विस्तृत व्याख्या:

Origins of Cytoplasmic Male Sterility (CMS की उत्पत्ति):

• CMS is controlled by mitochondrial genes (mtDNA) causing failure of viable pollen production.
• CMS originates via three primary pathways:

• Inter-specific / wide hybridization (A): Combining nuclear genome of one species with foreign cytoplasm of a related wild species (alloplasmic male sterility, e.g., Tift 23A pearl millet, WA cytoplasm in rice from wild rice Oryza rufipogon).
• Spontaneous mutation (C): Spontaneous mutations or rearrangements in the mitochondrial genome (e.g., Texas cytoplasm in maize, CMS-S, CMS-C).
• Induced mutation using mitochondrial mutagens (D): Chemical mutagens like Ethidium bromide and streptomycin specifically target and mutagenize extranuclear/mitochondrial DNA to induce CMS.
  • Self-incompatibility (B) is a genetic pre-fertilization barrier preventing self-pollen fertilization, governed by nuclear $S$-alleles, and has no causal relation to CMS cytoplasm.

विस्तृत व्याख्या:

Mechanisms Preventing Self-Pollination (स्व-परागण रोकने की प्रणालियाँ):

• Assertion (A) is TRUE: Self-incompatibility (physiological barrier), male sterility (lack of functional pollen), and pistillate condition (production of only female flowers, as in dioecious plants or gynoecious lines) all physically or genetically enforce cross-pollination by preventing self-fertilization.
• Reason (R) is FALSE: Pistillate lines (gynoecious lines) are widely utilized for commercial hybrid seed production—most notably in castor (Ricinus communis - e.g., VP-1, TSP 10R) and cucurbits (cucumber)—where 100% pistillate lines act as female parents without requiring emasculation. Inbred development, conversely, requires consecutive generations of selfing, which pistillate plants cannot achieve on their own without chemical sex reversion (e.g., silver nitrate/GA).

विस्तृत व्याख्या:

Chasmogamy and Floral Biology in Crop Plants (चैस्मोगैमी एवं पुष्प कार्यिकी):

• Cleistogamy (क्लिस्टोगैमी / अनुन्मील परागण): Flowers never open, strictly ensuring 100% self-pollination within closed petals (e.g., Commelina, subterranean flowers of peanut).
• Chasmogamy (चैस्मोगैमी / उन्मील परागण): Flowers open exposing their reproductive organs to the atmosphere.
• In many autogamous field crops (such as wheat, barley, and rice), anthesis exhibits a specialized chasmogamous behavior where anthers dehisce and self-pollinate the stigma while the glumes/florets are still closed, and flowers open only after self-pollination has already occurred (preventing outcrossing while allowing exhausted anthers to be extruded).
• Official Answer Key: Option 2 represents the accepted NTA definition in agricultural crop breeding context.

Correct Answer: Option 2.

विस्तृत व्याख्या:

Self-Incompatibility (SI) in Angiosperms (स्व-अनिषेच्यता):

• Definition: Self-incompatibility is the inability of viable pollen to fertilize the female gamete of the same flower or other flowers on the same plant due to physiological/biochemical recognition barriers.
• Statement (A) is TRUE: SI acts as a pre-zygotic reproductive barrier preventing self-fertilization.
• Statement (B) is TRUE: By enforcing cross-fertilization (allogamy/outcrossing), SI maximizes heterozygosity and genetic variability within plant populations, avoiding inbreeding depression.
• Statement (C) is FALSE: SI actively prevents self-fertilization, rather than allowing plants to self-fertilize.
• Statement (D) is TRUE: SI is genetically governed by multiallelic $S$-loci (exhibiting Gametophytic Self-Incompatibility / GSI or Sporophytic Self-Incompatibility / SSI).