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Plant Breeding

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Plant breeding is made up of two words- plant and breeding. This means there is breeding among two different species of plant of desired varieties.  The desired varieties mean plants should have increased tolerance to environmental stresses (salinity, extreme temperatures, drought, etc.), resistance to pathogens (viruses, fungi, and bacteria), and increased tolerance to insect pests. All these qualities will help in getting better yield and disease-free plants. These all traits altogether, increase the yield of plants and make plant disease free. Plant breeding was first used during the green revolution. Let’s understand the green revolution.

Objectives of Plant Breeding

The objectives of plant breeding are as follows: 

  1. To increase the yield of the crop.
  2. To get improved quality of the crop.
  3. To develop a disease-free crop.
  4. To obtain plants with desired agronomic characteristics or traits.
  5. To develop plants that can resist extreme environmental stress (salinity, high temperature, etc.)
Plant Breeding

 

Types of Plant Breeding

Breeding among the plants can be of the following types:

Inbreeding

Inbreeding refers to the breeding among closely related individuals.

Backcrossing Breeding

Backcrossing breeding refers to the breeding of a hybrid organism with one of its genetically similar parents. It is done to isolate desired characteristics in a related group of plants.

Mutation Breeding

Mutation breeding refers to the breeding that can be induced artificially induced in plants by exposure to radiation or chemicals. This results in new varieties.

Genetic Engineering Breeding

It involves genetic tools Genetic, recombinant DNA technology to insert desirable traits into plants. The resulting plants are known as transgenic plants or genetically modified organisms (GMOs).

Somatic Hybridization

A  hybrid produced by the fusion of somatic cells of two varieties or species is called a somatic hybrid and the process of producing somatic hybrids is known as somatic hybridization. It helps in the transfer of desirable characters from wild or unrelated crop species to crop plants.

Plant Breeding Steps

The steps involved in developing new varieties of plants are as follows:

Collection of Variability

Variability means variation in genetic composition (alleles of genes) which brings desired traits in progeny plants like tolerance to pests, extreme temperatures, etc. This can be achieved by the collection and preservation of natural genes of different wild varieties, species, and relatives of the cultivated species. This collection of plants/seeds with all the diverse alleles for all genes in a given crop is called germplasm collection. So, germplasm collection brings variability in plants. Once germplasm is collected, the next step is the evaluation and selection of parents.

Evaluation and Selection of Parents

Two or more plants with desired germplasm are known as parents. These parents are now selected and multiplied. For example-grain length in rice can be longer, intermediate, or shorter. If longer seeds are selected and sown then the next generation crop will have average and longer grains than the original population. Once parents are selected, the next step is cross-hybridization among selected parents.

Cross-hybridization among Selected Parents

Cross hybridization is the crossing of two or more types of plants with desired traits in such a way that future generations will have traits of both parents. For example, the high protein quality of one parent can be cross-hybridized with disease resistance from another parent. This will genetically combine the desired characteristics in the progeny plant. However, cross-hybridization is a very time-consuming and tedious process as first the pollen grains from the male parent have to be collected and placed on the stigma of the flowers female parent.  For example-wheat variety, HUW 468 took 12 years to develop. Once cross-hybridization is done, the next step is the selection and testing of superior recombinants.

Selection and testing of Superior Recombinants

This step involves the selection of progeny with desired character combination or called recombinants. The progeny crop is superior to both of the parents. The progeny obtained are self-pollinated for several generations till they reach a state of uniformity (homozygosity) so that the characters will not segregate in the progeny. The self-pollinated progeny for longer generations will produce a pure line. All plants in the pure line have identical genotypes. An example of the pure line is HUW 468 wheat variety. Once self-pollination is done, the next step is testing, releasing, and commercialization of new cultivars.

Testing, release, and commercialization of New Cultivars

The selected lines are evaluated for their yield and other agronomic traits like quality, disease resistance, etc. This can be achieved by growing these plants in the research fields and recording their performance under ideal fertilizer, irrigation, and other crop management practices, etc. for at least three growing seasons at different locations in the country. The evaluation in research fields is followed. The crop obtained is compared with the best available crop cultivar and seeds are multiplied and finally made available to farmers.

Applications of Plant Breeding

Plant breeding has several applications. Let’s understand them one by one-

Plant Breeding for Disease Resistance

The yield of plants can be reduced by a wide range of fungal, bacterial, and viral pathogens, especially in tropical climates. These pathogens cause several diseases, that can be fungal (rusts, e.g., brown rust of wheat, red rot of sugarcane, and late blight of potato); bacteria (black rot of crucifers), and viruses (tobacco mosaic, turnip mosaic, etc.) This can lead to 20-30% of crop loss. This loss can be overcome by plant breeding. To achieve this, the very first step is to know about the causative organism and the mode of transmission.

Plant Breeding for Developing Resistance to Insect Pests

Plants can also be damaged by pests and insects. So, plant breeding through hybridization and selection helps in getting pest and insect-free crop varieties. However, some plants themselves are pest resistant due to their morphological, biochemical, or physiological characteristics. For example- dairy leaves in several plants are associated with resistance to insect pests, e.g, resistance to jassids in cotton and cereal leaf beetle in wheat. Similarly, high aspartic acid, low nitrogen, and sugar content in maize lead to resistance to maize stem borers. Some insect pest resistance varieties are given below:

Crop Variety Insect pests

Brassica 

(rapeseed mustard)

Pusa Gaurav Aphids
Flat bean

Pusa Sem 2

Pusa Sem 3

Jassids, aphids, and fruit borer
Okra (Bhindi)

Pusa Sawani

Pusa A-4

Shoot and fruit borer

Plant Breeding for Improved Food Quality

Plant breeding helps in getting improved varieties of crops with higher levels of nutrition. This can be achieved by process biofortification in which crops with higher levels of vitamins and minerals, or higher protein and healthier fats are bred together. The improved crops have better protein content and quality, oil content and quality, vitamin content, and micronutrient and mineral content. For example-maize hybrids made in 2000 had twice the amount of the amino acids, lysine, and tryptophan, compared to existing maize hybrids. Similarly, Atlas 66 (wheat variety) has high protein content.

FAQs on Plant Breeding

Question 1: What are the major problems faced by farmers before plant breeding?

Answer:  

The problems faced by farmers before plant breeding are as follows:

  • The crops or seeds were easily infested by insects or pests.
  • The crops were not able to withstand extreme temperatures.
  • Yield of crops was very less.
  • Crops lack nutritional value.

Question 2: What is plant mutation?

Answer: 

Plant mutation means a change in the genetic (DNA) composition of a plant. It can be done physically by irradiating crops with gamma rays or chemically.

Question 3: What is an iron-fortified crop?

Answer: 

Iron-fortified is a rice variety that contains over five times as much iron as in commonly consumed varieties.

Question 4: Give an example of mutation breeding.

Answer: 

Mung bean is resistant to yellow mosaic virus and powdery mildew was induced by mutations.



Last Updated : 15 Feb, 2023
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