Plant Breeding Practices in Wheat
Triticum aestivum L. 2n= 6x=42)
Wheat ranks with rice in importance as world crop. Wheat, rice and corn together makeup ¾ the of the world grain population. In India productivity of wheat is 2150 kg /ha from 26 million hectares the worldwide importance of wheat can be realized from symbols of world organization like FAO ( Food and Agriculture Organization Rome) UNDP ( International Wheat and Maize Improvement Center, Mexico). It is world’s most widely cultured crop occupying 22% cultivated areas. Wheat crop is harvested some where in the world as far south as Argentina to as far north as Finland. It is the major crop of USA, Canada and Asia, it is C3 crop not well adapted to tropical and subtropical condition. It is cultivated on large scale in Punjab, Haryana, U.P, M.P, Bihar, Rajasthan, Gujarat and Maharashtra.
Wheat is evolved from wild grasses. The centre of origin is South Asia. Tegri- Euphatis drainage basin. Large genetic variability is observed in Iran, Isreal, and Bordering countires.
Wheat can be crossed with Aegilops and Agropyron species successfully. Man made hybrid, Triticale is the cross between wheat (Triticum monococum) and Rye ( Cecale Cereals).
There are 13 diploid, 12 tetraploid and hexaploid species of Triticum with genotypes given below:
2n =- 42
2n =- 42
Triticum monococum X Unknown wheat
(2n=14, AA) (2n-14,BB)
F1, (AB) Spontaneous chromosome doubling
Tetraploid wheat X Aegilops squrrosa or T. tauschii
(2n-28 AABB) (2n-14, DD)
F1 (ABD) Spontaneous chromosome doubling
Hexaploid wheat (2n=42, AABBDD)
Bread wheat or common wheat, Triticum aestivum.
Wheat is self pollinated crop due to chasm gamy. Blooming starts several days after the emergence of spike from flag leaf. Starts in the main stem (Mother tiller) followed by other tillers in the order of development. Flowering in the upper part of the spike and proceeds in both the directions. Blooming is continued throughout the day, and 3-5 days are required to complete. The cross pollination may take place to the extent of 1-2%. The immature anthers are green in colour, which turn yellowish when matured. The stigmatic lobs are closed together when young but spread out maturity. The lodicules absorb moisture and swell due to which glumes are separated apart in 20 minutes. Filament elongate and anther dehisce within 2 to 3 minutes. At the same time stigma is recessive. The glumes are again closed at the end of 15 to 20 minutes.
1) High grain yield,
2) Early maturity,
3) Photo and thermo insensitive varieties
4) Resistance to disease like rust, smut and leaf spots.
5) Response to high doses of fertilizers
6) Dwarf and lodging resistant varieties.
The spike enclosed in leaf sheath or partially emerged is selected for emasculation. The awns and tips of spiklets are cut off to avoid obstacle in the process of emasculation and pollination, similarly the central sterile flower also removed with forceps. The requisite numbers of spikelet are kept on the spike and with the half of forceps the glumes are separated and three young immature greenish yellow anthers are removed from each flower and the flower bagged.
On the next morning between 9.00 to 11.00 am the pollen grain collected desired protected plant in petridish and dusted on stigma of emasculated flower with the help of hair brush. The spike is covered with bag after pollination and labelled again.
The green revolution is successful in the world due to introduction of Norin-10 variety (dwarfing gene) developed in Japan. The variety Norin-10 was never important variety in Japan. The seed sample received in 1946 to Washington State University and Crosses were made in 1948 worht Brevor – 14 and the genotype become main source of two Norin-10 dwarfing gene. Then Dr. N.E. Borlaug ( Father of green revolution) who engineered development of semi dwarf wheat. Or his work he was awarded a Nobel peace Prize in 1970. In India, the dwarf wheat varieties were importance from Mexico, Sonoro-64, and Larma Rojo- 64 A in 1965-66. Latter on made green revolution successful India.
2) Pure Line Selection:
In this method individual progenies are evaluated and promising progenies are finally selected old Indian tall varieties E.g. N-P-4, N-P-6, N-P-12, PB-12, PB-11 were developed by pure line selection.
The most common method used in self pollinated crops is pedigree method of selection. The crosses are made between complimentary lines and records are maintained of selections made over number of generations. The procedure provide selection opportunities generation after generations. It allow breeder to identify bet combination with considerable uniformity. The hybrid bulk selection method is relatively inexpensive, in which generations are advanced without selection till F5 to F6 and much material can be handled, nut often difficulty is isolation of superior recombination. To overcome, this difficulty single decent method of selection is used in which population remain constant over segregation generations.
Varieties: a) Tilmely sown: NIAW-34, NIAW-301, NIAW-2496, HD-2278, HD-2189.
b) Late Sown : HD-2501, Sonalika, HI-977, etc.
Back Cross Method:
This method is used when variety otherwise is good, high yielding but deficient in simply inherited trait. The obvious effect of this method the production potential of improved variety is fixed at the level of recurrent variety. Recently identified donors always are used in back cross breeding programme.
Stem Rust: Resistance gene- Sr2 From variety Hope.
Leaf Rust: Resistance gene – Lr 13 from variety Sonalika
It is extension of back cross breeding and could be called Multilateral backcrossing. It consist of spontaneous back cross programme to produce isogenic lines for resistance to disease, in back ground of some recurrent parent. Each isogenic line will be similar to recurrent parent but they will differ for resistance to various physiological farms of diseases. A mixture of these isogenic lines is called multiline variety. E.g. ML-KS-11 (PAU, Ludhiana) and Bithoor developed at CSAUAT, Kanpur.
This method is used in depleted gene pool situation. Chemical mutagenes EMS provide broad spectrum genetic changes with lesser sterility effects, as compared to X ray or particular mutation. Varieties developed are 1) NP836, Sarbati Sonora, Pusa larma, etc. are examples of induced mutation and NP-11 is the examples of spontaneous mutation.
Hybrid Wheat Breeding:
Hybrid wheat breeding is not commercially successful through cytoplasmic genetic male sterile lines are available due to following problems.
1) Inadequate heterosis over wide range of environment.
2) Inadequate genetically controlled fertility restoration.
3) High cost of hybrid seed production.
In vitro production of haploids- Anther or pollen culture is used to produce the haploid plants. The frequency of obtaining haploids increase when anthers are treated with cold socks and heat treatments. The haploids when treated with colchicines, the homozygous diploid line can developed in short period and can be used in hybrid breeding programme. The plantlets can be tested in vitro for different stresses drought, salt, disease etc. to evaluate before field screening.
International wheat and maize development center- Mexico- It has 20 substations in the world.
United Nation Development Programme- Washington, financed by World Bank.
All India coordinated wheat Improvement Project Established – 1965 New Delhi IARI.
Wheat Project Directorate- Established -1991. Shifted to Karnal- Multidisciplinary multilicational Research Programme.
ARS Mahabaleshwar, ARS Niphad, MKV Parbhani, PDKV Akola, ARS Wasim and MACS Pune.