What does the term 'pathogen' refer to?

The term 'pathogen' specifically refers to a causal agent of disease, which is a fundamental concept in plant pathology. Pathogens can include various microorganisms such as fungi, bacteria, viruses, and nematodes that lead to diseases in plants. Understanding that pathogens are the organisms responsible for causing disease is crucial for identifying and managing plant health issues.

In contrast, a method for controlling plant diseases would refer to strategies or practices used to manage the effects of pathogens, but it does not define what a pathogen is. The study of plant diseases pertains to the field of plant pathology itself and involves researching and understanding how plant diseases manifest, rather than defining the pathogens responsible for those diseases. Symptoms observed in infected plants are the manifestations of disease caused by the pathogen, but they do not represent the pathogen itself. This distinction highlights why 'Causal agent of disease' is the precise meaning of 'pathogen.'