The concept of physiological races was given by

The concept of physiological races was given by Barrus (1911).
Physiological races are strains of a single pathogen species differing in their ability to attack different varieties of the same host species.
The physiological race is a biotype or group of biotypes within a taxonomic group distinguished by some physiological peculiarity as host preference, chemical dependence, or pathogenicity used especially of economically important fungi, insects, or bacteria.