The following are the methods of breeding autogamous plants.

Plant Introduction:

Definition Plant introduction involves bringing a genotype or group of genotypes into a new location or environment where they were not previously grown. This process includes the introduction of new crop varieties, wild relatives, or entirely new species to a specific area.

Examples:

• Introduction of IRRI rice varieties (e.g., IR8, IR20).
• Introduction of wild sunflower species from Russia.
• Introduction of oil palm into Tamil Nadu.

Types of Plant Introduction

1. Primary Introduction:

• • Involves direct cultivation of the introduced crop/variety if it is well-suited to the new environment without altering its original genotype.
  • Examples:
    • IR8, IR20, IR34 rice varieties.
    • Oil palm varieties from Malaysia.
    • Mashuri rice from Malaysia.

2. Secondary Introduction:

• • The introduced variety undergoes selection to isolate superior traits or is used in hybridization to transfer desirable characteristics.
  • Examples:
    • Soybean variety EC 39821 from Taiwan was selected to develop Co 1.
    • Rice variety ASD 4 crossed with IR20 to develop Co 44 for late planting.

Objectives of Plant Introduction

1. Development of New Industries: Example: Introduction of oil palm to build the palm oil industry.
2. Improvement of Food Production: High-yielding crop varieties are introduced to increase food security (e.g., IRRI rice, wheat varieties).
3. Enrichment of Germplasm: Enhancing genetic diversity for breeding purposes (e.g., sorghum and groundnut collections).
4. Resistance to Stresses: Introducing germplasm with resistance to biotic (pests, diseases) or abiotic (salinity, drought) stresses. Example: NCAC groundnut accessions for rust resistance; Dasal rice for saline resistance.
5. Aesthetic Value: Introduction of ornamental plants to enhance landscapes and gardens.

Plant Introduction Agencies

Historical Contributions:

• Early introductions were facilitated by invaders, traders, explorers, and pilgrims.
  • Muslim Invaders: Introduced cherries and grapes.
  • Portuguese: Introduced maize, groundnut, chillies, potato, sweet potato, guava, pineapple, papaya, and cashew.
  • East India Company: Brought tea into India.

Modern Agencies:

1. National Bureau of Plant Genetic Resources (NBPGR):
   • Established in 1976 in New Delhi.
   • Responsible for the introduction, maintenance, and quarantine of agricultural and horticultural plant germplasm in India.
   • Functions as the central agency for importing/exporting germplasm.
2. Forest Research Institute (FRI), Dehradun:
   • Focuses on the introduction and maintenance of forest tree germplasm.
3. International Board for Plant Genetic Resources (IBPGR):
   • Headquartered in Rome, Italy.
   • Coordinates plant introduction efforts globally.

Procedure for Plant Introduction

1. Request Submission: Scientists/universities submit germplasm requests to NBPGR.
2. International Coordination: If sourced from another country, NBPGR collaborates with IBPGR to collect, quarantine, and issue phytosanitary certificates.
3. Quarantine and Distribution: IBPGR ensures that material is free from pests/diseases. NBPGR assigns accession numbers, retains a portion for its germplasm repository, and sends the rest to the requesting scientist.

Functions of NBPGR

1. Introduction, Maintenance, and Distribution: Manages the import/export and preservation of germplasm.
2. Information Dissemination: Publishes data on available germplasm.
3. Training Programs: Conducts training for scientists in germplasm introduction and maintenance.
4. Exploratory Surveys: Organizes germplasm collection drives.
5. Gene Sanctuaries: Establishes natural reserves for in situ conservation of plant genetic resources.

Merits of Plant Introduction

1. Introduction of New Crops and Varieties: High-yielding crops directly benefit agriculture (e.g., IRRI rice varieties).
2. Expansion of Germplasm Pool: Enriches the genetic diversity available for breeding programs.
3. Parent Material for Breeding: Introduced plants serve as sources for genetic improvement.
4. Conservation through Relocation: Moving crops to disease-free areas protects them (e.g., coffee and rubber).

Demerits of Plant Introduction

1. Introduction of Weeds: Examples: Argemone mexicana, Eichornia (water hyacinth), Parthenium.
2. Introduction of Diseases: Late blight of potato (introduced from Europe). Bunchy top of banana (introduced from Sri Lanka).
3. Introduction of Pests: Potato tuber moth (introduced from Italy).
4. Ornamental Plants Becoming Weeds: Example: Lantana camara.
5. Ecological Imbalance: Example: Eucalyptus plantations causing changes in soil and water dynamics.

Examples of Important Introductions

• Tea: From China to India.
• Potato: From South America to Europe and then India.
• Groundnut: From South America by the Portuguese.
• Wheat Varieties (Sonora 64 and Lerma Rojo): From Mexico for India’s Green Revolution.

Acclimatization

Definition Acclimatization refers to the process by which plants, animals, or microorganisms gradually adapt to a new environment, particularly climatic and soil conditions, where they were not previously grown or found. This is an essential step following the introduction of plants or animals to ensure their survival and productivity in a foreign environment.

Key Features of Acclimatization

1. Gradual Adjustment:
   Plants undergo physiological and morphological changes to adapt to the new environmental conditions.
2. Influence of Environment:
   Success depends on factors like temperature, humidity, soil type, and day length in the new region.
3. Duration:
   Acclimatization may take a few generations to stabilize and achieve full adaptation.

Significance of Acclimatization

1. Survival and Establishment:
   Ensures that introduced plants or animals can thrive in new climatic conditions without significant loss of vigor.
2. Expansion of Cultivated Crops:
   Allows for the cultivation of crops in areas previously unsuitable for them.
   • Example: Coffee introduced from Ethiopia acclimatized successfully in South India.
3. Preservation of Genetic Resources:
   Promotes conservation of species by establishing them in new areas, safeguarding against habitat loss or climatic changes.
4. Foundation for Breeding Programs:
   Introduced germplasm may acclimatize and contribute to breeding programs, providing traits like pest resistance or higher yield.

Examples of Acclimatization

1. Crops:
   • Tea: Introduced from China and acclimatized to Indian climates, particularly in Assam and Darjeeling.
   • Rubber: Originally from the Amazon, acclimatized to tropical conditions in Kerala.
   • Wheat Varieties: Mexican varieties like Sonora 64 acclimatized to Indian agro-climatic zones during the Green Revolution.
2. Animals:
   • Jersey cows from cooler climates adapted to tropical conditions in India.
   • Merino sheep from Spain acclimatized to Australian environments for wool production.

Process of Acclimatization

1. Selection of Suitable Varieties: Varieties with genetic traits likely to withstand the new environment are selected.
2. Quarantine Measures: Ensures the introduced species are free from pests and diseases that could impact the new environment.
3. Testing and Trials: Conducted under controlled and field conditions to assess adaptability. Involves monitoring for growth, yield, and resistance to local biotic and abiotic stresses.
4. Breeding for Adaptation: Cross-breeding the introduced species with local varieties may be carried out to combine desirable traits with adaptability.
5. Gradual Introduction: Initial planting in small areas or controlled environments to observe responses before large-scale cultivation.

Selection in Self-Pollinated Crops

Selection in self-pollinated crops involves the identification and propagation of individuals with desirable traits to enhance the performance of future generations. Since self-pollinated crops predominantly maintain homozygosity, the genetic makeup of these crops is relatively stable, which influences the effectiveness of selection.

Prerequisites for Successful Selection

1. Presence of Variation:
   There must be genetic variability within the population for selection to act upon. Without variation, it is impossible to identify and isolate superior individuals.
2. Heritability of Variation:
   The observed variation must have a genetic basis, i.e., it should be heritable. Environmental variation cannot be passed to the next generation and, thus, does not contribute to genetic improvement.

History of Selection

Selection has been practiced for centuries, with notable milestones including:

Ancient Selection Farmers have practiced selection since ancient times to improve crops by saving seeds from superior plants.

Notable Historical Contributions

• 16th Century: Van Mons (Belgium), Andrew Knight (England), and Cooper (USA) used selection to release several improved varieties.
• Le Coutier (1843): A farmer from New Jersey demonstrated that progeny from single plants were more uniform than bulk populations. This was a foundational observation for individual plant selection.
• Patrick Shireff (1840s): Practiced selection in wheat and oats, developing valuable varieties.
• Hallet (1857): Conducted single plant selection in wheat, oats, and barley to create commercial varieties.
• Vilmorin (1850s):
  • Introduced the Vilmorin Isolation Principle, advocating progeny testing to determine a plant’s true genetic value.
  • Successfully improved sugar content in sugar beet.
  • This principle showed limited effectiveness in cross-pollinated crops, highlighting differences between breeding systems.

Pure Line Theory

The pure line theory was proposed by Johannsen after studying Phaseolus vulgaris (variety: Princess).

Definition: A pure line is the progeny of a single self-fertilized, homozygous plant.

Johannsen’s Experiment:

Initial Observations: Johannsen obtained seeds from the market and observed that the lot included a mixture of large and small seeds, indicating variation in seed size.

Selection Experiment:

• • He selected seeds of different sizes and grew them separately.
  • Result: Progenies from larger seeds produced larger seeds, while progenies from smaller seeds produced smaller seeds.
  • Conclusion: The variation in seed size had a genetic basis, and the market lot was a mixture of pure lines.

Within-Line Variation: Johannsen observed that variation within a pure line was due to environmental factors, not genetics.

Confirmatory Evidence for Pure Lines

i) Weight-Based Selection:

• • In pure line 13 (seed weight: ~450 mg), seeds were divided into different weight categories (200–500 mg).
  • Progeny from all categories showed weights between 458 and 475 mg.
  • Conclusion: Variation within the pure line was due to environmental factors.

ii) Ineffectiveness of Selection within a Pure Line:

• • In a pure line with an average seed weight of 840 mg, selection for larger and smaller seeds was practiced for six generations.
  • Both large and small-seeded selections ultimately reverted to the same seed weight (680–690 mg).
  • Conclusion: Selection within a pure line is ineffective because there is no genetic variability.

iii) Parent-Offspring Regression: Regression analysis between parent and offspring in pure line 13 showed a coefficient of zero, confirming that observed variation was non-heritable and environmentally influenced.

Origins of Variation in Pure Lines

Despite their uniformity, pure lines can occasionally exhibit variability due to:

1. Mechanical Mixtures: Accidental mixing of seeds.
2. Natural Hybridization: Occasional outcrossing introducing new variability.
3. Chromosomal Aberrations: Structural changes in chromosomes.
4. Natural or Spontaneous Mutations: Sudden genetic changes.
5. Environmental Factors: Variability caused by growing conditions.

Effect of Self-Pollination on Genotype

Self-pollination causes an increase in homozygosity and a corresponding decrease in heterozygosity.

Example: For a heterozygous individual (Aa):

• After 1 generation of selfing, heterozygotes (Aa) reduce by half, while homozygotes (AA and aa) increase.
• After multiple generations, the population becomes almost entirely homozygous.

Generational Progression:

Formula for heterozygosity reduction:
Frequency of Aa = 1/2^m​
Where m = number of generations of selfing.

Genetic Advance Under Selection

Phenotypic Variance (V_P):

The phenotype is determined by genetic (V_G​) and environmental (V_E​) factors:
V_P=V_G+V_E

Formula for Genetic Advance:

GS=(K)(H)(SD_P)
Where:

• GS: Genetic advance.
• K: Selection differential (the intensity of selection).
• H: Heritability (proportion of genetic variance in total variance).
• SD_P​: Phenotypic standard deviation of the base population.

Alternative Formula:

GS=(K)(V_P^1/2) (V_G/V_P)

Key Points

1. Selection in self-pollinated crops works effectively when genetic variation exists in the population.
2. Self-pollination increases homozygosity, leading to a stable genetic constitution.
3. Pure lines are essential for studying genetic effects, as variation within them is purely environmental.
4. Selection within pure lines is ineffective due to the absence of genetic variability.
5. Genetic advance depends on selection intensity, heritability, and phenotypic variance.

Pureline Selection

Pureline selection is a breeding method used primarily in self-pollinated crops to develop uniform and high-performing varieties by isolating and propagating the progeny of a single superior plant. This method exploits the homozygosity inherent in self-pollinated species, leading to uniform genotypes.

Process of Pureline Selection

1. Base Population:
   • A genetically mixed population is required as the starting material.
   • The population should exhibit significant genetic variability to allow effective selection.
2. Selection of Superior Plants (First Season):
   • Identify and select individual plants with desirable traits such as high yield, resistance to diseases, or superior quality.
   • Harvest seeds separately for each selected plant.
3. Progeny Evaluation (Second to Third Season):
   • Grow the seeds from each selected plant in individual progeny rows.
   • Evaluate the performance of each progeny row based on phenotypic traits.
   • Eliminate inferior progenies and retain the best-performing ones.
4. Preliminary Yield Trials (Fourth Season):
   • Conduct replicated yield trials for the selected progenies, comparing them with a suitable check or control variety.
   • Evaluate performance across multiple parameters such as yield, disease resistance, and adaptability.
5. Comparative Yield Trials (Fifth Season):
   • Conduct larger-scale comparative yield trials with local check varieties to assess the superiority of the selected lines.
6. Multilocation Trials (Sixth Season):
   • Test the selected lines across multiple research stations to evaluate their performance under diverse environmental conditions.
7. Adaptive Research Trials (Seventh Season):
   • Evaluate the best-performing lines in farmers’ fields to confirm their adaptability and yield performance under real-world conditions.
8. Variety Release:
   • Submit the selected line to the Variety Release Committee for approval and release as a new variety.

Characteristics of Purelines

1. Genetic Uniformity: All plants within a pureline have identical genotypes.
2. Variation: Any variation observed within a pureline is due to environmental factors and is non-heritable.
3. Genetic Stability:
   • Over time, purelines may become genetically variable due to:
     • Natural hybridization.
     • Mutations.
     • Mechanical seed mixtures.

Advantages of Pureline Selection

1. Maximum Genetic Improvement: Achieves the highest possible improvement over the base population because each variety is derived from the best individual plant.
2. Uniformity: Pureline varieties are extremely uniform in appearance, making them easy to manage and market.
3. Ease of Seed Certification: The genetic uniformity simplifies seed certification processes.

Disadvantages of Pureline Selection

1. Narrow Adaptability: Pureline varieties are typically adapted to specific environments, limiting their performance under varying conditions.
2. Time-Intensive: Developing a pureline variety takes longer compared to methods like mass selection.
3. Dependency on Genetic Variability: The success of pureline selection depends on the availability of sufficient genetic variation in the base population. Without variability, no improvement is possible.
4. High Effort Requirement: Breeders must invest significant time and resources to identify, evaluate, and test purelines.