Dothistroma septosporum, the primary causal agent of Dothistroma needle blight, is one of the most significant foliar pathogens of pine worldwide. Its wide host and environmental ranges have led to its global success as a pathogen and severe economic damage to pine forests in many regions. This comprehensive global population study elucidated the historical migration pathways of the pathogen to reveal the Eurasian origin of the fungus. When over 3800 isolates were examined, three major population clusters were revealed: North America, Western Europe, and Eastern Europe, with distinct subclusters in the highly diverse Eastern European cluster. Modeling of historical scenarios using approximate Bayesian computation revealed the North American cluster was derived from an ancestral population in Eurasia. The Northeastern European subcluster was shown to be ancestral to all other European clusters and subclusters. The Turkish subcluster diverged first, followed by the Central European subcluster, then the Western European cluster, which has subsequently spread to much of the Southern Hemisphere. All clusters and subclusters contained both mating-types of the fungus, indicating the potential for sexual reproduction, although asexual reproduction remained the primary mode of reproduction. The study strongly suggests the native range of D. septosporum to be in Eastern Europe (i.e., the Baltic and Western Russia) and Western Asia.

Dothistroma pini is one of two pathogens causing Dothistroma needle blight (DNB), a foliar disease of pines. The species was redefined in 2004 and subsequently recorded in several European countries. In Slovakia, the first report of the pathogen was in 2013. In this study, the population structure, genetic diversity, and reproductive mode of 105 isolates collected from 10 localities and seven hosts were determined in Slovakia. Species‐specific mating type markers, ITS haplotype determination, and 16 microsatellite markers were used to characterize and genotype the isolates. Overall, 15 unique multilocus haplotypes (MLHs) based on microsatellite markers and three ITS haplotypes were identified. Three independent methods (DAPC, STRUCTURE, EDENetwork) separated the isolates into two distinct population clusters corresponding with ITS haplotypes. A high level of clonality was recorded suggesting that conidia are the primary source of pathogen dispersal. The low genetic diversity, predominantly asexual reproductive mode of the pathogen, and the fact that most isolates were collected from introduced tree species and native species in artificially planted urban greenery, supports the hypothesis that D. pini has been recently introduced into Slovakia.

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