Vegetable seed companies strive towards developing varieties with resistance to various plant diseases caused by viruses, bacteria, fungi, nematodes and insects. As these new varieties are cultivated commercially, with time the associated pests evolve too. Pathogenic variation within a (sub)species, known as biotypes, pathotypes, races or strains, is not uncommon.

To identify and distinguish different biotypes, pathotypes, races or strains within a (sub)species, plant pathologists use sets of differential hosts (e.g., plant cultivars) with known susceptible and resistant reactions to any given pathogenic variation of a pest. ISF has gathered information on host differentials from peer-reviewed scientific publications to help seed companies and researchers identifying biotypes, pathotypes, races or strains of a pest. Different varieties or lines with the same resistance gene(s) can give the same reaction to a given biotype, pathotype, race or strain of a pest. Therefore, the differential varieties or lines used by various researchers in the scientific literature and other sources may differ.

The differential sets presented here are intended as a reference and will be updated if a new variation occurs. For the sake of uniformity biotypes, pathotypes, races or strains are all referred to as “race.” ISF accepts no liability for the use of the information provided in the documents below.