Model Answer
0 min readIntroduction
Plant disease resistance is a cornerstone of sustainable agriculture, minimizing yield losses and reducing reliance on chemical interventions. Traditionally, plant breeders focused on “vertical” or “gene-for-gene” resistance, offering high but often short-lived protection against specific pathogens. However, the emergence of new races and pathotypes frequently overcomes this single-gene resistance. "Horizontal" resistance, conferring broad-spectrum protection against a range of pathogens, is increasingly recognized as a more durable and sustainable solution. This response will explore why horizontal resistance is generally preferred over vertical resistance in modern agricultural practices.
Understanding Vertical and Horizontal Resistance
Vertical resistance, also known as gene-for-gene resistance, is conferred by a major gene providing strong resistance to a specific pathogen race. It's often achieved through single gene transfer. Horizontal resistance, on the other hand, is typically polygenic, conferring a more gradual, broad-spectrum resistance against a wider range of pathogen strains. It involves multiple genes contributing to a complex defense system.
Advantages of Vertical Resistance
- High initial efficacy: Provides excellent protection against a specific pathogen race.
- Relatively easy to incorporate: Single gene transfer is a simpler breeding process.
Disadvantages of Vertical Resistance
- Rapid breakdown: Pathogens quickly evolve to overcome specific resistance genes.
- Narrow spectrum: Provides protection against only a limited range of pathogen races.
- Requires constant monitoring: Breeders must continuously identify and deploy new resistance genes.
Why Horizontal Resistance is Preferable
The limitations of vertical resistance highlight the benefits of horizontal resistance. Its polygenic nature makes it significantly more durable.
Key Advantages of Horizontal Resistance
- Durability: Pathogens find it far more difficult to overcome multiple resistance genes simultaneously.
- Broad Spectrum: Offers protection against a wider range of pathogen strains and races.
- Reduced selection pressure: Slows down pathogen evolution, reducing the likelihood of resistance breakdown.
- Reduced need for new resistance genes: Less frequent replacement of resistance genes is required, reducing breeding costs and time.
Examples and Case Studies
The success of horizontal resistance is evident in several crops:
- Potato: Resistance to late blight (caused by Phytophthora infestans) is often based on multiple, quantitative trait loci (QTLs), providing more durable protection than single, major genes.
- Wheat: Resistance to rust diseases is often conferred by multiple, additive genes, contributing to a broad spectrum of protection.
- Rice: Efforts to develop broad-spectrum blast resistance in rice are focusing on combining multiple resistance genes.
Challenges in Developing Horizontal Resistance
While highly beneficial, developing horizontal resistance presents challenges:
- Complex genetics: Identifying and characterizing the multiple genes involved is more complex than single gene transfer.
- Lower initial efficacy: Horizontal resistance may not provide as strong initial protection as vertical resistance.
- Difficult to track and predict: The cumulative effect of multiple genes is harder to predict and track during breeding.
| Feature | Vertical Resistance | Horizontal Resistance |
|---|---|---|
| Genetic Basis | Single major gene | Multiple, polygenic genes |
| Spectrum of Protection | Narrow | Broad |
| Durability | Low | High |
| Breeding Complexity | Relatively simple | Complex |
Government Initiatives
The Indian Council of Agricultural Research (ICAR) has been actively involved in breeding programs focusing on developing varieties with horizontal resistance to major diseases in crops like rice, wheat, and pulses. The National Food Security Mission (NFSM) also supports research and development of disease-resistant varieties. (Knowledge cutoff: Current ICAR initiatives should be researched for updated information).
Conclusion
In conclusion, while vertical resistance offers initial advantages, its susceptibility to pathogen evolution makes horizontal resistance the more sustainable and preferable approach for long-term disease management in agriculture. The durability and broad-spectrum protection offered by horizontal resistance contribute to reduced reliance on chemical interventions and increased food security. Continued research and breeding efforts focused on harnessing the power of polygenic resistance are crucial for ensuring the resilience of our crops in the face of evolving pathogen threats.
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.