Plant Breeding
Plant breeding is the manipulation of plant species to create desired plant types suitable for better cultivation, higher yields, and disease resistance.
- Green Revolution: The development and flourishing of agriculture, heavily dependent on plant breeding.
- Classical Plant Breeding: Involves hybridization of pure lines and artificial selection to produce desirable traits.
- Modern plant breeding uses molecular genetic tools.
Desirable Traits for Plant Breeding
- Increased crop yield and quality.
- Increased tolerance to environmental stresses (salinity, extreme temperatures, drought).
- Increased resistance to insect pests and pathogens.
Steps of Plant Breeding
1. Collection of Genetic Variability
- In wild relatives of many crops, pre-existing genetic variability is available.
- Collection and preservation of wild varieties, species, and relatives of cultivated species is a prerequisite for effective exploitation of natural genes.
- The entire collection of plants/seeds having all the alleles for all genes in a given crop is called germplasm collection.
2. Evaluation and Selection of Parents
- The germplasm is evaluated to identify plants with desirable characters.
- Selected plants are multiplied and used for hybridization.
- Pure lines are created wherever desirable and possible.
3. Cross Hybridization of Selected Parents
- Desired characters are genetically combined from two different parents to produce hybrid plants.
- Example: High protein quality of one parent is combined with disease resistance from another parent.
- Limitations:
- Very time-consuming and tedious process.
- Hybrids may not combine the desirable characters; usually only hundreds to a thousand crosses show the desired combination.
4. Selection and Testing of Superior Recombinants
- Crucial to the success of the breeding objective, requiring careful scientific evaluation of the progeny.
- Yields plants that are superior to both parents.
- These are self-pollinated for several generations until they reach a state of uniformity (homozygosity) so that the characters will not segregate in the progeny.
5. Testing, Release, and Commercialization
- Newly selected lines are evaluated for yield and other agronomic traits of quality, disease resistance, etc.
- Tested in research fields under ideal fertilizer application, irrigation, and crop management practices.
- Evaluated in farmers’ fields for at least three growing seasons across multiple agro-climatic zones, compared to the best available local crop cultivar.
Crop Improvement Examples
Wheat and Rice
- In India, food production increased through high-yielding varieties of wheat and rice in the mid-1960s (Green Revolution).
- Wheat production increased from 11 million tons (1960) to 75 million tons (2000).
- Rice production increased from 35 million tons to 89.5 million tons.
- Nobel laureate Norman E. Borlaug (International Centre for Wheat & Maize Improvement, Mexico) developed semi-dwarf wheat.
- In 1963, high-yielding and disease-resistant wheat varieties like Sonalika and Kalyan Sona were introduced in India.
- Semi-dwarf rice varieties were derived from IR-8 (International Rice Research Institute, Philippines) and Taichung Native-1 (Taiwan). Later, better-yielding varieties Jaya and Ratna were developed in India.
Sugarcane
- Saccharum barberi (grown in North India, poor sugar content and yield) was crossed with Saccharum officinarum (tropical canes in South India, thicker stems, higher sugar content but poor growth in North India).
- Resulted in a hybrid sugarcane with high yield, thick stems, high sugar, and ability to grow in North India.
Millets
- Hybrid maize, jowar, and bajra developed in India, including high-yielding varieties resistant to water stress.
Plant Breeding for Disease Resistance
- Plant diseases cause crop losses up to 20-30% or even total.
- Disease-resistant cultivars enhance food production and reduce the use of fungicides and bactericides.
- Resistance is the genetic ability to prevent pathogens from causing disease.
Types of Plant Diseases
- Fungal: Rusts (e.g., brown rust of wheat, red rot of sugarcane, late blight of potato).
- Bacterial: Black rot of crucifers.
- Viral: Tobacco mosaic, turnip mosaic.
Methods of Breeding for Disease Resistance
1. Conventional Breeding
The steps include:
- Screening germplasm for resistance sources.
- Hybridization of selected parents.
- Selection and evaluation of the hybrids.
- Testing and release of new varieties.
Examples of Crop Varieties Bred by Conventional Method
| Crop | Variety | Resistance to |
|---|---|---|
| Wheat | Himgiri | Leaf & 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 blight |
| Chilli | Pusa Sadabahar | Chilli mosaic virus, Tobacco mosaic virus, leaf curl |
- Conventional breeding is constrained by the limited availability of disease resistance genes.
- Inducing mutations and screening for resistance help identify desirable genes, which can be multiplied directly or used in breeding.
- Other methods include selection amongst somaclonal variants and genetic engineering.
2. Mutation Breeding
- Mutation (sudden genetic change) can create new desirable characters not found in the parental type.
- Mutation breeding uses chemicals or radiation (e.g., gamma rays) to produce plants with desirable characters, which are selected and multiplied or used in breeding.
- Example: In mung bean, resistance to yellow mosaic virus and powdery mildew was induced by mutations.
- Resistant genes from wild species introduced into high-yielding varieties (e.g., resistance to yellow mosaic virus in Abelmoschus esculentus resulted in Parbhani Kranti).
- Resistance genes can be transferred by sexual hybridization between the target and source plant.
Plant Breeding for Developing Resistance to Insect Pests
- Morphological, biochemical, or physiological characteristics provide insect resistance in host crop plants, e.g.:
- Hairy leaves: Resistance to jassids in cotton and cereal leaf beetle in wheat.
- Solid stems in wheat: Non-preference by the stem sawfly.
- Smooth-leaved and nectar-less cotton varieties: Do not attract bollworms.
- High aspartic acid, low nitrogen, and sugar content in maize: Resistance to maize stem borers.
- Sources of resistance genes include cultivated varieties, germplasm collections, or wild relatives.
Examples of Crop Varieties Bred for Insect Pest Resistance
| Crop | Variety | Insect Pests |
|---|---|---|
| Brassica (Rapeseed Mustard) | Pusa Gaurav | Aphids |
| Flat Bean | Pusa Sem 2, Pusa Sem 3 | Jassids, aphids, fruit borer |
| Okra (Bhindi) | Pusa Sawani, Pusa A-4 | Shoot and fruit borer |
Plant Breeding for Improved Food Quality
- Over 840 million people lack adequate food, and 3 billion suffer from micronutrient, protein, and vitamin deficiencies (hidden hunger).
- Biofortification: Breeding crops with higher nutrient levels to improve public health.
Objectives of Breeding for Improved Nutritional Quality
- Improve protein content and quality.
- Improve oil content and quality.
- Improve vitamin content.
- Improve micronutrient and mineral content.
Examples of Hybrids with Improved Nutritional Quality
- Maize hybrids: Twice the amount of amino acids (lysine and tryptophan) compared to existing hybrids.
- Wheat: Variety Atlas 66 with high protein content.
- Iron-fortified rice: Contains over five times as much iron as common varieties.
- Vitamin and mineral-rich vegetables (released by Indian Agricultural Research Institute, New Delhi):
- Vitamin A-enriched carrots, spinach, pumpkin.
- Vitamin C-enriched bitter gourd, bathua, mustard, tomato.
- Iron and calcium-enriched spinach, bathua.
- Protein-enriched beans (broad, lablab, French, garden peas).
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1. Animal Husbandry 2. Plant Breeding 3. Single Cell Proteins and Tissue Culture