PB Ch 25. Mass Selection in Cross Pollinated Crops

Concept and Application

• Imagine walking through a massive field of crops and simply picking the biggest, healthiest-looking plants to save their seeds for next year. This is the oldest, simplest form of plant breeding, known as Mass Selection. 
• However, doing this in cross-pollinated crops (where pollen blows freely in the wind or is carried by bees) is fundamentally different from doing it in self-pollinated crops.
• In plant breeding, mass selection is defined as "selection without progeny testing." This means the breeder chooses plants based purely on how they look (their phenotype), without doing any complex genetic tests to see what kind of offspring they will produce.
• Mass selection in cross-pollinated crops has a different character than in self-pollinated crops
• The key distinction: The female parents are selected, but the male parents (pollen donors) are UNCONTROLLED — any plant in the field can contribute pollen. This means improvement from mass selection is based on only the maternal half of the progeny genotype.

• • When a breeder tags a superior, high-yielding plant to harvest its seeds, they are selecting the female parent (the seed parent). But because the field is open to the wind and insects, the male parent (the pollen donor) is completely uncontrolled. The pollen that fertilized that beautiful plant could have come from the weakest, scrawniest plant in the field. Therefore, any genetic improvement made through mass selection in cross-pollinated crops is based entirely on the maternal half of the genetics.

Standard Mass Selection Procedure

• Year 1: Select phenotypically superior plants (50-100 or more) from the base population; allow open-pollination; harvest separately
• Year 2: Grow progeny rows from selected plants; evaluate for desirable characters; select superior progenies; bulk seeds from superior plants to form the new population
• Year 3 onwards: Preliminary yield trial and then multilocation trials

Modified Mass Selection — Gardner (1961) — Stratified Mass Selection

This modification addresses a key limitation of standard mass selection in cross-pollinated crops: soil heterogeneity in the field confounds selection.

• Concept: The field is divided into a grid of equal-sized plots or sections (strata). A fixed number of the best plants are selected from EACH stratum. This controls for soil heterogeneity — a plant in a good soil patch is not unfairly selected over a plant in a poor soil patch that may have better genetic merit.
• Also called: 'Modified ear-to-row selection' or 'Grid mass selection' .
• Suitable for: Traits with high heritability — plant height, days to maturity, kernel colour. Not suitable for yield itself (low heritability without progeny testing).

4.2  Achievements of Mass Selection

Mass and progeny selections have been extensively used for the improvement of cross-pollinated crops.' Specific achievements:

• Early bajra varieties developed through mass selection from African introductions: Bajapuri, Jamnagar Giant, AF 3, S 530, Pusa Moti
• Toria (Brassica rapa var. toria): mass selection improved yield by 30% and oil content by 56%; a further 16% yield increase obtained by using mass-pedigree method

4.3  Merits and Limitations of Mass Selection in Cross-Pollinated Crops