An organism which causes a disease in plant is called as

An organism that causes a disease in a plant is called as Pathogen.
A pathogen in the oldest and broadest sense is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.
Typically, the term pathogen is used to describe an infectious microorganism or agent, such as a virus, bacterium, protozoan, prion, viroid, or fungus.