Model Answer
0 min readIntroduction
Hybrid seed production is a cornerstone of modern agriculture, offering superior yields and desirable traits compared to parental lines. It involves crossing genetically distinct parents to create offspring with combined characteristics. However, to ensure purity of the hybrid, one parent must be sterile, preventing self-pollination. This sterility is achieved through various mechanisms, broadly categorized as genetic and cytoplasmic. The demand for hybrid seeds, estimated at around 70% for maize and 30% for rice globally, underscores the importance of these sterility systems in securing food security.
Sterility Systems in Hybrid Seed Production
Sterility systems are crucial for preventing self-pollination and ensuring the genetic purity of hybrid seeds. They are broadly classified into genetic and cytoplasmic male sterility (CMS).
Genetic Male Sterility (GMS)
- Definition: GMS arises from recessive mutations in genes controlling pollen development. Plants with the recessive genotype (e.g., 'aa') are sterile, while those with at least one dominant allele (e.g., 'Aa' or 'AA') are fertile.
- Mechanism: The recessive gene disrupts pollen formation, rendering the pollen non-viable.
- Maintenance: Requires recessive gene to be maintained, which can be complex.
- Example: The 'ms' (male sterile) gene in wheat is a classic example of GMS.
Cytoplasmic Male Sterility (CMS)
- Definition: CMS is a maternally inherited trait controlled by genes located in the cytoplasm (mitochondria or chloroplasts) of the pollen mother cell.
- Mechanism: The cytoplasmic genes interfere with microsporogenesis (pollen development), resulting in non-functional pollen.
- Types: Several CMS systems exist, including:
- Ogura: Common in rice, characterized by pollen sterility and dwarfism.
- Virginia: Also found in rice, with less severe effects compared to Ogura.
- Wafangri: Another rice CMS system.
- Restoration of Fertility: CMS can be restored by nuclear genes (Rf genes) that counteract the cytoplasmic effect. This is vital for breeding subsequent generations.
Chemically Induced Male Sterility
Chemically induced male sterility (CIMS) offers an alternative approach to achieving sterility in hybrid seed production.
- Mechanism: Exposure to certain chemicals, typically at the microsporogenesis stage, disrupts pollen development, inducing temporary male sterility.
- Examples: Ethyl methylsulfonyl (EMS) and colchicine are commonly used.
- Advantages: Bypasses the need for specific genetic or cytoplasmic factors. Allows for flexibility in breeding programs.
- Disadvantages: The sterility is temporary and requires careful timing of chemical application. Potential environmental concerns related to chemical usage. Cost can also be a factor.
- Example: In some onion breeding programs, EMS is used to induce temporary male sterility, allowing for controlled pollination.
| Feature | Genetic Male Sterility (GMS) | Cytoplasmic Male Sterility (CMS) | Chemically Induced Male Sterility (CIMS) |
|---|---|---|---|
| Control | Recessive gene | Cytoplasmic genes | Chemicals |
| Inheritance | Mendelian | Maternal | Not inherited |
| Permanence | Permanent | Permanent (unless restored) | Temporary |
Conclusion
Sterility systems are indispensable for hybrid seed production, contributing significantly to improved crop yields and quality. While genetic and cytoplasmic male sterility have been widely adopted, chemically induced male sterility offers a flexible alternative. Future research should focus on developing more environmentally friendly and cost-effective methods for achieving sterility, ensuring sustainable hybrid seed production and contributing to global food security. Understanding the nuances of each system is vital for breeders.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.