UPSC Mains Answer PYQ 2024: Agriculture Paper 2 (Section- A) | Agriculture Optional for UPSC PDF Download

Q1: Answer the following questions in about 150 words each: (10 × 5 = 50 marks)
(a) Explain the ultrastructure of chloroplast with the help of diagram. Briefly discuss the chemical composition and functions of chloroplast in higher plants.
Ans: Chloroplasts are double membrane-bound organelles found in green plant cells and are the sites of photosynthesis. They belong to a group called plastids and contain the green pigment chlorophyll.

Ultrastructure of Chloroplast
Chloroplasts are lens-shaped or oval and consist of the following components:

1. Outer and Inner Membrane – Enclose the organelle and regulate transport.
2. Stroma – A protein-rich matrix that contains enzymes for the dark reaction of photosynthesis (Calvin cycle), ribosomes, DNA, and starch grains.
3. Thylakoids – Flattened sac-like structures arranged in stacks called grana; interconnected by stromal lamellae.
4. Grana – Stacks of thylakoids where the light reaction occurs.
5. Thylakoid Membrane – Contains photosynthetic pigments like chlorophyll a, b, carotenoids, and electron carriers like plastoquinone.

Chemical Composition:

• Proteins – ~50–60% (enzymes, structural proteins)
• Lipids – ~20–30%
• Pigments – Chlorophyll a & b, carotenoids
• DNA and RNA – Present in stroma for semi-autonomous replication
• Starch Granules – Energy storage

Functions of Chloroplast:

1. Photosynthesis: Light Reaction: Occurs in thylakoid membranes, producing ATP and NADPH.
   Dark Reaction: Occurs in stroma, fixes CO₂ into carbohydrates using ATP/NADPH.
2. Synthesis of Amino Acids and Fatty Acids: Enzymes present in stroma are involved in biosynthetic pathways.
3. Oxygen Release: Water-splitting during photosynthesis releases molecular oxygen.
4. Starch Storage: Excess glucose is converted into starch in stroma.

Example:
In C₃ plants like wheat, the entire Calvin cycle occurs in the stroma of mesophyll cell chloroplasts. In C₄ plants like maize, chloroplasts are differentiated in mesophyll and bundle sheath cells for spatial separation of carbon fixation.

Chloroplasts are central to life on Earth as they convert solar energy into chemical energy, forming the basis of the food chain.

(b) Describe the latest advances in biotechnology for crop improvement.
Ans: Biotechnology has transformed traditional crop improvement by enabling precise, faster, and targeted interventions. These advances help improve yield, stress tolerance, and nutritional quality.

Major Advances in Crop Biotechnology:
Genetic Engineering and GM Crops

• Involves insertion of foreign genes (transgenes) to express desirable traits.
  Example: Bt cotton containing Bacillus thuringiensis gene confers pest resistance.

Genome Editing (CRISPR-Cas9 Technology)

• Allows precise modification of specific DNA regions without foreign DNA.
  Example: CRISPR-edited rice with resistance to bacterial blight.

RNA Interference (RNAi)

• Silencing specific genes using small interfering RNAs.
  Example: Golden Rice with beta-carotene content; RNAi used in Brinjal to resist fruit and shoot borer.

Marker-Assisted Selection (MAS)

• Use of molecular markers to select plants with desired genes.
  Example: MAS used in developing drought-tolerant rice (DRR Dhan 42).

Transgenic Biofortification

• Enhancing nutritional content genetically.
  Example: Golden Rice enriched with provitamin A; Iron-rich wheat under development.

Tissue Culture and Micropropagation

• Produces disease-free, uniform planting material.
  Example: Banana, sugarcane, and potato propagated through tissue culture.

Speed Breeding

• Controlled environment for faster growth cycles.
  Example: Wheat breeding reduced from 10 to 6 years using speed breeding.

Synthetic Biology and Smart Crops

• Engineering entire biochemical pathways to create novel plant traits.
• Ongoing work in climate-resilient and nitrogen-fixing cereals.

Biotechnological tools are indispensable in developing crops suited for changing climates, increasing productivity, and ensuring food and nutritional security.

(c) Describe different approaches for improving the characteristics of inbred lines.
Ans: Inbred lines are genetically uniform lines developed through repeated self-pollination, commonly used as parents in hybrid breeding. While inbreeding improves genetic purity, it often leads to reduced vigor. Several methods are employed to improve inbred lines without losing desirable traits.

Approaches for Improving Inbred Lines:
Backcross Breeding

• Repeatedly crossing an elite inbred with a donor carrying a desired gene (e.g., disease resistance).
  Example: Incorporating bacterial blight resistance gene into rice inbred lines.

Recurrent Selection

• Selecting superior individuals from a population and recombining them to accumulate favorable alleles.
• Helps maintain genetic diversity in early inbred development.

Pedigree Selection

• Maintaining detailed family records while selecting for specific traits across generations.
• Useful for complex traits like drought tolerance or yield.

Marker-Assisted Selection (MAS)

• Using molecular markers to select inbreds with targeted genes.
  Example: MAS used to develop bacterial wilt-resistant tomato inbreds.

Haploid and Double Haploid Techniques

• Developing homozygous lines in one generation using anther or microspore culture.
• Accelerates breeding programs.

Introgression from Wild Relatives

• Incorporating stress-tolerant genes from wild species.
  Example: Transfer of salt tolerance from Oryza coarctata into rice inbreds.

Genomic Selection

• Predicts breeding value using genome-wide markers.
• Useful in early selection of inbred lines in crops like maize.

Improving inbred lines is crucial for producing high-yielding, disease-resistant, and climate-resilient hybrids.

(d) Discuss various tests undertaken in seed testing laboratories.
Ans: Seed testing ensures that the seed used by farmers meets quality standards in terms of germination, purity, moisture, and health. Seed testing laboratories conduct several tests based on ISTA guidelines to certify seed quality.

Major Tests in Seed Laboratories:
Germination Test

• Determines percentage of seeds that germinate under optimal conditions.
• Carried out in sand, paper towels, or germination chambers.

Moisture Content Test

• Measures moisture to assess seed storability.
• Conducted using oven dry method or moisture meters.

Purity Test

• Determines proportion of pure seed, inert matter, other crop seeds, and weed seeds.
• Essential for seed certification and labeling.

Seed Viability Test (Tetrazolium Test)

• Assesses living cells in seeds, even if germination fails.
• Quick test used in viability estimation for carry-over seeds.

Seed Health Test

• Detects seed-borne pathogens (fungi, bacteria, viruses).
• Techniques include blotter test, ELISA, and PCR.

Seed Vigour Test

• Evaluates the potential performance of seed under field conditions.
  Methods: Accelerated aging, cold test, electrical conductivity.

Genetic Purity Test

• Confirms varietal identity using Grow-Out Test or DNA fingerprinting.

Example:
Germination test on wheat seed lot indicates 92% germination, moisture 11%, purity 98%, ensuring high planting value.

Seed testing supports seed certification and helps farmers select high-quality, reliable planting material.

(e) Discuss various theories of ion uptake with respect to passive absorption.
Ans: Ion uptake is vital for plant growth, involving the movement of minerals from the soil into root cells. Passive absorption occurs without metabolic energy expenditure, primarily along electrochemical gradients. Several theories have been proposed to explain passive ion uptake.

Key Theories of Passive Ion Absorption:
Ion Exchange Theory

• Ions adsorbed on root cell walls are exchanged with soil ions.
• Exchange occurs between H⁺/OH⁻ released by roots and mineral ions.
• Example: Ca²⁺ in soil replaces H⁺ on root surface.

Mass Flow Theory

• Nutrient ions are carried to root surfaces along with water uptake during transpiration.
• Effective for mobile nutrients like nitrate and calcium.

Diffusion Theory

• Ions move from high to low concentration along a gradient through the soil solution.
• Important when transpiration is low or for immobile nutrients like phosphorus.

Donnan Equilibrium Theory

• Describes ion movement across semipermeable membranes due to fixed charges inside the cell.
• Explains accumulation of certain ions inside cells without energy input.

Facilitated Diffusion

• Involves carrier proteins aiding ion movement without ATP consumption.
• Selective and faster than simple diffusion.

Passive uptake is prominent when roots are inactive or during early stages of ion entry. However, for accumulation against concentration gradients, active transport mechanisms become essential.

Q2:
(a) What is chromosomal aberration? Briefly discuss the changes in chromosomal structure due to aberrations. (20 marks)
Ans: Chromosomal aberrations are changes in the normal structure or number of chromosomes. They occur naturally due to errors during cell division or can be induced by physical, chemical, or biological agents. Such aberrations play a crucial role in evolution, disease manifestation, and plant breeding.
Structural Changes in Chromosomes:
Deletion (Deficiency):

• A segment of the chromosome is lost.
• Leads to missing genes and often causes severe effects.
• Example: Cri-du-chat syndrome results from deletion on chromosome 5.

Duplication:

• A chromosome segment is repeated.
• May cause gene dosage effects leading to developmental abnormalities.
• Example: Charcot-Marie-Tooth disease involves duplication on chromosome 17.

Inversion:

• A chromosome segment breaks, flips, and reinserts in reverse order.
• Types:
• Paracentric Inversion (does not involve centromere)
• Pericentric Inversion (involves centromere)
•  Alters gene positions without loss of genetic material.

Translocation:

• A segment of one chromosome attaches to a non-homologous chromosome.
• Types:
• Reciprocal Translocation: Exchange between two chromosomes.
• Robertsonian Translocation: Fusion of two acrocentric chromosomes.
• Example: Chronic Myeloid Leukemia (Philadelphia chromosome between 9 and 22).

Conclusion:
Chromosomal aberrations have profound implications in genetics and breeding. While some cause severe disorders, others contribute to genetic diversity and species evolution. Understanding them is critical in medical research, crop improvement, and evolutionary biology.

(b) Discuss the importance of crop genetic resource conservation and utilization. (20 marks)
Ans: Crop genetic resources refer to the diverse genetic material found in traditional varieties, landraces, wild relatives, and improved cultivars. Conservation and utilization of these resources are crucial for food security, agricultural sustainability, and adaptation to climate change.
Importance of Conservation:

1. Preservation of Biodiversity:

   • Maintains genetic diversity critical for stable ecosystems.

2. Food Security:

   • Ensures availability of diverse crops to withstand pests, diseases, and climate stresses.

3. Breeding Programs:

   • Source of desirable traits like drought tolerance, disease resistance, and improved nutrition.

4. Climate Change Adaptation:

   • Wild relatives possess traits like heat, salinity, and drought tolerance.

5. Cultural and Economic Importance:

   • Traditional crops have historical, cultural, and economic value.

Importance of Utilization:

1. Development of Improved Varieties:

   • Breeders utilize genetic diversity to create high-yielding, resilient crops.

2. Nutritional Enhancement:

   • Biofortification programs use diverse germplasm to enrich crop nutritional profiles.

3. Restoration of Marginal Lands:

   • Hardy crop varieties can reclaim degraded soils.

Examples:

• Development of flood-tolerant rice variety "Swarna-Sub1" using wild rice genes.

• Introduction of orange-fleshed sweet potato to combat Vitamin A deficiency.

Conclusion:
Conserving and utilizing crop genetic resources is vital for agricultural resilience and sustainability. It provides the foundation for food security, economic development, and adaptation to emerging challenges like climate change.

(c) Briefly explain the Soil-Plant-Atmosphere Continuum (SPAC). How are rooting characteristics related to the moisture extraction pattern from the soil? (10 marks)
Ans: The Soil-Plant-Atmosphere Continuum (SPAC) describes the pathway of water movement from the soil, through the plant, and into the atmosphere. Water moves along a gradient of decreasing water potential, ensuring plant hydration and physiological functions.
Soil-Plant-Atmosphere Continuum (SPAC):

1. Water Movement:

   • Water is absorbed by roots from soil (higher water potential).

   • Moves upward through the xylem driven by transpiration pull.

   • Exits through stomata into the atmosphere (lowest water potential).

2. Driving Force:

   • Water potential gradient ensures unidirectional flow.

3. Importance:

   • Maintains turgor pressure.

   • Facilitates nutrient transport.

   • Cools plant surface through transpiration.

Rooting Characteristics and Moisture Extraction:

1. Root Depth:

   • Deep-rooted crops like pigeon pea extract water from deeper layers, surviving dry periods.

2. Root Density:

   • Dense root systems enhance water uptake from upper soil layers.

3. Root Distribution:

   • Uniform root distribution leads to efficient moisture extraction throughout the soil profile.

4. Root Hydraulic Conductivity:

   • Highly conductive roots allow better water absorption, even under dry conditions.

Example:

• Wheat and pearl millet with deeper, well-distributed roots show better drought tolerance due to efficient moisture extraction.

Conclusion:
SPAC is vital for water transport and plant survival. Rooting characteristics directly influence how effectively a plant extracts moisture, affecting crop performance, especially under drought or limited water availability.

Q3:
(a) What is allopolyploidy? Describe its applications and limitations in crops. (20 marks)
Ans: Allopolyploidy is a type of polyploidy where an organism contains two or more complete sets of chromosomes derived from different species. It typically arises from interspecific hybridization followed by chromosome doubling. Allopolyploids combine the traits of two species and are important in crop evolution and improvement.
Description:
Definition:

• Allopolyploidy is the presence of multiple sets of chromosomes originating from different species.
• It results from hybridization between two species followed by chromosome doubling to restore fertility.

• Mechanism:

  • Interspecific hybrid (usually sterile) → Chromosome doubling → Fertile allopolyploid.

• Example:

  • Wheat (Triticum aestivum): A hexaploid (2n = 6x = 42) formed by natural hybridization and chromosome doubling between three different grass species.

  • Cotton (Gossypium hirsutum): An allotetraploid (2n = 4x = 52) formed from Old World and New World cotton species.

Applications in Crops:

Development of New Species:

• New crops like wheat and cotton evolved through allopolyploidy.

Trait Improvement:

• Combines desirable traits like disease resistance, stress tolerance, and high yield.

Restoration of Fertility:

• Chromosome doubling restores fertility in sterile hybrids, enabling reproduction.

Expansion of Adaptability:

• Allopolyploids show greater adaptability to different environmental conditions.

Breeding Programs:

• Used to create synthetic varieties, e.g., synthetic hexaploid wheat for drought tolerance.

Limitations:
Hybrid Instability:

• Newly formed allopolyploids may show genetic instability.

Reduced Fertility Initially:

• F1 hybrids are usually sterile until chromosome doubling occurs.

Complex Breeding:

• Handling polyploid genomes during breeding and selection is difficult.

Reduced Genetic Diversity:

• May lead to narrowing of the gene pool if not properly managed.

Conclusion:
Allopolyploidy has played a vital role in crop evolution and improvement by combining beneficial traits from different species. Despite some
limitations like initial sterility and genetic complexity, its contribution to agriculture, especially in crops like wheat and cotton, remains significant.

(b) Discuss the involvement of public and private sectors in production and marketing of seeds. (20 marks)
Ans:Seed production and marketing are crucial for agricultural productivity. Both public and private sectors play complementary roles in
ensuring quality seed availability to farmers.
Public Sector Involvement:
Research and Development:

• Institutions like ICAR, State Agricultural Universities (SAUs) develop new varieties.

Foundation and Breeder Seed Production:

• Agencies like National Seeds Corporation (NSC), State Seed Corporations (SSCs) produce foundation and certified seeds.

Subsidized Seed Supply:

• Public sector ensures affordable seeds to marginal and small farmers.

Seed Certification and Quality Control:

• Public bodies conduct seed testing, certification, and monitoring to maintain quality standards.

Promotion of Minor Crops:

• Focus on pulses, oilseeds, and other crops less attractive to private firms.

Example:

• National Seed Corporation (NSC), State Seed Corporations.

Private Sector Involvement:
Hybrid Seed Production:

• Private companies like Mahyco, Rasi Seeds, and Monsanto produce high-value hybrid seeds.

Marketing and Distribution:

• Private companies use aggressive marketing and extensive distribution networks.

Research Investment:

• Significant investment in biotechnology and genetic engineering.

Quality Packaging and Branding:

• Better packaging, branding, and farmer awareness programs.

Example:

• Companies like Syngenta, Bayer CropScience, DuPont Pioneer.

Collaboration between Public and Private Sectors:
Public-Private Partnerships (PPP):

• Joint ventures in research, seed production, and dissemination.

Example: ICAR collaborations with private seed companies for hybrid development.
Conclusion:
Both public and private sectors play indispensable roles in seed production and marketing. While the public sector ensures equity and food security, the private sector brings in innovation, investment, and efficiency. A balanced collaboration between the two can ensure sustainable agricultural growth.

(c) Give an account of bulk method of breeding. Discuss its merits and demerits. (10 marks)
Ans: The bulk method is a simple, natural method of breeding primarily used for self-pollinated crops. It involves growing a large number of plants and allowing natural selection to act over several generations before selecting superior plants.
Bulk Method of Breeding:
Procedure:

• F2 and subsequent generations are grown in bulk without selection.

• Natural selection operates during field growth.

• After 5–6 generations, individual plants are selected based on desirable traits.

• Example:

  • Widely used in breeding wheat, barley, rice, and peas.

Merits:
Simple and Inexpensive:

• Requires minimal record-keeping and supervision.

Natural Selection Advantage:

• Plants selected are naturally adapted to local conditions.

Maintenance of Genetic Variability:

• Genetic diversity remains high during bulk generations.

Low Labour Requirement:

• No need for intensive selection until later generations.

Demerits:
Long Duration:

• Several generations required before selection begins.

Risk of Loss of Superior Genotypes:

• Superior but less competitive plants may get eliminated.

Uncontrolled Factors:

• Environmental factors may favor undesired traits.

Unsuitable for Traits Not Linked to Survival:

• Traits like seed quality or specific yield traits may not be selected naturally.

Conclusion:
The bulk method of breeding is a cost-effective and natural approach for improving self-pollinated crops. However, it requires patience and careful later-stage selection to ensure desirable traits are fixed without losing valuable genotypes.

Q4:
(a) Give an account of cytoplasmic genetic male sterility and its utilization in plant breeding. Also discuss its limitations. (20 marks)
Ans: Cytoplasmic Genetic Male Sterility (CGMS) is a phenomenon where plants fail to produce functional pollen due to the interaction between nuclear and cytoplasmic genes. It is widely used in hybrid seed production to avoid the need for manual emasculation.
Cytoplasmic Genetic Male Sterility (CGMS)
Definition:

• Male sterility governed by both the mitochondrial genome (cytoplasm) and specific nuclear genes.
• The sterile cytoplasm prevents pollen development, while fertility-restorer genes in the nucleus can restore fertility.

Types of Lines:

• A-line: Male sterile line (sterile cytoplasm + no restorer gene).
• B-line: Maintainer line (normal cytoplasm + no restorer gene) — used to maintain A-line.
• R-line: Restorer line (restorer gene present) — restores fertility in hybrids.

Utilization in Plant Breeding

1. Hybrid Seed Production:

   • CGMS systems are used for economical and large-scale hybrid production in crops like rice, sorghum, pearl millet, and sunflower.

2. Eliminates Manual Emasculation:

   • Saves time, labor, and cost by avoiding hand emasculation.

3. Enhances Hybrid Vigour (Heterosis):

   • Hybrid seeds produced using CGMS show improved yield, disease resistance, and stress tolerance.

4. Simplifies Seed Production:

   • Use of A, B, and R lines simplifies large-scale commercial seed production.

Examples:

• Sorghum Hybrid: CSH-1 was the first commercial hybrid using CGMS in India.
• Rice Hybrid: Pusa RH-10 uses WA-CMS (Wild Abortive cytoplasm).

Limitations

1. Cytoplasmic Uniformity Risk:

   • Vulnerability to diseases due to genetic uniformity (e.g., maize crop loss in the USA due to Texas cytoplasm).

2. Limited Availability of Restorer Genes:

   • Difficulty in finding suitable restorer lines in some crops.

3. Environmental Sensitivity:

   • Expression of male sterility and fertility restoration can vary with environmental conditions.

4. Maintenance Difficulty:

   • Continuous backcrossing required to maintain A and B lines.

Conclusion:
CGMS is a powerful tool for hybrid development, offering efficient seed production without manual emasculation. Despite some limitations, its proper use has revolutionized hybrid breeding in many important crops.

(b) What is distant hybridization? Discuss its applications, achievements and limitations in plant breeding. (20 marks)
Ans: Distant hybridization refers to the crossing of individuals from different species (interspecific) or genera (intergeneric) to combine desirable traits. It broadens the genetic base and introduces novel traits into cultivated crops.
Applications of Distant Hybridization

1. Transfer of Resistance:

   • Introduces disease, pest, and stress resistance from wild relatives.

2. Creation of New Crops:

   • New species or varieties with superior traits.

3. Crop Improvement:

   • Enhances yield, quality, adaptability, and resilience.

4. Introgression Breeding:

   • Specific genes from wild species are introgressed into cultivated varieties.

Achievements

1. Triticale:

   • A hybrid of wheat (Triticum) and rye (Secale), combining high yield and stress tolerance.

2. Wheat Improvement:

   • Resistance to rust diseases transferred from Aegilops species.

3. Tomato:

   • Resistance to late blight transferred from wild species (Solanum pimpinellifolium).

4. Rice:

   • Resistance genes from Oryza nivara and Oryza rufipogon introduced into cultivated varieties.

Limitations

1. Hybrid Sterility:

   • Hybrids often sterile due to genetic incompatibility.

2. Pre- and Post-fertilization Barriers:

   • Cross-incompatibility and embryo abortion.

3. Linkage Drag:

   • Unwanted traits may accompany desired traits.

4. Time-Consuming and Costly:

   • Requires advanced techniques like embryo rescue and backcrossing.

Conclusion:
Distant hybridization has significantly contributed to crop improvement by introducing valuable traits. Though it faces biological barriers and complexities, modern biotechnological tools help overcome many challenges.

(c) Discuss the guidelines for planning and organization of seed production programme. (10 marks)
Ans: Seed production is critical for ensuring the availability of quality seeds to farmers. Planning and organizing a seed production programme require systematic steps to maintain genetic purity, physical purity, and seed health.
Guidelines for Planning and Organization

1. Selection of Crop and Variety:

   • Choose varieties with high demand and proven performance.

   • Ensure availability of breeder or nucleus seed.

2. Site Selection:

   • Select isolated fields with suitable soil and climate to avoid contamination.

3. Quality Seed Source:

   • Use certified breeder seeds as the base material.

4. Field Standards:

   • Maintain proper isolation distances as per seed certification norms.

5. Crop Management:

   • Apply recommended agronomic practices: proper sowing time, seed rate, fertilizers, and pest management.

6. Roguing:

   • Regular removal of off-types, diseased, or unwanted plants to maintain genetic purity.

7. Inspection and Certification:

   • Field inspections at different crop stages by certification agencies.

8. Harvesting and Processing:

   • Harvest at physiological maturity, thresh carefully to prevent seed mixing, and process seeds to meet quality standards.

9. Storage:

   • Store seeds under proper temperature and humidity to maintain viability.

10. Record Keeping:

    • Maintain detailed records of seed source, field inspections, processing, and storage.

Conclusion: A successful seed production programme requires careful planning, adherence to quality standards, and strict monitoring at every stage. Ensuring the production of high-quality seeds helps in boosting agricultural productivity and farmer income.