Definition
Pathogenic refers to something that is capable of causing disease.
Etymology. "producing disease," 1852, from Fr. pathogénique, from Gk. pathos "disease" (see pathos) + Fr. génique "producing." Earlier pathogenetic (1838). Pathogen "a bacteria that produces disease" is an 1880 back-formation.
Discussion
Pathogenic Relations
1) Obligate parasite - requires a living host to complete its life cycle.
2) Facultative parasite - normally exists as a saprophyte, but may live parasitically.
3) Facultative saprophyte - normally exists as a parasite, but may live as a saprophyte.
4) Obligate saprophyte - only obtains nutrients from non-living carbon sources.
These developments led to the expression of the above concepts using different terminology, as follows:
1) Biotroph - obtains nutrients only from living cells in nature.
2) Transitory Biotroph - initially obtains nutrients from living cells, but causes cell death.
3) Necrotroph - obtains nutrients from dead cells.