Diplodia pinea is a new pathogen on Austrian pine (Pinus nigra) in Estonia

Abstract

Diplodia pinea (syn. Sphaeropsis sapinea), one of the most common and widely distributed pathogens of conifers worldwide (Whitehill et al., 2007), was found in Estonia for the first time in the autumn of 2007. The last decade is characterised by the fast movement of this pathogen from southern Europe to the north. Generally, a southern fungus moves north during drought periods: it is known that D. pinea can be released from its quiescent stage in the host by host water stress (Stanosz et al., 2001). Hard drought in 2003 encouraged D. pinea to become epidemic in Central Europe (e.g. Blaschke & Cech, 2007). Similarly hard droughts were registered in Estonia in 2002 and 2006, following the general trend of climatic change. In September 2007 D. pinea was found on the fallen cones of a middle-aged Austrian pine (Pinus nigra) tree in Järvselja (southeastern Estonia). Cones of an old Austrian pine 3 km to the west and of another middle-aged tree 3 km to the east were uninfected. During the same autumn, fallen Austrian pine cones in Tartu, Tallinn and Pärnu were not observed to be infected. By the middle of May 2008 the fungus was already documented from all the three Austrian pines in Järvselja, but not from the towns. However, by the middle of September 2008 D. pinea was recorded in Pärnu and in Muhumaa island (Pädaste), where there is a single large stand of old Austrian pine. How the fungus entered Estonia is not known – this may have been through insect vectors (Whitehill et al., 2007) or, more probably, by human activities (Burgess et al., 2004). Conidial dimensions in the sample from Järvselja were 30·6–44·7 (47·1) × (11·8) 14·1–16·8 µm. This sample was deposited in the Mycological Herbarium of the Estonian University of Life Sciences, TAA(M) 178 688. The identity of the D. pinea isolate was confirmed by partial sequencing of the internal transcribed spacer (ITS) region at the Finnish Forest Research Institute and deposited in GenBank (Accession No. EU330229). Comparison showed 100% similarity with thirty D. pinea sequences in GenBank (e.g. DQ458895, isolated from P. nigra, the Netherlands; DQ458898, P. patula, Indonesia; and DQ458897, P. radiata, South Africa). We thank Prof. Jarkko Hantula (Finnish Forest Research Institute) for help with the ITS analyses.