Q.55 For commercial production of hybrid seeds, the tlu•ee lines namely A. B and C refer to:
I. Maintainer, female parent and restorer. respectively.
2. Restorer, Maintainer, bisexual parent respectively
3. Bisexual parent, Restorer and Female parent respectively
4. Female parent. Maintainer and Male parent respectively
The correct answer for Q.55 is 4. Female parent, Maintainer and Male parent respectively.
Detailed Explanation (Three-Line Hybrid Seed Production)
In the three-line cytoplasmic-genetic male sterility (CGMS) system used for commercial hybrid seed production (rice, sorghum, sunflower, etc.):
A-line: Female parent (Cytoplasmic Male Sterile line) – cannot produce functional pollen, serves as seed parent for hybrid production.
B-line: Maintainer (fertile line, isogenic to A-line nuclear genes) – used to propagate/maintain the sterile A-line via A×B crosses.
R-line: Male parent (Restorer/Fertility Restorer) – fertile line with restorer genes (Rf) that restore pollen fertility in F1 hybrids (A×R).
Production scheme:
-
Maintenance: A-line × B-line → A-line seeds (maintains sterility)
-
Commercial hybrid: A-line × R-line → F1 hybrid seeds (fertile, heterotic)
Options Explained
1. Maintainer, female, restorer: Wrong—A-line is female, not maintainer.
2. Restorer, Maintainer, bisexual: Wrong—No “bisexual parent”; A-line is strictly female sterile.
3. Bisexual, Restorer, Female: Wrong—Reversed; A-line is female parent.
4. Female parent, Maintainer, Male parent: Correct—Standard A (♀), B (maintainer), R (♂) nomenclature.
Introduction
For commercial production of hybrid seeds, the three lines namely A, B and C refer to Female parent (A-line CMS), Maintainer (B-line), and Male parent (R-line restorer). This three-line CGMS system exploits cytoplasmic male sterility for controlled cross-pollination yielding heterotic F1 hybrids.
Three-Line System Workflow
Maintenance Cross: A-line (♀ sterile) × B-line (♂ maintainer) → A-line seeds
Commercial Hybrid: A-line (♀ sterile) × R-line (♂ restorer) → F1 Hybrid seeds (fertile)
Line Functions Table
| Line | Role | Genotype | Cross Function |
|---|---|---|---|
| A | Female parent | CMS (sterile) | Hybrid seed production |
| B | Maintainer | Normal fertility, isogenic nuclei | Maintains A-line sterility |
| R | Male parent | Normal + Rf genes | Restores F1 fertility |
Key Genetic Basis
-
A-line: Sterile cytoplasm + recessive nuclear sterility genes (rf/rf)
-
B-line: Normal cytoplasm + rf/rf (matches A-line nuclei)
-
R-line: Normal cytoplasm + Rf/Rf (dominant restorers)
Exam Memory Aid
“A = Female (sterile), B = Backup maintainer, R = Restorer male”. Standard across rice, pearl millet, sunflower hybrids.
