Mass Selection Method – Procedure, Applications, Merits, Demerits

What is Mass Selection Method?

• Mass selection is a breeding method used to improve plant populations by selecting and mixing seeds from plants with desirable traits. This technique involves choosing a large number of plants that exhibit similar phenotypic characteristics, such as plant height, grain color, and disease resistance. The seeds from these selected plants are then combined to create a new variety.
• The selection process in mass selection is based on observable traits, which makes it a relatively straightforward method. Traits such as plant height, ear type, grain size, and disease resistance are commonly used as criteria. Sometimes, yield may also be considered, though this depends on the variability of traits within the population.
• Once the plants are selected, the resulting population is expected to be more uniform in terms of the selected traits compared to the original population. For example, characteristics governed by one or a few major genes, like seed color or plant height, tend to be more uniform. However, the population may still exhibit significant variation in quantitative traits such as yield and adaptability due to the complex genetic factors influencing these characteristics.
• The original population often consists of several pure lines, and the selected plants from this population are generally homozygous for the traits being selected. By mixing the seeds of these selected plants, the resulting variety contains a blend of these similar-looking pure lines. This genetic variation within the new variety suggests that further mass selection or even pure line selection might be necessary for further refinement.
• Progeny testing is not typically used in mass selection; however, some experts, such as Allard (1960), argue that it can be beneficial. In progeny testing, seeds from selected plants are grown, and poor or defective progenies are discarded. The remaining progenies are then mixed to form the new variety. This additional step can help ensure the consistency and quality of the newly developed variety.

Definition of Mass Selection Method

Mass selection is a plant breeding method where a large number of plants with desirable traits are selected based on observable characteristics, and their seeds are pooled together to create a new variety. This method aims to improve the population’s uniformity for these traits while retaining genetic diversity for quantitative characteristics.

The Procedure of Mass Selection

Mass selection involves a systematic process to develop a new plant variety by selecting and combining seeds from plants with desirable traits. The procedure typically follows these steps:

1. First Year: Selection of Plants
   • Process: A large number of plants exhibiting similar phenotypic traits—such as vigor, plant type, and disease resistance—are selected. The number of selected plants can range from a few hundred to a few thousand.
   • Considerations: Selecting too many plants may result in minimal improvement, while selecting too few could lead to poor adaptation of the new variety. Seeds from these selected plants are then combined to form a composite seed lot for the next generation.
2. Second Year: Preliminary Testing
   • Process: The composite seed is planted in a preliminary yield trial, which includes standard varieties as controls and the original variety for comparison. This step assesses whether the selection process has led to any significant improvement.
   • Evaluation: The phenotypic characteristics of the new variety are closely examined to determine its performance relative to the controls.
3. Third to Sixth Year: Coordinated Yield Trials
   • Process: The new variety undergoes coordinated yield trials at multiple locations within the same agroclimatic zone.
   • Stages: Initially, the variety is evaluated in an initial trial for one year. If promising, it advances to uniformity regional trials for two or more years. Performance in these trials helps determine if the variety meets the required standards for release.
4. Seventh Year: Variety Release
   • Process: If the variety proves suitable and meets performance criteria, it may be recommended for release by the Central or State Variety Release Committee.
   • Outcome: Successful varieties are then made available for cultivation.

Variations in Mass Selection

1. Improvement of Local Varieties:
   • Selection and Testing: In this variation, a large number of plants are selected and their seeds harvested separately. Progenies from these plants are grown and tested. Poor, weak, or defective progenies, as well as those from heterozygous plants, are rejected, with no more than 20-25% of progenies discarded. Seeds from the remaining progenies are mixed to create a new variety.
   • Evaluation: The new variety undergoes yield trials in various environments to ensure its performance and adaptability, retaining the adaptation of the original variety while offering improved performance.
2. Purification of Existing Pureline Varieties:
   • Selection and Purification: In this process, 200-300 or more plants typical of the pureline variety are selected and harvested separately. Progenies from these plants are grown, and those deviating from the typical features are discarded.
   • Maintenance: This purification process may be repeated periodically to maintain the purity of the variety. The purified variety is then used to produce basic seeds, which are subsequently used for breeder seed production.

Advantages/Merits of Mass Selection

Mass selection offers several advantages in plant breeding, particularly when aiming to develop or improve varieties. The key benefits include:

1. Preservation of Original Adaptation:
   • Stability: By selecting a large number of plants, mass selection helps retain the adaptation of the original variety. This approach ensures that the new variety maintains the environmental suitability of the original.
   • Adaptability: Varieties developed through mass selection, often composed of a mixture of closely related purelines, tend to be more stable across various environments compared to single pureline varieties. This broad adaptability can be advantageous for cultivating crops in diverse conditions.
2. Reduced Need for Extensive Trials:
   • Efficiency: Mass selection often eliminates the need for extensive and prolonged yield trials, which can streamline the development process.
   • Cost and Time Savings: This reduction in trial duration and complexity lowers both the time and costs associated with developing new varieties, making it a more efficient method.
3. Retention of Genetic Variability:
   • Flexibility: Mass selection maintains significant genetic variability within the population. This inherent variability allows for subsequent rounds of mass selection to further enhance the variety over time.
   • Future Improvement: The retained genetic diversity enables ongoing improvement of the variety, adapting to new challenges or changing conditions.
4. Less Demanding Method:
   • Breeder Efficiency: The simplicity of mass selection allows breeders to allocate more time and resources to other breeding programs or research activities.
   • Practicality: The method’s less complex nature makes it a practical choice for many breeding programs, especially where extensive data collection and complex analyses are not feasible.

Disadvantages/Demerits of Mass Selection

Mass selection, while beneficial in many aspects, has several limitations that affect its effectiveness and applicability:

1. Lack of Uniformity:
   • Variation: Varieties produced through mass selection often exhibit greater variation compared to pureline varieties. This variability can result in a less consistent performance across different environments.
   • Perception: Consequently, these varieties are typically less preferred than purelines, which offer more uniform traits.
2. Limited Improvement:
   • Comparison: The level of improvement achieved through mass selection is generally less pronounced than that obtained through pureline selection.
   • Issue: This limitation arises because the new variety may include some progenies that are inferior to the best pureline that could have been selected from the same population.
3. Uncertainty of Plant Homogeneity:
   • Progeny Testing: Without progeny testing, it is difficult to confirm whether the selected plants are homozygous. There is a possibility of heterozygosity due to occasional cross-pollination, even in self-pollinated species.
   • Environmental Influence: Additionally, it is challenging to determine if the observed phenotypic superiority of the selected plants is due to genetic factors or environmental conditions. Incorporating progeny testing, as suggested by Allard, can help address this issue.
4. Limited Use in Self-Pollinated Crops:
   • Popularity of Purelines: The dominance of pureline varieties in crop improvement often limits the use of mass selection. While it is a rapid and convenient method for enhancing old local varieties, its application in widely improved crops is less common.
5. Seed Certification Challenges:
   • Identification: Varieties developed through mass selection are more difficult to identify and categorize compared to purelines during seed certification processes. This can complicate the management and distribution of these varieties.
6. Dependency on Existing Variability:
   • Genetic Variation: Mass selection relies on the existing genetic variability within a variety or population. Therefore, it cannot create new genetic variation. This limitation restricts its use to varieties that already exhibit some level of genetic diversity.

Applications of Mass Selection

Mass selection is a versatile breeding technique with specific applications, particularly for self-pollinated crops. Its primary uses are:

1. Improvement of Local Varieties:
   • Objective: Mass selection enhances land, desi, or local varieties of self-pollinated crops. Local varieties often consist of diverse genotypes that can dilute overall performance.
   • Process: By selecting and eliminating inferior plant types, mass selection aims to increase the uniformity and performance of these varieties.
   • Benefits: This method improves variety performance without significantly affecting its adaptability or stability, as it retains the advantageous traits present in the original local varieties. Local varieties, being well-adapted to their environments, typically show stable performance.
2. Purification of Existing Pureline Varieties:
   • Objective: Mass selection helps maintain the purity of existing pureline varieties, which may become variable over time due to mechanical mixtures, natural hybridization, or mutations.
   • Process: Regular mass selection is used to eliminate undesirable variants and preserve the genetic purity of pureline varieties.
   • Benefits: This ensures that the pureline varieties remain true to their original characteristics and maintain consistent performance.

Achievements of Mass Selection

Mass selection has played a significant role in the development and improvement of crop species throughout history. Its contributions and achievements include:

• Historical Impact on Crop Development:
  • Early Use: Mass selection was utilized by early agriculturalists to enhance and develop modern crop species from their wild ancestors. This method allowed prehistoric humans to differentiate and improve cultivated varieties, highlighting its effectiveness in crop improvement.
  • Historical Contribution: The ability of mass selection to select plants based on desirable traits and improve them over generations contributed significantly to the evolution of present-day crop species.
• Predecessor to Pureline Selection:
  • Traditional Use: Before the advent of pureline selection, mass selection was extensively employed for improving self-pollinated crops. It provided a practical approach for enhancing crop characteristics before more refined techniques became available.
  • Historical Preference: Although mass selection has largely been replaced by pureline selection in modern crop improvement, its historical use underscores its value in the early stages of crop breeding.
• Current Application in Purification of Pureline Varieties:
  • Maintenance of Purity: Today, mass selection is primarily used for the purification of pureline varieties in self-pollinated crops. This practice is essential for maintaining the genetic purity of these varieties, which can become variable due to mechanical mixtures, mutations, or other factors.
  • Routine Practice: Mass selection is performed routinely, either annually or biennially, to ensure the continued superiority and stability of pureline varieties. This process helps preserve the desirable traits and performance of pureline varieties over time.
• Preservation of Genetic Integrity:
  • Addressing Variability: Pureline varieties can lose their genetic uniformity and superiority if not regularly maintained. Mass selection helps address this issue by eliminating unwanted variations and preserving the integrity of the variety.
  • Continued Relevance: Despite its reduced scope compared to pureline selection, mass selection remains a crucial method for sustaining the quality of existing pureline varieties.