Vegetable seed companies strive towards developing varieties with resistance to various diseases. As these new varieties are cultivated commercially, with time the associated pathogens evolve too. Pathogenic variation known as races or strains within a species is not uncommon.

To identify and distinguish different species of a pathogen and races/strains within a species plant pathologists use ‘differential hosts’. Differential hosts are sets of plant cultivars used to define pathotypes of pathogens based on known susceptible and resistant reactions.

ISF has gathered information on host differentials from peer-reviewed scientific publications to help seed companies and researchers identify selected pathogen races and strains. Different varieties or lines with the same resistance gene(s) can give the same reaction to a given race or strain of pathogen. Therefore, the differential varieties or lines used by various researchers may differ. The differential sets presented here may be different than those found in the scientific literature and other sources. ISF accepts no liability for the use of the information provided in the documents below.