Define pedigree method and give its importance in crop improvement, with suitable examples.

Defining the Pedigree Method

The pedigree method is a breeding technique primarily used for self-pollinating crops like wheat, rice, soybean, and groundnut. It involves several generations of self-pollination, starting from a genetically variable hybrid or a segregating population. The objective is to segregate the genes of the parents and ultimately recover pure lines, each homozygous for specific traits. The process essentially traces the lineage (pedigree) of each plant back to its original parentage, allowing breeders to select plants with the desired combination of traits.

Principles of the Pedigree Method

The core principles guiding the pedigree method are:

• Self-Pollination: Every plant in each generation is self-pollinated, ensuring that the offspring inherits genes from the same parent.
• Selection: At each generation (usually F2, F3, and onwards), plants exhibiting the desired traits are selected.
• Row-to-Row Selection: In early generations (F2 and F3), selection is often done on a row-to-row basis, eliminating entire rows of plants that don't meet the selection criteria. This helps to quickly eliminate undesirable combinations of genes.
• Plant-to-Plant Selection: As the generations progress (F4 and onwards), selection shifts to plant-to-plant selection, allowing for finer discrimination and the recovery of pure lines.
• Maintaining Records: Detailed records are maintained for each plant, tracing its ancestry and performance.

Importance in Crop Improvement

The pedigree method holds significant importance in crop improvement for several reasons:

• Recovery of Pure Lines: It's particularly effective for self-pollinating crops where hybrid vigor is not desired, and pure, homozygous lines are essential for maintaining genetic stability.
• Gradual Incorporation of Traits: Allows for the gradual and controlled incorporation of multiple desirable traits.
• Adaptability to Complex Traits: Suitable for improving complex traits that are controlled by multiple genes (polygenic traits) like yield, protein content, and disease resistance.
• Cost-Effective: Relatively less expensive compared to some other advanced techniques like marker-assisted selection.

Advantages and Disadvantages

Here's a comparison of the advantages and disadvantages of the pedigree method:

Advantages	Disadvantages
Suitable for self-pollinating crops.	Time-consuming process (typically 6-8 generations).
Effective for recovering pure lines.	Requires large planting areas for selection.
Can handle complex traits.	Less efficient for cross-pollinating crops.
Relatively cost-effective.	Requires skilled personnel for selection.

Examples of Application

The pedigree method has been instrumental in developing improved varieties of several crops:

• Wheat: Numerous wheat varieties with improved yield and disease resistance have been developed using the pedigree method. For example, the development of 'PBW 343', a popular wheat variety in India, involved pedigree selection.
• Rice: The pedigree method has been used extensively in rice breeding programs to develop varieties with improved grain quality and resistance to biotic stresses.
• Soybean: Development of soybean varieties with higher protein content and improved oil quality often relies on the pedigree method.
• Groundnut: The technique has been vital for improving groundnut yield and disease resistance in various regions.

Case Study: Development of Improved Wheat Variety ‘PBW 343’

The ‘PBW 343’ wheat variety, widely cultivated in India, exemplifies the successful application of the pedigree method. It was developed by the Punjab Agricultural University (PAU). The initial hybrid was created by crossing two diverse parents. Subsequent generations underwent rigorous selection based on yield, disease resistance (particularly to rust), and grain quality. Row-to-row selection was used in early generations to eliminate undesirable plants. Plant-to-plant selection was employed in later generations to isolate pure lines with the desired combination of traits. This resulted in a high-yielding, rust-resistant wheat variety that significantly contributed to India’s food security.

Relationship to Other Breeding Methods

The pedigree method can be integrated with other breeding approaches. For instance, marker-assisted selection (MAS) can be incorporated to accelerate the selection process by identifying plants carrying desirable genes at the molecular level. The bulk population method, another breeding technique, can be used in conjunction with pedigree selection to generate diverse populations for further improvement.

In conclusion, the pedigree method remains a valuable tool in crop improvement, particularly for self-pollinating crops. Its strength lies in its ability to recover pure lines and gradually incorporate desirable traits. While time-consuming, its cost-effectiveness and adaptability to complex traits make it a preferred choice for many breeding programs. With advancements in molecular biology, integrating the pedigree method with techniques like marker-assisted selection holds immense potential for further enhancing crop productivity and resilience in the face of evolving challenges.