NCERT-As traditional breeding techniques failed to keep pace with demand and to provide sufficiently fast and efficient systems for crop improvement,another technology called tissue culture got developed

Traditional Breeding Limitations and the Rise of Tissue Culture

Traditional breeding techniques, while instrumental in agricultural development, often struggle to keep pace with the growing demand for improved crops. To address these limitations, a revolutionary technology called tissue culture emerged in the 1950s.

What is Tissue Culture?
Tissue culture is a technique that allows scientists to regenerate whole plants from explants, which are any part of a plant (shoot tip, leaf disc, etc.) carefully removed and grown under sterile conditions in a specialized nutrient medium within a test tube. This remarkable phenomenon, where a complete plant can be regenerated from a single cell or explant, is called totipotency.

The nutrient medium used in tissue culture is crucial for successful plant growth. It typically includes:

• Carbon source: Sugar (e.g., sucrose)
• Minerals: Inorganic salts
• Vitamins
• Amino acids
• Growth regulators: Auxins, cytokinins, etc.

By manipulating the composition of this medium, particularly the ratio of auxin to cytokinin, scientists can influence the development of the explant, promoting:

• Callus induction: Undifferentiated mass of cells (achieved with high auxin and Intermediate low cytokinin)
• Shoot induction: Development of multiple shoots from the callus (achieved with low auxin and high cytokinin)
• Root induction: Formation of roots on the shoots (achieved with high auxin and low cytokinin)

Benefits of Tissue Culture
This remarkable technique offers several significant advantages over traditional breeding methods:

• Micropropagation: Rapid multiplication of genetically identical plants (somaclones) from a single explant, allowing for the production of thousands of plants in a short period.
• Disease-free plants: Recovery of healthy plants from diseased individuals. By extracting the virus-free meristems (apical and axillary buds) and growing them in vitro (in a controlled environment), scientists can obtain disease-free plantlets.
• Conservation: Propagation of endangered or rare plant species for conservation purposes.
• Improved disease resistance: Selection of plants with desirable traits, such as enhanced resistance to specific diseases, through somaclonal variation.

Applications of Tissue Culture
Tissue culture plays a crucial role in various agricultural and scientific fields, including:

• Commercial production: Mass production of important food crops like tomatoes, bananas, apples, etc.
• Disease-free propagation: Production of virus-free plant material for various crops like banana, sugarcane, and potato.
• Conservation efforts: Propagation of endangered or rare plant species for botanical gardens and conservation programs.
• Genetic modification: Introduction of desired traits into plants through genetic engineering, often followed by tissue culture for regeneration.

Conclusion
Tissue culture offers a powerful tool for addressing the challenges faced by traditional breeding methods. Its ability to rapidly produce large numbers of disease-free plants with desirable traits makes it invaluable in modern agriculture and plant science.

**Start**
| 1. Explant Selection: Choose healthy, young plant tissue (e.g., shoot tip, leaf disc). |
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| 2. Surface Sterilization: Eliminate contaminants using appropriate methods (e.g., sodium hypochlorite solution). |
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| 3. Preparation of Growth Medium: Formulate basal medium (e.g., MS or White) with: |
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|   - High Auxin:Intermediate or Low Cytokinin (CK) ratio: Promotes callus induction (e.g., 2:1 auxin:cytokinin). |
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| 4. Transfer of Explants to Culture Vessels: Aseptically transfer sterilized explants to the medium. |
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| 5. Incubation for Callus Induction: Maintain controlled environment (temperature, light, humidity) for callus formation. |
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| 6. Periodic Subculturing: Regularly transfer healthy callus tissue to fresh medium, adjusting the auxin:cytokinin ratio based on the desired outcome: |
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|   - Maintain high auxin:low CK for callus proliferation. |
|   - Reduce auxin and increase CK gradually for shoot induction. |
|   - Increase auxin and decrease CK for root induction. |
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| 7. Shoot Induction (Optional): Transfer callus to medium with a low auxin:high CK ratio (e.g., 1:2) to initiate shoot development. |
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| 8. Root Induction (Optional): Transfer shoots to medium with a high auxin:low CK ratio (e.g., 2:1) to encourage root formation. |
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| 9. Acclimatization of Plantlets (Optional): Gradually adapt rooted plantlets to greenhouse or outdoor conditions for successful establishment. |
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**End**