Step 1: Understanding the Question:
This question tests knowledge of plant diseases and their causal organisms.
Step 2: Detailed Explanation:
Seed gall of wheat is caused by the nematode Anguina tritici (ear cockle nematode).
It causes galls to form on the seeds of wheat.
Insect (A): Not the cause.
Fungus (B): Not the cause.
Mite (D): Not the cause.
Thus, nematode is the causal organism.
Step 3: Final Answer:
Thus, seed gall of wheat is caused by a nematode, which corresponds to option (C).
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