Population structure and genetic diversity suggest recent introductions of Dothistroma pini in Slovakia

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.