Q.47 Given below are two statements: one is labelled as Assertion-A and the other is labelled as Reason-R
Assertion-A: Bud pollination overcomes sexual incompatibility.
Reason-R: At bud stage stigma lacks the exudate.
In the light of the above statements, choose the most appropriate answer from the options given below:
- Both A and R are correct and R is the correct explanation of A
- Both A and R are correct but R is NOT the correct explanation of A
- A is correct but R is not correct
- A is not correct but R is correct
Both A and R are correct but R is NOT the correct explanation of A. Bud pollination bypasses stigma-based sexual incompatibility by allowing pollen tube growth before rejection mechanisms activate fully, while stigma lacking exudate at bud stage is true but represents only one factor among several.
Question Analysis
Bud pollination involves pollinating unopened flower buds to overcome self-incompatibility (SI), particularly sporophytic SI where rejection occurs at stigma surface. The immature stigma at bud stage hasn’t fully developed recognition proteins or exudates that mediate pollen rejection.
Option Breakdown
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Both correct, R explains A: Incorrect. While reduced exudate contributes, bud pollination succeeds through multiple mechanisms including bypassed style/style canal rejection and pollen tube outgrowing rejection response timing.
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Both correct, R NOT explanation: Correct. A describes the technique’s efficacy; R notes an accurate observation (immature stigmas drier, less proteinaceous) but doesn’t comprehensively explain success mechanism.
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A correct, R incorrect: Incorrect. Bud pollination established technique for SI overcoming in Brassicaceae, Solanaceae; R observation confirmed across studies.
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A incorrect, R correct: Incorrect. Bud pollination demonstrably successful in many species despite occasional failures in late-acting SI systems.
Correct Answer: Both A and R are correct but R is NOT the correct explanation of A.
Bud pollination overcomes sexual incompatibility in self-incompatible plants by applying pollen to unopened buds before full SI system activation. This timing advantage allows pollen tubes to penetrate ovary before stigma rejection response matures.
Mechanism Details
Immature Stigma: Bud stage stigmas lack full complement of S-RNase proteins (Garnotophytic SI) or S-locus glycoproteins (SSI). Reduced exudate limits hydration/rejection signaling.
Temporal Bypass: Pollen tubes traverse style before papillae fully differentiate rejection response—critical 24-48 hour window.
Success Rates: 60-90% in Brassicaceae vs <5% open flower selfing; variable in Malvaceae with late-acting SI.
Statement Validity Mechanism Contribution Assertion A True Bypasses stigma rejection Reason R True Immature stigma fact R explains A No Partial mechanism only Applications & Limitations
Breeding: Essential for hybrid seed production in ornamentals, vegetables.
Limitations: Fails in late-acting ovular SI (Ceiba chodatii); requires precise developmental timing.
Alternatives: Mentor pollen, CO₂ treatment, heat/aging flowers.Crucial distinction for plant breeding entrance exams—R contributes but doesn’t fully account for bud pollination efficacy.
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