What is the Difference Between Mass Selection and Pure Line Selection

The main difference between mass selection and pure line selection is that a mass selection contains a mixture of pure lines, whereas a pure line selection contains a set of uniform characteristics. Furthermore, in a mass selection, both self- and cross-pollinated species occur while only self-pollinated species occur in a pure line selection. Moreover, genetic variation is present in a mass selection, while genetic variation does not occur in a pure line selection.  

Mass selection and pure line selection are two types of selective breeding methods used to improve crops. Generally, they belong to artificial selection methods along with the clonal selection, which is another selection method. 

Key Areas Covered 

1. What is Mass Selection
     – Definition, Characteristics, Process
2. What is Pure Line Selection
     – Definition, Characteristics, Process
3. What are the Similarities Between Mass Selection and Pure Line Selection
     – Outline of Common Features
4. What is the Difference Between Mass Selection and Pure Line Selection
     – Comparison of Key Differences

Key Terms 

Artificial Selection, Breeding methods, Pure Line Selection, Mass Selection

What is Mass Selection 

Mass selection is an artificial method of crop improvement. Moreover, it is the oldest and simplest method of artificial selection. It mainly involves the selection of individual plants from a mixed population on the basis of phenotypes. Then, the seeds of these plants can grow in the next generation. Moreover, the main purpose of mass selection is to develop a new cultivar with improved average performance in the population. Also, it helps to increase the frequency of superior genotypes from a genetically variable population, purifying the population.

Figure 1: Corn Selection – Over Time, Selective Breeding Modifies Teosinte’s Few Fruitcases (left) into Modern Corn’s Rows of Exposed Kernels (right)

Furthermore, during mass selection, 200-2000 plants with similar and desirable characteristics are selected from a population. Then, the seeds can be grown in a preliminary yield trial along with standard checks. After that, the phenotypes of this generation are clearly evaluated. Therefore, promising selections can stand out as a new variety. Finally, the seeds of the new variety are collected. 

What is Pure Line Selection 

Pure line selection is another artificial method of crop improvement. Basically, a pure line refers to a progeny of a single, homozygous, and self-pollinated plant. Therefore, in the pure line selection, around 200-3000 plants can be selected from a self-pollinated crop. Then, the seeds of these plants can grow as individual progenies. Out of them, the best progeny will serve as the pure line variety. Furthermore, the main characteristic feature of the pure line is that it contains identical and homozygous genotypes. 

Figure 1: Pure Line Selection of Carrots

However, pure lines may achieve genetic variations due to the mechanical mixture, natural hybridization, and mutations with time. Due to the presence of extreme uniformity, both farmers and consumers prefer pure line varieties. However, these varieties do not have more adaptations and stability when compared to the mass-selected varieties.  

Similarities Between Mass Selection and Pure Line Selection 

• These are two types of artificial selection methods. 
• They are breeding methods are important to improve crops by farmers.  
• Also, they take part in animals breeding as well. 

Difference Between Mass Selection and Pure Line Selection 

Definition 

Mass selection refers to a method of crop improvement in which individual plants are selected on the basis of phenotype from a mixed population, and their seeds are bulked and used to grow next generation. On the other hand, pure line selection refers to a method in which new variety is developed by a selection of single best plant progeny among traditional varieties or landraces.  

Significance 

Mass selection is the simplest and oldest method of crop improvement while pure line selection was first introduced by W. L. Johannsen in Denmark in 1903. 

Characteristics 

Moreover, mass-selected variety is a mixture of pure lines while pure line selected variety contains a single pure line, which is a progeny of a single individual obtained by selfing. 

Type of Pollination 

While mass selection uses both self-pollination and cross-pollination, pure line selection uses only self-pollination. Thus, this is the main difference between mass selection and pure line selection.

Genetic Variation 

Therefore, genetic variation is present in mass selection, while pure line selection does not contain genetic variation. 

Homozygous or Heterozygous 

Also, another difference between mass selection and pure line selection is that mass-selected variety is heterozygous while pure line selected variety is homozygous. 

Adaptations and Stability 

Furthermore, mass-selected variety contains a wide range of adaptations and has more stability while the pure line has a few adaptations and less stability. 

Uniformity 

Mass-selected variety is less uniform characteristics while pure line selected variety is highly uniform characteristics. 

Identification in Seed Clarification Programs 

The seeds of mass selected variety are difficult to identify while the seeds of pure line selected variety are easy to identify. 

Conclusion 

Mass selection is the oldest method of artificial selection to improve crops. Generally, it allows both self and cross-pollination. Therefore, the mass-selected variety has genetic variation, more adaptations, and stability. Typically, it contains a mixture of pure lines. On the other hand, pure line selection is a method of artificial crop improvement that involves the development of only a single progeny through self-pollination. Therefore, this variety contains no genetic variation, fewer adaptations, and less stability. Hence, the main difference between mass selection and pure line selection is the characteristics of each variety.   

References:

1. Shimona, K. “Mass Selection: Features & Types: Methods: Crop Improvement: Botany.” Botany Library, 22 July 2017, Available Here.
2. Shimona, K. “Pure-Line Selection in Crops: Meaning and Theory: Plant Breeding: Botany.” Botany Library, 22 July 2017, Available Here.

Image Courtesy:

1. “Cornselection” By John Doebley – Genetically Modified Corn— Environmental Benefits and Risks Gewin V PLoS Biology Vol. 1, No. 1, e8 doi:10.1371/journal.pbio.0000008 Jornual Pbio (CC BY 2.5) via Commons Wikimedia  
2. “Carrots of many colors” By Stephen Ausmus – Agricultural Research Service (Public Domain) via Commons Wikimedia