Diplodia sapinea is a cosmopolitan endophyte and opportunistic pathogen having occurred on several conifer species in Europe for at least 200 years. In Europe, disease outbreaks have increased on several Pinus spp. in the last few decades. In this study, the genetic structure of the European and western Asian D. sapinea population were investigated using 13 microsatellite markers. In total, 425 isolates from 15 countries were analysed. A high clonal fraction and low genetic distance between most subpopulations was found. One single haplotype dominates the European population, being represented by 45.3% of all isolates and found in nearly all investigated countries. Three genetically distinct subpopulations were found: Central/North European, Italian and Georgian. The recently detected subpopulations of D. sapinea in northern Europe (Estonia) share several haplotypes with the German subpopulation. The northern European subpopulations (Latvia, Estonia and Finland) show relatively high genetic diversity compared to those in central Europe suggesting either that the fungus has existed in the North in an asymptomatic/endophytic mode for a long time or that it has spread recently by multiple introductions. Considerable genetic diversity was found even among isolates of a single tree as 16 isolates from a single tree resulted in lower clonal fraction index than most subpopulations in Europe, which might reflect cryptic sexual proliferation. According to currently published allelic patterns, D. sapinea most likely originates from North America or from some unsampled population in Asia or central America. In order to enable the detection of endophytic or latent infections of planting stock by D. sapinea, new species-specific PCR primers (DiSapi-F and Diplo-R) were designed. During the search for Diplodia isolates across the world for species specific primer development, we identified D. africana in California, USA, and in the Canary Islands, which are the first records of this species in North America and in Spain.

Bioeconomy and Environment Natural Resources Institute Finland P O Box 2 00791 Helsinki Finland

Center of Mycology and Microbiology Institute of Ecology and Earth Sciences University of Tartu 14a Ravila 50411 Tartu Estonia

Department of Plant Pathology and Mycology Institute of Forest Ecology Slovak Academy of Sciences 949 01 Nitra Slovakia

Estonian Environment Agency Mustamäe Tee 33 10616 Tallinn Estonia

Forest Pathology Research Group Department of Forest Botany and Tree Physiology Faculty of Forest Sciences and Forest Ecology Georg August University 37073 Göttingen Germany

Institute of Agricultural and Environmental Sciences Estonian University of Life Sciences 51014 Tartu Estonia

Institute of Forestry and Rural Engineering Estonian University of Life Sciences 51014 Tartu Estonia

Latvian State Forest Research Institute Silava Rigas 111 LV 2169 Salaspils Latvia

Norwegian Institute of Bioeconomy Research 1431 Ås Norway

Phytophthora Research Centre Department of Forest Protection and Wildlife Management Faculty of Forestry and Wood Technology Mendel University in Brno Zemědělská 3 613 00 Brno Czech Republic

Section Mycology and Complex Diseases Department of Forest Protection Northwest German Forest Research Institute 37079 Göttingen Germany

Tallinn Botanic Garden Kloostrimetsa Tee 52 11913 Tallinn Estonia

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