What is Rice – everything you need to know

What is Rice

Rice is one of the most important grains and food items in the world. Half of the world’s population depends on rice as a staple food. There are currently “tens of thousands of types of rice” in the world, but they are two general main categories of rice.

Evidence suggests that rice originated in the Pearl River Valley of China between 1300 and 13500 years ago. Earlier, archeological documents speculated that rice was domesticated in the Yangtze River Valley in China. Rice spread from East Asia to the southern regions and South Asia. Rice introduced to Europe and the United States by European colonizers from West Asia.


rice field

Rice is a plant that has early cultivars (growth period 130 to 145 days), medium growth (150 to 160 days) and late cultivars (170 to 180 days). To better understand the rice plant, we will mention its different parts such as roots, stems, leaves, etc.:


Rice roots are shallow and diffuse and penetrate to a maximum depth of 20 to 25 cm into the soil. In this plant, in addition to embryonic roots, roots also arise from the nodes. The higher the growth of the leaves, the higher the growth of the roots, and as a result, if the number of tillers increases, the number of leaves increases, and as a result, the growth of the roots increases.

When the flowers open and the rice clusters, the root growth has its maximum value.


Rice Cluster

American long stem rice

The rice stem is closed and hollow, and at different distances from the stem, there are hard walls in which the stem is solid and is called a node. The distance between two nodes calls the node. There is a lot of intercellular space between the stem cells, which provides some of the oxygen needed by the roots through the pores. The leaves of this plant are elongated and have parallel veins and are without petioles and the base of the leaf is wider than other parts of it; It surrounds part of the plant stem or the entire perimeter of the plant, which calls the pod or pod.

At the base of the leaf on the sides of the pod are two small or large plates called stipules. There is also a small appendage calls the ligule at the junction of the pod with the stem. Also, the number of nodes in this plant varies from 10 to 20. At equal levels of leaf area index (LAI), long-stemmed shrubs can make better use of light but are easily wilted. The height of rice plants in different cultivars varies from 50 to 150 cm and sometimes up to 200 cm.


The leaves of this plant are alternate and are located on opposite sides of the stem. The number of leaves varies in different rice cultivars, in early cultivars it is 14 to 15 leaves, in medium cultivars it is 16 to 17 leaves and in late cultivars the number of leaves is 18 to 19 leaves per stem. Increasing the ambient temperature has a decisive effect on increasing the leaf area and increases the number of leaves. At equal levels of leaf area index (LAI), plants with smaller and larger leaves are better than plants with large and small leaves.


The claws are called primary buds, which turn into stems if the weather conditions are right. From 4 to 5 leaves, the tillering plant begins. In the early stages of growth, the tillers use the main stem to supply their food, and this process continues until at least 3 leaves and 4 roots appear. When the seedlings are transferred from the nursery to the main land, tillering begins and continues for a month. At the end of one month, the growth of the claws reaches its maximum and after that, their number will decrease. Climatic conditions, especially climate, are very important and effective in the growth of tillers. The power of claw production in rice is so high that each rice plant usually produces 4 to 5 paws.

Inflorescence building

what is rice

The inflorescence in rice is in the form of a panicle and the difference with the inflorescence of the cluster is that in the panicle each cluster has a narrow and long tail and for this reason it is also called a cluster. Panicles in different rice cultivars are compact, open or semi-open. Of course, from the point of view of plant breeders, they are better at producing hybrids and erites whose flowers are more open, because the amount of metamorphosis and consequently their seed production is higher.

Rice panicle is located at the end of the stem and has sub-branches with secondary axes. Clusters form on two short flowers, the tip of which develops on infertile glomeruli (sterile lamellae) and become concave; Therefore, the cup-shaped and swollen tip is similar to a pair of real glomeruli and is called true glomerulus. Each cluster has a small axis called the axis of the spike, on which a flower forms on the axis of the leaf blade, which is called infertile glomeruli. Flowering in rice starts from the tip of the inflorescence and continues downwards. At the time of cluster emergence, the roots need a lot of nutrients, especially nitrogen, phosphorus and potash.

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Flower building in rice

Inflorescence in rice is clustered and has sub-branches and contains single-flowered spikelets. Unlike other grains that have 3 to 4 flags, rice has 6 flags. The umbilicus is short and the anthers are double and have a female that contains an ovary. The stigma has two branches and feathers. The female has a single-leafed ovary. The upper leaf, or flowering glume, forms a flower (glomer or spike cover on which the apricot grows) and the palea (glume, which does not have an apricot), forms a flower with the enclosed flower. Around each flower there are two leaves called Glumelle, one called Lemma and the other Palea.

There are also two leaves at the end of each spike called a glume. In rice, the glomeruli are very small and may even sometimes be omitted. The length of the outer glomeruli is 1.4 Lama and Palea and in some varieties it is the same size as Lama and Palea. Generally, Lama has an aura and Palea has no aura. 7 to 9 days after flowering, the aleurone layer is formed by the deformation of the outer layer of endocrine tissue.

Pollination and fertilization

Rice is a plant in itself and has between zero and 3% metamorphism. Pollination occurs almost simultaneously with the opening of the flowers under natural conditions. The optimum temperature for pollination is about 31 to 32 degrees Celsius. Pollution stops at temperatures below 10 to 13 ° C and also above 60 ° C. Dryness and low temperatures can adversely affect pollination. The minimum temperature for fertilization is 15 degrees Celsius. The flowers open from 8 am to 2 pm and the inflorescences open in a period of 7 to 10 days, and most of them do this 2 to 4 days after the inflorescence leaves the leaf sheath.

Global rice varieties

Global rice varieties

There are more than 120,000 varieties of rice in the world. The European Union and the customs authorities of the member countries have classified and separated the rice species for assessment and collection of import duties between 5,000 and 18,000 (Germany).

Major species

Javanese species

Japanese species

Indian species

Iranian white rice

From the Iranian species, we can mention pollen, Dabo, Tarom, Charam 1, Charam 2, Sadri (including black tails, yellow tails and red tails), Binam, Ali-Kazemi, Champa, etc. Among the improved and productive types, we can mention Neda. , Sefidrood and Caspian.

Rice cultivars in the northern region of Iran:

Iranian Rice

In the plain areas of Mazandaran province, such as the paddy fields of Fereydunkenar, Babolsar, Mahmoudabad, Noor, Joybar counties, more traditional and high quality cultivars such as (local Tarom or Sang Tarom), Hashemi and Binam are cultivated and high yielding cultivars such as Shiroodi, Fajr, Khazar and Neda are more cultivated in paddy. The cities of Babol, Amol, Sari, Neka and Behshahr are cultivated.

In Gilan province, there are Indian cultivars such as Gharib, Hashemi, Hassani and Gardeh, which seem to be the result of traditional selection by farmers (and possibly a number of researchers) in each of the plains and valleys of Gilan province, respectively. The areas around the cities of Soomehsara, Fooman, and Talesh have been developed over time.

A type of rice that has been cultivated for many years in the Sirvan region of Ilam is called Anbarbo rice, which is very fragrant but because of the area of ​​cultivation. It may not have been sold in bulk, but it has been exported to Iraqi Kurdistan and Tehran for several years. Also, in the western part of Isfahan and Zayandehrud, a brass called Lenjan is cultivated, which is tall and irregular when cooked. Its color is slightly yellowish and it has a special taste and aroma. Due to recent droughts, rice cultivation in Isfahan has decreased slightly.

Characteristics of native rice types

What do you know about rice?

Numerous indigenous types of rice are more distinct than any of the native Japanese, Javanese, and Indian varieties. Factors that induce differentiation of native species and indigenous types should depend on the environmental factors of their plant habitats.

Differences in light and heat sensitivity in flowering, resistance to dehydration in growth, resistance to large amounts of fertilizers and salts in the culture medium, resistance to flood tolerance, resistance to high and low temperatures, etc. have been identified in native species. In addition, morphological characteristics of grain size and size are considered as a reliable primary indicator of native species. The distinctions of such features can be recognized among the six indigenous types mentioned. At present, however, one researcher has stated that this index is not always sufficient to classify the three native species.

Rice grain dimensions and size

Interesting tips about rice

In general, one of the salient differences between Indian, Javanese and Japanese cultivars is the grain shape. Following Kato’s (1930) report on grain shape in Hindi and Japanese, Matsu endorsed three grain types: 1) short, 2) large, and 3) long. These three seed species were shown in Japanese, Javanese and Indian, respectively. Most Indian rice grains are slender and large, and Japanese rice grains have small, short grains with a round cross section.

Most cultivars of India, Indochina, South China, Taiwan and the Philippines are Indian (Type C). Many cultivars of Java, North and West China, Europe, the United States, and most Japanese rainfed rice belong to Java (type B). Japanese blue rice and Manchurian cultivars are very similar to Japanese (type A). Watab and Akihama studied the shape of ancient rice grains grown in Burma, Thailand and Colombia. They suggested the existence of early cultivars in the foothills of the Himalayas that did not distinguish between Indian and Japanese. They also consider the origin of crop rice. As mentioned above, short-grain cultivars such as Boro have been approved in the native Indian variety. There is a theory that shows a specific differentiation of grain shape in native varieties of Asian rice that may be due to the response to temperature differences in them.

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Suitable conditions for rice cultivation



The average temperature required for rice to grow should be between 20 and 37 degrees Celsius. Low temperatures early in the growing season or irrigating the field with cold water can delay seed ripening. High temperature also reduces the number of fertile spikelets and seed weight.


Light is also one of the effective factors in plant growth. So, Light intensity early in the growing season may be a limiting factor for rice growth. But as the crop season draws to a close, especially when clusters form, competition for light absorption between plants increases.


The most suitable moisture content for flowering rice plant is 70 to 80%. Humidity below 40% is a deterrent to flowering. Wind and rain and hail are harmful during flowering. Rainfall at harvest also delays the drying process. Rice is generally considered a hydrophilic plant, but it is not aquatic. Because the roots of aquatic plants are not able to produce deadly fibers and sub-roots. While rice root has both lethal fibers and secondary roots.


Rice needs more water than other grains. Eighty percent of the water needed for rice production in the world, especially in the tropics, comes from rainwater. The remaining 20% ​​comes from river water and well water. The results show that if the water temperature is less than 19 degrees Celsius, the grain ripening time is delayed. If it is more than 30 degrees, the root growth and yield of the rice plant will decrease due to the limited oxygen in the water, and the yield of the plant will decrease.


Rice is grown in different soils, from poor to rich, which provide only the water needed by the plant. Of course, the amount of water used in light soils is more than heavy soils. The most suitable soil for rice cultivation is clay soil with an impermeable layer at a depth of 50 to 150 cm and with a large amount of organic matter. Rice is generally resistant to soil salinity and water salinity. If there is enough water to wash the soil salt, rice can be used to improve saline soils.

Planter tools

Summer seedlings are machines or devices that transfer plant seedlings to the ground mechanically (automatically or semi-automatically). The high accuracy of planting seedlings, both in depth and in the distances between rows, as well as the speed of their transfer to the soil, increases yield and also significantly reduces labor costs. One of the important parameters in selecting seedlings (multi-row seedlings) is the spacing between rows. Achieving the minimum distance between rows is always one of the limitations of production.

The second parameter is the efficiency of the device or the number of seedlings planted per hour. In rotating seedlings, the number of cups or holes on the distributor is very important in the speed of the machine. So that distributions with six or eight cavities, in addition to slower speeds than twelve distributions, sometimes in cases where short planting distances (about 30 to 40 cm) are required, disrupt the movement of the tractor so that the tractor is continuous.

Move-in half-clutch mode to reduce the speed of the device and consequently the speed of rotation of the distributor and the operator of the transplanting machine has the opportunity to drop the seedlings inside the cups. Another parameter is the direction of seedling movement. Planters that move in the opposite direction of the tractor, allow the operator to see the field and how to plant to make the necessary changes in the planter settings if necessary.

type of rice

Reflection of the effect of temperature on growth

Thermal reflectance of tropical cultivars, such as seed germination, tillering, seedling growth, growth time and stem length, as far as is known, are very different from cultivars in temperate regions. However, the relationships between native species and temperature reflectance in growth, and tillering capacity in six native Indian and Japanese cultivars in different combinations of light and temperature in well-controlled growth chambers were studied.

Kaki Zaki suggested that at low light intensities and at low temperatures, regardless of the indigenous type, the rate of tillering at low temperatures was higher than the incidence of leaflet jaundice at low temperatures (15 ° C) among the six native Asian types. , Os, Tajre, Bolo, and Japanese cultivars were tested. Aws and Tajra became very yellow. Japanese and Bolo, especially Japanese at low temperatures, showed more tolerance to jaundice. Boro was the middle type between Bolo and Os or Tajre.

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