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Differential hosts are sets of plant varieties used to define strains of plant pathogens based on susceptible and resistant reactions. Reference strains are known characterized isolates of a given pathogen.


A differential set for a pathogen is defined by varieties from within one or several plant species that are hosts to the pathogen. For example, races of Bremia lactucae causing downy mildew in lettuce are determined solely by using lettuce cultivars. But in the case of root knot caused by Meloidogyne spp. the set is made up of several host species – tobacco, cotton, watermelon, tomato, pepper and peanut. The hosts utilized within differential sets are often existing varieties or experimental species known as indicator hosts.

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.


Use of differential hosts

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.


Differential hosts


This table provides information on the availability of differential hosts and isolates.

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