Everything about Rice totally explained
Domesticated
rice comprises two
species of
food crops in the
Poaceae ("true grass") family,
Oryza sativa and
Oryza glaberrima. These
plants are native to tropical and subtropical southern
Asia and southeastern
Africa. (The term "
wild rice" can refer to the wild species of
Oryza, but conventionally refers to species of the related genus
Zizania, both wild and domesticated.) Rice is grown as a
monocarpic annual plant, although in tropical areas it can survive as a
perennial and can produce a
ratoon crop and survive for up to 20 years. Rice can grow to 1–1.8 m tall, occasionally more depending on the variety and
soil fertility. The grass has long, slender
leaves 50–100 cm long and 2–2.5 cm broad. The small
wind-pollinated flowers are produced in a branched arching to pendulous
inflorescence 30–50 cm long. The edible
seed is a
grain (caryopsis) 5–12 mm long and 2–3 mm thick.
Rice is a
staple for a large part of the world's
human population, especially in the
East,
South and
Southeast Asia, making it the second-most consumed
cereal grain. Rice provides more than one fifth of the
calories consumed worldwide by humans. In early
2008, some governments and retailers began
rationing supplies of the grain due to fears of a global
rice shortage.
Rice
cultivation is well-suited to countries and regions with low
labour costs and high
rainfall, as it's very labour-intensive to cultivate and requires plenty of water for
cultivation. Rice can be grown practically anywhere, even on a steep hill or mountain. Although its species are native to
South Asia and certain parts of
Africa, centuries of trade and exportation have made it commonplace in many cultures.
The traditional method for cultivating rice is flooding the fields with or after setting the young seedlings. This simple method requires sound planning and servicing of the water damming and channeling, but reduces the growth of less robust weed and pest plants that have no submerged growth state, and deters vermin. Whilst with rice growing and cultivation the flooding isn't mandatory, all other methods of irrigation require higher effort in weed and pest control during growth periods and a different approach for fertilizing the soil.
Preparation as food
The seeds of the rice plant are first milled using a
rice huller to remove the
chaff (the outer husks of the grain). At this point in the process, the product is called
brown rice. The milling may be continued, removing the '
bran' (for example the rest of the husk and the
germ), thereby creating
white rice. However the use of
white rice, although more convenient for the food processing industries (white rice keeps longer), and in the eyes of some consumers more 'attractive', has in the past been associated with serious deficiency diseases amongst consumers (see
Beriberi).
Brown rice contains all of the ingredients of a healthy meal, but isn't standard for commercial offerings. The removal of bran was blamed for
Beriberi disease; however, it's possible that
aflatoxins and other
mycotoxins contributed to the problem.
In the future,
parboiling may be used to move some of the nutrients from the bran to the rice corn before stripping off the bran, thereby reducing the loss in nutrition. However, the energy requirements for parboiling are high compared to dry processing technologies.
White rice may be also buffed with glucose or
talc powder (often called
polished rice, though this term may also refer to white rice in general),
parboiled, or processed into
flour. White rice may also be enriched by adding nutrients, especially those lost during the milling process. While the cheapest method of enriching involves adding a powdered blend of nutrients that will easily wash off (in the United States, rice which has been so treated requires a label warning against rinsing), more sophisticated methods apply nutrients directly to the grain, coating the grain with a water insoluble substance which is resistant to washing.
Despite the hypothetical health risks of
talc (such as stomach cancer), talc-coated rice remains the norm in some countries due to its attractive shiny appearance, but it has been banned in some and is no longer widely used in others such as the United States. Even where
talc isn't used, glucose, starch, or other coatings may be used to improve the appearance of the grains; for this reason, many rice lovers still recommend washing all rice in order to create a better-tasting rice with a better consistency, despite the recommendation of suppliers. Much of the rice produced today is water polished.
Rice bran, called
nuka in
Japan, is a valuable commodity in Asia and is used for many daily needs. It is a moist, oily inner layer which is heated to produce an oil. It is also used as a pickling bed in making
rice bran pickles and
Takuan.
Raw rice may be ground into
flour for many uses, including making many kinds of
beverages such as
amazake,
horchata,
rice milk, and
sake. Rice flour is generally safe for people on a
gluten-free diet. Rice may also be made into various types of
noodles. Raw wild or brown rice may also be consumed by raw foodist or fruitarians if soaked and sprouted (usually 1 week to 30 days).
Processed rice seeds are usually boiled or steamed to make them edible, after which they may be fried in
oil or
butter, or beaten in a tub to make
mochi.
Although rice is a good source of protein and a staple food in many parts of the world, it isn't a
complete protein. That is, it doesn't contain all of the essential amino acids in sufficient amounts for good health, and should be combined with other sources of protein, such as nuts, seeds, soybeans or meat.
Rice, like other
cereal grains, can be
puffed (or popped). This process takes advantage of the grains'
water content and typically involves heating grain pellets in a special chamber. Further puffing is sometimes accomplished by processing pre-puffed pellets in a low-
pressure chamber. The
ideal gas law means that either lowering the local pressure or raising the water
temperature results in an increase in
volume prior to water
evaporation, resulting in a puffy
texture. Bulk raw rice density is about 0.9 g/cm³. It decreases more than tenfold when puffed.
Cooking
Rice is cooked by
boiling or
steaming. It can be cooked in just enough water to cook it through (the absorption method), or it can be cooked in a large quantity of water which is drained before serving (the rapid-boil method). Electric
rice cookers, which are popular in Asia and Latin America, simplify the process of cooking rice.
In
Arab cuisine rice is the ingredient of many soups and dishes with fish, poultry and meat. It is also used to stuff vegetables or is wrapped in grape leaves. When combined with milk, sugar and honey, it's used to make desserts. In some regions, such as
Tabaristan, bread is made using rice flour. Medieval Islamic texts spoke of medical uses for the plant.
Also extremely popular are combination cooking methods; for example
fried rice is boiled (or steamed) rice that has afterwards been stir-fried in oil.
Rice may also be made into
rice porridge (also called congee or rice gruel) by adding more water than usual, so that the cooked rice is saturated with water to the point that it becomes very soft, expanded, and fluffy. Rice porridge is commonly eaten as a breakfast food, and is also a traditional food for the sick.
Rice may be soaked prior to cooking, which decreases cooking time. For some
varieties, soaking improves the texture of the cooked rice by increasing expansion of the grains.
In some culinary traditions, especially those of
Latin America,
Italy, and
Turkey, dry rice grains are
fried in
oil before cooking in water.
In some countries, rice is commonly consumed as
parboiled rice, also known as
Minute rice or easy-cook rice. Parboiled rice is subjected to a steaming or parboiling process while still a brown rice. This causes nutrients from the outer husk to move into the grain itself. The parboil process causes a gelatisisation of the starch in the grains. The grains become less brittle, and the colour of the milled grain changes from white to yellow. The rice is then dried, and can then be milled as usual or consumed as brown rice. Milled parboil rice is nutritionally superior to standard milled rice. Parboiled rice has an additional benefit in that it doesn't stick to the pan during cooking as happens when cooking regular white rice.
A nutritionally superior method of preparing brown rice known as
GABA Rice or GBR (Germinated Brown Rice) may be used. This involves soaking washed brown rice for 20 hours in warm water (38
°C or 100
°F) prior to cooking it. This process stimulates
germination, which
activates various
enzymes in the rice. By this method, a result of research carried out for the
United Nations Year of Rice, it's possible to obtain a more complete
amino acid profile, including
GABA.
Cooked rice can contain
Bacillus cereus spores which produce an
emetic toxin when left between 4-60 degrees Celsius
(External Link
). When storing cooked rice for use the next day, rapid cooling is advised to reduce the risk of contamination.
Production history
Etymology
According to the
Microsoft Encarta Dictionary (2004) and the
Chambers Dictionary of Etymology (1988), the word
rice has an
Indo-Iranian origin. It came to
English from
Greek óryza, via
Latin oriza,
Italian riso and finally
Old French ris (the same as present day
French riz).
It has been speculated that the Indo-Iranian
vrihi itself is borrowed from a Dravidian vari (< PDr. *warinci) or even a Munda language term for rice or the
Tamil name
ar-risi from which the
Arabic ar-ruzz, from which the
Portuguese and
Spanish word
arroz originated.
Genetic history
Two species of rice were
domesticated, Asian rice (
O. sativa) and African rice (
O. glaberrima). According to Londo and Chiang,
O. sativa appears to have been domesticated from wild (Asian) rice,
Oryza rufipogon around the
foothills of the
Himalayas, with
O. sativa var.
indica on the
Indian side and
O. sativa var.
japonica on the
Chinese and
Japanese side. The different histories have led to different ecological niches for the two main types of rice. Indica are mainly lowland rices, grown mostly submerged, throughout tropical Asia, while japonica are usually cultivated in dry fields, in temperate East Asia, upland areas of Southeast Asia and high elevations in South Asia. (Oka 1988)
Current genetic analysis suggests that
O. sativa would be best divided into five groups, labeled indica, aus, aromatic, temperate japonica and tropical japonica. The same analysis suggests that
indica and
aus are closely related, as are
tropical japonica,
temperate japonica, and
aromatic. Further analysis of the genetic material of various types of rice indicates that
japonica was the first cultivar to emerge, followed by the
indica, aus, and
aromatic groups, whose genome did show significant differences in age. Within the
japonica group, there's some genetic evidence that
temperate japonica is derived from
tropical japonica.
Other studies have suggested that there are three groups of
Oryza sativa cultivars: the short-grained "japonica" or "sinica" varieties, exemplified by
Japanese rice; the long-grained "
indica" varieties, exemplified by
Basmati rice; and the broad-grained "javonica" varieties, which thrive under tropical conditions (Zohary and Hopf, 2000). The earliest find site for the japonica variety, dated to the
5th millennium BCE, was in the earliest phases of the
Hemudu culture on the south side of
Hangzhou Bay in
China, but was found along with japonica types.
Global history and methodology of cultivating rice
South Asia
According to the Encyclopædia Britannica:
The origin of rice culture has been traced to India in about 3000 BCE. Rice culture gradually spread westward and was introduced to southern Europe in medieval times. With the exception of the type called upland rice, the plant is grown on submerged land in the coastal plains, tidal deltas, and river basins of tropical, semitropical, and temperate regions. The seeds are sown in prepared beds, and when the seedlings are 25 to 50 days old, they're transplanted to a field, or paddy, that has been enclosed by levees and submerged under 5 to 10 cm (2 to 4 inches) of water, remaining submerged during the growing season.
Wild rice appeared in the Belan and
Ganges valley regions of
northern India as early as 4530 BCE and 5440 BCE respectively. Agricultural activity during the second millennium BC included rice cultivation in the
Kashmir and
Harrappan regions. Mixed farming was the basis of
Indus valley economy. Farmers planted their crops in integrated fields. Rice, grown on the west coast, was cultivated in the Indus valley. Rice, along with barley, meat, dairy products and fish constituted the dietary staple of the ancient
Dravidian people.
There is mention of ApUpa, Puro-das and Odana (rice-gruel) in the
Rig Veda, terms that refer to rice dishes, The rigvedic commentator
Sayana refers to
"tandula" when commenting on RV 1.16.2., which means rice. The Rigvedic term
dhana (dhanaa, dhanya) means rice. Both
Charaka and
Sushruta mention rice in detail. The
Arthasastra discusses aspects of rice cultivation. The
Kashyapiyakrishisukti by
Kashyapa is the most detailed ancient Sanskrit text on rice cultivation.
Continental East Asia
Z. Zhao, a Chinese
palaeoethnobotanist, hypothesizes that people of the
Late Pleistocene began to collect wild rice. Zhao explains that the collection of wild rice from an early date eventually led to its domestication and then the exclusive use of domesticated rice strains by circa 6400 BC at the latest. Stone tool evidence from the Yunchanyan site in
Hunan province suggests the possibility that Early
Neolithic groups cultivated rice as early as circa 9000 BC. Crawford and Shen point out that calibrated radiocarbon dates show that direct evidence of the earliest cultivated rice is no older than 7000 BC.
Jared Diamond, a biologist and popular science author, summarizes some of the research done by archaeologists and estimates that the earliest attested domestication of rice took place in China by 7500 BC.
An early archaeological site from which rice was excavated is
Pengtoushan in the
Hupei basin. This archaeological site was dated by AMS radiocarbon techniques to 6400–5800 BC (Zohary and Hopf 2000), but most of the Neolithic sites in China with finds of charred rice and radiocarbon dates are from 5000 BC or later. This evidence leads most archaeologists to say that large-scale dry-land rice farming began between 5000 and 4500 BC in the area of
Yangtze Delta (for example
Hemudu culture, discovered in 1970s), and the wet-rice cultivation began at approximately 2500 BC in the same area (
Liangzhu culture). It is now commonly thought that some areas such as the alluvial plains in
Shaoxing and
Ningbo in
Zhejiang province are the cradle-lands of East Asian rice cultivation. Finally, ancient textual evidence of the cultivation of rice in China dates to 3000 years ago.
Bruce Smith of the
Smithsonian Institution advises caution on the Chinese rice hypothesis. No morphological studies have been done to determine whether the grain was domesticated. The media reports of the Soro-ri charred grains are brief and lack sufficient detail for archaeologists and scientists in related fields to properly evaluate the true meaning of this unusual find.
Reliable, mainstream archaeological evidence derived from palaeoethnobotanical investigations indicate that dry-land rice was introduced to
Korea and
Japan some time between 3500 and 1200 BC. The cultivation of rice in Korea and Japan during that time 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 isn't 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 (c. 850–550 BC) and reached Japan by the Final Jōmon or Initial
Yayoi circa 300 BC.
Southeast Asia
Rice is the staple for all classes in contemporary
South East Asia, from
Myanmar to
Indonesia. In Indonesia, evidence of wild 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 labour 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 sixteenth 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 fifteen hundred years.
Evidence of wet rice cultivation as early as 2200 BC has been discovered at both Ban Chiang and Ban Prasat in Thailand.
By the 19th Century, encroaching European expansionism in the area increased rice production in much of South East Asia, and Thailand, then known as Siam. British Burma (now Myanmar) became the world's largest exporter of rice, from the turn of the 20th century up till the 1970s, when neighbouring Thailand exceeded Myanmar.
Africa
African rice has been cultivated for 3500 years. Between 1500 and 800 BC,
O. glaberrima propagated from its original centre, the
Niger River delta, and extended to
Senegal. However, it never developed far from its original region. Its cultivation even declined in favour of the Asian species, possibly brought to the African
continent by Arabs coming from the east coast between the 7th and 11th centuries CE.
In parts of Africa under Islam, rice was chiefly grown in southern Morocco. During the tenth century rice was also brought to
east Africa by Muslim traders. Although, the diffusion of rice in much sub-Saharan Africa remains uncertain, Muslims brought it to the region stretching from
Lake Chad to the
White Nile.
Europe
The Muslims (later known as
Moors) brought Asiatic rice to the
Iberian Peninsula in the tenth century. Records indicate it was grown in
Valencia and
Majorca. In the case of Majorca, the rice cultivation stopped after the Christian
conquest, although historians aren't certain.
In the southern United States, rice has been grown in southern
Arkansas,
Louisana, and east
Texas since the mid 1800s. Many
Cajun farmers grew rice in wet marshes and low lying prairies. In recent years rice production has risen in North America, especially in the
Mississippi River Delta areas in the states of
Arkansas and
Mississippi.
Rice cultivation began in
California during the
California Gold Rush, when an estimated 40,000 Chinese laborers immigrated to the state and grew small amounts of the grain for their own consumption. However, commercial production began only in 1912 in the town of
Richvale in
Butte County. By 2006, California produced the second largest rice crop in the United States, after Arkansas, with production concentrated in six counties north of
Sacramento. Unlike the Mississippi Delta region, California's production is dominated by short- and medium-grain
japonica varieties, including cultivars developed for the local climate such as
Calrose, which makes up as much as eighty five percent of the state's crop.
References to wild rice in the Americas are to the unrelated
Zizania palustris
More than 100 varieties of rice are commercially produced primarily in six states (Arkansas, Texas, Louisiana, Mississippi, Missouri, and California) in the U.S.
According to estimates for the 2006 crop year, rice production in the U.S. is valued at $1.88 billion, approximately half of which is expected to be
exported.
The U.S. provides about 12% of world rice trade.
The majority of domestic utilization of U.S. rice is direct food use (58%), while 16 percent is used in processed foods and
beer respectively. The remaining 10 percent is found in pet food.
Australia
Although attempts to grow rice in the well-watered north of Australia have been made for many years, they've consistently failed because of inherent
iron and
manganese toxicities in the soils and destruction by
pests.
In the 1920s it was seen as a possible
irrigation crop on soils within the
Murray-Darling Basin that were too heavy for the cultivation of fruit and too infertile for
wheat.
Because irrigation water, despite the extremely low runoff of temperate Australia, was (and remains) very cheap, the growing of rice was taken up by agricultural groups over the following decades. Californian varieties of rice were found suitable for the climate in the
Riverina, and the first mill opened at
Leeton in 1951.
Even before this Australia's rice production greatly exceeded local needs, and rice exports to Japan have become a major source of foreign currency. Above-average rainfall from the 1950s to the middle 1990s encouraged the expansion of the Riverina rice industry, but its prodigious water use in a practically waterless region began to attract the attention of environmental scientists. These became severely concerned with declining flow in the
Snowy River and the lower
Murray River.
Although rice growing in Australia is exceedingly efficient and highly profitable due to the cheapness of land, several recent years of severe drought have led many to call for its elimination because of its effects on extremely fragile aquatic ecosystems. Politicians, however, have not made any plan to reduce rice growing in southern Australia.
Rice biotechnology
High-yielding varieties
The High Yielding Varieties are a group of crops created intentionally during the
Green Revolution to increase global food production. Rice, like corn and wheat, was genetically manipulated to increase its yield. This project enabled labor markets in Asia to shift away from agriculture, and into industrial sectors. The first ‘modern rice’, IR8 was produced in 1966 at the
International Rice Research Institute. IR8 was created through a cross between an Indonesian variety named “Peta” and a Chinese variety named “Dee Geo Woo Gen.”
With advances in molecular genetics, the mutant genes responsible for reduced height(rht),
gibberellin insensitive (gai1) and slender rice (slr1) in
Arabidopsis and rice were identified as cellular signaling components of gibberellic acid (a phytohormone involved in regulating stem growth via its effect on cell division) and subsequently cloned. Stem growth in the mutant background is significantly reduced leading to the dwarf phenotype. Photosynthetic investment in the stem is reduced dramatically as the shorter plants are inherently more stable mechanically. Assimilates become redirected to grain production, amplifying in particular the effect of chemical fertilizers on commercial yield. In the presence of nitrogen fertilizers, and intensive crop management, these varieties increase their yield 2 to 3 times.
Potentials for the future
As the UN Millennium Development project seeks to spread global economic development to Africa, the ‘Green Revolution’ is cited as the model for economic development. With the intent of replicating the successful Asian boom in agronomic productivity, groups like the
Earth Institute are doing research on African agricultural systems, hoping to increase productivity. An important way this can happen is the production of ‘
New Rices for Africa’ (NERICA). These rices, selected to tolerate the low input and harsh growing conditions of African agriculture are produced by the African Rice Center, and billed as technology from Africa, for Africa. The NERICA have appeared in
The New York Times (
October 10,
2007) and
International Herald Tribune (
October 9,
2007), trumpeted as miracle crops that will dramatically increase rice yield in Africa and enable an economic resurgence.
Golden rice
German and Swiss researchers have
engineered rice to produce
Beta-carotene, with the intent that it might someday be used to treat
vitamin A deficiency. Additional efforts are being made to improve the quantity and quality of other nutrients in golden rice.
Expression of human proteins
Ventria Bioscience has
genetically modified rice to
express lactoferrin,
lysozyme, and
human serum albumin which are
proteins usually found in
breast milk. These proteins have
antiviral,
antibacterial, and
antifungal effects.
Rice containing these added proteins can be used as a component in
oral rehydration solutions which are used to treat
diarrheal diseases, thereby shortening their duration and reducing recurrence. Such supplements may also help reverse
anemia. As a result, the carotene turns the rice gold.
World production and trade
Production and export
World production of rice has risen steadily from about 200 million tons of paddy rice in 1960 to 600 million tons in 2004. Milled rice is about 68% of paddy rice by weight. In the year 2004, the top three producers were China (26% of world production), India (20%), and Indonesia (9%).
World trade figures are very different, as only about 5–6% of rice produced is traded internationally. The largest three exporting countries are
Thailand (26% of world exports),
Vietnam (15%), and the
United States (11%), while the largest three importers are Indonesia (14%), Bangladesh (4%), and Brazil (3%). Although China and India are the top two largest producers of rice in the world, both of countries consume the majority of the rice produced domestically leaving little to be traded internationally.
Price
In the Spring of
2008, the price of rice rose greatly due to a
rice shortage.
In late
April 2008, rice prices hit 24
cents a
pound, twice the price that it was seven months earlier.
On the 30th of
April, 2008,
Thailand announced the project of the creation of the
Organisation of Rice Exporting Countries (OREC) with the potential to develop into a price-fixing
cartel for rice.
Rice consumption around the world
Between 1961 and 2002,
per capita consumption of rice increased by 40%. Rice consumption is highest in
Asia, where average per capita consumption is higher than 80 kg/person per year. In the subtropics such as
South America,
Africa, and the
Middle East, per capita consumption averages between 30 and 60 kg/person per year. People in the developed West, including
Europe and the
United States, consume less than 10 kg/person per year.
Rice is the most important crop in Asia. In Cambodia, for example, 90% of the total agricultural area is used for rice production. See
The Burning of the Rice by Don Puckridge for the story of rice production in Cambodia
(External Link).
U.S. rice consumption has risen sharply over the past 25 years, fueled in part by commercial applications such as
beer production. Almost one in five adult Americans now report eating at least half a serving of white or brown rice per day.
Environmental impacts
In many countries where rice is the main
cereal crop, rice cultivation is responsible for most of the methane emissions. Farmers in some of the arid regions try to cultivate rice using
groundwater bored through pumps, thus increasing the chances of
famine in the long run. Rice also requires much more water to produce than other grains.
Rice pests
Rice pests are any
organisms or
microbes with the potential to reduce the yield or value of the rice crop (or of rice seeds) (Jahn et al 2007). Rice pests include
weeds,
pathogens,
insects,
rodents, and
birds. A variety of factors can contribute to pest outbreaks, including the overuse of
pesticides and high rates of
nitrogen fertilizer application (for example Jahn et al. 2005)
(External Link). Weather conditions also contribute to pest outbreaks. For example, rice gall midge and army worm outbreaks tend to follow high rainfall early in the wet season, while
thrips outbreaks are associated with drought (
Douangboupha et al. 2006).
One of the challenges facing crop protection specialists is to develop rice pest management techniques which are
sustainable. In other words, to manage crop pests in such a manner that future crop production isn't threatened (Jahn et al. 2001). Rice pests are managed by cultural techniques, pest-resistant rice varieties, and
pesticides (which include
insecticide). Increasingly, there's evidence that farmers' pesticide applications are often unnecessary (Jahn et al.
1996,
2004a,b) (External Link) (External Link) (External Link). By reducing the populations of natural enemies of rice pests (Jahn 1992), misuse of insecticides can actually lead to pest outbreaks (Cohen et al. 1994). Botanicals, so-called “natural pesticides”, are used by some farmers in an attempt to control rice pests, but in general the practice isn't common. Upland rice is grown without standing water in the field. Some upland rice farmers in Cambodia spread chopped leaves of the bitter bush (
Chromolaena odorata (L.)) over the surface of fields after planting. The practice probably helps the soil retain moisture and thereby facilitates seed germination. Farmers also claim the leaves are a natural fertilizer and helps suppress weed and insect infestations (Jahn et al. 1999).
Among rice cultivars there are differences in the responses to, and recovery from, pest damage (
Jahn et al. 2004c, Khiev et al. 2000). Therefore, particular cultivars are recommended for areas prone to certain pest problems. The genetically based ability of a rice variety to withstand pest attacks is called
resistance. Three main types of plant resistance to pests are recognized (Painter 1951, Smith 2005): as nonpreference, antibiosis, and tolerance. Nonpreference (or antixenosis) (Kogan and Ortman 1978) describes host plants which insects prefer to avoid; antibiosis is where insect survival is reduced after the ingestion of host tissue; and tolerance is the capacity of a plant to produce high yield or retain high quality despite insect infestation. Over time, the use of pest resistant rice varieties selects for pests that are able to overcome these mechanisms of resistance. When a rice variety is no longer able to resist pest infestations, resistance is said to have broken down. Rice varieties that can be widely grown for many years in the presence of pests, and retain their ability to withstand the pests are said to have durable resistance. Mutants of popular rice varieties are regularly screened by plant breeders to discover new sources of durable resistance (for example Liu et al. 2005,
Sangha et al. 2008).
Major rice pests include the brown
planthopper(External Link) (Preap et al. 2006),
armyworms(External Link),
the green leafhopper, the rice gall midge (Jahn and Khiev 2004), the
rice bug (Jahn et al. 2004c), hispa (Murphy et al. 2006),
the rice leaffolder,
stemborer, rats (Leung et al 2002), and the weed
Echinochloa crusgali (Pheng et al. 2001). Rice Beevils are also known to be a threat to rice crop. Taiwan is the only known country in which Rice Beevils are inhabitants. Though rare, these small insects can prove devastating to annual rice crop yield.
Rice diseases
Major rice diseases include
Rice Ragged Stunt,
Sheath Blight and
Tungro. Rice blast, caused by the
fungus Magnaporthe grisea, is the most significant disease affecting rice cultivation.
Cultivars
While most breeding of rice is carried out for crop quality and productivity, there are varieties selected for other reasons. Cultivars exist that are adapted to deep flooding, and these are generally called 'floating rice'
(External Link).
The largest collection of rice cultivars is at the
International Rice Research Institute (
IRRI), with over 100,000 rice accessions
(External Link) held in the International Rice Genebank
(External Link). Rice
cultivars are often classified by their grain shapes and texture. For example, Thai
Jasmine rice is long-grain and relatively less sticky, as long-grain rice contains less
amylopectin than short-grain cultivars. Chinese restaurants usually serve long-grain as plain unseasoned steamed rice. Japanese
mochi rice and Chinese
sticky rice are short-grain. Chinese people use sticky rice which is properly known as "glutinous rice" (note: glutinous refer to the glue-like characteristic of rice; doesn't refer to "gluten") to make
zongzi. The
Japanese table rice is a sticky, short-grain rice. Japanese
sake rice is another kind as well.
Indian rice cultivars include long-grained and aromatic
Basmati (grown in the North), long and medium-grained
Patna rice and short-grained Masoori. In South India the most prized cultivar is 'ponni' which is primarily grown in the delta regions of
Kaveri River.
Kaveri is also referred to as ponni in the South and the name reflects the geographic region where it's grown. In the Western Indian state of
Maharashtra, a short grain variety called
Ambemohar is very popular. this rice has a characteristic fragrance of Mango blossom.
Aromatic rices have definite aromas and flavours; the most noted cultivars are Thai fragrant rice, Basmati, Patna rice, and a
hybrid cultivar from America sold under the trade name, Texmati. Both Basmati and Texmati have a mild
popcorn-like aroma and flavour. In Indonesia there are also
red and
black cultivars.
High-yield cultivars of rice suitable for cultivation in
Africa and other dry
ecosystems called the
new rice for Africa (NERICA) cultivars have been developed. It is hoped that their cultivation will improve
food security in
West Africa.
Draft
genomes for the two most common rice cultivars,
indica and
japonica, were published in April 2002. Rice was chosen as a
model organism for the biology of grasses because of its relatively small genome (~430 mega
base pairs). Rice was the first crop with a complete genome sequence. Basmati rice is the oldest, common
progenitor for most types.
On
December 16,
2002, the
UN General Assembly declared the year 2004 the International Year of Rice. The declaration was sponsored by more than 40 countries.
Further Information
Get more info on 'Rice'.
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