Dothistroma needle blight (DNB) is an important disease of Pinus species that can be caused by one of two distinct but closely related pathogens; Dothistroma septosporum and Dothistroma pini. Dothistroma septosporum has a wide geographic distribution and is relatively well-known. In contrast, D. pini is known only from the United States and Europe, and there is a distinct lack of knowledge regarding its population structure and genetic diversity. The recent development of 16 microsatellite markers for D. pini provided an opportunity to investigate the diversity, structure, and mode of reproduction for populations collected over a period of 12 years, on eight different hosts in Europe. In total, 345 isolates from Belgium, the Czech Republic, France, Hungary, Romania, Western Russia, Serbia, Slovakia, Slovenia, Spain, Switzerland, and Ukraine were screened using microsatellite and species-specific mating type markers. A total of 109 unique multilocus haplotypes were identified and structure analyses suggested that the populations are influenced by location rather than host species. Populations from France and Spain displayed the highest levels of genetic diversity followed by the population in Ukraine. Both mating types were detected in most countries, with the exception of Hungary, Russia and Slovenia. Evidence for sexual recombination was supported only in the population from Spain. The observed population structure and several shared haplotypes between non-bordering countries provides good evidence that the movement of D. pini in Europe has been strongly influenced by human activity in Europe.

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

Department of Forest Mycology and Plant Pathology Swedish University of Agricultural Science Uppsala Sweden

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

Phytophthora Research Centre Mendel University in Brno Brno Czechia

Slovenian Forestry Institute Ljubljana Slovenia

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

Swiss Federal Research Institute WSL Birmensdorf Switzerland

Ukrainian Forest Research Institute Forestry and Forest Melioration Kharkiv Ukraine Slovakia

Université de Lorraine INRAE Grand Est UMR1136 Interactions Arbres Microorganismes Nancy France

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Dothistroma septosporum and Dothistroma pini, the causal agents of Dothistroma needle blight, are infected by multiple viruses