Introduction
Pedigree selection is a widely used breeding procedure in self-pollinated crops wherein individual plants are selected from segregating generations starting from F2, and their ancestral records (pedigree) are meticulously maintained throughout subsequent generations until homozygosity is attained. The ultimate objective of this method is the development of superior, genetically uniform pure-line varieties.
Pedigree Record Maintenance and Numbering System
Ancestry tracking forms the operational backbone of this method. A systematic numbering convention is followed to trace each plant's lineage back to the original cross. For example, the designation 73-12-5 denotes the 5th individual plant selected in the F3 generation, descending from the 12th plant chosen in the F2 generation originating from Cross Number 73.
Stepwise Selection Sequence Across Generations
- F1 Generation: Plants are space-planted to maximize seed production and bulk harvested. No selection is practiced because plants derived from homozygous parents are genetically uniform, despite being completely heterozygous.
- F2 Generation: Maximum genetic segregation occurs in this generation. Typically, 2,000 to 10,000 plants are raised with adequate spacing. Rigorous individual plant selection is carried out for traits with high heritability, such as disease resistance, plant architecture, and maturity duration.
- F3 to F5 Generations (Progeny Rows): Progenies of individual selected F2 plants are grown in separate rows. Selection shifts from individual plants to progeny performance, combining both between-family and within-family selection. Inferior or heavily segregating families are eliminated entirely.
- F6 Generation: With repeated selfing, plants achieve near-complete homozygosity (over 96%). Uniform, non-segregating progenies are bulked to constitute distinct pure lines. Any lines still exhibiting segregation are discarded.
- F7 to F10 Generations: Advanced homozygous lines are evaluated in Preliminary Yield Trials (PYT) followed by multi-location Coordinated Varietal Trials (CVT) against standard commercial check varieties for yield and quality parameters.
- F11 to F12 Generations: The best performing line is multiplied as breeder seed and officially released for commercial cultivation as a pure-line variety.
Technical Evaluation: Advantages and Limitations
- Advantages: Enables the recovery and identification of superior transgressive segregants; maintains a documented lineage that prevents the mating of closely related lines in subsequent hybridization programs; selection is guided simultaneously by phenotype and progeny performance.
- Limitations: Highly labor- and land-intensive due to the maintenance of vast progeny rows; pedigree record-keeping becomes unwieldy; ineffective for traits governed by polygenes with low heritability in early generations (e.g., yield).
Conclusion
Pedigree selection has served as the cornerstone of conventional crop improvement in self-pollinated crops worldwide. Although labor-intensive, its integration with modern marker-assisted selection (MAS) helps overcome early-generation selection constraints, continuing its relevance in modern plant breeding programs.