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Wednesday, 16 October 2013

Rice (Oryza sativa and Oriza glaberrima)

Rice is the most widely consumed staple food of the world’s, especially in Asia. Rice is the seed of the Rice Plant a monocot plant that have two main species Oryza sativa (Asian rice) and Oriza glaberrima (African rice). This plant is origin to China (Pearl River valley) and spread to Southeast and South Asia since 1500 BC. Rice introduced to Europe through Western Asia. European colonization then bring it to Americas.

Rice cultivation is also one of the most important human civilizations, now rice cultivation become the second largest food plant cultivation after maize (corn), and rice is the most important carbohydrate source of worldwide humans. 

The importance of rice for mankind was illustrated from so much research projects and development of the quality and quantity of rice production, continues holds either by the various state agencies, universities and world research institutes such as the International Rice Research Institute (IRRI). IRRI is an international independent research and training organization with headquarters in Los Banos, Laguna in the Philippines. This organization has offices in sixteen countries.

Characteristic of the tree:

Rice or Paddy included in the tribe or Poaceae grains. Terna season, fibrous roots, stems very short. Similar structures formed from a series of rods that support each leaf midrib between the leaf midrib perfect and upright. Lancet-shaped leaves, light green to dark green, parallel veined leaves, covered with short hairs and sparse, composed of compound interest section, type branched panicles, flowers called florets units located on a single spikelet sitting on paniculate.

Seed and Reproduction:

Type of grain or fruit that cannot be distinguished caryopsis where fruits and seeds, nearly spherical to oval shapes, sizes 3mm to 15mm, covered by paleas and lemma which in everyday language is called chaff, the dominant structure of ordinary rice is kind endosperm.

Each rice flower has six anthers (anthers) and the stigma (stigma) forked shaped bottlebrush. Both of these sexual organs are generally sexually mature at the same time. Anthers sometimes out of the paleas and lemma if it has been ripe. In terms of reproduction, rice is self-pollinating plant, because 95% or more pollen to fertilize the same egg plant. Once fertilization occurs, the zygote and the fertilized polar nuclei divide immediately.

Form a zygote develops into an embryo and endosperm polar nuclei. At the end of development, most of the rice grains starchy endosperm section. For young plants, starch is used as a source of nutrition.

Genetics and breeding:

A set of rice genome consists of 12 chromosomes. Because rice is a diploid plant, each cell has 12 pairs of chromosomes of rice (except sex cells). Rice is a model organism in plant genetics study, was based for two reasons: its importance to humankind, and the relatively small size of the chromosomes, which is 1.6 ~ 2.3 × 108 base pairs (base pairs, bp). As a model plant, rice genome has been sequenced, as well as the human genome. Genetic improvement of rice has been going on since humans cultivate rice. The result of this action is the knowledge of a variety of local races, such as 'Rajalele' from Klaten or 'Pandanwangi' of Cianjur in Indonesia or 'Basmati Rice' from northern India.

New rice breeding systematically carried out since the establishment of IRRI in the Philippines as part of a world movement of agricultural modernization, dubbed as the Green Revolution. Since then comes the variety of rice cultivars with high yield to feed the world. The first two modern rice cultivars is 'IR5' and 'IR8'. Thousands of crosses then designed to produce cultivars with high yield potential and resistance to various pests and diseases of rice.

Since the 1970s have sought the development of hybrid rice, which has a higher yield potential. Due to the high cost of manufacture, this type cultivars are sold at higher prices than rice cultivars that are assembled with other methods.

In addition to improved yield potential, rice-breeding objectives also include the plants that are more resistant to a variety of plant pests and pressure (stress) a biotic (such as drought, salinity, and acid soils). Breeding aimed at improving the quality of rice was also performed, for examples by designing cultivars that contain carotene (pro vitamin A).

The presence of biotechnology and genetic engineering in the 1980s allows improvement of rice quality. A number of research teams in Switzerland developed transgenic rice that can produce toxins for pest-eating grain in the hope of lowering the use of pesticides.

IRRI, in collaboration with several other institutions, assemble "golden rice" (Golden Rice) which can result in provitamin A in rice, which is directed to the alleviation of vitamin A deficiency in developing countries. A team of Japanese researchers are also developing rice that produces cholera toxin to bacteria. Paddy rice produced expected this to be an alternative immunization cholera, especially in developing countries.

Genetic diversity :

Until now there are two species of mankind cultivated rice in bulk : Oryza sativa originating from Asia and O. glaberrima originating from West Africa .

In the early O. sativa is considered consists of two subspecies , indica and japonica ( synonym sinica ) . Japonica rice are generally long-lived , high but easy posture fall , lemmanya has a " tail " or " feather " ( awn ) , seeds tend to be rounded , and sticky rice . Indica rice , by contrast , shorter-lived , smaller stature , the lemma is not her " fur " or just short , and grains tend to be oval to oblong . Although both members of this subspecies can fertilize each other , is not a high percentage of success . Famous example of this is the result of crossing cultivars ' IR8 ' , which were selected from crosses japonica ( cultivar ' Deegeowoogen ' of Formosa ) and indica ( cultivar ' Map ' of Indonesia) . In addition to these two varieties , known javanica minor varieties which have the properties of the two main types above . Javanica varieties are only found on the island of Java.

Study with the help of molecular biological techniques have now shown that in addition to the two subspecies of O. sativa, indica and japonica, but there is also a minor subspecies be adaptive based on location. The subspecies mentioned are such as Upland rice from Bangladesh, royada (tidal swamp rice from Bangladesh), Ashina (tidal rice from India), and aromatic (fragrant rice from South Asia and Iran, including the famous basmati rice). This grouping is done using RFLP marker assisted with isozyme.

Genetic studies using SSR markers to the cell nucleus and two genomic loci on the chloroplast genome suggests that indica and japonica differentiation is steady, but it turns out japonica typically divided into three groups: temperate japonica ("japonica cool region" of China, Korea, and Japan), tropical japonica ("japonica tropical regions" of the archipelago), and aromatic. Subspecies aus a separate group.

Based on the evidence of the molecular evolution estimated indica and japonica groups separately since 440,000 years ago from an ancestral species populations of O. rufipogon. Rice domestication occurred in different places point to separate the two groups who had this. Based on archaeological evidence of rice began to be cultivated (domesticated) 10,000 to 5,000 years BC.

Continuous struggle of humankind to find the best rice varieties will never stop, along with increased consumption of these carbohydrates in the world that is inversely proportional to the area of agricultural land continues to decline.

There are about 723 metric tons worldwide rice production in the recent years with China, India, Indonesia, Bangladesh, and Vietnam in the five biggest rice producers of the world.

Scientific classification:

  • Kingdom         : Plantae (Plants)
  • Subkingdom    : Tracheobionta (Vascular Plants)
  • Super Division: Spermatophyta (Produces seeds)
  • Division          : Magnoliophyta (flowering plants)
  • Class               : Liliopsida (dashed one / monocot)
  • Sub Class       : Commelinidae
  • Order              : Poales
  • Family            : Poaceae (grasses tribe)
  • Genus             : Oryza
  • Species            : Oryza sativa,Oriza glaberrima