Convergent evolution of plant parasitism among nematodes, and the relevance of comparative genomics to improve our understanding of (in)compatible host-parasite interactions

Parasitism is a wanted life strategy among nematodes: among the  16,000 described terrestrial species about 25% parasitizes plants, and another 25% animals. Plant parasitism has arisen independently in four different major clades, and even within individual clades plant parasitism arose multiple times. Massive convergent evolution combined with a limited number of informative morphological characters made it nearly impossible to robustly deduce systematic relationships. Wide-scale use of multiple molecular markers allowed for the generation of a more stable overall framework, and currently we have a reasonably good idea about inter-clade and intra-clade relationships among plant parasitic nematodes. Among the 4,100 described plant parasites slightly more than a dozen species are responsible for the major part of the economic losses (worldwide estimated at about €110 billion annually). Here, we will pinpoint the phylogenetic relationships between these high-impact species mainly based on small subunit (SSU) ribosomal DNA sequences. In a next step, we generated PacBio-based reference genomes for a number of major cyst and root knot nematode species to serve as a reference for comparison of re-sequenced field populations. We are currently investigating whether genetic variants can be found that are associated with (a)virulence vis-à-vis a given resistance (R) gene included in crop cultivars. Most R proteins are activated by effector variants present in a subset of the populations of a given species only. We are currently investigating whether effector variants (or tightly associated markers) can be found that are associated with (a)virulence. To illustrate our approach, progress on the effectiveness of resistant potato varieties in relation to the genetic constitution of potato cyst nematode populations will be presented.