Insights into the pathways of spread and potential origins of Dothistroma septosporum in Britain

Dothistroma needle blight (DNB) is a disease caused by two fungi, Dothistroma septosporum and Dothistroma pini, that has resulted in significant damage to pine forests worldwide. Analysis of 1194 British Dothistroma isolates revealed that only D. septosporum occurred in Britain; D. pini was not detected. The genetic diversity, population structure, and reproductive mode of D. septosporum in Britain were investigated using species-specific mating type markers and eleven microsatellite markers, revealing 382 multilocus haplotypes. Comparison of clustering methods (STRUCTURE, BAPS, DAPC) as well as spatial principal component analysis (sPCA) showed some differences between the methods but similar groupings. A clear north-south cline was found with attributes consistent with a native fungus. Other groups were most probably introduced, with one nearly exclusive lodgepole pine group exhibiting links with Canada. Evidence for the movement of specific multilocus haplotypes via nursery stock as well as across borders is provided and the implications discussed.