• Sugar Beet Cyst Nematode (Heterodera schachtii):
• Quarantine Importance: Heterodera schachtii is the notorious cyst nematode of sugar beet and brassicas causing 'beet-weariness' in Europe and North America.
• Indian Status: It is a strictly regulated quarantine pest under Indian Plant Quarantine regulations to safeguard domestic temperate sugar beet and cruciferous seed production.
• Other Cyst Nematodes: H. glycines affects soybean; H. goettingiana affects peas; H. humuli affects hops.
• Conclusion: H. schachtii is the nematode of quarantine importance for sugar beet (Option 2).

Correct option: (2) H. schachtii

• Assertion (A): True. Plant quarantine comprises legal regulatory measures enforced by government authorities to prevent the introduction and spread of dangerous foreign plant pathogens, nematodes, insects, and weed seeds into a country or geographical region.
• Reason (R): True. The primary operational mechanism of quarantine is the statutory restriction and prohibition of moving potentially infested vegetative planting material, seeds, and soil from infested zones to uninfected areas.
• Relationship: Reason (R) provides the direct operational rationale that explains why and how the regulatory mechanism in Assertion (A) functions (Option 1).

Correct option: (1) Both (A) and (R) are true and (R) is the correct explanation of (A)

• Hot Water Treatment for White Tip Nematode (Aphelenchoides besseyi):
• Seed Sanitation in Rice: Aphelenchoides besseyi survives in anhydrobiotic dormancy beneath the hull (lemma and palea) of infested rice seeds.
• Temperature-Time Protocol: Soaking pre-conditioned paddy seeds in hot water at $50^\circ\text{C}$ to $52^\circ\text{C}$ for 10 minutes (or $52-53^\circ\text{C}$ for 15 min without prior soaking) achieves $100\%$ mortality of dormant nematodes without impairing seed germination percentage.
• Conclusion: Hot water at $50^\circ\text{C}$ for 10 min is the recommended treatment (Option 4).

Correct option: (4) Hot water at 50°C for 10 min