Fern leaf disorder in potato is associated with deficiency of . . . . . . . .

Answer: Option C

Fern leaf disorder in potatoes is associated with a deficiency of Zinc.
Zinc deficiency symptoms of potatoes, also known as "fern leaf" or "little leaf", appear on young developing leaves as chlorosis, followed by the formation of narrow upwardly cupped leaf blades, often with tip burn.
As the deficiency progress, these symptoms develop into intense interveinal necrosis but the main veins remain green, as in the symptoms of recovering iron deficiency.