The classical gene-for-gene model underlying the current pathotype scheme for potato cyst nematodes may not properly explain virulence patterns in natural populations of potato cyst nematodes. This conclusion is supported by the recent discoveries of resistance-breaking populations of potato cyst nematode across Europe. These resistance-breaking populations have remained unnoticed for a long time, because of the wide application of soil fumigants until 2008 and the intrinsically low reproduction rate of potato cyst nematodes. The objective of this project is to resolve the genetic mechanisms underlying virulence patterns of potato cyst nematodes based on immune suppressors and elicitors in the SPRYSEC gene family. It is expected that changing complements of elicitors and suppressors of immunity determine virulence in potato cyst nematodes.