• Races and Speciation of the Burrowing Nematode (Radopholus):
• Banana Race (Radopholus similis): Infests banana, ginger, and black pepper, but cannot parasitize or reproduce on citrus roots.
• Citrus Race (Radopholus citrophilus): First described from Florida causing 'spreading decline' of citrus orchards. It was elevated to species rank (R. citrophilus) based on karyotype ($n=5$ vs $n=4$) and is able to parasitize both citrus and banana.
• Conclusion: Statement (I) is incorrect (the citrus race parasitizes both) but Statement (II) is correct (Option 4).

• Comparative Histopathology of Banana Root Lesions:
• Helicotylenchus multicinctus (Spiral nematode): Semi-endoparasitic feeder that invades only the superficial layers of the root cortex, creating small, discrete, shallow necrotic spots ($\lt 2-3\text{ mm}$ deep).
• Radopholus similis (Burrowing nematode): Extensive migratory endoparasite that creates massive, continuous, deep reddish-brown to black necrotic cavities penetrating through the entire cortex to the stele, destroying structural support.
• Diagnostic Distinction: Lesions differ fundamentally in their size and depth within root tissues (Option 2).

Correct option: (2) Size and depth

• Nurse Cell Complex of Citrus Nematode (Tylenchulus semipenetrans):
• Feeding Site Structure: The posterior swollen body of the sedentary semi-endoparasitic female remains outside the root while the slender anterior neck penetrates deep into the inner cortex.
• Cellular Anatomy: Surrounding the nematode head, 6–10 cortical cells are transformed into a specialized feeding site called a 'nurse cell unit'.
• Cytology: Unlike root-knot nematodes which induce giant multinucleate cells, nurse cells in citrus roots remain multicellular, with each cortical cell remaining uninucleate, exhibiting dense cytoplasm, hypertrophied nucleoli, and absence of central vacuoles.
• Conclusion: The feeding sites are cortical cells, multicellular, uninucleate (Option 3).

Correct option: (3) Cortical cell, multicellular, uninucleate