Lecanosticta acicola is a pine needle pathogen causing brown spot needle blight that results in premature needle shedding with considerable damage described in North America, Europe, and Asia. Microsatellite and mating type markers were used to study the population genetics, migration history, and reproduction mode of the pathogen, based on a collection of 650 isolates from 27 countries and 26 hosts across the range of L. acicola. The presence of L. acicola in Georgia was confirmed in this study. Migration analyses indicate there have been several introduction events from North America into Europe. However, some of the source populations still appear to remain unknown. The populations in Croatia and western Asia appear to originate from genetically similar populations in North America. Intercontinental movement of the pathogen was reflected in an identical haplotype occurring on two continents, in North America (Canada) and Europe (Germany). Several shared haplotypes between European populations further suggests more local pathogen movement between countries. Moreover, migration analyses indicate that the populations in northern Europe originate from more established populations in central Europe. Overall, the highest genetic diversity was observed in south-eastern USA. In Europe, the highest diversity was observed in France, where the presence of both known pathogen lineages was recorded. Less than half of the observed populations contained mating types in equal proportions. Although there is evidence of some sexual reproduction taking place, the pathogen spreads predominantly asexually and through anthropogenic activity.

Austrian Research Centre for Forests Department of Forest Protection Vienna Austria

Department of Agricultural Food Environmental and Forest Sciences and Technologies University of Florence Florence Italy

Department of Biochemistry Genetics and Microbiology Forestry and Agricultural Biotechnology Institute University of Pretoria Pretoria South Africa

Department of Plant Pathology and Mycology Institute of Forest Ecology Slovak Academy of Sciences Nitra Slovak Republic

Department of Plant Protection Federal Research Centre the Subtropical Scientific Centre of the Russian Academy of Sciences Krasnodar Russia

Faculty of Forestry Çankırı Karatekin University Çankırı Turkey

Forest Protection and Forest Health Section Federal Office for the Environment FOEN Bern Switzerland

GREEN IT Bioresources for Sustainability ITQB NOVA Oeiras Portugal

Institute for Plant Protection in Horticulture and Forests Julius Kuehn Institute Braunschweig Germany

Institute of Botany Nature Research Centre Vilnius Lithuania

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

Institute of Forestry and Park Gardening Ukrainian National Forestry University Lviv Ukraine

Instituto Nacional de Investigação Agrária e Veterinária IP Oeiras Portugal

Kyushu Research Center Forestry and Forest Products Research Institute Kumamoto Japan

National Forestry Agency of Georgia Tbilisi Georgia

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

Slovenian Forestry Institute Ljubljana Slovenia

Southern Swedish Forest Research Centre Swedish University of Agricultural Sciences Alnarp Sweden

Swiss Federal Research Institute WSL Birmensdorf Switzerland

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The increasing threat to European forests from the invasive foliar pine pathogen, Lecanosticta acicola