An ectomycorrhizal symbiosis differently affects host susceptibility to two congeneric fungal pathogens

The role of ectomycorrhizal fungi in modulating host susceptibility to fungal pathogens is poorly known. Pinus sylvestris susceptibility to two congeneric fungal pathogens was compared between mycorrhizal and non-mycorrhizal plants. The ectomycorrhizal fungus was Suillus luteus, while the pathogens were Heterobasidion irregulare and H. annosum. H. irregulare is native to North-America and invasive to Europe, whereas S. luteus and H. annosum are native to Eurasia. Non-mycorrhizal plants were equally susceptible to both pathogens. Mycorrhizal plants were significantly less susceptible to H. annosum than non-mycorrhizal plants, whereas there were no differences when considering H. irregulare. The abundance of ectomycorrhizas was negatively and significantly correlated to the level of host susceptibility only to H. annosum. This study shows that the protective role of ectomycorrhizal fungi may differ when the host is challenged by congeneric fungal pathogens. Results add a further clue to explain and predict the invasiveness of H. irregulare in Europe. (C) 2018 Elsevier Ltd and British Mycological Society. All rights reserved. This work was supported by the Italian Ministry of Education, University and Research, within the FIRB program (grant number RBFR1280NN). Authors are grateful to Francois Rineau for assistance with mycorrhiza inoculations and to Matteo Garbelotto for helpful comments on the manuscript and for revising the English. The authors wish to thank the Editor and the anonymous Reviewers for insightful suggestions on how to improve the manuscript.