Rice

I

Introduction

Rice, common name for over 100 species of the genus Oryza in the grass family. Common or cultivated rice (Oryza sativa) is an economically important crop that is the staple food for almost one half of the world’s population. It is native to the tropics and sub-tropics, and according to the United Nations Food and Agriculture Organization (FAO) may have been cultivated for more than 15,000 years, in east and south Asia. Most rice is grown on flooded land (paddy fields); however, there are varieties of rice that are suitable for drier conditions, such as those found in the Middle East and Africa. FAO figures show that world production of paddy rice in 2003 was 589 million tonnes; of this, 92 per cent was grown in Asia.

Rice takes between three to six months to reach maturity, depending on location and variety, and achieves a height of about 1 m (3 ft), with flowers bearing six stamens and a solitary pistil. The FAO estimates that it takes 2,000 litres of water to produce 1 kg (2.2 lb) of paddy rice, and thus effective water supplies and irrigation systems are necessary for its production. The fruit, a grain, is produced on a nodding inflorescence (flower cluster) of spikelets at the top of the stalk. When the grain is ripe, rice resembles the oat plant. The white endosperm is enclosed by a layer of bran surrounded by a brown husk.

Rice grains are extensively used as human food; according to the International Rice Commission, rice is the staple food for 3 billion people. The bran of the rice grain contains oils, B vitamins, and minerals. White rice, which is rice from which the bran has been removed, is less nutritious, and diet of white rice can cause deficiency diseases such as beriberi. White rice contains mainly carbohydrate; small amounts of iodine, iron, magnesium, and phosphorus; and almost negligible amounts of protein and fat.

In eastern Asia, starch is sometimes extracted from rice and fermented to produce rice wine. Unlike most other cereals, rice is rarely made into bread; it is generally eaten boiled and flavoured according to custom. Rice grain is not commonly used as feed for farm animals; its by-products, however (meal, bran, or rice polish), are used as feed, especially in rice-growing areas. The straw is also fed to livestock.

In early 2005, through the International Rice Genome Sequencing Project, a complete and highly accurate sequence of the japonica rice genome was made available. Rice has important syntenic relationships with the other cereal species and is a model plant for the grasses. It has the smallest genome of all the cereals: 430 million nucleotides. This makes rice a good entry point for characterizing the genes of other cereals, and associating them with various agronomic traits.

II

Cultivation

Rice is cultivated in most countries of eastern Asia. Egypt and the countries of southernmost Europe, the southern United States, and Brazil are other important rice-producing regions. Wetland or paddy rice, commonly grown in lowland areas, requires a very moist soil, either rain-fed or artificially flooded. A few dry-land varieties, often grown on higher land, do not require flooding. In the rice-growing developing countries, a lot of cultivations are still performed by hand. In more developed countries, including the more developed Asian nations, much of the work is aided by the use of machinery. Paddy rice is kept under water during most of the growing season. It is drained only at harvest time. In favourable conditions, rice needs only about three months between sowing and harvesting, and three or even four crops can be harvested annually. Rice mills are usually located near the growing regions. Brown rice is dried and cleaned before it is packed. When white rice is desired, the bran is removed in special machines and care is taken not to break the white kernel. The rice kernels are then polished with glucose and talc in order to enhance their appearance.

Rice is classified into three types: short-grain rice, which is no more than 5 mm (‚ in) long; medium-grain rice, which is 5 to 6 mm (‚ in) long; and long-grain rice, which is 6 to 8 mm (€ in) long. The majority of rice varieties grown in tropical regions are long grain, while most of the varieties grown in more temperate climates are short or medium grain.

In the late 1960s, experiments by the International Rice Research Institute produced a variety of rice that promised to increase world output dramatically. Working with dwarf varieties of rice from Taiwan and with disease-resistant, high-yield varieties from other Asian countries, researchers developed a short, vigorous, narrow-leaved rice that yielded more grain and tolerated unfavourable weather better than traditional varieties. The new rice was non-lodging; it did not bend over when ripe and was thus more easily harvested, did not rot because of immersion, and was less subject to rodent damage. Despite initial concerns that these new varieties were biased against small-scale farming (because they require more inputs such as fertilizers than traditional varieties), adoption by farmers in countries such as the Philippines and India was rapid, leading to substantial increases in production. Development and testing of new strains and new cultivating procedures continue in an effort to increase world yield. At present, about 90,000 traditional varieties and wild species of rice are managed by the International Rice Research Institute. See Crop Farming; Food Supply, World.

III

Diseases of Rice

The most serious diseases of rice are seedling blight, leaf and leaf-sheath spots, leaf smut, stem rot, kernel spots, and straighthead. Seedling blight is an infection of seedlings, caused by any of four fungi. Blast, a form of leaf spot caused by a fungus, is one of the most serious rice diseases. Leaf smut, also caused by a fungus, attacks rice in the United States. Stem rot, caused by either of two fungi, attacks the stalks of rice, causing them to break. Several fungi produce discoloration, or spotting, of rice kernels. Straighthead is an important non-fungal disease, characterized by the failure of seemingly healthy plants to develop seeds, and caused by insufficient preparation of the soil. See also Diseases of Plants; Pest Control.

IV

Statistics

Rice production represents 30 per cent of world cereal production today. It has doubled since the mid-1970s, in part due to the introduction of new varieties, but its present growth barely follows consumption: in 2025, there will be 4.6 billion people that depend on rice for their daily nourishment, compared with 3 billion today. FAO data show that, in 2004, the leading rice producers were China (177 million tonnes), India (129 million tonnes), and Indonesia (54 million tonnes). The major rice exporters were Thailand (8.8 million tonnes), Vietnam (3.8 million tonnes), and the United States (3.8 million tonnes).

Scientific classification: Rice makes up the genus Oryza of the family Poaceae (or Gramineae). Common rice is classified as Oryza sativa.

See also Wild Rice.