• Etiology of Tundu / Yellow Ear Rot Disease of Wheat:
• Synergistic Association: Tundu disease (yellow slime rot) is a classic disease complex requiring the obligatory interaction between a nematode vector and a bacterium:
• Nematode Vector: Anguina tritici (wheat gall nematode).
• Bacterial Pathogen: Clavibacter tritici (now classified as Rathayibacter tritici).
• Mechanism: $J_2$ juveniles of Anguina tritici carry bacterial cells adhering to their cuticles as they migrate upward on dew films into the floral meristem, where the bacterium proliferates and exudes copious bright yellow gum/slime that glues the earhead.
• Conclusion: The bacterium carried is Clavibacter tritici (Option 3).

Correct option: (3) Clavibacter tritici

• Stylet Morphology Across Developmental Stages in Cyst Nematodes (Heterodera / Globodera):
• Juvenile Stages: Second-stage juveniles ($J_2$) hatch from eggs equipped with a robust, heavily sclerotized stylet used to penetrate host roots and induce syncytia.
• Third ($J_3$) and Fourth ($J_4$) Stages: During post-infection swelling, the developing $J_3$ and $J_4$ juveniles retain their stomatal stylet, which remains functional for continuous nutrient ingestion from the syncytium until the final molt.
• Conclusion: Statement (I) is incorrect but Statement (II) is correct (Option 4).

• Quarantine Plant Parasitic Nematodes in India (Plant Quarantine Order 2003):
• Quarantine Species:
• Ditylenchus dipsaci (Stem and bulb nematode): Regulated quarantine pest of temperate bulbs and garlic, completely prohibited from introduction.
• Ditylenchus destructor (Potato rot nematode): Regulated quarantine pest targeting potato tubers and bulbs.
• Domestic/Endemic Species:
• (C) Ditylenchus angustus: Endemic to rice-growing regions of West Bengal and Assam.
• (D) Ditylenchus composticola: Mushroom pest occurring domestically.
• Conclusion: Species of quarantine importance are (A) and (B) only (Option 1).

Correct option: (1) (A) and (B) only.

• Odontophore Morphology in Longidorus vs Xiphinema:
• Taxonomic Differentiation: Both genera belong to Longidoridae but are differentiated by their feeding apparatus:
• Xiphinema (Dagger nematode): The odontophore (stylet base) bears three prominent basal flanges or swellings for protractor muscle attachment.
• Longidorus (Needle nematode): The odontophore is a simple, slender, rod-like tube that lacks basal flanges completely.
• Conclusion: Statement (I) is incorrect but Statement (II) is correct (Option 4).