)|minerals]] into the white part of the rice so these are retained after milling. Rice does not contain [[gluten]], so is suitable for people on a [[gluten-free diet]]. Rice is a good source of protein and a staple food in many parts of the world, but it is not a [[complete protein]] as it does not contain all of the [[essential amino acids]] in sufficient amounts for good health.
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<gallery mode=packed heights=150>
File:Stages of rice milling.jpg|Unmilled to milled [[Japanese rice]], from left to right, [[brown rice]], rice with [[Cereal germ|germ]], [[white rice]]
</gallery>
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=== Trade ===
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World trade figures are much smaller than those for production, as less than 8% of rice produced is traded internationally. China, an exporter of rice in the early 2000s, had become the world's largest importer of rice by 2013. Developing countries are the main players in the world rice trade; by 2012, India was the largest exporter of rice, with Thailand and Vietnam the other largest exporters.
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=== Worldwide consumption ===
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As of 2016, the countries that consumed the most rice were China (29% of total), India, and Indonesia. By 2020, Bangladesh had taken third place from Indonesia. On an annual average from 2020 to 2023, China consumed 154 million tonnes of rice, India consumed 109 million tonnes, and Bangladesh and Indonesia consumed about 36 million tonnes each. Across the world, rice consumption per capita fell in the 21st century as people in Asia and elsewhere ate less grain and more meat. An exception is Sub-Saharan Africa, where both per capita consumption of rice and population are increasing.
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{{Infobox nutritional value
| name=Cooked white rice, medium-grain, unenriched
| water=69 g
| kJ=544
| protein=2.4 g
| fat=0.2 g
| carbs=28.6 g
| calcium_mg=3
| iron_mg=0.2
| magnesium_mg=13
| phosphorus_mg=37
| potassium_mg=29
| sodium_mg=0
| zinc_mg=0.4
| manganese_mg=0.38
| thiamin_mg=0.02
| riboflavin_mg=0.02
| niacin_mg=0.4
| pantothenic_mg=0.41
| vitB6_mg=0.05
| folate_ug=2
| note=[https://fdc.nal.usda.gov/fdc-app.html#/food-details/168930/nutrients FoodData Central  entry]}}
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=== Eating qualities ===
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Rice is a commonly-eaten food around the world. The [[List of rice varieties|varieties of rice]] are typically classified as short-, medium-, and long-grained. ''Oryza sativa indica'' varieties are usually long-grained; ''Oryza sativa japonica'' varieties are usually short- or medium-grained. Short-grain rice, with the exception of Spanish Bomba, is usually sticky when cooked, and is suitable for puddings. Thai [[Jasmine rice]] is aromatic, and unusually for a long-grain rice has some stickiness, with a soft texture. Indian [[Basmati|Basmati rice]] is very long-grained and aromatic. Italian [[Arborio rice]], used for [[risotto]], is of medium length, oval, and quite sticky. Japanese [[sushi]] rice is a sticky short-grain variety.
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=== Nutrition ===
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Cooked white rice is 69% water, 29% [[carbohydrate]]s, 2% [[protein (nutrient)|protein]], and contains negligible [[fat]] (table). In a reference serving of {{convert|100|g}}, cooked white rice provides 130 [[calorie]]s of [[food energy]], and contains moderate levels of [[Manganese in biology|manganese]] (18% DV), with no other [[micronutrient]]s in significant content (all less than 10% of the [[Daily Value]]).
In 2018, the [[World Health Organization]] strongly recommended [[food fortification|fortifying]] rice with [[iron]], and conditionally recommended fortifying it with [[vitamin A]] and with [[folic acid]].
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=== Golden rice ===
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{{main|Golden rice}}
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Golden rice is a variety produced through [[genetic engineering]] to synthesize [[beta-carotene]], a precursor of vitamin A, in the [[endosperm]] of the rice grain. It is intended to be grown and eaten in parts of the world where [[Vitamin A deficiency]] is prevalent. Golden rice has been opposed by activists, such as in the [[Philippines]]. In 2016 more than 100 [[Nobel laureate]]s encouraged the use of [[genetically modified organism]]s, such as golden rice, for the benefits these could bring.
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== Rice and climate change ==
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=== Greenhouse gases from rice production ===
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[[File:NP Rice Emissions18 (5687953086).jpg|thumb|Scientists measuring the greenhouse gas emissions of rice]]
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In 2022, [[greenhouse gas emissions]] from rice cultivation were estimated at 5.7 billion tonnes CO2eq, representing 1.2% of total emissions. Within the agriculture sector, rice produces almost half the greenhouse gas emissions from [[croplands]], [[Methane]] is released from rice fields subject to long-term flooding, as this inhibits the soil from absorbing atmospheric oxygen, resulting in [[anaerobic fermentation]] of organic matter in the soil. Emissions can be limited by planting new varieties, not flooding continuously, and removing straw.
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It is possible to cut methane emissions in rice cultivation by improved water management, combining dry seeding and one drawdown, or executing [[alternate wetting and drying|a sequence of wetting and drying]]. This results in emission reductions of up to 90% compared to full flooding and even increased yields.
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=== Effects of climate change on rice production ===
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Predictions of climate change's effects on rice cultivation vary. Global rice yield has been projected to decrease by around 3.2% with each 1&nbsp;°C increase in global average temperature while another study predicts global rice cultivation will increase initially, plateauing at about 3&nbsp;°C warming (2091–2100 relative to 1850–1900).
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The impacts of climate change on rice cultivation vary across geographic location and socioeconomic context. For example, rising temperatures and decreasing solar radiation during the later years of the 20th century decreased rice yield by between 10% and 20% across 200 farms in seven Asian countries. This may have been caused by increased night-time respiration. IRRI has predicted that Asian rice yields will fall by some 20% per 1°C rise in global mean temperature. Further, rice is unable to yield grain if the flowers experience a temperature of 35°C or more for over one hour, so the crop would be lost under these conditions.
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In the [[Po Valley]] in Italy, the [[Arborio rice|arborio]] and [[carnaroli]] risotto rice varieties have suffered poor harvests through drought in the 21st century. The {{ill|Ente Nazionale Risi|it}}  is developing drought-resistant varieties; its ''nuovo prometeo'' variety has deep roots that enable it to tolerate drought, but is not suitable for risotto.
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{{Anchor|Pests}}
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== Pests, weeds, and diseases ==
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=== Pests and weeds ===
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[[File:Chinese rice grasshopper (Oxya chinensis).jpg|thumb|Chinese rice grasshopper (''[[Oxya chinensis]]'')]]
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Rice yield can be reduced by weed growth, and a wide variety of pests including insects, nematodes, rodents such as rats, snails, and birds. Major rice insect pests include armyworms, [[rice bug]]s, [[Scotinophara|black bugs]], cutworms, field crickets, grasshoppers, leafhoppers, mealybugs, and planthoppers. High rates of [[nitrogen fertiliser]] application may worsen aphid outbreaks.
Weather conditions can contribute to pest outbreaks: [[Orseolia oryzae|rice gall midge]] outbreaks are worsened by high rainfall in the wet season, while [[Stenchaetothrips biformis|thrips]] outbreaks are associated with drought.
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{{main|:Category:Insect pests of rice}}
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=== Diseases ===
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{{main|List of rice diseases}}
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[[File:Rice blast.jpg|thumb|upright|Healthy rice (left) and rice with [[Magnaporthe grisea|rice blast]] ]]
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[[Magnaporthe grisea|Rice blast]], caused by the fungus ''Magnaporthe grisea'', is the most serious disease of growing rice.
It and [[bacterial leaf streak]] (caused by [[Xanthomonas oryzae pv. oryzae|''Xanthomonas oryzae'' pv. ''oryzae'']]) are perennially the two worst rice diseases worldwide; they are both among the ten most important diseases of all crop plants. Other major rice diseases include [[sheath blight]] (caused by ''[[Rhizoctonia solani]]''), false smut (''[[Ustilaginoidea virens]]''), and bacterial panicle blight (''[[Burkholderia glumae]]''). Viral diseases include rice bunchy stunt, rice dwarf, rice [[tungro]], and rice yellow mottle.
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=== Pest management ===
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{{further|Integrated pest management|rice-duck farming}}
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[[Crop protection]] scientists are developing [[Sustainable agriculture|sustainable]] techniques for managing rice pests. Sustainable pest management is based on four principles: biodiversity, host plant resistance, landscape ecology, and hierarchies in a landscape—from biological to social. Farmers' pesticide applications are often unnecessary. Pesticides may actually induce [[resurgence (pest)|resurgence]] of populations of rice pests such as the [[brown planthopper]], both by destroying beneficial insects and by enhancing the pest's reproduction. The [[International Rice Research Institute]] (IRRI) demonstrated in 1993 that an 87.5% reduction in pesticide use can lead to an overall drop in pest numbers.
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[[File:Penggembala Bebek.jpg|thumb|left|A farmer [[Rice-duck farming|grazes his ducks]] in [[paddy field]]s, Central Java]]
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Farmers in China, Indonesia and the Philippines have traditionally managed weeds and pests by the [[polyculture|polycultural]] practice of [[Rice-duck farming|raising ducks]] and [[Rice-fish system|sometimes fish]] in their rice paddies. These produce valuable additional crops, eat small pest animals, manure the rice, and in the case of ducks also control weeds.
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Rice plants produce their own chemical defences to protect themselves from pest attacks. Some synthetic chemicals, such as the herbicide [[2,4-Dichlorophenoxyacetic acid|2,4-D]], cause the plant to increase the production of certain defensive chemicals and thereby increase the plant's resistance to some types of pests. Conversely, other chemicals, such as the insecticide [[imidacloprid]], appear to induce changes in the gene expression of the rice that make the plant more susceptible to certain pests.
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Plant breeders have created rice cultivars incorporating [[plant resistance to insects|resistance to various insect pests]]. Conventional plant breeding of resistant varieties has been limited by challenges such as rearing insect pests for testing, and the great diversity and continuous evolution of pests. Resistance genes are being sought from wild species of rice, and genetic engineering techniques are being applied.
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{{Anchor|Ecotypes|Ecotype|Cultivars|Cultivar}}
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==Ecotypes and cultivars==
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{{ Main |List of rice cultivars }}
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[[File:Rice diversity.jpg|thumb|upright=0.9|A few of the many cultivars in [[IRRI]]'s rice seed collection ]]
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The [[International Rice Research Institute]] maintains the International Rice Genebank, which holds over 100,000 rice varieties. Much of southeast Asia grows [[sticky rice|sticky]] or glutinous rice varieties. High-yield cultivars of rice suitable for cultivation in Africa, called the [[New Rice for Africa]] (NERICA), have been developed to improve [[food security]] and alleviate poverty in Sub-Saharan Africa.
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The complete [[genome]] of rice was [[Whole genome sequencing|sequenced]] in 2005, making it the first crop plant to reach this status. 
Since then, the genomes of hundreds of types of rice, both wild and cultivated, and including both Asian and African rice species, have been sequenced.
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== Biotechnology ==
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=== High-yielding varieties ===
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{{main|Green revolution}}
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The high-yielding varieties are a group of crops created during the [[Green Revolution]] to increase global food production radically. The first Green Revolution rice variety, [[IR8]], was produced in 1966 at the [[International Rice Research Institute]] through a cross between an Indonesian variety named "Peta" and a Chinese variety named "Dee Geo Woo Gen". Green Revolution varieties were bred to have short strong stems so that the rice would not lodge or fall over. This enabled them to stay upright and productive even with heavy applications of fertiliser.
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=== Expression of human proteins ===
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[[Ventria Bioscience]] has [[genetically modified]] rice to [[gene expression|express]] [[lactoferrin]] and [[lysozyme]] which are [[proteins]] usually found in [[breast milk]], and [[human serum albumin]]. These proteins have [[Antiviral protein|antiviral]], [[antibacterial]], and [[Antifungal protein|antifungal]] effects.
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=== Flood-tolerance ===
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{{Main|Deepwater rice}}
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[[File:Researchers checking deep water rice.jpg|thumb|upright=1.2|International Rice Research Institute researchers checking [[deepwater rice]] in the Philippines ]]
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In areas subject to [[flooding]], farmers have long planted flood tolerant varieties known as [[deepwater rice]]. In South and [[South East Asia]], flooding affects some {{convert|20|e6ha|e6acre|abbr=off}} each year. 
Flooding has historically led to massive losses in yields, such as in the Philippines, where in 2006, rice crops worth $65&nbsp;million were lost to flooding.
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Standard rice varieties cannot withstand stagnant flooding for more than about a week, since it disallows the plant access to necessary requirements such as sunlight and gas exchange. The Swarna Sub1 cultivar can tolerate week-long submergence, consuming carbohydrates efficiently and continuing to grow. So-called "[[Scuba diving|scuba]] rice" with the Sub1A [[transgene]] is robustly tolerant of submergence for as long as two weeks, offering much improved flood survival for farmers' crops. IRRI has created Sub1A varieties and distributed them to Bangladesh, India, Indonesia, Nepal, and the Philippines.
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===Drought-tolerance===
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[[Drought]] represents a significant environmental stress for rice production, with {{convert|19-23|e6ha|e6acre|abbr=off}} of rainfed rice production in South and South East Asia often at risk. Under drought conditions, without sufficient water to afford them the ability to obtain the required levels of [[nutrients]] from the soil, conventional commercial rice varieties can be severely affected—as happened for example in India early in the 21st century.
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The [[International Rice Research Institute]] conducts research into developing drought-tolerant rice varieties, including the varieties Sahbhagi Dhan, Sahod Ulan, and Sookha dhan, currently being employed by farmers in India, the Philippines, and Nepal respectively. In addition, in 2013 the Japanese National Institute for Agrobiological Sciences led a team which successfully inserted the ''DEEPER ROOTING 1'' (''DRO1'') gene, from the Philippine [[Upland and lowland (freshwater ecology)|upland]] rice variety Kinandang Patong, into the popular commercial rice variety IR64, giving rise to a far deeper root system in the resulting plants. This facilitates an improved ability for the rice plant to derive its required nutrients in times of drought via accessing deeper layers of [[soil]], a feature demonstrated by trials which saw the IR64 + DRO1 rice yields drop by 10% under moderate drought conditions, compared to 60% for the unmodified IR64 variety.
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=== Salt-tolerance ===
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{{further|Crop tolerance to seawater}}
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[[Soil salinity]] poses a major threat to rice crop productivity, particularly along low-lying coastal areas during the dry season. For example, roughly {{convert|1|e6ha|e6acre|abbr=off}} of the coastal areas of [[Bangladesh]] are affected by saline soils. These high concentrations of salt can severely affect rice plants' [[physiology]], especially during early stages of growth, and as such farmers are often forced to abandon these areas.
Progress has been made in developing rice varieties capable of tolerating such conditions; the hybrid created from the cross between the commercial rice variety IR56 and the wild rice species ''Oryza coarctata'' is one example. ''O. coarctata'' can grow in soils with double the limit of salinity of normal varieties, but does not produce edible rice. Developed by the [[International Rice Research Institute]], the [[Hybrid (biology)|hybrid]] variety utilises specialised leaf glands that remove salt into the atmosphere. It was produced from one successful [[embryo]] out of 34,000 crosses between the two species; this was then [[Backcrossing|backcrossed]] to IR56 with the aim of preserving the genes responsible for salt tolerance that were inherited from ''O. coarctata''.
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=== Cold tolerance ===
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Rice is sensitive to temperatures below 12C. Sowing takes place once the daily average temperature is reliably above this limit. Average temperatures below that reduce growth; if sustained for over four days, germination and seedling growth are harmed and seedlings may die. In larger plants subjected to cold, rice blast is encouraged, seriously reducing yield. As of 2022, researchers continue to study the mechanisms of chilling tolerance in rice and its genetic basis.
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=== Reducing methane emissions ===
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Producing rice in [[Paddy field|paddies]] is harmful for the environment due to the release of methane by [[Methanogen|methanogenic bacteria]]. These bacteria live in the anaerobic waterlogged soil, consuming nutrients released by rice roots. Putting the [[barley]] gene ''SUSIBA2'' into rice creates a shift in biomass production from root to shoot, decreasing the methanogen population, and resulting in a reduction of methane emissions of up to 97%. Further, the modification increases the amount of rice grains.
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'''C4 rice''' is a proposed rice that uses [[C4 photosynthesis]]. It is currently in development by the C4 Rice Consortium.
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=== Model organism ===
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Rice is used as a [[model organism]] for investigating the mechanisms of [[meiosis]] and [[DNA repair]] in higher plants. For example, study using rice has shown that the gene ''OsRAD51C'' is necessary for the accurate repair of DNA double-strand breaks during meiosis.
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{{Anchor|Culture}}
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== In human culture ==
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[[File:COLLECTIE TROPENMUSEUM Beeld van Dewi Sri de rijstgodin TMnr 60016918.jpg|thumb|upright|Ancient statue of the rice goddess [[Dewi Sri]] from Java ({{Circa|9th century}}) ]]
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Rice plays an important role in certain religions and popular beliefs. In Hindu wedding ceremonies, rice, denoting fertility, prosperity, and purity, is thrown into the sacred fire, a custom modified in Western weddings, where people throw rice over the wedded couple. In Malay weddings, rice features in multiple special wedding foods such as sweet glutinous rice. In Japan and the Philippines, rice wine is used for weddings and other celebrations. [[Dewi Sri]] is a goddess of the Indo-Malaysian archipelago, who in myth is transformed into rice or other crops. The start of the rice planting season is marked in Asian countries including Nepal and Cambodia with a [[Royal Ploughing Ceremony]].
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* [[Artificial rice]]
* [[Direct seeded rice]]
* [[List of rice dishes]]
* [[Rice Belt]]
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{{Cookbook|Rice}}
{{Varieties of rice}}
{{Cereals}}
{{Rice dishes}}
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[[Category:Rice|Rice]]
[[Category:Crops originating from China]]
[[Category:Grasses of Asia]]
[[Category:Plant models]]
[[Category:Types of food]]
[[Category:Tropical agriculture]]
{{二次利用|date=9 June 2025, at 20:40}}
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