Summary

Synchytrium endobioticum is the causal agent of potato wart. This quarantine potato pathogen is believed to originate in the Andean mountains of Latin America and spread to Europe and further to other parts of world at the end of the nineteenth century. The pathogen is found as different pathotypes displaying differences in virulence against different potato cultivars. Currently around 40 different pathotypes have been described in Europe. There is no clear relationship between pathotypes and genotypes and therefore isolates of the pathogen with different genotypes and origin can still display the same virulence profile in bioassays.

Several collaborative research initiatives have been undertaken and the detection and diagnostics methods available has been improved and updated. However, the EPPO standard bioassay available to describe the different pathotypes is limited to the detection of the major pathotypes 1(D1), 2(G1), 6(O1) and 18(T1). There is currently no agreed standard assay available to detect and describe other pathotypes.

The resistance breeding is complicated by the complex inheritance pattern of cultivated potato and that different genes and different alleles are involved in the resistance against different pathotypes. Nevertheless breeding for resistance in potato has been very successful against pathotype 1(D1). However, it has proven more difficult against the other pathotypes. Fewer potato cultivars that are resistant against e.g. pathotypes 2(G1), 6(O1) and 18(T1) are thus available and even fewer for the more rarely found pathotypes.

S. endobioticum is extremely resistant and the only efficient way to control the disease is to prevent the spread into new locations. The use of resistant potato cultivars is an essential part of the current control strategy to limit further spread. The level of resistance required to prevent further spread is however not known and no standard is currently available for the assessment of the level of resistance of different potato cultivars, although it is under development at EPPO. The level of resistance of the potato cultivars used is not only important in terms of preventing secondary spread of the pathogen but has also been found to affect the potential for development of new pathotypes.