Introduction

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. Information is reviewed and validated by ISF DRT. Sometime the set has been subject to an ISF DRT project. The reports of these projects are available following the link in the overview of the differential sets.

About differential sets

Although different levels of resistance to a given pest may exist, the differential varieties are selected for providing a clear, preferable black and white, response to the individual races.  

The different levels of resistance, presented in each table are explained in the legenda of the specific table. If the intermediate level does not exist in a set, the explanation is not mentioned. When genetics are known/named, this is also included in the differential table.

In the sets there is a preference for open-pollinated non-commercial varieties or lines of the relevant species as these are mostly easier to maintain. In those cases where wild relatives are used, the species is indicated between brackets.

Most differential varieties are maintained and publicly available via dedicated collections (Harmorescoll, GEVES, Naktuinbouw, CPPSI).