Rice
Rice is a
Many varieties of rice have been bred to improve crop quality and productivity. Biotechnology has created Green Revolution rice able to produce high yields when supplied with nitrogen fertilizer and managed intensively. Other products are rice able to express human proteins for medicinal use; flood-tolerant or deepwater rice; and drought-tolerant and salt-tolerant varieties. Rice is used as a model organism in biology.
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
Production of rice is estimated to have caused over 1% of global greenhouse gas emissions in 2022. Rice yields are predicted to fall by some 20% with each 1°C rise in global mean temperature. In human culture, rice plays a role in certain religions and traditions, such as in weddings.
Description
The rice plant can grow to over 1 m (3 ft) tall; if in deep water, it can reach a length of 5 m (16 ft). A single plant may have several leafy stems or
Rice is a cereal belonging to the family
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Detail of rice plant showing flowers grouped in panicle. Maleanthers protrude into the air where they can disperse their pollen.
Agronomy
Growing
Like all crops, rice depends for its growth on both biotic and abiotic environmental factors. The principal biotic factors are crop variety, pests, and plant diseases. Abiotic factors include the soil type, whether lowland or upland, amount of rain or irrigation water, temperature, day length, and intensity of sunlight.[5]
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 kg of grain per hectare, while transplanting needs less, around 40 kg per hectare, but requires far more labour.
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Ploughing a rice terrace withwater buffaloes, Java
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Farmers planting rice by hand in Cambodia
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Mechanised rice planting in Japan
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Ancient mountainside rice terraces at Banaue, Philippines
Harvesting
Across Asia, unmilled rice or "paddy" (Indonesian and Malay padi), was traditionally the product of
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Rice combine harvester in Chiba Prefecture, Japan
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After the harvest, rice straw is gathered in the traditional way from small paddy fields inMae Wang District, Thailand
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Drying rice in Peravoor, India
Evolution
Phylogeny
The edible rice species are members of the
Poaceae |
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History
Cultivation, migration and trade spread rice around the world—first to much of east Asia, then further abroad, and eventually to the Americas as part of the Columbian exchange after 1492.[20] The now less common Oryza glaberrima (African rice) was independently domesticated in Africa around 3,000 years ago,[20] and introduced to the Americas by the Spanish.[21]
Commerce
Rice production – 2021 | |
---|---|
Country | Millions of tonnes |
China | 213 |
India | 195 |
Bangladesh | 57 |
Indonesia | 54 |
Vietnam | 44 |
Thailand | 30 |
World | 787[22] |
Production
In 2021, world production of rice was 787 million tonnes, led by China and India with a combined 52% of the total.[22] This placed rice fourth in the list of crops by production, after sugarcane, maize, and wheat.[23] Other major producers were Bangladesh, Indonesia and Vietnam.[23] 90% of world production is from Asia.[24]
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Production of rice (2021)[23]
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Rice's share (orange) of world crop production fell in the 21st century.
Yield records
The average world yield for rice was 4.7 metric tons per hectare (2.1 short tons per acre), in 2022.[25] Yuan Longping of China's National Hybrid Rice Research and Development Center set a world record for rice yield in 1999 at 17.1 metric tons per hectare (7.6 short tons per acre) on a demonstration plot. This employed specially developed hybrid rice and the System of Rice Intensification (SRI), an innovation in rice farming.[26]
Food security
Rice is a major food staple in Asia, Latin America, and some parts of Africa,[27] feeding over half the world's population.[24] 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 mould fungi if the rice is not dried sufficiently. In China, losses in modern metal silos were just 0.2%, compared to 7–13% when rice was stored by rural households.[28]
Processing
The dry grain is milled to remove the outer layers, namely the
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Rice processing removes one or more layers to create marketable products.
A: Rice with chaff
B: Brown rice
C: Rice with germ
D: White rice with bran residue
E: Polished
(1): Chaff
(2): Bran
(3): Bran residue
(4): Cereal germ
(5): Endosperm
Trade
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.[33] 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.[34]
Worldwide consumption
As of 2016, the countries that consumed the most rice were China (29% of total), India, and Indonesia.[35] By 2020, Bangladesh had taken third place from Indonesia. On an annual average from 2020-23, 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.[36]
Food
Nutritional value per 100 g (3.5 oz) | |
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Energy | 544 kJ (130 kcal) |
28.6 g | |
0.2 g | |
2.4 g | |
Niacin (B3) | 3% 0.4 mg |
Pantothenic acid (B5) | 8% 0.41 mg |
Vitamin B6 | 4% 0.05 mg |
Folate (B9) | 1% 2 μg |
Minerals | Quantity %DV† |
Calcium | 0% 3 mg |
Iron | 2% 0.2 mg |
Magnesium | 4% 13 mg |
Manganese | 18% 0.38 mg |
Phosphorus | 5% 37 mg |
Potassium | 1% 29 mg |
Sodium | 0% 0 mg |
Zinc | 4% 0.4 mg |
Other constituents | Quantity |
Water | 69 g |
†Percentages estimated using US recommendations for adults.[37] |
Eating qualities
Rice is commonly consumed as food around the world. The
Nutrition
Cooked white rice is 69% water, 29%
Golden rice
Golden rice is a variety produced through
Rice and climate change
Greenhouse gases from rice
In 2022,
Effect of global warming on rice
A 2010 study found that, as a result of rising temperatures and decreasing solar radiation during the later years of the 20th century, the rice yield, measured at over 200 farms in seven Asian countries, decreased by between 10% and 20%. This may be caused by increased night-time respiration.[50][51] 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.[52][53]
In the Po Valley in Italy, the arborio and carnaroli risotto rice varieties have suffered poor harvests through drought in the 21st century. The Ente Nazionale Risi is developing drought-resistant varieties; its nuovo prometeo variety has deep roots that enable it to tolerate drought, but is not suitable for risotto.[54]
Pests, weeds, and diseases
Pests and weeds
Rice yield can be reduced by weed growth, and a wide variety of pests including insects, nematodes, rodents such as rats, snails, and birds.
Diseases
Rice blast, caused by the fungus Magnaporthe grisea, is the most serious disease of growing rice.[59] It and
Pest management
Farmers in China, Indonesia and the Philippines have traditionally managed weeds and pests by the polycultural practice of raising ducks and 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.[67][68]
Rice plants produce their own chemical defences to protect themselves from pest attacks. Some synthetic chemicals, such as the herbicide 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.[69] 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.[70]
Plant breeders have created rice cultivars incorporating
Ecotypes and cultivars
The
The complete genome of rice was sequenced in 2005, making it the first crop plant to reach this status.[76] 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.[77]
Biotechnology
High-yielding varieties
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".[78] 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 fertilizer.[78]
Expression of human proteins
Flood-tolerant rice
In areas subject to
Drought-tolerant rice
The
Salt-tolerant rice
Soil salinity poses a major threat to rice crop productivity, particularly along low-lying coastal areas during the dry season.[83][87] For example, roughly 1 million hectares (2.5 million acres) of the coastal areas of Bangladesh are affected by saline soils.[88] 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.[89]
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.[90] O. coarctata can grow in soils with double the limit of salinity of normal varieties, but does not produce edible rice.[90] Developed by the International Rice Research Institute, the 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 backcrossed to IR56 with the aim of preserving the genes responsible for salt tolerance that were inherited from O. coarctata.[89]
Environment-friendly rice
Producing rice in paddies is harmful for the environment due to the release of methane by 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.[91][92]
Model organism
Rice is used as a model organism for investigating the mechanisms of meiosis and DNA repair in higher plants.[93] For example, study using rice has shown that the gene OsRAD51C is necessary for the accurate repair of DNA double-strand breaks during meiosis.[94]
In human culture
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.[95] In Malay weddings, rice features in multiple special wedding foods such as sweet glutinous rice.[96] In Japan and the Philippines, rice wine is used for weddings and other celebrations.[97] Dewi Sri is a goddess of the Indo-Malaysian archipelago, who in myth is transformed into rice or other crops.[98] The start of the rice planting season is marked in Asian countries including Nepal and Cambodia with a Royal Ploughing Ceremony.[99][100][101]
See also
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Further reading
- Liu, Wende; Liu, Jinling; Triplett, Lindsay; Leach, Jan E.; Wang, Guo-Liang (August 4, 2014). "Novel insights into rice innate immunity against bacterial and fungal pathogens". S2CID 9244874.
- Deb, D. (October 2019). "Restoring Rice Biodiversity". Scientific American. 321 (4): 54–61.
India originally possessed some 110,000 landraces of rice with diverse and valuable properties. These include enrichment in vital nutrients and the ability to withstand flood, drought, salinity or pest infestations. The Green Revolution covered fields with a few high-yielding varieties, so that roughly 90 percent of the landraces vanished from farmers' collections. High-yielding varieties require expensive inputs. They perform abysmally on marginal farms or in adverse environmental conditions, forcing poor farmers into debt.
- Singh, B. N. (2018). Global Rice Cultivation & Cultivars. New Delhi: Studium Press. ISBN 978-1-62699-107-1. Archived from the originalon March 14, 2018. Retrieved March 14, 2018.