In this essay we will discuss about:- 1. Distribution of Rice 2. Cultivated Species of Rice 3. Origin and Evolution 4. Reproduction and Pollination 5. Breeding Objectives 6. Breeding Procedures 7. Breeding Centres 8. Achievements.
Essay on Rice
Essay # 1. Distribution of Rice:
Rice is an important cereal food crop of global significance. It belongs to the family Gramineae. It is grown in humid tropical and subtropical climates. The major rice growing countries are China, India, Japan, Pakistan, Southeast Asia and Brazil.
Rice is one of the principal food crops of the world. In India, rice is grown in almost all the states. South and South-east Asia is considered as the primary centre of diversity of cultivated rice. North eastern and Southern China constitutes the primary centre of diversity of cultivated rice.
Essay # 2. Cultivated Species of Rice:
There are two cultivated species of rice, viz. Asian rice (Oryza sativa L.) and African rice (Oryza glaberrima). Both the species are diploid (2n = 24). Asian rice is the predominant species which has spread to different parts of the world. The African rice is still confined to tropical west Africa.
There are three races of Asian rice, viz. Indica, Japonica and Javanica. Indica is grown in tropical climate, Japonica in the temperate region and the race Javanica is intermediate between Indica and Japonica. There are 22 wild species of rice which are found in the tropics of the world. Out of these, 8 are tetraploid species (2n = 4x = 48). Wild species are utilized in breeding programmes for transfer of various desirable characters to the cultivated species.
Essay # 3. Origin and Evolution of Rice:
It is generally believed that the Asian rice (O. sativa) has originated in Asia from the perennial Asian wild species O. rufipogon. The African cultivated species (O. glaberrima) is believed to have originated in West Africa from wild species O. breviligulata. Still there is controversy about the progenitor of Asian rice. Some researchers believe that Asian rice has originated from perennial wild species, while others consider annual form as the ancestor of cultivated rice.
Essay # 4. Reproduction and Pollination of Rice:
Rice propagates by sexually produced seeds. Rice is an autogamous (self-pollinated) crop. Cross pollination is less than 2 per cent. Apomixis is absent. Tillering is an important feature of rice crop. An isolation distance of 3 metres is absolutely safe for the production of breeder and foundation seeds.
Essay # 5. Breeding Objectives in Rice:
In rice, the main breeding objectives are higher grain yield, wider adaptation, better quality, early maturity, resistance to biotic (diseases and insects) and abiotic stresses (drought, salinity, lodging etc.). The important yield contributing characters are panicle length, number of grains per panicle (fertile florets per panicle), numbers of productive tillers per plant and test weight.
Quality includes milling, cooking and processing characteristics. Moreover, shape, size, colour and texture decide the grain quality. Protein and lysine contents also determine the quality of rice. In rice, fragrance is also an important quality attribute. Major diseases of rice are, blast, bacterial blight, stem rot, brown spot, virus diseases etc.
Among the insects, stem borers, brown plant hopper, gandhi bug and Gall fly are the major ones. Cooking qualities include kernel elongation, volume expansion, water absorption, gel consistency, aroma, amylose content and gelatinisation temperature.
Essay # 6. Breeding Procedures in Rice:
Breeding methods which are commonly used for genetic improvement of rice can be divided into two groups, viz.:
(1) General methods, and
(2) Special methods.
General methods include introduction, pure line selection, backcross method, pedigree method and bulk breeding method.
Special breeding methods include mutation breeding, heterosis breeding and distant hybridization. Mutation breeding has played significant role in rice improvement. In India, several improved varieties of rice have been developed through mutation breeding. The important rice varieties released through mutation breeding are Biraj, CNM 6, CNM 20, CLM 25, CLM 31, Jagannath, Au 1, Au 4, K 84, Hybrid mutant, Mohan, Padmini, Rasmi, Sattari, PL 56, I.I.T. 60, Indira and Prabhavati.
Hybrid rice has been developed for commercial cultivation in China through the use of cytoplasmic genetic male sterility. Wild species have not been used extensively in breeding programmes. Tissue culture technique has played significant role in rice improvement. In China, 8 varieties of rice have been developed for commercial cultivation by anther culture technique.
Biotechnology is expected to play an important role in future in rice improvement by creating vast genetic variability for various economic characters. The somaclonal variation may help in developing resistant cultivars for biotic and abiotic stresses, besides early maturing cultivars.
Essay # 7. Breeding Centres in Rice:
International Rice Research Institute (IRRI), Philippines, serves as a world centre for the genetic improvement of rice. It also serves as a global centre of gene bank of rice. Various International varietal improvement programmes are carried out by IRRI. This Institute deals with global improvement of tropical rice with special emphasis on Asia.
In India, rice breeding work is carried out by Central Rice Research Institute, Cuttack (Orissa), Directorate of Rice Research, Hyderabad, (Andhra Pradesh), State Agricultural Universities, and Private registered seed companies. New varieties are released through All India Coordinated Rice Improvement Project (ACRIP) which is located at Hyderabad in the form of Directorate of Rice Research.
Essay # 8. Practical Achievements of Rice:
IRRI has played significant role in the genetic improvement of rice. Several semi-dwarf, high yielding, varieties with wider adaptation have been released by IRRI for different countries. The Chinese Indica line Dee Geo-woo-gen has been used as a source of dwarfing gene in evolving semi-dwarf varieties of rice.
Evolution of semi-dwarf varieties resulted in green revolution in rice. Important rice varieties developed by IRRI include, IR 8, IR 20, IR 22, IR 24, IR 26, IR 28, IR 29, IR 30, IR 32, IR 34 and IR 36. Out of these, IR 8, IR 20 and IR 36 have been released for India. In China, hybrid rice using cytoplasmic genetic male sterility system has been developed for commercial cultivation.
Hybrid rice has also been developed in India by Directorate of Rice Research, Hyderabad. However, its commercialization will take some more time. In India, more than 100 improved varieties of rice for different states have been released by CRRI. DRR and State Agricultural Universities.
The bacterial blight resistant varieties developed by IRRI and salinity resistant, scented and high yielding varieties developed for cultivation in India are listed below:
1. Bacterial Blight Resistant Varieties:
IR 20, IR 22, IR 26. IR 28, IR 29, IR 30, IR 32 and IR 34.
2. Salinity Resistant Varieties:
Usar Dhan 1 (U.P.), PVR 1 (Tamil nadu), MCM 1, MCM 2 (A.P.) Bhurarata, Kalarata (Maharashtra), Korekagga, Bilikagga (Karnataka), Damodar, Getu, Dosal, Nanobokhra, Nonasail, Rupsail (West Bengal), Pokkai and Chotupokkali (Kerala).
3. Scented Varieties:
Type 3, N 12, N 10 (B), Kasturi, Pusa, Basmati.
4. High Yielding Varieties:
IR 8, IR 20, IR 36, Vikas, Savitri, Anamika, Mansarovar etc.
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