In this essay we will discuss about:- 1. Distribution of Wheat 2. Cultivated Species of Wheat 3. Origin and Evolution 4. Reproduction and Pollination 5. Breeding Objectives 6. Breeding Procedures 7. Breeding Centres 8. Achievements.
Essay on Wheat
Essay # 1. Distribution of Wheat:
Wheat is an important cereal crop of cool climates. It belongs to the family Gramineae. It is widely grown the world over and stands first among cereals in area and production. Wheat is cultivated in USA, U.K. Russia, Ukrain, China, Japan, Argentina, Canada, Mexico, India, Pakistan and many other countries.
In India, Uttar Pradesh, Madhya Pradesh, Punjab, Haryana, Rajasthan, Bihar and Gujarat are the major wheat growing states. Wheat is used for human consumption in a variety of products such as bread, cakes, noodles, cookies, chapati, macaroni etc., in various countries. The South Western Asia (Iran, Iraq, Afghanistan) is considered to be the centre of origin and genetic diversity of wheat.
Essay # 2. Cultivated Species of Wheat:
There are two cultivated species of wheat, viz. common wheat (Triticum aestivum) and durum wheat (T. turgidum L.). Common wheat is hexaploid (2n = 6x = 42), whereas duram wheat is tetraploid (2n= 4x = 28). The former is more widely adapted than the latter. Common wheat is used for bread, cakes, noodles, cookies, chapati etc., whereas the durum wheat is used mainly for macaroni and some flat bread.
There are 16 wild species of wheat, out of which six are diploids (2n = 14), seven tetraploids (2n = 4x = 28), and three hexaploids (2n = 6x = 42). Wild species are used in hybridization programmes for transfer of resistance to biotic and abiotic factors, adaptation and other desirable characters into cultivated species.
Essay # 3. Origin and Evolution of Wheat:
Near East is the centre of origin of bread wheat. It is believed that evolution of common wheat in nature took place in two important steps. First an amphidiploid tetraploid species originated from a cross between two diploid species one with A genome and other with B genome.
The amphidiploid after crossing with a diploid species with D genome gave birth to the common wheat as given below:
The chromosome doubling took place in nature in above crosses. The other two forms of hexaploid wheat, viz. T. compactum and T. spherococcum originated through spontaneous mutations of T. aestivum. The durum wheat probably originated from cultivated emmer wheat (T. turgidum var dicoccum) after several spontaneous mutations.
Essay # 4. Reproduction and Pollination of Wheat:
Wheat is a seed propagated and self-pollinated crop. Cross pollination is less than one per cent. The sexually produced seeds are used for propagation and apomixis does not occur. Wheat has bisexual flowers. Flowers generally open after the pollination is over. This chasmogamous behaviour promotes autogamy.
Tillering is a common feature of wheat crop. An isolation distance of 3 metres is absolutely safe for the production of breeder and foundation seeds. The flower is covered by two membraneous structures. The outer is called lemma and the inner as palea.
Essay # 5. Breeding Objectives in Wheat:
In wheat, the major breeding objectives include, higher grain yield, wider adaptation, better quality, early maturity, resistance to biotic (diseases and insects) and abiotic (drought, salinity, lodging etc.) factors. The important components of grain yield are ear length, kernels per ear, number of productive tillers per plant and kernal (seed) size.
Quality characters include grain colour, size and lustre, protein content, lysine content etc. The main diseases for which genetic resistance is required are black or stem rust, brown or leaf rust, yellow or stripe rust, loose smut, hill bunt, Karnal bunt, powdery mildew and leaf blight. In India, insects are not the serious problem. In USA, Hessian fly, stem sawfly and green bugs are the major insect pests of wheat crop.
Essay # 6. Breeding Procedures of Wheat:
Breeding methods which are used for genetic improvement of wheat crop can be divided into two groups, viz.:
(1) General methods, and
(2) Special methods.
General methods include introduction, pure line selection, backcrossing, pedigree breeding, single seed descent, bulk breeding and multiline breeding.
Special methods include wide crosses, mutation breeding and heterosis breeding. Wide crossing is used for transfer of desirable genes from alien germplasm. Mutation breeding is used for developing new varieties as well as creating variability. In USA and Japan, hybrid wheat has been developed using CGMS system. However, commercial exploitation of hybrid wheat needs further research.
Recently recurrent selection has been successfully used for improvement of protein content, kernel size and number of tillers besides earliness. Jensen (1970) suggested the use of diallel selective mating system (DSM) for genetic improvement of wheat. This is a modified form of recurrent selection which permits incorporation of several parents in the hybridization programme.
This technique helps in breaking linkage blocks and creating vast genetic variability. In future, biotechnology especially tissue culture is expected to play an important role in creating somaclonal variation for resistance to biotic and abiotic stresses, besides early maturity.
Essay # 7. Breeding Centres of Wheat:
International programmes of wheat improvement are carried out by the International Maize and Wheat Improvement Centre (CIMMYT), Mexico. International multi-locational testing is carried out by CIMMYT for identification and release of varieties for different countries. The global gene poll of wheat is also maintained at this centre.
In India, wheat breeding work is carried out by State Agricultural Universities and Directorate of Wheat Research, Karnal. The new varieties are released through coordinated project after multi-location testing for 3-5 years. Earlier the All India Coordinated Wheat Improvement Project (AICWIP) was located in IARI campus, New Delhi till 1991. In 1992 it was shifted from New Delhi to Karnal.
Essay # 8. Practical Achievements on Wheat:
Remarkable work on wheat breeding has been done by CIMMYT which led to green revolution in wheat production the world over. The semi-dwarf varieties of wheat have been developed through the use of Japanese line Norin 10 as a source of dwarfing gene. The semi dwarf varieties developed by CIMMYT at Mexico have spread to different wheat growing countries resulting in revolution in wheat production.
The productivity of semi-dwarf varieties is about two and half times more than old tall growing varieties. Moreover, semi-dwarf varieties are highly resistant to lodging and are highly responsive to fertilizer doses. In India, several high yielding varieties of wheat have been released for different states through coordinated project.
Some high yielding varieties of common wheat for different situations are listed below:
1. Irrigated Timely Sown (Punjab, Haryana, Western U.P., Rajasthan):
HD 2329, HD 2009, HD 2428, PBW 154, CPAN 3004
2. Irrigated Late Sown (Above 4 States):
HD 2285, HD 2270, PBW 226, PBW 138
3. Rainfed Timely Sown (Above States):
C 306, WL 410, IWP 72, PBW 65, PBW 175, WL 2265
4. Salt Affected Soils:
WH 157, KRL 1-4
5. Hilly Regions (U.P., J&K and H.P.):
CPAN 1796, HD 208, HD 2380, HS 240, UP 1109
Varieties of durum wheat are PBW 34, PBW 215 and Raj 1555 for irrigated timely sown areas and JK 12 for rainfed timely sown areas.
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