Question

Male sterile cytoplasm in crop plants usually arises from- 
• [(A).] Inter-specific hybridization 
• [(B).] Self-incompatibility 
• [(C).] Spontaneous mutation 
• [(D).] Induced mutation through Ethium Bromide Choose the correct answer from the options given below: 
 

• A. (A), (B) and (C) only.
• B. (A), (B) and (D) only.
• C. (A), (C) and (D) only.
• D. (B), (C) and (D) only.

Hint:

CMS is maternally inherited because organelles (like mitochondria) are transmitted through the egg cell, not the pollen.
To produce fertile hybrid seeds using a CMS line, breeders must cross it with a male line carrying nuclear Restorer of fertility (Rf) genes.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Cytoplasmic Male Sterility (CMS) is a maternally inherited condition where plants cannot produce functional pollen.
It is caused by mutations or rearrangements in mitochondrial DNA (mtDNA).

Step 3: Detailed Explanation:
Let us evaluate how CMS cytoplasm can arise in plants:
- Inter-specific hybridization (A): Crossing an elite crop species with a wild relative and repeatedly backcrossing with the crop species replaces the wild nuclear genome with the crop genome.
This places the crop's nucleus into a foreign cytoplasm, and the resulting genomic-cytoplasmic incompatibility often causes CMS. Thus, (A) is correct.
- Self-incompatibility (B): This is a pre-zygotic genetic barrier controlled by nuclear S-alleles to prevent self-pollination, and is unrelated to mitochondrial CMS. Thus, (B) is incorrect.
- Spontaneous mutation (C): Natural mutations, deletions, or rearrangements within mitochondrial DNA can create chimeric mitochondrial genes that disrupt pollen development, causing CMS. Thus, (C) is correct.
- Induced mutation (D): Exposure to chemical mutagens that target organelle DNA (such as Ethidium Bromide or acridine dyes) can induce mitochondrial mutations that lead to CMS. Thus, (D) is correct.
Therefore, (A), (C), and (D) are valid sources of cytoplasmic male sterility.

Step 4: Final Answer:
The correct combination is (A), (C) and (D) only, matching Option (C).