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In this article we will discuss about the methods of plant breeding for disease and pest resistance.
Plant Breeding for Disease Resistance:
Crops are required to be disease, resistant, as a wide range of fungal, bacterial and viral pathogens that affect the yield of cultivated crop species, especially in tropical climates. Resistance of the host plant is the ability to prevent the pathogen from causing disease and is determined by the genetic constitution of host plant.
Plant breeding for disease resistance has two advantages given below:
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(i) It enhances the production of food by reducing dosses due to diseases.
(ii) Reduces the dependance on fungicides and bacteriocides.
The causative agents of diseases in plants are:
(i) Fungi Diseases caused by fungi are brown rust of wheat, red rot of sugar cane, late blight of potato, etc.
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(ii) Bacteria Diseases caused by bacteria are black rot of crucifers, blight of rice, citrus canker, etc.
(iii) Virus Diseases caused by virus are tobacco mosaic, turnip mosaic, etc.
Methods of Breeding for Disease Resistance:
It is carried out by either of the following two breeding methods:
1. Conventional Breeding:
Conventional plant breeding has been going on for hundreds of years, and is still commonly used today. It is known as the breeding or planting, which uses chemical ways like chemical fertilisers or synthetic components. In conventional breeding, genetically modified foods or non-ecological foods are used in breeding animals.
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It is carried out by following steps:
(a) Selection and screening of germplasm for the disease resistance.
(b) Hybridisation of selected plants.
(c) Selection and evaluation of hybrids.
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(d) Testing and release of new varieties into the market.
Some Important Varieties Developed by Conventional Breeding:
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Disadvantages of conventional breeding:
Limited number of disease resistance genes have been identified in crop varieties or wild relatives.
2. Mutation Breeding:
Mutation is a process by which genetic variation is achieved through the changes in base sequences within genes. This creates a new character or trait absent in parental generation. Mutation breeding can be defined as the process of breeding by artificially inducing mutations using chemicals or radiations.
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It is carried out by the following steps:
(a) Inducing mutations in plants by various means.
(b) Screening the plant by various means.
(c) Selecting the desirable plant for the multiplication for breeding.
In mung bean, resistance to yellow mosaic virus and powdery mildew were introduced by mutations.
Resistance to yellow mosaic virus in bhindi Abelmoschus esculentus was transferred from a wild species and resulted in a new variety of A. esculentus called Parbhani Kranti.
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Currently, mutation heeding is being carried out for disease resistance, as there is limited availability of disease resistance genes in the crop plants and their wild relatives.
Plant Breeding for Developing Resistance to Insect Pests:
The insect resistance in host crop plants may be due to the morphological, biochemical or physiological characteristics.
The important characters that lead to pest resistance are:
(i) Hairy leaves in plants. For example, resistance to jassids in cotton and cereal leaf beetle in wheat.
(ii) Solid stem in wheat exhibits non-preference by stem sawfly.
(iii) In cotton, smooth leaf and absence of nectar repel bollworms.
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(iv) In maize, high aspartic acid, low nitrogen and sugar content protect them from stem borers. Breeding methods for insect pest-resistance involve the same steps as those for any other agronomic trait.
Some Crop Varieties Breed by Hybridisation and Selection for Insect Pest Resistance:
