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Front. Plant Sci. | doi: 10.3389/fpls.2018.01818

Diplodia tip blight on its way to the north: drivers of disease emergence in Northern Europe

  • 1Department of Forest Mycology and Plant Pathology, Faculty of Forest Sciences, Swedish University of Agricultural Sciences, Sweden
  • 2Institute of Forestry and Rural Engineering, Estonian University of Life Sciences, Estonia
  • 3Instituto Pirenaico de Ecología, Consejo Superior de Investigaciones Científicas, Spain
  • 4Instituto de Investigación en Manejo Forestal Sostenible, Universidad de Valladolid, Spain
  • 5Faculty of Forestry, Bursa Technical University, Turkey
  • 6Istituto per la Protezione Sostenibile delle Piante (IPSP), Italy
  • 7Departamento de Producción Vegetal y Ciencia Forestal, Universitat de Lleida, Spain

Disease emergence in northern and boreal forests has been mostly due to tree-pathogen encounters lacking a co-evolutionary past. However, outbreaks involving novel interactions of the host or the pathogen with the environment have been less well documented. Following an increase of records in Northern Europe, the first large outbreak of Diplodia pinea was discovered in Sweden in 2016. By reconstructing the development of the epidemic, we found that disease started ca. 10 years back from several isolated trees in the stand, and ended up affecting almost 90% of the trees in 2016. Limited damage was observed in other plantations in the surroundings of the affected stand, pointing to a new introduced pathogen as the cause of the outbreak. Nevertheless, no genetic differences based on SSR markers were found between isolates of the outbreak area and other Swedish isolates predating the outbreak, nor from other populations in Europe and Asia Minor. On a temporal scale, we saw that warm May and June were associated with higher damage and low tree growth, while cold and rainy conditions seemed to favour growth and deter disease. At a spatial scale, we saw that spread occurred predominantly in the SW aspect-area of the stand. Within that area and based on tree-ring and isotope (δ13C) analyses, we saw that disease occurred on trees that over the years had shown a lower water-use efficiency (WUE). Spore traps showed that highly infected trees were those producing the largest amount of inoculum. D. pinea impaired latewood growth and reduced C reserves in needles and branches proximal to the damaged area. D. pinea attacks can cause serious economic damage by killing new shoots, disrupting the crown and affecting the quality of stems. Our results show that D. pinea has no limitations in becoming a serious pathogen in Northern Europe. Management should focus on reducing inoculum, especially since climate change is making climatic conditions increasingly favourable for this pathogen. We speculate that D. pinea was introduced in the stand via infected planting material. Seedlings should be carefully inspected as D. pinea may be present in a latent stage in asymptomatic tissues.

Keywords: Carbon isotope (σ13C), Water-use efficiency (WUE), Latewood (LW), Range Expansion (RE), Forest pathogens

Received: 15 Jul 2018; Accepted: 22 Nov 2018.

Edited by:

Kristian Forbes, University of Arkansas, United States

Reviewed by:

Luana Giordano, Dipartimento di Scienze Agrarie, Forestali e Alimentari, Università degli Studi di Torino, Italy
Bruno Scanu, University of Sassari, Italy  

Copyright: © 2018 Brodde, Adamson, Camarero, Castaño, Drenkhan, Lehtijarvi, LUCHI, Migliorini, Sánchez-Miranda, Stenlid, Özdağ and Oliva. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Jonàs Oliva, Departamento de Producción Vegetal y Ciencia Forestal, Universitat de Lleida, Lleida, Spain, jonas.oliva@pvcf.udl.cat