Purposeful manipulation of plant species to create desired plant types is called plant breeding. Classical plant breeding involves crossing of pure lines, followed by artificial selection to produce plants with desirable traits.
The main steps in breeding a new genetic variety of a crop are as follows:
Some crop varieties bred by hybridisation and selection, for disease resistance to fungi, bacteria and viral diseases are shown in this table.
|Crop||Variety||Resistance to diseases|
|Wheat||Himgiri||Leaf and stripe rust, hill bunt|
|Brassica||Pusa swarnim (Karan rai)||White rust|
|Cauliflower||Pusa Shubhra, Pusa snowball K-1||Black rot and Curl, Blight black rot|
|Cowpea||Pusa Komal||Bacterial blght|
|Chilli||Pusa Sadabahar||Chilly mosaic virus, Tobacco mosaic virus and Leaf curl|
Limited number of disease resistance genes is present and identified in various crop varieties or wild relatives. This works as a constraint for conventional breeding for disease resistant varieties. Hence, mutations are introduced in plants; followed by screening of plants materials for resistance is done. This sometimes leads to identification of the desirable genes. Plants thus identified are then multiplied directly or used in breeding. Genetic engineering and soma-clonal variants are also used for producing plants with disease resistant traits.
Mutation: Changes in the base sequence within genes results in appearance of a new trait. This change is called mutation. Mutation can be artificially induced through use of chemicals or radiations. In mung bean, resistance to yellow mosaic virus and powdery mildew were induced by mutations.
Resistance to yellow mosaic virus in okra (Abelmoschus esculentus) was transferred from a wild species. It resulted in a new variety of okra called Parbhani kranti.
Some released crop varieties bred by hybridisation and selection, for insect pest resistance are given in this table.
|Flat bean||Pusa Sem 2, Pusa Sem 3||Jassids, aphids and fruit borer|
|Okra||Pusa Sawani, Pusa A-4||Shoot and fruit borer|
Biofortification: Breeding crops with higher levels of vitamins and minerals or other nutrients is called biofortification.
Conventional agricultural production of crops won’t be able to meet the demand of the growing human population. Shift from grains to meat diet also creates more demand for cereals because 3 to 10 kg of grains are required to produce 1 kg of meat by animal farming. More than 25% of population is suffering from hunger and malnutrition. Single Cell Protein can prove to be a viable alternate source of protein for animal and human beings.Microbes; like Spirulina can be easily grown on materials like wastewater from potato processing plants (containing starch), straw, molasses, animal manure and even sewage. Large quantities of such microbes can serve as food rich in protein, minerals, fats, carbohydrates and vitamins. It has been calculated that a 250 kg cow produces 200 g of protein in a day. On the other, hand 250 g of a microorganism (like Methylophilus methylotrophus) can produce 25 tonnes of protein in a single day. This shows the high rate of biomass production and growth in these organisms.
The whole plant can be regenerated from any part of a plant taken out and grown in a test tube under sterile conditions in special nutrient media.
Explant: Any part of a plant that is taken out and grown in a test tube under sterile conditions in special nutrient media is called explants.
Totipotency: The capacity to generate a whole new plant from any cell/explants is called totipotency.
Micropropagation: The method of producing thousands of plants through tissue culture is called micro-propagation.
Somaclones: Each of the plants grown by tissue culture is identical to the original plant and hence is called somaclone.
Somatic Hybridisation: When hybridization involves fusing two somatic cells to obtain hybrid protoplasts, it is called somatic hybridization.
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