Pathogenicity and host range of Heterodera arenaria in coastal foredunes

In coastal foredunes, the cyst nematode Heterodera arenaria has been supposed to play a role in degeneration of the pioneer grass Ammophila arenaria (marram grass). However, recent field surveys and field inoculation experiments suggested that the abundance of this cyst nematode is controlled by the host plant. Here, we test pathogenicity of H. arenaria by inoculating a range of densities of second-stage juveniles (J2) onto A. arenaria in sterilised soil. Plant root biomass was reduced after 6 weeks of growth, but not after 13 weeks, when cyst formation was completed. Shoot biomass was not influenced. In the field, H. arenaria occurred in sand and on roots of Elymus farctus and A. arenaria in mobile dunes, but not on A. arenaria in stable dunes. Although we observed Heterodera cysts and juveniles in later succession stages, this cyst nematode appeared to be H. hordecalis. In a host suitability test, H. arenaria produced cysts on E. farctus and A. arenaria, while there were almost no cysts produced when J2 had been added to the later succession species Festuca rubra ssp. arenaria, Carex arenaria, Elymus athericus and Calamagrostis epigejos. Heterodera arenaria did not negatively affect its natural host plants. However, H. arenaria reduced root growth of one later succession plant species, E. athericus, which was a poor host for H. arenaria. The effects of H. arenaria inoculation on plant biomass production did not differ when J2 were added to plants growing in non-sterilised soil. We conclude that H. arenaria is specialised on the pioneer grasses E. farctus and A. arenaria, and also on mobile dunes as a habitat. Our results confirm recent suggestions that H. arenaria may cause little direct growth reduction to its natural host plants.