Concept:Maize rust is a plant disease caused by a fungal pathogen.Explanation:The causative organism of maize rust is a fungus, scientifically known as Pucciniasorghi.Fungi are distinct from protozoa, bacteria, and viruses in their cellular structure and reproduction.This fungal infection appears as rust-colored pustules on maize leaves.Protozoa, bacteria, and viruses do not cause maize rust.Answer:C. fungus