Plant breading or crop improvement : Crop improvement is related with the development of improved and new crop varieties that are superior to existing ones.
Objectives of crop improvement—
(i) To increase the crop yield.
(ii) To improve the crop quality.
(iii) To develop crops which are resistant to diseases, insects, drought, frost, floods etc.
(iv) To develop fast maturing crops.
(v) To produce dwarf kinds of crops.
Plant Introduction : This is the process of introducing high yielding varieties of plants to new localities from their native place.
Principles of Plant Breeding
Following breeding principles are used for the improvement of crops—
1. Selection
(a) Natural Selection
(b) Artificial Selection
(c) Mass Selection
d) Pure line Selection
(e) Conal Selection
(f) Bud Selection
2. Hybridization
(a) Intravarietal Hybridization
(b) Intervarietal hHydridization
(c) Intrageneric Hybridization
(d) Inter generic Hybridization
3. Polyploid Breeding
(a) Autopolyploidy
(b) Allopolyploidy
4. Induced Mutation
5. Tissue Culture
6. Genetic Engineering.
Details of these are given below—
1 (a) Natural Selection : This is based on—‘Survival of the fittest’. According to this law only the fittest can survive and the rest will die out. This process has proved very useful.
1 (b) Artificial Selection : Artificial selection is the one in which desirable plants are selected. Such a selection is made to get better crops.
1 (c) Mass Selection : In this the selection is made from the bulk of plants. The best and the most vigorous plants are selected.
1 (d) Pureline Selection : In this the desirable homozygous individuals from the mixed population are separated and the selected plants are used to develop a better variety.
1 (e) Clonal Selection : Desirable clones are selected from the mixed population of vegetatively propagated crop. This is particularly useful for sugarcane, banana, sweet potato, mango, onion, etc. Clonal selection has proved very useful.
1 (f) Bud Selection : It is a kind of clonal selection where the unit of selection is a bud. This is used for the improvement of fruits. Main fruits are mangoes, oranges etc.
2. Hybridization : Two genetically unlike plants obtained for crossing, is called hybrid. The process of the development of these hybrid plants is known as hybridization.
2 (a) Intravarietal hybridization: Two plants of the same variety when crossed between with different genotypes is called intravarietal hybridization.
2 (b) Intervarietal hybridization: This is also called intraspecific hybridization. This is a cross between two different varieties of the same species.
2 (c) Interspecific hyridization : This is also called intrageneric hybridization. The cross between two different species of the same genus is called inter-specific hybridization.
2 (d) Inter generic hybridization : This is also called wide cross hybridization. In this a cross between two plants of different genera belonging to the same family is done.
Procedure of hybridization
1. Selection of parents : Locally available healthy plants with desired characters are to be selected as parents for crossing (Both male and female).
2. Selfing of parents (inbreeding) : In order to eliminate undesired characters and to increase homozygosity in parents they are self pollinated.
3. Emasculation : The process of removing stamens from the female parent before the dehiscence of anthers is called emasculation.
4. Bagging : After emasculation the flowers of female parent are kept enclosed in bags in order to prevent pollination with unknown pollen.
5. Artificial cross pollination : The bags of the emasculated flowers are temporarily removed, and the pollen grains collected from the male parent are dusted on the stigma of the female parent. These flowers are again covered immediately after artificial cross pollination.
6. Harvesting the seeds and raising of F1 plants : After the formation of seeds the bags are removed. The seeds are sown in the next season and F1 generation hybrid plants are raised.
7. F2 generation : F2 generation plants are produced by selfing F1 hybrids. From F2 generation, plants with desirable characters are identified and subsequent generations are developed by various methods.
3. Polyploid Breeding : The production of polyploidy for improvement of crops, is called polyploid breeding. This is of two types—
(a) Autopolyploidy : In this the chromosomes sets are all of the same kind as they are derived from the same species.
(b) Allopolyploidy : Allopoly-ploidy is one in which different kinds of chromosomes are derived from two or more species by hybridization.
4. Induced Mutations : Artificial mutations in organisms are called induced mutations. For mutations X-rays, ultraviolet rays, gamma rays, etc. are used.
5. Tissue culture : In this technique a tissue of a plant is cultured on a culture medium and entire plant can be obtained. This was invented by Steward in 1950. Through this technique new plants are developed.
6. Genetic Engineering : In this recombined DNA is developed by introducing desired DNA segment of one cell to the other. It forms a recombinant DNA.
In India plant breeding started in the beginning of 20th century by Howard. He was a British scientist. It was started on wheat and sugarcane. Some Indian scientists like Venkata Raman, B.P. Pal, Ramdhan Dhawan, et al. came in this field only in the second decade.
Acclamatization : It is the adjustment of an individual plant in the changed conditions of climate. It is a kind of natural process.
Achievements of Plant Breeding
1. Crops : Indian economy has been considerably affected by introducing plant breeding in several crops. These are maize, potato, sweet potato, coffee, cinchora, pumpkin, groundnut, chillies, pimento, Ipecac, willows, etc. In these some are agricultural crops and others are industrial crops.
2. Fruits : Many fruits like guava, grape fruits, custard apple, pineapple, papaya, pumpkin, cashewnut, cacao, chiku (sapota), litchi, loquat, tomato were imported in the past and are contributing a lot of wealth of fruit industry to the country.
3. Ornamentals : Many ornamentals such as peltophorum, Cassia, Quisqualis, Colvillea, gulmohar, aster, snapdragon, etc. are foreign introduction which today enhance the beauty of gardens all over the country.
New strains of crops : Plant Introduction Division of I.A.R.I. has introduced many varieties of crops and vegetables and tested them under Indian conditions. Several of them have been found useful for direct utilization and have drawn the attention of farmers.
Some promising strains are given below cropwise :
(i) Wheat : ‘Ridley’, a wheat variety introduced from Australia is very popular among hill farmers and covers thousands of acres of area in the hilly regions of Punjab, Himachal Pradesh and Uttar Pradesh.
(ii) Sonara-63 and Sonara–64 : These are the Mexican wheat varieties introduced by I.A.R.I. in 1962. These gave 5,000 to 6,000 pounds yield per acre during 1965 and are still under cultivation.
(iii) Oat : ‘Kent’, a type of milling oat from Australia has proved very good for cultivation in India for use by the breakfast food industry.
(iv) Cow-pea : Three grain varieties, viz. ‘Branco’ from Brazil and ‘E.C. 4211’ and ‘Cream-pea’ from America and two fodder varieties viz. B.C. 4216 and E.C. 4893 from America have been found very suitable for cultivation in different seasons in India.
(v) Peas : ‘Mahndordet’, white and bold seeded and ‘Rimpus’, blue and round seeded, varieties were originally introduced from Germany and are considered very useful for the harvest of dry peas to use in processing.
(vi) Rice bean : Two green-seeded varieties, one from Russia (E.C. 12436) and the other from China (E.C. 16167), were introduced and are very famous for their dwarfness among the farmers of eastern hills.
(vii) Soyabean : Many varieties like ‘Monentta’, ‘Palmetto’, ‘Clemson’, ‘Seminole’ and ‘Willomi’ introduced from America and ‘Herman-36’, ‘Merman-107’ and ‘Glycine-2’ from Australia are being cultivated in India to meet the requirement of antibiotic industries.
(viii) Garden pea : Two American varieties viz. ‘Bonnevile’ and ‘Early Badger’ both wrinkle seeded, are considered very good for vegetable purposes. They are being grown largely in Delhi, U.P. and Poona area.
(ix) Tomato : ‘Sioux’, a high yielding early ripening variety suitable for cultivation in hill area was introduced from U.S.A. This variety is now popular in Andhra Pradesh and Madhya Pradesh.
(x) Onion : ‘Texas Early Grano’ is high yielding salad onion introduced from U.S.A. and is growing well under Indian field conditions.
(xi) Watermelon : Two watermelon varieties viz. ‘New Hampshire Midget’ from U.S.A. and ‘Asshi Yamato’ from Japan have been found useful for adoption in India.
