Pedigree Selection in Plant Breeding

Introduction

Pedigree selection is a systematic method of plant breeding especially effective in self-pollinated crops. It involves selecting superior individual plants from segregating generations and maintaining detailed records (pedigree) that track the ancestry of each selected plant. Over successive generations, this strategy concentrates desirable alleles and allows breeders to fix useful combinations of traits into stable lines.

Objectives of Pedigree Selection

• To combine complementary traits from chosen parents into a single improved line.
• To fix favourable genetic variation through selection and selfing.
• To identify and conserve superior genotypes from segregating populations.
• To develop genetically uniform purelines with desirable agronomic traits.
• To keep precise ancestry records for scientific evaluation and future crosses.

Principles

The pedigree method relies on the principles of segregation and recombination in early generations and uses individual plant selection in segregating generations (especially F₂ and F₃). It combines both within-family and between-family selection while continuously recording the origin of each selected plant so that lines with desirable parentage can be tracked and tested.

Step-by-Step Procedure (Generation-wise)

1. Choice of Parents

Select parents that are complementary for target traits (for example, parent A: high yield; parent B: disease resistance). Make planned crosses to produce F₁ hybrids.

2. F₁ Generation

F₁ plants are largely uniform and heterozygous. No selection is usually applied in F₁. Harvest seeds in bulk to raise the F₂ generation.

3. F₂ — First Segregating Generation

Maximum phenotypic segregation appears in F₂. Perform individual plant selection for target traits (plant type, disease resistance, maturity, yield components). Mark and harvest each selected plant separately; each harvested plant becomes the source of a pedigree family (a progeny row) in F₃.

4. F₃ — Progeny-row Evaluation

Grow progeny rows derived from each selected F₂ plant. Perform:

• Between-family selection: discard entire families (rows) that perform poorly.
• Within-family selection: from the promising families, select the best individual plants to advance.

5. F₄

Progeny rows become more uniform as homozygosity increases. Continue family-level selection and maintain pedigree records for each selected family. Eliminate families showing segregation for undesirable characters.

6. F₅

Most families are approaching homozygosity. Emphasize between-family comparisons and select superior families for advancement to replicated trials.

7. F₆ — Preliminary Yield Trials

Lines are nearly homozygous and uniform. Begin small-scale replicated trials to estimate yield and stability. Discard lines with poor adaptation or unacceptable traits.

8. F₇ and Later Generations — Multi-location Trials

Conduct multi-environment trials and compare selected lines with standard checks. Superior, stable lines with consistent performance are candidates for release as new varieties.

Selection Techniques Used

• Individual plant selection — used in segregating generations (F₂, F₃).
• Progeny-row selection — families evaluated as rows from selected parents.
• Family/recurrent selection — eliminating poor families and advancing best families.

Record Keeping (Pedigree Charts)

Accurate records are essential. A pedigree record typically links each selected plant to its ancestors, recording: cross details, plant ID, family/progeny row ID, selected traits, and notes on performance. These records allow tracing of favourable alleles and decision-making for future crosses.

Advantages

1. Highly effective in self-pollinated crops for producing purelines.
2. Enables combination of multiple desirable traits from parents.
3. Maintains ancestry information — useful for later breeding decisions.
4. Progressive elimination of inferior genotypes yields uniform, stable varieties.

Limitations

• Record-keeping is laborious and requires organization.
• Time-consuming; variety development may take many generations (often several years).
• Early-generation selection risks losing favourable genotypes if selection criteria are too strict.
• Less suitable for highly cross-pollinated crops unless adapted carefully.

Practical Tips for Breeders

• Be cautious in early-generation discard decisions — retain enough families to preserve genetic breadth.
• Use clear plant and family labelling to avoid mix-ups.
• Integrate disease screening and stress tests early to remove highly susceptible families.
• Consider small-scale replicated trials from F₆ onwards to identify promising lines.

Applications

Pedigree selection is commonly used in breeding programs for crops such as wheat, rice, barley, soybean, pulses, and cotton where selfing and fixing lines is practical and desirable.

Summary

Pedigree selection remains a cornerstone method in classical plant breeding where the objective is to obtain homozygous, uniform, and high-performing cultivars from controlled crosses. Its strength lies in combining purposeful selection with meticulous record-keeping, enabling breeders to follow the inheritance of valuable traits.