Vegetable seed companies strive towards developing varieties with resistance to various diseases. As these new varieties are cultivated commercially, with time the associated plant pathogens evolve too. Pathogenic variation known as races within a species is not uncommon. To identify and distinguish different species of a pathogen and/or races within a species plant pathologists use 'differential sets'.
A differential set for a pathogen can be made up of 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 varieties/lines. But in the case of root knot caused by the Meloidogyne genera of nematodes, the set is made up of several species - tobacco, cotton, watermelon, tomato, pepper and peanut. The hosts utilized within differential sets are often times existing varieties or experimental species known as indicator hosts.
Race denomination varies from region to region. In some instances the same system is in use everywhere, as in the case of leaf mould in tomato (Ff) and near wilt in pea (Fop). But often there are different systems. In some instances this causes no problem because there is no overlap in denomination, as in anthracnose in bean ( Cl) in Europe and USA, or where by using joint host differential sets the systems are linked as in the case with downy mildew in lettuce (Bl) in Europe and USA. However, the use of differing systems causes an overlap in strain names, e.g. in Fusarium wilt in tomato (Fol 0, 1 and 2 in Europe, Fol 1, 2 and 3 in USA) and downy mildew in spinach (Pfs).
In its desire to inform customers in a way that does not create confusion, the Pathogen Codification Working Group is trying to identify all known differential sets for key vegetable host/pathogen combinations. As and when the sets are complete they will be posted on this website with the name(s) of person(s) who can be contacted for more information.
Differential Sets:
Announcement
ISF Secretariat - Chemin du Reposoir 7 - 1260 Nyon Switzerland
tel +41 22 365 44 20 - fax +41 22 365 44 21 - isf@worldseed.org
ISF Secretariat
Chemin du Reposoir 7
1260 Nyon Switzerland
tel +41 22 365 44 20
isf@worldseed.org
