Specific strain of species adapted to a particular set of environment is called as

Specific strain of species adapted to a particular set of the environment is called an Ecotype.
An ecotype is a variant in which the phenotypic differences are too few or too subtle to warrant being classified as a subspecies. These different variants can occur in the same geographic region where distinct habitats such as meadow, forests, swamps, and dunes provide ecological niches.
An ecotype is different than a subspecies, which may exist across several different habitats. In animals, ecotypes owe their differing characteristics to the effects of a very local environment.